Good Signs Of The Long Awaited Pattern Change

Good Evening and Happy Holidays

The weather lately has been pretty boring unless you like rain (It's certainly not my cup of tea) if you are a regualr reader of this blog you have probably heard me speak of a pattern change to more winter like conditions in several different posts and each time they never seem to stick and that has been due to the lack of blocking signals.

The pattern of late has been one of a "here today and gone tomorrow" type but several well trusted models are in general agreement that this is gonna change abrubtly in the new year. Blocking signals are starting to show up strongly in the NAO and PNA regions....lets not confuse the 500mb signals with the teleconnection signals because they are two different signals and dont always support each other. I expect a strong cold front near New Years that will be transported by what looks to be a clipper type system and if enough cold air is already in place we might get to witness one of those rare snow squall lines that set up along the cold front of some clippers during favorable conditions.

Several forecasters originally called for a cold winter but several of the same long range forecasters have since changed their tune to more of a warmer winter. Not me...im sticking with my guns and I fully expect the pattern change to happen around New Years. The AO has been off the charts positive for nearly two months and that is about as long as that usually happens so our saving grace is that it went positive early in fall and now has nowhere to go but to more neutral or negative values.


Toot

Winter Cancel? What?

Im growing tired of the cancel winter calls I am hearing...meteorological winter so far has not been a torch by any means...its been near normal to slightly above tempwise so far this December... Calendar winter has not even started yet and yeah that does have meaning..it's called winter solstice. With that said.... long periods of a tanking AO and a NAO block are not the normal December conditions here either... no matter how bad you may want to see those conditions...Wild swings in temps and patterns are more normal at this lattitude during the period of seasonal change from fall to winter.

Now I realize that people (including me) were expecting the neg NAO/AO to happen in December and it hasn't but it seems people have been spoiled by the last two winters and somehow think that cold and snowy is the normal pattern in December...its not!! People seem to forget that this is the southeastern united states and most unelevated places around here only average one or two days of an inch or more of snowfall during winter. Just remember there has already been two snow events already in the south even though they might have not been in your backyard.

Anybody making such broad statements as "cancel winter weather in so and so month" is completely wacko..I dont care who they are or what forum they post on. Nobody can make such a broad statement like that with ANY accuracy. If they cancelled winter weather for the months of November and December they are already wrong for parts of the mid-south... as they have already had two winter events no matter how long it may have stayed on the ground.

When there is not much confidence in any guidance it's pretty hard to argue with January climatology (which would be our snowiest month) especially if your basing your argument on relatively new teleconnect indices in the long range. People seem to think its allright to trust forcasted teleconnections in the long range but not model graphics when neither is very accurate for some reason. So no thanks...I will stick with climatology at this point

Rumors of Christmas snow

Good evening

Its been a beautiful day today with highs in the 60's to near 70 in some locations and it felt great...but I like to think of this as the calm before the storm. Mid to late December is climatalogically a favorable time for cold and snow around here and when it gets this warm in December you know big changes are coming. There are rumors flying around of some possible snow around Christmas and thats just what they are at this point..rumors!! With that said the pattern is starting to look more favorable after Dec 20th and it is possible that  a major pattern changing storm will occur with possible severe wx. I am talking about the storm around the 20th...

I think a STRONG lakes cutter with possible severe wx along a nice cold front that it will eventually push into the gulf of mexico around the 20th where another low pressure system MAY form along that boundary and ride up it in a path similar to a Miller A...of course this will need great timing and all but the possibility seems to be there. These two systems may be enough to dislodge the PV feature from eastern Canada and Greenalnd long enough where higher heights would then be able to form and in theory high lattitude blocking could then initiate in the NAO region near the new year. At least thats my take on the long range ensembles and teleconnections and any help from the PNA might speed this process up.

Importance of the Polar Vortex

Good afternoon

Most of the time on sundays I find myself wanting to research or write about a related aspect of the current pattern and today is no different.


Since there is a buzz going around about a possible stratospheric warming event I thought i would write about the relationship between the Arctic Oscillation...North Atlantic Oscillation and the Polar Vortex. These features are very important regarding sudden stratospheric warming and the Polar Vortex is the engine that drives NAO/AO. The polar vortex and the AO/NAO are directly related to each other and a general rule of thumb is a strong Polar Vortex equals a positive AO/NAO and a weak Polar Vortex equals a negative AO/NAO. A negative Arctic Oscillation (weakPV) generally means colder temperatures in the eastern United States during Boreal winter and a Positive Arctic Oscillation (Strong PV) generally means warmer temperatures in the eastern United States during boreal winter.

A strong Polar Vortex tends to be more concentated near the pole and circular in shape... it will generally keep the cold air bottled up near the polar regions (as seen in the past 60 days)... but a weaker Polar Vortex will become less concentrated near the polar regions and will become elongated and may even split into several smaller vorticies (as seen in the current pattern)...these smaller vorticies tend to move away fron the polar region and this allows higher pressures to settle in near the polar and arctic regions (yet to be seen). As higher pressures take hold near the pole... lower pressures and Arctic air are transported southward via the smaller vorticies that once were a strong polar vortex.

Strong Polar Vortex
 
Weak Polar Vortex




There is also a direct relationship between the AO and the NAO due to the NAO being measured in close vicinity to the Arctic region. When stratospheric warming occurs lower pressures are generally replaced with higher pressures in the Arctic regions. This usually means some type of blocking occurs in the high lattitudes of the NAO region due to these higher pressures. When this blocking pattern occurs the colder temperatures of the Arctic are forced southward into the eastern United States by a buckle in the jet stream caused by this blocking pattern that is the negative NAO/AO.


To illustrate just how related the NAO and AO are.. here is a graph showing the fall readings of the AO and NAO indicies. Notice how they behave in a very similar fashion to each other




Hopefully this little writeup will help somebody get a better understanding of how the Polar Vortex is the most important feature regarding a cold and snowy pattern here in the eastern United States. I have been watching this feature becoming weaker and displaced here on our side of the globe lately... this and the recent changes in modeling of the AO indice is a VERY good sign that the NAO/AO could be headed to a more conducive value for us winter wx lovers this season... only time will tell.

Persistent Polar Vortex

Good evening.. its December and it sure feels like it outside also. As long as the circumpolar vortex is positioned over northeastern North America its going to be seaonably to unseasonably cold over the eastern US overall. Any forecast that tells you there will be longterm warm spells including teleconnections and/or model graphics should be taken very lightly and with a huge grain of salt. This feature is currently controlling our weather and doesnt look to let up anytime soon. 

GFS at Day 8

Is Winter Over?

I wanted to talk a little about the pattern of the last 45-50 days. The fall/winter pattern that has developed is very unusual and is not behaving in any form or fashion the way it should. During October you had a raging negative PNA which in theory should have torched us...but we come out tempwise well below normal for that month. During the month of November the NAO and AO went positive... but the southeast managed to score an anomalous snow storm in November.

The Arctic oscillation (AO) is raging positive and at near record levels...but as you can feel it's still decently cold outside. On top of all that we are in a La Nina ENSO state... but yet there is a very active and visible El Nino like subtropical Jet stream. Despite La Nina conditions that say we should be warm and dry... we have actually been more cold and wet. We have been able to stay near or below normal despite unfavorable teleconnection indices and a pesky little southeast ridge..also there seems to be an abundance of strong cutoff lows this fall/winter.

Those that say winter is in trouble are totally looking way too much at numbers and teleconnection indices. They're not taking synoptics and verified data into account. As we get closer to a more climatalogical favored time period for winter weather... I see no reason why there wont be nice winter events with plenty of cold air. This fall/winter so far has been very wet compared to most and there has already been two snow events pretty far south for this time of year. We're getting closer to the real winter season here and when we have a nice arctic airmass in place I can totally see one of those big bowling ball cutoff lows dumping snow in a very widespread fashion despite a positive AO/NAO if that is still the case.

Our winter will happen...it's just not going to happen the way we have gotten used to it happening the last two years.

Early December Snow

Good Afternoon

Pattern Starting To Look Very Active

Good Evening


Im becoming very interested in the pattern. The timeframe around the Dec10-Dec20 is so close to being something nice...with the ridge off the east coast blocking the frontal systems from exiting the area and the arctic air piling up behind the front....it sets up a very nice baroclinc zone for many waves of low pressure to ride up.

Im starting to think someone gets a nice surprise. This stalled out boundary may hang around our backyards for several days and the snow chances will be on the rise with this setup. Im not ready to call for accumulating snow just yet...but it sure seems to be trending that way. Would like to see more model runs before totally coming on board but its a very conducive setup that will probably send the NAO and AO into  a freefall

Arctic Air Set To Invade The SE

Good Morning

Well it seems the Euro was onto something a few days back and the polar vortex will drop into the northern states to say hello and it will push frigid air all the way into the south around the 10th of the month. There may be a few snow showers that accompany this cold front but that is yet to be determined.


This will set the table for a possible widespread winter type system in the east. Temps will be as much as 20 degrees below normal in some areas. So bundle up

Toot

Weekend Stalling Frontal System

Good Evening

Another system near the weekend is starting to get a little interesting but in reality it will likely not produce any snow except for the higher elevations. A cold front will stall across the region with an area of low pressure forming near the SE that will ride up that frontal boundary producing some moderate rains and mountain snow.

If that LPS is a little stronger than modeled it would be possible for some valley snow but i'm seeing pretty good model agreement that argues against any snow in the valley. After this system the pattern is starting to look a little better for cold and snow.

The middle of December holds nice potential for some type of widespread winter event in the east IMO.

Toot