Troughs and Next weeks weather.

I've been getting a few questions on what exactly is a trough and want causes it to form. So I thought I would answer in it in the blog.

The weather Next Week

This morning places in New York, Pennsylvania,  and northern New England saw temps in the upper 30's and low 40's. make it feel like Fall.  Pennsylvania and Mid Atlantic States will see heat and humidity this weekend. New York State and New England will see temperatures and dewpoints rise this weekend...but not as much as those to the south.

 But as I said on my Facebook page, the warmer air will be temporary.  We're going to see a trough move in from the north and west. The trough will set up shop over the East Coast, allowing cooler than average July temperatures to invade even the Deep South.  The reason for this is the jet stream pattern, we're still basically in the same pattern we had during the Winter of 2013-2014.   

In The Great Lakes and  New England it will feel more like late September than July. Those around the Great Lakes and Higher Elevations of New York and northern New England.... a few days next week will see highs in the upper 50's into the 60's, with night time lows in the 30's-40's.

 

 
What is a trough?

A trough is an elongated area of low atmospheric pressure that can occur either at the Earth's surface or at higher altitudes.  Upper-level troughs influence many surface weather features, including the formation and movement of surface low pressure areas and the locations of clouds and precipitation.

Normally precipitation will fall to the east of the trough axis while colder, drier air tends to prevail to the west of the trough (in the Northern Hemisphere).

When the height contours bend strongly to the south, (as in the diagram above), it is called a trough. Strong troughs are typically preceded by stormy weather and colder air at the surface.

Troughs and Ridges deal with things like geopotential heights,  Vorticity Advection, Temperature Advection. These are very complex and deal with a lot of  physics, differential geometry and complicated math equations. I will try to keep the math and science out of the discussion .

The primary characteristic of a trough is that it is a region with relatively lower heights. Height is a primary function of the average temperature of the air below that height surface.

For example, if it is 500 mb heights then the 500 mb height is based on the average temperature between the surface and 500 millibars. The density of air changes with temperature. As the temperature of air cools down it becomes more dense and thus more compacted (takes up less volume). Therefore, as air cools the height lowers since the air is becoming more dense. Air will cool when it rises, thus a trough can be found where there is a lifting of air.

What is geopotential?

1 geopotential metre=0.98 dynamic metres

geopotential height is a better measure of height in the atmosphere as energy, is in general, lost or gained when air moves along a geometrically level surface. This is because geopotential depends on geometric height and gravity with mean sea level being selected as the zero potential height.

The unit of geopotential is the potential energy acquired by unit mass on being raised through unit distance in a field of gravitational force of unit strength.

Low geopotential height (compared to other locations at the same latitude) indicates the presence of a storm or trough in the mid-troposphere.

Relatively high geopotential height indicates a ridge, and nice quiet weather.

Decreasing geopotential height usually indicates an approaching or intensifying storm.

Increasing heights usually indicate clearing weather for the period.

Vorticity Advection:

 

The term advection refers to the transport of something from one area to another. In Meteorology advection deals with variables like temperature, moisture, and vorticity.

In Meteorology, vorticity is a property of the stream flow, namely the amount of localized rotation of the air, air that rotates counterclockwise, such as the low pressure associated with troughs, is said to have positive vorticity. Clockwise rotating air, such as in high pressure systems and ridges, has negative vorticity.  Vorticity advection is indicative of rising motion/falling pressures at the surface. In the atmosphere vorticity is caused by a change in wind speed (shear), change in wind direction (curvature), and the spin of the earth on its axis.

The advection of vorticity at high levels will result in a response at the surface which will attempt to offset the effects of the advection. More specifically, vorticity advection is indicative of rising motion/falling pressures at the surface.  

Vorticity advection does not amplify the wavetrain. But what it does do is allow the eastward movement of the  trough/ridge

Temperature Advection:

Temperature advection  occurs when  wind transfers heat energy horizontally through the atmosphere.  Cold air advection is when the wind is carrying cooler air into an area that already contains warmer air.  On the other hand, warm air advection is when the wind pushes warmer air into an area that already contains cooler air.  Temperature advection is measured in terms of the amount of temperature change that occurs in a given interval of time.   

Temperature advection  will deepen a trough, and build a ridge

So basically this all means.......As high and low pressure build up in the atmosphere, between places where the air rises (low) and sinks (high). There are also long elongated areas between those. Often we say that areas of low pressure are separated by a ridge of high pressure. it is not exactly a high pressure center but rather, a region of higher pressure between two areas of lower pressure.

Likewise, a trough is a region of lower pressure without being exactly a center of it. The difference is that, spin counter-clockwise along a trough, the air doesn't (in the northern hemisphere) but rather, influenced by the nearby clockwise motion of the surrounding high pressures.

 

It's a complex subject.... but I hope I made it more clear...................

Tropics are still quiet.

Satellite imagery over the tropical Atlantic for this Thursday afternoon,  shows no areas of  real convection. There are four or five tropical waves out over the Atlantic and Gulf, but none show very much in the way of thunderstorm activity. But we do have a Cape Verde wave that does have some potential, low potential but potential none the less.

 

Cape Verde Waves can become classic Cape Verde hurricanes, so-named since their development can begin soon after a tropical wave leaves Africa and passes near or over the Cape Verde Islands.

I've been saying the reason for the slow season is dry dusty air, cool  surface water temperatures, and disruptive wind shear.  El Nino is on the stove cooking, but it's not quite ready to put on the table yet.

Here's a look at the latest Saharan Air Layer (SAL) image. You can see it is setting right over the normal tropical cyclone formation zone.  The Models show this continuing for the next 6-10 days, and maybe longer. The teleconnections are all showing it should be quiet in the Tropical Atlantic Basin for the next week and a half to two weeks.

 

                                                                 Saharan Air Layer

We also have a giant area of high pressure setting in the middle of the Atlantic. This is forcing the tropical waves to the south. Looking at the wave emerging off the West Coast of Africa, you can see it is south of where waves normally emerge. 

 

                                             GFS showing high pressure over the Atlantic

As I said this Cape Verde wave has potential. The environment is hostile. But this could be slowly changing.  Wind shear has started to relax over the last few days.....this tendency looks to continue for the next week to ten days.

                                                           Wind Shear yesterday

                                                               Wind Shear Today 

Hurricane Donna was a Cape Verde storm, she too emerged south of Dakar. I'm not saying this wave will do the same thing, in fact it odds of development are low... But it has possibilities.

 

                                                Areas where development is possible

                                                          Hurricane Donna's track

 

We also have an area in the northern Caribbean and off the Southeast Coast that has a chance for development, as well.

So while it is quiet now, anything can happen. Tropical Cyclone Bertha is bound to form sometime this season.

Are there more tornadoes occuring than ever before?

This past Tuesday at a news conference, after surveying the destruction in Smithville, NY, and other tornado damage,  New York Governor Andrew Cuomo said that "We don't get tornadoes in New York, right? Anyone will tell you that. Well, we do now.". Now while this is factually incorrect, I know what he meant; That being most people don't think dangerous, powerful, and deadly tornadoes occur in New York State, or even the Northeast for that matter. But they all would be wrong.

This data comes from the Online Tornado Project....Database is dated for 1950-2012.

As far as I know these numbers are correct .

F5/EF5

Pennsylvania:

Mercer County on MAY 31, 1985.

F4/EF4

Pennsylvania:

Allegheny County  June  3, 1980.   

Clearfield County  May 31, 1985.

Erie County  May 31, 1985  (at 15:25).

Erie County  May 31, 1985 (at 15:01).

Mercer County May 31, 1985.

Somerset County June  2, 1998.

Venango County May 31, 1985.

Warren County May 31, 1985.

New York State:

 Columbia County on Aug 28, 1973

Chautauqua County  on  May 31, 1985

Montgomery County  on July 10, 1989.

Connecticut:

Hartford County  Oct 3, 1979.

New Haven County  July 10, 1989.

Maine:

0

Massachusetts:

Berkshire County on Aug 28, 1973.

The great  Worcester County  tornado, on Jun  9, 1953.  I will come back to this tornado in a bit.

New Hampshire:

0

Vermont:

0

Rhode Island:

0

New Jersey:

0

Delaware:

0

Maryland:

Charles County  Apr 28, 2002.

Garrett County  Jun  2, 1998.

Could there have been others ?  I know there have been other F4 and F5 tornadoes, beyond a shadow of a doubt.  Decent  record keeping on tornadoes only goes back more or less to 1950. Before that  Tornadoes were mentioned sometimes, but many weren't.  But even after 1950 the records can be sketchy.   The F-scale was introduced in 1971.  Tornadoes that have F-scale rating before that time, are estimates based on secondhand evidence.

One Such tornado was the 1878 Wallingford  Connecticut  tornado.  Estimated to have been an F4. This is the deadliest tornado in Connecticut history.

The violent 1953 Worcester tornado, which killed 94 and left at least 288 injured, was rated an F4 . Several  people myself included believe it was probably an F5. The tornado was rated F5 by Thomas P. Grazulis in Significant Tornadoes 1680-1991: A Chronology and Analysis of Events.

Grazulis is an author, producer,  meteorologist, and storm chaser. Grazulis amassed one of three authoritative tornado databases, those being the National Tornado Database assembled and maintained by NOAA agencies, the University of Chicago DAPPL database founded by Fujita which ended at his retirement in 1992, and the Grazulis Tornado Project database.

The list of F1/EF1 - F3/EF3 is much longer, than the above list.

A partial list of outbreaks that have stuck the Northeast.

Four-State Tornado Swarm  August 15, 1787. This has the distinction of being the first known U.S tornado outbreak.

September 9, 1821. New England tornado outbreak .

September 20, 1845 New York outbreak.

May 1896 tornado outbreak sequence.

1926 La Plata, Maryland tornado outbreak.

June 22–23, 1944 Appalachians tornado outbreak, deadly tornadoes were observed in Pennsylvania and Maryland.

May 2, 1983  New York State  

May 31, 1985 United States–Canada tornado outbreak.

July 10, 1989  Northeastern United States tornado outbreak.

May 31 1998 Pennsylvania, New York, New Hampshire, and Connecticut outbreak.

So you can see that New York and the rest of the Northeast is no stranger to violent tornadoes. Governor Andrew Cuomo said "New York State doesn't get tornadoes".  However, when you crunch the numbers of total tornadoes by state, from 1950-2012, New York State ranks 30th among all states in total tornadoes.  On average New York State sees 10 tornadoes a year, Pennsylvania sees 16 on average, For the entire Northeast, the number of yearly tornadoes is  46.

 

I've been asked by several people, are there more tornadoes now than there was 15-30 years ago? I've seen the same question inferred on my Facebook weather page. It's a fact, the number of reported tornadoes across the northeast is rising slightly when compared to the 1950-2012 tornado data bases, especially over the last 12-14 years.

So based on those statistics, the number of annual tornadoes is increasing. But there are a couple of other facts we have to take into consideration,  People are interconnected now more than any other time in human history. We have social media, we have portable tablets, and smart phones, and many other little gadgets. Most of these gadgets have cameras on them. Most people always have a camera of some kind with them most of the time. So it is very easy to take pictures of severe weather events, like tornadoes. With social media sites like Facebook, Twitter, YouTube, and many others, it is very easy to show the world what you saw.

For example, take the EF1 tornado that touched down in Deerfield, NY, Tuesday evening. That was caught on video. Without that video evidence, the NWS most likely wouldn't have done a storm survey at all. Without  a survey, there wouldn't have been a record of a tornado in Deerfield on that date. The actual number of tornadoes that occur in the Northeast (and the U.S.) every year, is very likely much higher than what is reported. There are many tornadoes that are not seen by human eyes. So like the proverbial Bear in the Woods......if no one saw the tornado...was there a tornado?

Also, the NWS has better equipment than they did just 10 years ago. Things like Dual-Polarization Radar (Dual-Pol) that lets us see into severe thunderstorm like never before.

So is the number of tornadoes increasing? Maybe. But I think it is far more likely that  the  improved detection and reporting systems we have at our disposal, is the reason for the increased reported tornado activity. 
       
The tornado that took the lives of four people in Smithfield, NY, on Tuesday evening, is not the first deadly tornado in the Northeast, and sadly it won't be the last. The only good thing that could possibly come from the tragedy in Smithfield, is that people take severe weather seriously, that they become weather-aware.

The tropics and it's going to get chilly next week.

The Tropics in the Atlantic Basin  are quiet, and look to stay that way for at least the next five days. The reason is  strong wind shear and dry stable air.  When you have this kind of setup the tropical waves moving off of Africa heading across eastern and  the central Atlantic have no chance of forming tropical cyclones.  

El Nino is still missing in action. But the teleconnections and sea surface temperatures ( SST's) show a good likelihood of El Nino.  The Climate Prediction Center (CPC) still has the chances for El Nino at 70% for later this Summer and up to 80% for the Fall. As I've been saying, I think it will happen later this Fall. Some are calling for a strong El Nino. But I don't think its going to be that strong.... more likely weak to maybe moderate.   As I've said in many blog post and on my accompanying Facebook page...eastern based El Nino's cause wind shear to increase over the tropical Atlantic Ocean.  So with the Setup in the Pacific still strongly pointing toward El Nino, it is really no surprise to see all the wind shear over the Atlantic.  

 

 

I've also mentioned quite a few times that  Saharan Dust inhibits tropical formation as well. It typically brings dry air that is not conducive to storm development, and some studies have suggested the dust itself has an effect on cloud formation, dust that is suspended in the wind absorbs and scatters solar radiation. This means less sunlight reaches the ocean surface,  resulting in cooler temperatures in the tropical Atlantic Ocean, therefore cutting off the fuel supply to any waves moving over the tropical Atlantic, and inhibits development of tropical cyclones.  Just remember inhibits doesn't mean excludes tropical cyclone formation in the Atlantic Basin.  

 

 

Any tropical waves that do make it into the Caribbean and Gulf; they can become tropical Storms and hurricanes. As was the case of Arthur.  Because of the setup over the Atlantic Basin, the East and Gulf Coast are more at risk for land falling tropical systems.  

 The week of July 13th-19th.

This coming week is going to see an old friend return. That being the Polar Vortex.  I'm sure most of us can remember the havoc the polar vortex caused last winter..........

Next week unseasonable very chilly air looks to move into the Midwest and Northeast. The vortex is going to allow a very cool air out of the Gulf of Alaska  to plunge into the northern tier of the U.S. typhoon Neoguri that just hit Japan, is going to play a huge role in the pattern, by amplifying  the area of low pressure over Alaska. The west coast trough will act like a slide giving a clear path for the cooler air to the south.  Right now it looks like the Midwest will take the brunt of the cold. However the Northeast will see temps 10-20 degrees below average, especially in the northern parts of New York and New England. I expect to see record lows set this coming week.  

 

Current surface chart, note the low in the Gulf of Alaska.

 

Here is the position of the vortex on Monday.

For Tuesday

And for Wednesday.

 

We had a very volatile  Winter....The Spring saw the same type of validity... I expect Summer of 2014 to continue the same theme ...long range teleconnections and models are showing a pattern of wild temperature swings and possibly an active severe season this Summer. One only has to look back to this past Tuesday to see just how severe it could get.......