Friday, October 31, 2014

The 2014-2015 winter outlook

Well it's that time to turn our eyes to the upcoming winter of 2014-2015.  There are many things I look at to try and determine  how our winter will shape up: Sea Surface Temperatures  Anomalies, Eurasia snow cover, sea ice, solar activity, and many other things. I  will touch on some of these things in this outlook.
Last winter we saw plenty of cold air, with below average temperatures and above average snowfall across most of the Northeast and Mid Atlantic.... the Great Lakes saw near record amounts of ice. The phrase "polar vortex" became part of our vernacular.
This is a detailed  discussion that will provide insight into the factors that have lead me to my thoughts on the upcoming winter. I think it's important for you to read the details...but I will understand if you just want to move to the bottom and read the summery, but in doing so you will miss some of the science involved in my decision. 
Many of the factors that led to last winter will again be in play this winter, but we will have some new factors as well.

The pattern for winter 2013-2014, for the most part stuck with us during this summer. Which resulted in a cooler than average summer in 2014.  The jet stream was more amplified. The ridging we saw this year that lead to the drought in California, also allowed cooler air out of Canada to slide down the trough along the East Coast,  that was fairly predominant this year.

 The years that I  got my data from were the winters of: , 1918, 1919, 1958,  1964, 1966, 1970, 1977,1978,1979, 1984,1985, 1986, 1994, 1996, 2003, 2010, 2014. 

 Pacific Ocean Sea Surface Temperatures  Anomalies :

Look at the latest SSTs in the Pacific....



I've circled the areas I will be writing about.
I've brought up the idea that we will see a weak El Nino quite a few times over the summer and into the fall.  But will this be the case?
SSTs in the Gulf of Alaska and Pacific Northwest are above normal for this time of year.  But this area of the Pacific had the same conditions for winter 2013-2014.....This will be an important player in the pattern for winter 2014-2015 as well.


Something new this year will be the warming in the Pacific equatorial region.  Temperatures across this area of the Pacific are above average ..... with SST profiles showing a weak  to moderate El Nino.  Right now the warmest SST anomalies are off the West Coast of South America..... what we should see happen over the four to eight weeks is this area of warm water will shift more to the west..... This upcoming winter should feature a weak central based El Nino.

Both the location and strength of the an El Nino is very important.....


Above  is a  CFS V2  image for January, February, and March 2015 ...this shows most of the warmth is in the  Central Pacific.  It supports the idea of a weak central based El Nino......

Below are two Jamtec (Japanese)  SST model images for Dec, Jan, and Feb and Mar, April and shows the same basic setup as the CFS V2.


The combination of a centrally based  El Nino in the tropical Pacific along with the warm anomaly in the northern Pacific normally leads  to high pressure ridging along the West Coast of North America.....with troughing over the  East Coast......This kind of pattern greatly increases the likelihood of arctic and polar air masses making there way into the central and eastern US.   

The reason for this is that  weather normally moves from west to east in the northern hemisphere..... storms moving across the Pacific will move north along the ridge.... then storms and cold air will slide down the trough. This kind of pattern does favor Clipper systems and cold outbreaks.

NECP NCAR Reanalysis  ....     surface air composite anomalies 1981-2010, you can see the analog years I entered on the bottom of the chart.


This shows that the Mid Atlantic and Northeast saw colder than average temperatures ....with Maine seeing average to slightly above average wintertime temperatures. Based on an average of the temperature anomalies of the analog winter years. 
Here is an image that show how the jet stream behaves, during winters that see warm SST in the Gulf of Alaska.

The  NOAA Extended SST for shows the same pacific SST  pattern....warm waters in the Gulf of Alaska and a weak central based El Nino...The same pattern that will be developing for the upcoming winter......again the analog years are on the bottom of the chart  



High Latitude Blocking:

This is important as it acts as  another cold air transport for the cold air in Canada, Greenland, and the even Siberia.

The question being will there be upper level winds to help move those air masses south into the CONUS? 

High latitude blocking is a pressure pattern in the northern latitudes. It normally sets up blocking near Greenland.

500 mb Geopotential Anomalies:

This is the 500 mb level........departures from average for the coldest winters .

Looking back at the same cold winters.. Notice the reds and oranges around Greenland.. we see high pressure situated near Greenland  ...with the troughing along the East Coast of the US....again the same conditions that look to unfold for this upcoming winter. 

AO and the NAO:

When these are negative they support  persistent  blocking high pressure over  Quebec,  Newfoundland, and Greenland. 
Here is the AO index...

I've circled in blue where the AO index went very negative in early October..... when I looked back at the coldest and snowiest winters over the last 10 -20 years..... those winters had a very negative AO in October.

The AO and NAO indices are likely to spend much of the time this winter in negative territory....This is normally the case during winters that feature  frequent high-latitude blocking patterns

Solar activity:

If you remember your Grade School Science, you will remember it's the Sun that controls our climate and weather. If you follow my space weather page you will know the current solar cycle 24  has seen fairly low solar activity, as in  a low number of sunspots.......... I believe this lower than average solar activity will continue to be the case this upcoming winter.
When I factored in the analog years, they correlate with the years that saw low sunspot cycle activity ..... we again see the same general setup........ a weak El Nino, warm Pacific waters in the Pacific Northwest, and high latitude blocking around Greenland.... the following shows this...... 

You can see the blocking high pressure over Greenland and the troughing over the East Coast of the US.

Here is a current image of the can see there are very few sunspots showing up.

Snow pack:

There is quite a bit of snow in Canada...right now it at near record amounts for this time of year. North America snow cover extent actually reached record highs at the end of September in records dating back all the way to 1967 . I got this data from the Rutgers snow lab.

Also snow cover is advancing across Eurasia; it's also running above average for this time of year.
Here are a few images that show snow cover across Eurasia and North America.


All of this supports the idea of  a deep cold air pack setting up across  northern Canada and the Polar regions, along with the idea of high latitude blocking. The buildup of snow in North America and Eurasia would help keep the temperatures cold in the arctic region...... It would also increase the odds of a cross polar connection, increasing the likelihood of Polar and Siberian air moving south into North America.

The Great Lakes and lake effect snow:

In spite of ice being on the Great Lakes into June this year,  that won't have an effect on this season, currently the lake temperatures on Erie and Ontario are just slightly below average for this time of year.. 

This year is shaping up to be  average for those who live in the snow belts , leeward of both Erie and Ontario.

Coastal /Nor'easters:

A weak central based El Nino allows above average  moisture to infuse the southern branch of the jet stream, with  extra moisture, we could see large coastal storms moving up the East Coast.

The high latitude blocking over the Canadian Maritimes and Greenland often allows the coastal storms to track along the coast....with upstream blocking the storms have a tendency to slow down.  

The waters of the Atlantic are still quite warm for this time of year.  The warmer than average  water temps, will continue into Winter 2014-2015.

Nor'easters are fueled from the cold arctic air from the north, and  the moist air from the Gulf of Mexico and Atlantic ocean off the east coast. When this happens the storm undergoes rapid strengthening (bombing); this causes the storm to pull in even colder air from the northwest side of the storm....resulting in the snow amounts  that often stack up.

Colder air and warmer Atlantic SST along the East Coast, increases the odds for stronger coastal storms. 

Before I conclude, I want to remind you,  this winter outlook is based on averages of the analog years I listed above.   A winter outlook is not a forecast; it's a broad overview of what I expect to unfold this year..... an outlook can't tell when  individual storms are going to move through, nor how big those storms will be. It can't foretell the air and surface temperatures each individual storm is going to encounter.  There is no way I can tell how much snow will be on the ground at any given time, nor the amount of snow that will fall from a storm.  The reason I give them is to give you an idea what the winter will look like based the factors I've looked at......basically a winter outlook is just a highly educated guess.




I looked at past winters going back over 60 years. The winters I listed above matched up fairly well to the conditions I expect to unfold for winter 2015-2015. A positive PDO with warm sea surface temperatures in the waters of the Pacific Northwest up into the Gulf of Alaska. Featured a weak to moderate El Nino, and had high latitude blocking around Greenland.

The analog winters of 1958, 1964, 1966, 1970, 1977, 1978, 1979, 1984, 1986, 1994, 1996, 2003, 2010, and 2014....were some of the coldest winters in the last 60 years.

So based on this, I think winter 2014-2015 will be colder than average in the Northeast and Mid Atlantic.  If fact, it could be a very cold winter.  The exception will be northeast New England  Mainly central and northern Maine. This area of the Northeast will see average to slightly above average temperatures. December into January could be above average to average; but for the end of January and especially for February it could be much colder than average.   

Wintertime precipitation:

 As for lake effect snow....this year is shaping up to be  average for those who live in the snow belts , leeward of both Erie and Ontario.  I expect to snowfall across the Tug Hill and other areas affected by lake snow  from Lake Ontario will see average snowfall  for the upcoming winter.  The same should be the case for those areas impacted by Lake Erie in western New York and northwest Pennsylvania.  Lake snow is dependent on wind direction, some areas might see higher than average amounts, but on average the snow amounts region wide should be fairly typical .

With high pressure ridging out West and troughing in the East, it's a pattern that will allow Clippers to move out of Canada.  These should increase the odds for above average snowfall .  

We've already seen three fall  nor'easters  this year.  The reason for this is the weak El Nino taking affect in the Pacific.  There is a very good likelihood this will be a weak El Nino during winter 2014-2015 , making the nor'easter king.  Based on the likelihood this will be a  very weak El Nino winter, we most likely will see quite a few coastal storms during winter 2014-2015.   The likelihood of at least one major coastal impacting the major cities along the I-95 is fairly high. 

Based on this, I feel seasonal totals across central and eastern New York, much of New England, and the Mid Atlantic will see seasonal snowfall that is above average...... ending up 25-45% above average. Of course the track the coastal storms end up taking will decide who sees what. So again some areas will see less snow than others, but on average region wide  what I've outlined should be the case. When I looked back at the analog years, one thing I noticed was southern and eastern New England seeing more snow than average . So it is quite possible that southern and eastern New England could be very well, in fact it could be a near to record breaking season.

As for far northern New York, northern Vermont, New Hampshire, into western and northern Maine  average to slightly above average snowfall looks more likely.  so average to perhaps 15% above seasonal averages.

I didn't have time to look up the seasonal averages for all the cities in the Northeast or Mid Atlantic states. ... If You want, I will add those either to this outlook or post them  in another post with a link back to this one. As always I welcome your questions.


Thursday, October 30, 2014

The Storm Prediction Center new convective categorical outlook system.

I've posted on my Facebook Weather Page a few times about the Storm Prediction Center (SPC)  proposing to change the Convective Categorical Outlooks.  Well earlier this month that became official.  The SPC  has gone from the old four overall risk levels to six overall risk levels. The SPC has also dropped the SEE TEXT portion of the outlook; something I'm a big fan of.

The Outlooks are  products that I often use when I post  when I'm talking about the likelihood of severe weather. So I wanted to take a moment to discuss the new changes.

Why the change? The old system was often imprecise. Also, the See Text was very confusing for laypeople to understand. The SPC hopes the new system will better delineate low end severe weather treats.   

Here's an example of the old outlook. ( this is an example and doesn't reflect the current weather)

As you can see it has the slight, moderate, high risk, as well as SEE TEXT.

Under the old system, areas highlighted  in the green color  could indicate anything from garden variety storms to strong thunderstorms ( hail smaller than 3/4 of an inch and winds less than 58 mph).   In order to know where the greater risk was, one had to go to the dreaded SEE TEXT. When reading the SEE TEXT, it helped to have a degree in Meteorology to better understand all the jargon.

Here's an example of the new outlook. ( this is an example and doesn't reflect the current weather)

You can see,  SPC has changed the categories to now include the risk for general storms and then marginal, slight, enhanced, moderate, and high severe weather risks.

Having more risk categories may seem confusing. So let me explain the changes.

General Thunderstorms will be split into two new categories...General and Marginal.

The General category: is where conditions support the  possibly of garden variety storms.  This area is colored pea green. 

The Marginal (MRGL) category:  replaces the SEE TEXT, this means there is the possibility of stronger thunderstorms, maybe a few that reach severe criteria. This area is colored green. 

The Slight (SLGT) category: this means there is the chance for organized severe weather. But the likelihood of widespread severe weather is very unlikely. This area is colored yellow.

The Enhanced (ENH) category: This one  may seem more confusing. The ENH risk is assigned when conditions are becoming more favorable for severe weather, but the likelihood of a severe outbreak is fairly low.  Greg Carbin with SPC suggests the best way to utilize this new outlook is by examining probabilities that are associated with each category and the individual probabilistic threats. This area is colored mustard

The Moderate (MDT) category: when the risk for a widespread severe outbreak is moderately high, including the risk for  several tornadic supercells,  large hail, and squall lines with damaging winds.   This area is colored red

The High category:  means the risk for a major severe weather outbreak is extremely high. This category is reserved for extreme severe weather setups, including the risk for  violent EF4 and EF5  tornadoes,  extremely large hail, and very damaging wind events like significant derechos. This area is colored  fuschia

You can better see how the new system works in the tables below (note the colors are as close as I can get them).



The SPC updates the Day 1 Outlook five times a day. It is used to provide specific guidance based on type of threat:  Tornado, Damaging Wind and Hail

For Day 2 and Day 3 outlooks, probabilities for specific type of storm impacts are not provided.

Well that  should give you a good understanding of the new Categorical Outlooks. As always I welcome your feedback and questions.