WHY THIS WINTER HAS SUCKED FOR EASTERN US
In order to answer the question
WHATS GOING ON WITH THIS WINTER OVER THE EASTERN CONUS (and other questions such as " (and other questions such as "
where all the snow is"....and ....and
" is there any chance for any actual Winter weather over next 60 days" it is important to understand how snow storms develop over the central and eastern portions of the CONUS. Lets keep it pretty basic.
Snowstorms consist of two parts.
1. The SOUTHERN jet stream, which sometimes may also include a fairly strong piece of energy in the southern jet stream. This is the moisture source.
2. The NORTHERN jet stream which provides the cold air.
When these two Jet streams merge or " phase 'it can produce a powerful area of LOW pressure and these will become major winter storms whether it is for the Midwest or Great Lakes ...the Ohio Valley ....the Middle Atlantic or the entire East Coast.
But when the southern jet stream and the northern jet stream do not PHASE then the surface LOW pressure that forms over TX or the Gulf coast states or the Southeast US ....usually slides off the North Carolina Coast and heads out to sea.
That is exactly what is happening this weekend. Several days ago the various weather models showed a large powerful major east coast winter storm a true Nooreaster) for this weekend with heavy snow in New England and the mountains of the Middle Atlantic region and rain over the eastern areas of the Middle Atlantic region and the southeastern states. But that was based upon the idea that the northern jet stream and the southern jet stream are going to Phase.
However over the past few days the model data very clearly shows that on Friday and Saturday the Northern jet stream is NOT going to phase with a Southern jet stream. Instead the Northern jet stream will push the southern LOW off the North Carolina Coast and out to sea. Moreover because the two jet streams are not going to Phase the LOW pressure area does not become a big huge LOW BUT a rather ordinary garden variety type of LOW pressure area.
This has happened several times this winter and it is symptomatic of what has been happening for much of the winter. Because of the speed and power of the jet stream over the northern Pacific and Alaska .... it has been very difficult this winter to get the cold air coming out of Canada AND to have the northern and southern jet streams phase and produce a big storm on the East Coast. For the Midwest and the Plains regions... there have been a number of major winter storms. This winter the overall pattern has favored these areas getting hit by the winter storms. That is where will the snow has been.
Going into this winter there was a lot of forecasts including mine which believe that the solar minimum this winter combined with the very weak near neutral phase of the QBO and the persistent blocking in the jet stream patterns we saw in the Summer months into early autumn over Canada and Greenland ... meant that we were going to have an active and stormy winter over the eastern CONUS. .
That forecast is wrong... and MY winter forecast is wrong. Even if by some chance February and March turn out to be fairly decent winter months... the fact of the matter is that any forecasted that called for an average or colder than normal winter for th eastern half of the CONUS is going to be wrong. Likjewise any forecast that calld for an average snowfall or above average snowfall for the eastern third of the country is also going to end up being quite wrong.
So the next question is how come winter pattern keeps repeating and keeps favoring the Plains... Rockies... and the Midwest with big winter storms while the eastern third of the CONUS sees mostly mild temperatures and a lot a rain?
First keep this rule in mind--for every action there is an equal and opposite reaction.
To get a classic significant East coast snowstorm and /or a sustained cold and snowy pattern for the eastern third of the CONUS we need to be Jet stream patterns to be set in
5 special jet stream configurations which some of you may have read or hard about . They are:
The AO ( Arctic Oscillation):
When the AO is in the “negative phase” it means that the Polar Vortex is no longer large and powerful and centered over the North Pole. A –AO means a much weaker Polar Vortex which means northern jet stream is weaker so the chances of seeing blocking patterns developing In Alaska Canada or Greenland is greatly increased turn along with increased chances of seeing cold air coming south and for the northern jet stream to merge with a southern jet stream.
THE NAO ( North American Oscillation)
When the NAO is in the “ negative phase” it usually means that we have some sort a blocking pattern over eastern Canada / Greenland. When this happens it tends to suppress any sort a Ridge in the jet stream over the Southeastern states. In other words it allows LOW pressure areas to stay to the south so we are on the cold side which is where the snow is. (when LOW pressure areas pass over you or to your north and west ... you are on the warm side so the precipitation is usually rain or snow changing to rain)
THE PNA
When the PNA (Pacific North America) is in the "positive phase" it means that there is a Ridge in the jet stream along the West Coast which extends in the Western Canada. The Ridge supplies cold air from western Canada into the central and eastern CONUS . Without a sustained Ridge in the jet stream over western Canada it is very hard to get sustained below normal temperatures over the eastern third of the country.
THE EPO
When the EPO is in the "negative phase" -- think Siberian Express.
(If you are not familiar with that term it is a popular term use to describe an Arctic air mass outbreak from northern Canada into the central and eastern CONUS). Technically what happens is that when the EPO is in the negative phase it means that the ridge in western Canada is enhanced or stronger than normal and extends up into Alaska and the arctic regions. This establish is a “cross polar flow” from Siberia across the Arctic region into central Canada and then eventually into the U.S. (the Siberian Express).
The 50/ 50 LOW -
this is a term used to describe an area of LOW pressure at the surface and at the mid levels the atmosphere which is located over southeastern Canada near nova Scotia / New Brunswick or Newfoundland . When there is a large slow moving area of LOW pressure over southeastern Canada areas.. other LOW pressure areas coming out of the Gulf coast/ Texas are forced to stay to the south. This means the air mass stays colder over the Middle Atlantic region as well as the Ohio and Tennessee Valleys... which increases the chances of snow and or ice and reduces the chances of rain.
Now all that being said let me be clear about this.
You don't need all 5 of these things special jet stream configurations in order to get snow. Some of these features can be neutral and you can still end up with a fairly good pattern for snowfall. But to get the really big snowstorms and/or an extended interval of winter weather we usually need four of the five special jet stream configurations to be in the ideal winter weather / snowstorm.
WHAT HAS GONE WRONG
1 As I stated my original winter forecast October and then again in November the biggest concern I had was the development of a larger pool of warm ocean where temperatures in the northern Pacific and the Gulf of Alaska. I had hoped that this pool of warm water which lie to the west coast of North America and in doing so would greatly enhance the chances of seeing a much colder weather pattern in the jet stream for the central and eastern U.S.. Clearly that has not happened.
2 Instead the large and persistent pool of warm ocean water temperatures in the northern Pacific and the Gulf Alaska have forced done two things to the Jet stream as it crosses the Pacific ocean and reaches West coast of North America.
A - the persistent Ridge in the jet stream over Alaska and the deep and persistent Trough in the jet stream over the western third of the CONUS means that the EPO pattern has consistently been in the Positive phase (.not that much desired Negative phase)
B- the persistent trough in the jet stream over the West Coast or western third of the CONUS means that PNA jet stream pattern is in the " Negative Phase" -- and not in the much desired "Positive Phase"
3
The deep and persistent trough over the western third of the CONUS means that the atmosphere responses by a persistent developing a Ridge in the jet stream over the Southeastern states. The result is that the cold air coming out of Canada is more likely be going into the Plains and Midwest regions as opposed to the East Coast.
4
The Polar Vortex (PV) has been very large and very intense and mainly situated over North Pole. This is unusual because research shows that when the sun is at its weakEST cycle (called the Solar Min in the Climate business) the Polar Vortex is weak and fractured. For some unknown reason, this Winter the PV has been large.. intense ... and persistent. A large intense PV means that AO (Arctic oscillation) has consistently been in the positive phase all winter
5.
The large intense PV has also been located over northeast Canada . This prevents any sort of " blocking pattern" from developing over or near Greenland. Hence the NAO has been persistently Positive (again a +NAO is the exact opposite of what you want for a cold and snowy winter). The combination of the +AO and the +NAO both running consistently positive and at times strongly positive has been greatly reducing the chances of seeing sustained cold air coming into the eastern CONUS and reduces the chances of seeing any sort of significant East coast Winter .
Parenthetically the only good thing about the large PV... strongly + AO ... and strongly +NAO is that they are both causing a massive increase in the snow ice over the Arctic regions and has stopped the rapid melting of the ice / snow cover in Greenland. So the next time you read the story or comment about how the snow and ice in these areas have made a big comeback ... remember that it came about because the eastern CONUS has had a particularly mild winter.
IS THERE ANY HOPE AT ALL for the Middle Atlantic to see any sort of significant winter weather before April 1?
Well it depends on which you mean by "hope" There is always some chance that 2 or 3 of the 5 special jet stream configurations might change. However none of the extended data which is fairly good out to 2 or 3 weeks is showing any sort of significant changes in any of these five special Jet stream configurations.
Perhaps the only way to get ANY sort of significant winter weather into the Middle Atlantic region is to develop a type of event which does not require the 5 special jet stream configurations to be set in a certain way.
One such possibility might be the first full weekend of February. That is to say the weekend of February 7 -8-9. A strong cold front is going to move into the East Coast on February 6 bringing widespread heavy rain and maybe even some thunderstorms. It will be ending the warm pattern most of us will see February 3-4-5-6. .
This cold front will push deeper into the Carolinas and the Southeastern states but the question becomes how far does the cold air penetrate.? Some models have the cold air reaching the North Carolina Virginia border on Saturday morning February 7 while other models have the cold air over the northern half of Virginia Maryland and West Virginia. This is important because the models develop a weak of LOW pressure that develops on the stalled cold front and tries to push mild air into the cold air over the Middle Atlantic region.
This kind of event is not a coastal storm at all. It is refer to as an
OVERUNNING EVENT because one air mass tries to overrun another. Usually a warm front is trying to move north and in doing so because one air mass tries to overrun another. Usually a warm front is trying to move north and in doing so
overruns the cold air at the surface. These types of events can produce significant amounts of precipitation and occasionally have produced moderate to heavy snow or even some significant ice storms. But more importantly overrunning event which might bring some snow and or ice into portions of the Middle Atlantic on February 7 does not require any of the 5 special Jet stream configurations to be set in any particular kind of pattern.
It is the one way -- the only way - to get around this problem of not having a great jet stream pattern over North America and still get some kind of winter weather.
Finally let me point out that because of the changing climate conditions over the last 20 years... the month of December has been known for being quite mild and at times snowless. There have been a few exceptions. December 2002...2009 and 2013 all featured significant snow storms over the Middle Atlantic and/or New England areas. And those winters went on to become significant winters with lots of snow storms and colder than normal temperatures over the eastern CONUS and the especially in the Middle Atlantic.Finally let me point out that because of the changing climate conditions over the last 20 years... the month of December has been known for being quite mild and at times snowless. There have been a few exceptions. December 2002...2009 and 2013 all featured significant snow storms over the Middle Atlantic and/or New England areas. And those winters went on to become significant winters with lots of snow storms and colder than normal temperatures over the eastern CONUS and the especially in the Middle Atlantic.
But outside of those three Decembers.. most of them have been quite mild over the last 20 years
On the other hand the month of
MARCH over the last 20 years has persistently run colder than normal with a number of significant snow storms over portions of the Middle Atlantic New England Ohio and Tennessee Valley areas. This has led to a number of people noticing that March seems to be a continuation of winter and that the Spring season never really starts in Virginia North Carolina Maryland or Delaware until April.
It is somewhat uncommon but not unheard of for all five of special jet stream configurations to be "locked in" for three consecutive months without any real change. But it has happened before.
But it is rare to see this current hostile upper air jet stream patterns since December 1 continuing throughout the entire month of March. That would make four consecutive months of having a pretty awful Jet stream pattern across North America for the eastern CONUS.
The odds do favor some sort a shift in the pattern in the month of March and a shift towards something more favorable for seeing winter weather over the East Coast. Interestingly my experience has been that a cold and snowy March brings about an interesting dichotomy of attitudes and perspectives. Some hold the attitude " big deal it's March... the winter is over so a cold/ snowy March doesnt count", Others seem to have different perspective about March Winter weather-- "well a least we are getting something".
^Dave Tolleris
