Saturday, December 31, 2011

Top 10 weather events for the U.S. for 2011

Hi It's Rebecca again, well today is the end of 2011. I wanted to post this the other day. However, time got away from me.  What a destructive year! Several big events don't even make it to the top 10 and many of these could be #1 in a quieter year. Back in 2010 we thought that was an extreme year. That is until this year. 2011  broke all the records that were broken in 2010.  2011 will be remembered as the year the tornado reined supreme.  Anyway here are my picks for  the top 10 weather events for the U.S. for 2011


A few of the things that almost made this list.

The Indiana State Fair tragedy  

On August 13th, a severe thunderstorm hit the Indiana State Fair creating extremely strong wind gusts, ultimately collapsing a stage where the band Sugarland was about to play. The result, 7 dead people and questions whether or not the public heeded warnings issued by State Fair personnel about the approaching storms

The Southwest High wind event

 Earlier this month a very impressive western high wind event causes significant damage in large areas, such as in Utah, New Mexico, Arizona and southern California

The Iowa-Illinois-Michigan-Ohio derecho

This was an impressive long-lived derecho. Back in July the derecho produced widespread wind damage across parts of the Midwest. Winds gusted as high as 85 mph in some locations. Numerous trees and power lines were downed. Some roofs were damaged or completely taken off buildings. Grain bins were crushed.


10) The Southern Plains drought

 The Southern Plains knows about heat. It’s not uncommon for temperatures to top out above 100 degrees in the summertime. In 2011 though, it was nearly an everyday occurrence. Day-after-day, temperatures across the region surged above 100 degrees. In fact, Dallas/Fort-Worth endured 70 days with temperatures exceeding 100 degrees, beating the record of 69 days set in 1980. Wichita Falls and San Angelo, Texas both tallied over 100 days of triple-digit heat, by far a record for any year! The National Climatic Data Center reported that the 2011 United States Summer was actually the hottest summer since the Dust Bowl era Summer of 1936. 2011 marked the hottest summers on record for Texas, Oklahoma, New Mexico and Louisiana. As of this writing, some locations in Texas were nearly 2 feet below average yearly precipitation levels. The drought has claimed 600,000 Cattle. Estimates from the Texas Forest Service show that the yearlong drought may have claimed as many as a half-billion trees. The state has a tree population of about 4.9 billion. Researchers have determined that 100 million to 500 million trees, or from 2 to 10 percent of all trees, have been lost.  To make bad news worse, some climate experts feel the drought could be worse next year.


9) The Groundhog Day Blizzard.

The Groundhog Day Storm impacted nearly 100 million people as it stretched from Northeast Mexico to Canada from January 31 – February 2. Blizzard conditions affected many large cities along the storm's path, including Kansas City, St. Louis, Des Moines, Milwaukee, Detroit, Indianapolis, and Cleveland, perhaps the most memorable portion of this blizzard was its overall effect on the Chicago area where 1-2 feet of snow fell combined with winds over 60 mph. The conditions stranded hundreds on Lake Shore Drive.  21.2 inches of snow fell at Chicago O’Hare International Airport, making it the 3rd largest snowfall event on record in Chicago history. An ice storm ahead of the blizzard conditions affected much of the Midwest and into New England. Areas in New York, Connecticut, and Vermont reported several inches of snow and one half to one inch of ice accumulations resulting in numerous power outages, some of which lasted several days after the storm. 36 people perished in this storm and estimates of total damage are at 3.9 billion dollars.



8)  The April and May Record flooding on the Mississippi River.

The Mississippi River floods in April and May 2011 were among the largest and most damaging recorded along the U.S. waterway in the past century, comparable in extent to the major floods of 1927 and 1993. Excessive rainfall occurred from April 23 to May 7, 2011 across northern Arkansas, southern Missouri, and portions of the Ohio River Valley. The fourteen day rainfall totaled a staggering  800% above normal across parts of the Ohio, White and mid-Mississippi River valleys, with rain amounts up to 20 inches at some locations. The lower Mississippi River was overwhelmed when that additional water combined with the springtime snowmelt, the river and many of its tributaries began to swell to record levels by the beginning of May. Areas along the Mississippi itself experiencing flooding include Illinois, Missouri, Kentucky, Tennessee, Arkansas, Mississippi, and Louisiana. This deluge resulted in record flooding on the lower Mississippi River. Arkansas City and Greenville reached flood stage on April 28, 2011 and the lower Mississippi River remained in flood at some point through late June with Natchez remaining in flood until June 22. Fourteen people were killed in Arkansas and tens of thousands  were displaced from their homes along the banks of the Mississippi. 

7) The Springfield Tornado

 Just over a week after Joplin another American city was under attack from a tornado.   Though New England is not a tornado-prone region they still do occur. Springfield, Massachusetts watched in shock as a tornado ripped through the city’s center during the evening rush hour. Television stations covered the storm live as it passed over the Connecticut River and Interstate 91 into downtown Springfield. Although not as strong as the ones in the south  it was still amazing to see a tornado of this size moving through such a densely populated area of the country. The tornado killed 4 people and injured hundreds in Springfield. Two of the four fatalities occurred in West Springfield, and there was one each in Springfield and Brimfield. The Springfield tornado was a part of the 2011 New England Tornado Outbreak.  This tornado outbreak spawned 6 tornadoes across New England. The Tornado in Springfield has been dubbed  The Greater Springfield Tornado. The Tornado was rated an  EF3 with winds that reached 160 mph at its peak. The Greater Springfield Tornado caused  over 100 million dollars in damage.  

6) Tropical Storm Lee

From September 5th to the 9th remnants of Tropical Storm Lee drench the Northeast and Mid-Atlantic. The same areas that had be pounded by Irene. This was especially true of  the Susquehanna River basin which sustained catastrophic flooding. Up to nine inches of rain fell in parts of Pennsylvania, and a similar amount fell around Binghamton New York. Rivers and streams passed or approached flood stage from Maryland to Massachusetts. The rain made this the worst flooding event since Hurricane Agnes impacted the region in 1972. Over 100,000 people were forced to evacuate from the Susquehanna River's worst flooding in nearly 40 years.  At least 11 deaths have been blamed on Lee: four in central Pennsylvania, two in northern Virginia and one in Maryland, along with four others killed when it came ashore on the Gulf Coast. Overall, this event is estimated to have caused 1 billion dollars worth of damage.


 
 
5) The Pre Halloween Nor'easter


It formed early on October 29 along a cold front to the southeast of the Carolinas. As it moved northeastward,  the storm produced record-breaking snowfall totals in dozens of cities. The highest snowfall was in Peru, Massachusetts with 32.0 in. New York City received its earliest inch of snow since the Civil War. (The Civil War was in a long cold period known as the Little Ice Age). In Massachusetts, the nor'easter brought wind gusts peaking at 69 mph. What this storm will be remembered for is the widespread and long-lived power outages across Eastern New York State and Southern New England. Snow fell on trees that were often still in leaf, adding extra weight. Trees and branches that collapsed under it caused considerable damage, particularly to power lines.  An estimated 3.3 million people experienced power outages from this event, some the outages  lasted for 10-12 days.  The storm affected 60 million people and caused at least 39 deaths.
 
 
 

4)  Southern States Tornado Outbreak


From April 14 to 16, One of the worst recorded U.S. tornado outbreaks occurred across the Southern United States. This outbreak resulted in 178 confirmed tornadoes across 16 states. A total of 38 people were killed from tornadoes and an additional five people were killed as a result of straight line winds associated with the storm system. This was the largest number of fatalities in an outbreak in the United States since the 2008 Super Tuesday tornado outbreak (at the time).  The hardest hit states included North Carolina, Alabama, Georgia, Mississippi and Virginia. In Northern New York State, there were very high winds, sometimes gusting upwards of 70 miles per hour associated with the massive storms that were active on April 16.   Overall, 2.5 billion dollars of damage occurred from this event.

3)  Hurricane Irene 

 August 22-29: Hurricane Irene tracked just north of Hispaniola as an intensifying cyclone, pelting the coast with heavy rain and strong winds and killing seven people. After crossing the Turks and Caicos Islands, the hurricane quickly strengthened into a Category 3 major hurricane while passing through The Bahamas, leaving behind a trail of extensive structural damage in its wake. Curving toward the north, Irene skirted past Florida with its outer bands producing tropical-storm-force winds. It made landfall over Eastern North Carolina's Outer Banks on the morning of August 27 as a Category 1 hurricane, the first land falling hurricane on the U.S mainland since Hurricane Ike. She then moved along southeastern Virginia, affecting the Hampton Roads region. After briefly reemerging over water Irene made a second U.S. landfall near Little Egg Inlet in New Jersey early in the morning on August 28th. Irene is the first hurricane to make landfall in the state since 1903. Irene reemerged over water soon thereafter  Irene was downgraded to a tropical storm. Irene then made its third U.S. landfall in the Coney Island area of Brooklyn, New York, at approximately 9:00 am on August 28. The flooding in Vermont, eastern New York and New Jersey was some of the worse in centuries. One thing that made Irene unique. was her massive size. Tropical storm force winds extended out 255 miles from the eye making Irene a massive 510 miles in diameter.  Through the course of her lifetime Irene impacted over 75  million people from Puerto Rico to Florida and up to Maine. At least 56 deaths are blamed on the storm. In the U.S. alone Irene caused an estimated 10.1 billion dollars in damage. 


2) The Joplin Tornado
Not even a month had passed after the Tuscaloosa tornado;  when we heard of another city hit by a monster. On May 22, a lazy Sunday evening turned into hell on earth for the residents of Joplin Missouri. This tornado moved through the southern part of the city as an EF5 .  This means it had winds of at least 200 mph or greater. When all was said and done, 25% of the city was obliterated, with 75% seeing moderate to severe damage. The estimated damage of this tornado is estimated to be at $2.8 billion. The tornado injured 900 people.  However, the real tragedy was in the 162 lives taken in the blink of an eye. Which makes it the 7th deadliest tornado in U.S. history and the deadliest tornado in almost 65 years.. The Joplin tornado was part of a May 21-26 tornado outbreak. There were 180 confirmed tornados resulting in 185 deaths, stretching from central Texas to the Upper Midwest.

01) The Super Dixie Tornado Outbreak


The largest tornado outbreak ever recorded in United States history occurred from April 25-28. It was the deadliest tornado outbreak in most of our lifetimes .  It produced 359 tornadoes , resulting in 346 deaths, and causing an estimated 11 billion dollars in damage.. During the  3 day outbreak, tornadoes caused widespread catastrophic damage from Texas to New York State. On April 27 a total of 207 tornadoes tore across several states, 53 occurred in Alabama alone. The 27th of April went down as breaking the record for the number of tornadoes in a 24 hour period; a record set during the super outbreak of 1974. The most noteworthy tornado of the outbreak was the April 27 Tuscaloosa Tornado. The EF-4 tornado was a wedge tornado with peak winds of 190 mph; the tornado had a path 80.7 miles long; At it's widest point it reached one and a half miles wide. The Tuscaloosa Tornado caused incredible damage when it move through the city of Tuscaloosa where it took 43 lives. The total death count with this tornado was 64 and it injured more than 1500. It forever put to rest the mistaken belief that tornadoes don't strike cities.

With 2012 on the way, all we can do is hold our breath and hope it's not as bad as 2011. I'm almost done with a top ten list that's local to the northeast.....I hope to have it done by Monday. I hope you enjoyed reading this.........Let me know if you think others should have been added.

Rebecca

Sunday, December 11, 2011

Lake Effect Snow

Hi it's Rebecca again, I've been mentioning lake effect snow lately; so I thought I would post an blog entry about it. I'm sure some of you living outside of the snowbells are curious about what it is. This blog entry will give you a broad overview of what lake effect snow is, how it forms, and where it can occur. As well as the difference between a lake effect snow storm and a synoptic scale snow storm.

Before I get into lake effect snow amounts I want to give you a broad overview of the Tug Hill Plateau. Nestled in the ‘North Country between Lake Ontario and the Adirondacks, Tug Hill is a region of unbroken northern hardwood forests and pristine wetlands drained by a vast network of coldwater streams. The Tug Hill region is located in four Upstate New York counties: Jefferson, Lewis, Oneida, and Oswego. The top of the plateau is relatively flat compared to other areas in New York State.  The most outstanding characteristic of the Tug Hill region is its undeveloped state. There are some small, scattered hamlets and villages along the outer edges of the region, but the core area is heavily forested and relatively unpopulated. In spite of the region being sparsely populated (for some strange reason), a few  places like Boonville, Barnes Corners, Redfield, and Montague occasionally make the news during the winter. Many old timers up here think Tug Hill got its name sometime  around the 18th and 19th centuries. in this time span the term "tugging" was use to describe  areas that were reached by horses or oxen pulling a wagon up a long road to get to a high area.  H.E. Krueger in an article "The Lesser Wilderness - Tug Hill" he claims the Tug Hill was named by two early settlers, Isaac Perry and a Mr. Buell when traveling up the hill west of Turin The Tug Hill covers an area of 2,100 square miles with an elevation from about 350 feet on the west to over 2,000 feet in the east. The area because of its location on the east-end of Lake Ontario, along with the combination of winter winds blowing over almost 200 miles of Lake Ontario waters, and the 2,000-foot rise of Tug Hill creates these heavy lake snows. These storms are responsible for the majority of the over 200 inches of snow the Tug receives annually, turning the region into a winter wonderland. The heavy snowfall is one of Tug Hill’s greatest recreational assets.

            Several towns in the region hold impressive records. An out of the way place called Hooker (near Barnes Corners) recorded 466.9” of snow in the winter of 1976-77. The monthly record for snow accumulation belongs to Bennet Bridges and is 192” in January 1978. The official record for a one day snowfall in NY State belongs to Montague NY. The hamlet had 77” of snow in 24 hours on the 11th/12th of January 1997. Montague also holds the single storm record for snowfall in NY with 95” from January 10th-14th in 1997.  Not to be outdone, Redfield received 141 inches during the 12 day lake effect event of February, 2007. Well that tells you a little bit about this fascinating area...now on to lake effect snow.

Just what is Lake Effect Snow?

Lake effect snow, also called snow squalls, results from cold, arctic air traveling over a relatively warm body of water. The cold, dry air picks up the water moisture and deposits it, in the form of snow, over land areas in- lee of the warmer water. In the case of the Northeast lake effect snows can occur around Lakes Ontario and Erie and to a lesser extent around Lake Champlain and the Sound off of Long Island.  After the passage of a cold front the relatively warm waters of the Great Lakes often create convective instability in an otherwise stable, arctic continental airmass. Therefore, while areas in eastern New York and the rest of New England are clearing up after a recent cold front or storms passage, The Great Lakes communities hold their breath waiting for the lake effect snow machine to awaken. Lake-enhanced snow is different from lake-effect as it is part of an already present system.
How does Lake Effect Snow form?
The first two ingredients
These come under the heading of temperature contrast. The temperature between the lake surface and overlying air promotes "convective instability" that provides the basic energy source for lake effect snow. Ideally, the ambient air temperature at 850mb should be at least 13°C cooler than the surface water temp. Heat and moisture from the warm lakes rises into the "modified" arctic air where it then cools and condenses into snow clouds.   The intensity of the lake effect snowfall also depends upon how far the wind moved over the  lake surface (the fetch) . The longer the fetch, the more moisture the air can obtain and more snow it can form. One reason that mid-lake bands are so impressive is that the fetch is maximized. In the case of Lake Ontario the band can be 150 miles or longer. Major storms rarely develop unless the fetch is at least 50 miles. If the lake has a lot of ice cover; the band intensity is greatly reduced. This is because the ice cuts down on evaporation. Therefore the fetch can't pick up much moisture. This is the reason Lake Erie normally only has lake effect snow during the early winter. Lake Erie is the most likely of the Great Lakes to freeze because it is by far the shallowest. whereas, Lake Ontario is the least likely due to its vast depth and southern location compared to the upper Great lakes.  
The wind speed determines how far inland and the horizontal spreading of lake-effect snow. With relatively light winds, the snow maximum will be closer to the shore. Strong winds tend to blow the snow further inland and produce a snow maximum which is more than 10 miles inland. The heaviest snows rarely occur right at shoreline. Wind speed needs to be light enough across the lake in-order for moisture convergence to occur. The moisture content of the air depends on the previous dewpoint of the air moving over the lake and the moisture acquired through evaporation over the lake. If winds are too strong ( over 50 miles per hour), enough moisture may not be able to evaporate to produce heavy lake effect snow. The best combination is cold arctic air moving between 10 and 40 miles per hour.
The third ingredient
Forecasting lake effect snow can be a huge challenge. Therefore knowing the wind direction is vidal. Wind direction is measured in degrees, as on a compass where 360 degrees is north, 90 degrees is east, 180 degrees is south, and 270 degrees is west. Since Lake Ontario is elongated west-east, and since the Tug Hill is on the eastern end of the lake. Winds with a 270 flow will often bring in a single extremely intense snow band that dumps huge amount of snow. Sometimes the Capital District will be affected by snow off of Ontario this usually occurs when winds 30 to 40 mph set up on a 280-290 flow.
The forth ingredient       This is the topography around the lake.  Elevation plays a major role in lake effect snow production  ( this is called orographic lift ).  This occurs when the wind comes over the flat, nearly frictionless (somewhat ice covered) Great Lakes and then plows into the shore and over the land. This creates friction as well as lift when it hits the land and elevation change. When the air is lifted, you get clouds and eventually lake effect snow showers. For the Great Lakes this would include locations such as the Keewenaw Peninsula of Michigan, the Bruce Peninsula in southern Ontario, the Tug Hill and Allegheny Plateaus of upstate New York; It is estimated that annual snowfall increases by 65 cm (25 1/2 inches) per 100-meter  (slightly more than 328 feet) in elevation gain leeward of the Great Lakes.

 There are other factors as well. Some of these are wind shear, thermal convergence, and  frictional convergence. I will not go into these. However, if you want to know about them. Drop me  an Email and I would be happy to answer any questions you may have.
Where can it Occur?

The lake effect I've been discussing has been on the Great Lakes. However,  these types of snowstorms can occur anywhere cold air moves over a fairly large area of relatively warmer water during the winter.
Below are a few maps that show some of these places.




                                                                   Pictures courtesy of NWS Buffalo


The  difference between a synoptic scale snow storm and a lake effect storm
The main difference between a lake effect snow and a synoptic scale snow storm, is that lake effect snow storms are not low pressure system storms. Instead it is cold, dry air  moving over the  Lakes that brings the snow. Another major difference is a winter storm may last a few hours to a day or so with on and off snow, Where-as a lake effect snow storm will often produce snow continuously for 48 hours or longer in a particular area. Lake effect snows can precipitate as much as 76 inches  of light-density snow in 24 hours with snowfall rates as high as 6 to 8 inches per hour. In fact in 2007 a lake snow band lasted over 10 days; when it was over anywhere from 100 to 141 inches had fallen. The good news was that the band meandered around a lot during that time. Imagine what the snow amounts would have been if the band had more or less stayed in one place.

                        Here are a few pictures of the Tug Hill. To give you an idea what it looks like.

The Winteridge near Lowville run by the Northrup family


There is always a wind on the Tug. So wind skiing can be a lot of fun



One of the windmills outside of Lowville.




A good way to get around in winter







Well that's about it. I hope you enjoyed reading this post. Again I will be happy to answer any questions you may have.
Rebecca

Tuesday, November 29, 2011

2011 - 2012 Winter Outlook.

Hi it's Rebecca, I've been meaning to post this for the last 3 weeks. But things and events interfered. Anyway, I thought I would take the time to put it together today. This outlook is based on several key factors: the ENSO (El Nino/Southern Oscillation),the Pacific Decadal Oscillation (PDO), the North Atlantic Oscillation (NAO), the Arctic Oscillation (AO), past years that had a similar pattern, and Snow Cover in Alaska, Canada, and Siberia. I even looked at solar activity.

Before I get into the specifics of the outlook, I want to spend a little time explaining what an outlook is. First a winter outlook is not a forecast. A forecast deals with specific weather events such as storms.  With a forecast you look at data, in order to figure out precipitation type, severity, and timing of a storm. Where as an outlook talks about how the winter pattern will set-up, it attempts to show where the major storm tracks will set-up and how the winter will trend. It will not tell you how many Blizzards, Nor'easters, or ice storms there will be, or when they will occur.

The winter pattern starts with a strengthening jet as it makes it's migration south. Something we're just starting to see. How the jet acts and sets up effects how the troughs will act and move during the winter. Most agree that the winter of 2011-2012 will see the return of a moderate La Nina. The long range models are supporting this idea, more or less. If this is the case, then the key to our upcoming winter will be the return of some strong high pressure blocking over northeastern Canada. The good news is the Euro long-range does not show much if any high pressure setting up over NE Canada. The Bad news is Last year's Euro long range showed some blocking but nowhere near as strong as what actually setup . Last year was a La Nina and we all know how that turned out. Now if the Euro is right we won't have a block setup this would mean just to our north in Ontario and southern Quebec would see tons of snow; while we had a warmer than normal winter with more or less normal snowfall. Now back to the outlook.

For those who don't want to read the science, you can skip to the summary at the end of the post. However, if you do so you will miss a lot of interesting information and how I came to my conclusion.

The Factors:

Factor #1: ENSO:
Probably the most talked-about index. You always hear the words El Nino and La Nina thrown around. The positive phase, or El Nino, is when the winds at the equator are pushed west to east. These keep sea surface temperatures fairly warm. A negative, or La Nina phase, is when the winds reverse. This allows for waters to be "dragged" from east to west, thus pulling to the surface, or upwelling, cooler waters just under the surface around South America.  A weak to moderate  La Nina winter will be the case for  Winter 2011 - 2012. Historically, La Nina favors a warmer than usual fall. As we have seen so far this year supports this idea. Last year’s La Nina November brought much less snowfall than average. The lakes stayed on the warmer side heading into December. Weak to moderate La Nina patterns tend to give more snow to New England, New York State, and the interior mid-Atlantic. La Nina is a little more transient, usually producing a ridge of high pressure across the West which drives the jet stream north, and then it dives down across the Midwest. Up here in the Northeast our weather will depends on how the storms track along the Jet and how the trough axis sets up. How much snow we get really depends on the exact track of individual storms. A difference of just 60 to 100 miles can make a huge difference in snowfall amounts. However, this is just the first factor.
 


 
Factor #2 the PDO:
To put it briefly, PDO is another sea temperature phenomena. It has two phases, a warm phase (positive) and a cool phase (negative).  The other oscillations have the same phases. The warm and cool phases in the PDO last a lot longer than El Nino and La Nina, typically lasting 10 to 40 years - with a few shorter intervals occasionally in between. The cool PDO phases have been linked to cooler temperatures, and vice versa. I feel we are at the beginning of a longer cool PDO phase. The PDO focuses on the northern portion of the Pacific Ocean, towards Alaska and the Aleutian Islands. It accounts for Northern Pacific Ocean temperatures.  Since 2008 the PDO has flipped back into a negative cold phase. When the PDO is in a negative phase the Jet tracks north of Alaska, which sets up a trough axis that lines up from Great Lakes down in to Alabama. This kind of track sends a lot of storms into the Great Lakes and Midwest.  When the PDO is in a cold phase the Great Lakes and Ohio Valley into New England tend to see below normal temperatures. The PDO was in this same phase for the  winters from the 1950’s, 60’s and 70’s. I will get more into past years in a little bit. The main thing to remember is: on average, we see more snow during a negative phase than during a positive phase. That's it for the second factor.





Factor #3 the NAO:
There will be a couple of wildcards this winter. The NAO will be one of them. This oscillation is quite different than the ENSO and PDO. Because it's not solely driven by ocean temperatures; which makes it extremely hard to predict.



The top image shows what happens when there is no block in the East, allowing storms to track generally West to East across the United States. This is call a flat pattern

The bottom image shows how a negitave NAO effects the storm track. When the NAO is negative, it sets up a block of the jet stream, making it more amplified, and storms are forced up the coast as potential blockbuster storms. This is also known as the "Greenland block" since high pressure blocking sets up near Greenland. When the NAO is negative the overall pattern is more unsettled weather , frequent and sustained cold snaps, and above normal snowfall.

The NAO this past month has been positive much of the time, and combined with a strong ridging and -PNA out West, it has resulted in warmer weather. In the near future, I see the NAO returning to negative, and will alternate from positive to negative this winter, but I think the primary phase will be negative for the most part, especially the first two thirds of the Winter.

Factor #4 the AO:
This is the other wildcard. The AO takes place over the North Pole.  This flow from the Arctic can and often does work hand in hand with the NAO. The Arctic Oscillation (AO) has a significant influence on winter weather in the U.S. Especially, the northern and eastern U.S.  By this I mean the AO plays a big part in how much cold air will get pulled into systems in the Lower U.S. The AO was at a  record low for the 2010 -2011 winter season.  Because of that many places saw well above average in snowfall. When the AO is negative storms will take a more northern track. The AO has been on the positive side for a little while. However, it's starting to show signs of a tilt to the negative side.  I think the AO will be negative for the first half of this winter (Mid Dec- end of Jan) then starting to turn positive sometime in February. in my opinion, the AO is the hardest oscillation to predict; because it changes so often.  The past two winters have produced times of very negative values. This resulted in  very snowy winters.



Factor #5 snow cover:
One of the things I do in trying to figure out what an upcoming winter will be like; is look at the extent of snow and ice in the Arctic. I start looking at the snow cover in Siberia in October. In November,  I look at the snow cover in both Alaska and Northern Canada.

The images below shows the current snow cover in Alaska, Canada and Siberia along with a comparison to this time last year.







From the images above I can see three very important things:

1) The snow pack in Canada is creating a cold air pocket, you can call it the  "icebox effect" This will cause colder than average temperatures in the Northern half of the US during the typically colder Winter months. The snow pack in Siberia is quite extensive right now.  Snow cover is important to factor into a winter outlook, because it establishes a cross Polar flow. By this I mean the Arctic cold over Siberia will be able to flow over the North Pole/Arctic region into Central and North Central Canada... and right now we don't have that. If there is no cold Arctic air in Canada, which is the case right now, it can't get cold no matter how strong the cold looks to be in long range guidance. So the build-up of serious deep cold Arctic air in Canada is a huge deal.
2) As I've been saying in my weather page, once winter decides to make an appearance Winter will come in with a vengeance once the pattern changes, and cold air in Canada can make it to the lower 48 and Northeast US.

3) From the look of things, I feel the Northern Hemisphere will be under the influence of a strong polar vortex (PV). this will only make things worse, it will help amplify the northern and Southern branches of the Jet.  Combine that with a -PDO, -NAO, -AO. now add in the ridging out West and the expected trough (remember 2011-2012 will have a --NAO and -AO) .... and look out. storms will be following one after another.




 
Factor #6 Solar
The study “Solar forcing of winter climate variability in the Northern Hemisphere”, led by a team of scientists in the United Kingdom, examined how weather patterns changed when the amount of solar radiation reaching the Earth rises and falls. The authors reached the conclusion of when solar activity is low; it produces colder winters in the United States and northern Europe and milder winters in Canada and southern Europe.

Link to the solar study

"The Sun has recently been in a quiet phase of its regular 11-year cycle, which coincided with three years in which the UK, along with other places in northern Europe and parts of the US, experienced cold conditions unusual in the recent record. But unusually warm weather was felt both further south, around the Mediterranean Sea, and further north in Canada and Greenland." - UK MET OFFICE

The solar minimum of 2008 is said to have played a huge role in the negative NAO that dominated the previous 3 winters. I've read that low solar activity leads to high latitude blocking. Solar activity has started to increase of late. But since the cycle runs for 11 years; I don't think the increase will be much of a contributing factor this year. So it's influence on the negative NAO will be negligible.


Nor'easters:

A Nor'easter is a storm characterized by a central low pressure area that deepens dramatically as it moves northward along the East Coast.  The heaviest snow in a Nor'easter falls to the north and west of the track of the surface low. Nor'easters can be classified into one of two categories, Miller A and Miller B

Miller A 's are what I call a classic Nor'easter, they develop primarily on the Gulf Coast or East Coast along an old cold front and deepen as they move north.  The "Superstorm of March 1993" is considered to have been a "Miller Type-A" storm.

Miller B's are a little different, they normally dump snow in the Midwest/Ohio Valley . As it approaches the Appalachian Mountains they lose their power and transfer it to a developing low on the coast.  

 


Above are images of Nor'easter's the top one is a Miller A and the bottom one is a Miller B.

If there are coastal storms, the Miller B pattern set-up will be more common than in a Miller A scenario in this type of pattern.

 
Past Winters: 
Besides all of the above data, I looked at past winters. I am a firm believer in patterns. The ability to recognize these patterns is what makes a good forecaster. I looked at several winters over the last 60-65 years. I paid special attention to  second and third year La Nina's since 1950. I also looked at years that were neutral. when all was said and done, I came up with this  list of winters for analog years.
1950-1951
1955-1956
1961-1962

1974-1975

1975-1976

2010-2011

The above list comprises the years that strongly matched this year's set-up. There were differences of course. both last year's and 55-56 were fairly strong La Nina's; whereas this year shouldn't be as strong. As for 50- 51 that year didn't have strong blocking. I think this year will see blocking more like last years, though not quite as strong.


Storm Tracks:

These will be the dominant storm tracks for the winter of 2011-2012



These storms tracking to the west would lead to rain, mix, and ice and slop storms along the coast. Places inland would see more in the way of snow. what you saw would depend on the exact setup and location of where you live. I expect a fair share of these this winter.



The red tracks are the coastals and the purple tracks are clippers.

The blue line shows the average axis of the trough for 2011-2012
The purple lines show how the jet will set-up the main storm track

Here is the temperature outlook for the United States for the winter of 2011-2012

The Purple is well below normal
Dark blue is below normal
Lite blue  slightly below normal
Orange is normal
Yellow is above normal
Red is well above normal




Above is the Northeast snowfall outlook for 2011-2012

Purple well above average
Indigo above average
Green slightly above average
Dark blue average
Lite blue below average

Summary:

Now the good stuff. What  the heck does this mean?

Now that were officially going into winter; we have to start thinking  pattern change. I think we will see a pattern change by the middle of December. for the last five or six weeks we've had above normal temperatures. (Even with the Halloween and Thanksgiving snowstorms thrown in) However, out in the western US and Canada along with Alaska its been the opposite. So, the weather out there has not been as nice and they've seen colder temps. Over the last month and a half, the AO and NAO as be positive to neutral. The result our relatively nice weather. Well all of this is about to change, starting next week we will see the pattern began to change. By Hanukkah we will be in a much colder pattern. This will be especially true for the Great Lakes.

What do I think:

As I've outlined above, Storms will enter the Pacific Northwest move into the Plains and Midwest then head into the Northeast. It will be difficult to get a lot of Nor' Easters this year; the pattern doesn't support them as much as it did last year. For the snow lovers, the Halloween Nor' Easter is not a sign of things to come. But, that doesn't mean there won't be some. The pattern will have the storms phasing more west than we saw last year. this is why I feel 2011-2012 will be a snowy winter for the Great Lakes. But those in eastern NYS and New England shouldn't laugh. Because we will see quite a few Clippers these will make the northeast quite cold for the winter of 2011-2012.  

What to expect from the winter of 2011-2012 across the U.S.

The West:
Because of the way the storm track will setup. The Pacific northwest looks to see normal to above normal precipitation. whereas California and the Southeast will see normal precipitation.

The states in the Rockies:
If you like snow skiing Stay in the Northeast, The ridge that will develop over them, which will keep  places like Aspen Colorado from seeing as much snow as normal.

The Northern Plains:
Like last year, the northern Plains will see an extremely cold winter. I’m expecting yet another very cold winter for the Northern Plains Because I think there will be a higher than average number of Alberta Clipper's this year they should see as much snow as last year.

The Southern Plains:
They will see quite a few ice storms this winter. Parts of Texas could also see more severe weather outbreaks than normal.

The Mid West and Ohio Valley:
The storm track for the most part will be to the south and southeast. So they will see a cold and snowy winter.  

The Southeast and Gulf Coast:
If you like the sun, this will be the place to be. So they will be warmer than average. However, this could come with a price. they run the risk for more severe weather than normal.

The Northeast:

The pattern looks to be classic for a cold and snowy 2011-2012 winter. With the PDO,  AO, and the NAO being negative. we will see a deeper and more easterly jet this year. this will lead to a higher than average number of cold spells. There will be quite a few lake cutters. Also, with the larger than average number of Clippers and the greater threat of Miller B's, will keep the Great Lakes busy.  Because of the warm summer and warm fall the Lakes are very warm this year. So lake effect snows will be above normal to well above normal this winter.  Much of the Northeast will be affected by the same storm systems. Most of NYS and New England will see more snow than avearge. The exception being extreme southeast NYS and areas closer to the coast. This is because  most of the storms will track more to the west this winter. So places like the  Philadelphia and New York City metropolitan areas will see less snow and more of a mix or sloppy mess. I don't think we will see an early spring.  Traditionally, La Nina years see a cold and snowy March and first part of April.

Here is my call for snowfall amounts for some places in the Northeast.

The Tughill east of Lake Ontario will see 200-425 inches of snow this year.
Syracuse looks to see  170-180 inches.

Boston Massachusetts 46-50 inches.

Along the Mohawk Valley  100-130 inches (The higher amounts Just to the south and east of Utica.)

Albany 75-85 inches.

New York City right around 26 inches.

Buffalo 125-135 inches


Here is a link you can also checkout.

NOAA 2011-2012 winter outlook.

Well that's about it......remember this is an outlook not an forecast. I tried to be as accurate as I could. But when all is said and done, an outlook is no more than a educated  guess. I looking forward to seeing how right I am. However, we will have to wait until next spring to see.

Rebecca

Friday, November 11, 2011

Weather Models part 2

Hi It's Rebecca again,In part two, I will show five GFS model plots at most of the mandatory levels. As I go along, I will explain what you're seeing on the chart and explain what the information it's giving you is used for. I will also go into a little about Forecasting wintertime precipitation. This part will build off my post How to Read a Skew-T-log-p .  This lesson is geared toward an intermediate level and assumes you know what most of the terms used stand for. If I had to stop and explain every term this post would go on and on. However, at the same time I will try not to make it overly complicated. That said, let's dive into the wonderful world of the GFS model.

Below is the GFS surface plot.




Above is the GFS showing Saturday's model forecast. If you look at the model you will see writing on the top and bottom of the image.

To make it easier to read I've retyped them below.

11/09/11 12UTC 066HR FCST VALD Sat 1112/11 06UTC NCEP/NWS/NOAA

This is the top line. it tells you the date the model was produced, The model run, how far it's looking in the future; in this case 66 hours, the date and time in the future it is showing, and who developed and maintain the forecast model; in this case it's the National Centers for Environmental Prediction which is part of the National Weather Service.


111112/0600V066 GFS MSLP.06-HR PCPN (IN). 1000-500 THICK

The first set of numbers is just restating the date, UTC time, and where it's looking at in the future. Then it tells you which model it is; in this case it's the GFS. The next part shows the Mean Sea Level Pressure and 6 hour precipitation, and the important field of 1000-500 mb thickness. One final thing before I move on to thickness - you will notice the colored bar on the left hand side. This shows the rainfall accumulations the model thinks will fall. This is only a rough idea and you should always view it with caution.

Thickness:

When you look at the model you will see the thickness lines running across the image. These represent the physical thickness of the atmosphere between the 1000hPa level and the 500hPa level. This is normally around 5500m, but varies by up to 200m on either side of this value.

Because colder air is denser than warmer air, it's also thinner, because of this the thickness values of cold air will be lower than those of warm air. Being able to see this will give you a a general idea how warm or cold the atmosphere is over a certain point.

You will notice that thicknesses rise from south to north, reflecting the warmer air near the equator compared to the air near the poles. If you look you will see the 540 (5400m) line is shaded blue. This is to make it easier to find. One more thing I should mention is upper troughs; these are areas where colder (lower thickness) air advances to the north. The areas where warmer (higher thickness) air proceeds south are called upper ridges.
By and large, when an upper trough is moving through, there is a greater chance for weather that is more unstable. Whereas upper ridges have weather is usually more settled.


Why is the 540 line important:

The 540 line is in reference to a 5,400 geopotential meter thickness between 1000 and 500 mb. Thickness is a principal function of the air temperature and a secondary function of the moisture content present in the air. Moisture and temperature and moisture are combined together to produce the virtual temperature. The average virtual temperature from 1000 to 500 mb determines the thickness displayed for model analysis. If the temperature of the air is warmed or if moisture is added to the air; it will raise the virtual temperature; which will increase the 1000 to 500 mb thickness. When the thickness gets low enough, snow has the chance to reach the surface. Because of this, the 540 thickness is generally called the snow line. When the thicknesses is 540 or lower it indicates there is a 50% chance that snow will fall at elevations below 1000 feet. However, this is a very lose rule, There are times when lower than 540 thickness will generate rain; and visa versa , when a higher than 540 thickness can produce snow/ice pellets. So never use the thickness value as the sole means of determining precipitation type.

Some of the things that must be taken into consideration:

1 Elevation
2 Warm or cold biasing of 540 thickness
3 Evaporative cooling potential
4 Temperature in the planetary boundary layer  (PBL)

The PBL is the lowest layer of the troposphere where wind is influenced by friction. The thickness of the PBL is not constant. During nighttime and the winter season the PBL has a tendency to be lower in thickness. Then during the daytime and Summer it most likely to have a higher thickness.

The first, elevation is easy to understand. This is because the higher the elevation the closer it is to mid-level colder air. Also the higher the elevation the lower the pressure.

540 thickness can have a warm or cold bias. Generally, temperatures decrease with height in the troposphere. However, differential advection (two or more air masses increasing or decreasing of advection with height) can cause layers in the atmosphere to be warmer or colder than they normally would be. You may have heard terms like Vorticity advection or warm air advection affecting a forecast.

Warm air advection occurs between 800 and 650 mb, which causes the temperature in that layer to increase and thus results in the thickness increasing above 540. If the temperature between the surface and 650 millibars continues to stay below freezing, the precipitation will fall as snow. Whether the 700 mb temperature is -20 C or -5 C, the precipitation will fall as snow if the temperatures are below freezing at all levels aloft in the troposphere. Cold thickness bias is when a shallow layer of warm air in PBL melts the snow before it reaches the ground.

As you can see the temperatures in the PBL are very important in determining the precipitation type. If you have a shallow layer of cold air at the surface you can get freezing rain or sleet even if the thickness is well above 540. This is because deep layers of the troposphere will have more influence in determining the thickness than shallow layers.

Evaporative cooling causes the thickness value to decrease. If precipitation falls into a deep layer of dry air, expect thicknesses to lower.

850mb plot:


The 850mb plot: is good for seeing the locations of highs/lows along with isobars, winds, and temperatures. If you remember, In part one I said the 850mb level corresponds to roughly 5,000 feet in the atmosphere. This height can a lot more useful for determining precipitation types at the ground. The temperature readings at 850mb are high enough above ground level that it's not influence to a great degree by topography as a surface plot. Therefore it is very useful in determining where warm or cold air advection might affect a forecast.

To get a fairly good estimate at the surface for a particular day's high temperature use this method  with the the 850mb temperature chart:

1) find the temperature at 850 mb  for the area in question
2) add the following to the 850mb temperature depending on the time of year: spring/fall(+12 C); summer (+15 C); winter (+9 C); this will give you an estimate of surface temperature.
3) to convert to Fahrenheit: C x 1.8 +32 = F

For example, if the 850 mb temp is 8 C in summer, the afternoon temperature could reach 8+15=23C= just a tad under 73 and a half degrees F. In the winter, 9+9=18C= just over 62 and a half degrees F. This formula works fine in the eastern half to the US and it also assumes little to no cloud cover or precipitation is expected. However, out west the altitude is a lot higher so it doesn't work there.


If you look at the map you will find a line that says 0C on it; this line will give you a good idea of where it will rain, or where it will snow. This tends to be more accurate than using the 5400m line on surface plots. Temperatures 0 C or lower at 850mb mean that precipitation will likely fall as snow (but not always).

The wind barbs show wind direction (remember wind direction is named from which direction the wind is coming FROM)  and speed. The barbs can give you a good clue where there the atmosphere will be unstable. This can come in very handy when you're trying to figure out the severe weather potential. The thing to look for is southern warm moist air northward.
The height field works very similar to the sea level pressure field. Lows and highs can found and compared to sea level locations. Strength of winds are again related to the packing of the height contours.



700mb plot:


The 700mb Heights, Relative Humidity, and Omega Panel is an important panel used by meteorologists. The black contours are called isohypse at the 700mb level, and are contoured every 3dm (the isohypse are in decameters, so 300dm is actually 3000m). The height of the 700mb level is how far you would have to go up in the atmosphere before the pressure drops to 700mb. You will notice that there are colors on the map. The green shading indicates the amount of relative humidity in the atmosphere at 700mb. (NOT the relative humidity at the surface). The green shading represents areas with a 700mb RH greater than 70% as indicated by the legend below the panel, with dark green areas displaying RH greater than 90%. White areas on the map indicate regions where the RH is between 30% and 70%.

The 700mb height lines are similar to the isobars shown on the surface map, they can help you determine where pressure systems are located, and the relative speed of winds(tightly packed height lines indicate areas of strong winds). 700mb height field .... The height field works very similar to the sea level pressure field. Lows and highs can be found and compared to sea level locations. Strength of winds are again related to the packing of the height contours.

The 700mb wind barbs work the same as the 850mb barbs At the 700mb they can be a good indicator of divergence or convergence; in the middle and upper levels of the troposphere.

700mb “omega” is also contoured here. Areas of negative omega indicate upward vertical motion in the atmosphere and areas were precipitation could very well occur. while areas of positive omega show where there is downward motion and areas which normally will be dry.

500mb plot:


The 500mb plot is very important. This level of the atmosphere is often referred to as the steering level. Because most major weather systems follow the winds at this level. Again, the wind vectors will give a clue as to how fast and from which direction the storm system will track. This information will allow you to approximate the storms time of arrival.

You will notice the color shaded areas on the map. These are the vorticity values at 500mb. These eddies in the atmosphere can affect weather in many ways. They can strengthen an existing low pressure center, or cause one to form. They often produce lighter precipitation as they pass over an area. During the winter months,when passing overhead they can produce light snow showers.

Large storm systems will often run parallel to the height lines. So you can use them to give yourself an idea how a system will move.

300mb plot:


The 300 mb plot investigates the upper portion of the troposphere where most of the weather making occurrences happen. This level is often referred to as the jet stream level. Jet streams are simply rivers of fast-moving winds aloft in the atmosphere. Jet streams form along the upper-air boundaries of large masses of warm and cold air. They are created by strong temperature contrasts in the lower and middle tropopause and reflect areas of potential storm development. The temperature contrasts control the speed of the jets. The larger the temperature difference, the tighter the pressure gradient and the stronger the wind speed. There are several jet streams influencing weather in all areas of the globe. I will discuss a few of them, The most commonly referred-to jet streams are the polar front jet. The polar jet typically occurs at latitudes between 50°and 60°, both north and south of the equator. Then there is the subtropical jet located around the 20° to 30° latitudes. A jet stream can theoretically occur anywhere in the upper atmosphere when wind speeds exceed 50 knots. Wind speeds in jet streams average about 110 mph, although they can reach as high as 300 mph. Another example is the tropical easterly jet, which occurs between India and the equator during July and August. Low-pressure systems form along these boundaries and are often near the jet streams. The jets, highs, and lows are nothing more than waves in the ocean of air over our heads; they are always interacting with each other which causes storms to amplify and strengthen. One thing to remember is storms don't create the jet stream. However, a strong jet stream can provide enough influence that it helps create a very powerful storm. The jets move south in the wintertime. As I said above, Jet stream winds blow along boundaries between warm and cold air. As cold air advances farther south in the winter it pushes warm-cold boundaries, and jet streams, south with it. When warm air moves north, the boundaries and jet streams are pushed back to the north.

The 300mb chart is useful for the prediction of temperature. The jet stream divides colder air to the north from warmer air to the south. The transition between temperatures on each side of the jet is very abrupt. When a trough builds over a region it often indicates cooler temperatures due to cloudier weather and northerly winds. A ridge builds by low level warm air advection between the 1000mb and 700mb sections of the atmosphere and upper level forcing (negative vorticity). Air in a ridge sinks and expands thus creating higher heights. Therefore, temperatures are warmer in a ridge due to the compression of the air that results from the sinking motion that occurs within a ridge.

Windspeed: a color-coded map indicates the wind velocities at the 300mb level. The jet stream longwave pattern usually shows up clearly here, as the regions of higher wind speeds indicate the location of the jet stream. Height Lines: indicate the height (in meters) of the 300mb level. Again, the more tightly packed the height lines, the stronger the winds.

Another phenomenon associated with the jet stream are jet streaks. these are detached, high-speed units of the jet stream surrounded by slower winds. Jet streaks are often big weather makers as they move over an area. They can aid in the development of severe weather as air is exhausted from the top of the troposphere or enhance the development of a surface low as they move overhead.

300 mb wind vectors at the 300mb level work the same as vectors at the lower levels.

Winter Forecasting:

Forecasting wintertime precipitation is a huge challenge. Above I said, the 850mb is better at deterring who will see snow than using the 540 line. However, don't think that the 850mb level is the only way or the best way to forecast wintertime precipitation. The method of choice that's best to use when forecasting cold season precipitation is the profile sounding method. If you go to the Penn State e-Wall you will see a link on the left hand side for forecast atmospheric soundings. If you want to make an accurate winter forecast viewing atmospheric soundings for precipitation events is a must. The reason for this is that you want to follow the temperature profile of the atmosphere. I covered how to do this In my post on reading a SKEW-T, there are several atmospheric temperature profiles that correlate to the different types of winter precipitation that may fall. I won't rehash SKEW-T soundings. However, I will show three different types of atmospheric snow soundings.

For sleet to fall, you would expect a layer of air from 500mb up to the 700mb to be below freezing. Then you would like to see a layer between 700mb and 850mb to be slightly above freezing (so it will melt the snowflakes). The layer of air below the 850mb level should then be below freezing all the way to the surface. Use the 850-700mb thickness to help determine if sleet may be a possibility when you are forecasting cold season precipitation.

To forecast freezing rain, you want to see a large layer in the atmosphere from just above the surface to about 850mb above freezing. This layer is sufficient to melt the snowflakes to rain drops. However, to get freezing rain, you want your surface temperature below freezing.

To forecast rain during the cold season, you would expect to see the same setup for freezing rain as explained above, but with a surface temperature that is above freezing.

For snow to fall, you would expect the whole layer from 500mb to the surface below freezing (As I said in past blog post, the surface temperature itself doesn't have to be below freezing for snow to fall. However, if the surface temperature is above freezing you want to see a below freezing temperature profile to at least 950mb to get snow to fall at the surface

OK lets get to our snowstorm. Elevation will pay a huge role. The surface temperatures will be too warm to support all snow in places below 500 feet. Other than the surface conditions the upper air looks great to support wintry precipitation.


The yellow shows the freezing line and the blue lines (temperature and dew point) remain below that point except at the surface. The location this sounding covers shows snow and rain. Making accumulating snow hard to come by. there will be times when there will be heavy bands of precipitation. The evaporative cooling will help to cool the surface layer for brief periods and allow snow to accumulate in those areas. Now let's look at a sounding for the same storm; but a different location.



NOW this is an all snow sounding for the whole event since the temp remains below freezing all the way to the surface.

Here is a SKEW-T that shows a classic setup for lake effect snow.


The things that are key are

1) Unidirectional shear intensifies moisture convergence
2) Inversion is above 700 millibars
3) Plenty of PBL moisture (saturated in PBL)
4) Steep lapse rate from surface to 700 millibars
5) Average wind speed below inversion is 30 knots
6) Wind direction results in a large lake fetch

The distance that an airmass travels over a body of water is called fetch.

For a big lake effect snow event off the east end of Lake Ontario; A flow of 270 is key, A 270 flow allows the wind to move over 193 miles of open water. I will be getting into lake effect snow in a future blog post.

Well that's about it. I hope you learned something and enjoyed going through part 2. If you want to learn more, there are two good books that will teach you more about weather models. The books are "Weather map Handbook" and another called "weather forecasting handbook" by Tim Vasquez. You should be able you find them online at Amazon or at a local bookstore.


Rebecca