SnowTALK! Saturday Edition- FOCUS: The Big COLD Coming or Not?

Risks Today:
1) None

Snow showers late tonight/tomorrow look too light to warrant any concern.

The forecast is now on what lies ahead.  There has been LOTS of talk about a major cold blast..and /or winter weather rivaling 1978 and 1994 moving toward us.  As I have said many times before---no two winters are a like. 

The post below can be technical at times..and wordy. But there is not "simple" way to explain this subject---so I apologize in advance!!!

This young one so far has been dominated by short cold snaps combined with a very active southern jet to feed us many storm systems. Our cold has been marginal with each event---so the active south winds that comes before each low pressure---have placed us in a zone of "rain or snow" almost every time.  That is just the way the pattern goes.    I still feel our best snows this seasons will come from over-performing clippers (like last March) and when we warm up from an extended period of Arctic air.

Neither one is likely for the next 7-10 days.

The main change that is of note that many of you have heard about is the Stratospheric Warming.  This is then the upper layers of the atmosphere near the North Pole...warm.  When that happens, high pressure builds in and the cold air that WAS there....gets broke lose and heads into lower latitudes.  It is when that happens---the winter fun begins.

So how does it warm?  The winds around the Polar Vortex (core of the cold) are westerly. Sometimes there are changes in the lower levels of the atmosphere (some we still cannot explain to this day) that allow for those winds to relax.  Even if they relax, the lower latitudes (where we live) can still have just a so-so winter.  But it is when those winds not only relax  but it is when they REVERSE...that things get exciting.  When the core up north develops an east wind..the Polar Vortex gets broken up and flies in all directions south.  Sometimes is over the United States.  Sometimes Europe..sometimes Siberia/Asia.  Unfortunately, we cannot predict that in long term models very well at all.  We saw the stratosphere warming last year---but the main piece that broke off went to Siberia.  Not the United States.  Therefore---we had a warm winter with no help from up above.

Having said all of this---the latest trends are showing warming now taking place.  And the Polar Vortex looks to be taking a beating from different directions.  This is already slowing the westerly winds in the stratosphere.  Look how they have calmed in recent days:

The end result?  Warming is now developing over one section over Asia and expanding into more of the stratosphere.  Click the link below to see that animation.

http://www.cpc.ncep.noaa.gov/products/intraseasonal/temp10anim.gif

Other models are hinting that more warming will soon react to the west winds slowing up there..and a major warming will take place over Canada.  Click to see the animation below.

http://www.cpc.ncep.noaa.gov/products/intraseasonal/temp50anim.gif

So for the first time this year---- the stratosphere is about to take a significant beating and the winds will likely reverse east.  This means the Polar Vortex is about to break up.  Into how many pieces is unclear, but it will likely break up and head south.  The AO index we use a lot is the main display for such events like this.  Look how it is forecast to tank....indication the cold air (polar vortex) is on the move.

The whole process above takes about 14 days to complete and mature.  So we have plenty of time to fine tune specifics.  I would highly caution the cold outbreaks on the GFS/EURO until we get a bit closer in time of the event completing.  They are certainly sniffing out the chances that one or two pieces may impact the western USA first----then spread into the east after the 20th.

GFS sees the cold by the 15th sinking south. I think this will go a bit more west.

EURO--- sees the cold dropping as well.

One of the driving factors will be blocking.  This is where the NAO will be key. Stratopheric warming leads to blocking patterns...but there are many out there.  For our area, the NAO needs to go negative.  And the latest indicator is seeing this.  I, again, think that is why the models are showing cold in our future.

So what would happen if this all DOES take place?

This is generally how it works:

You get cold air into the west coast.  Strong areas of low pressure in the Plains.  At some point, one of those strong lows will push into the eastern Great Lakes.  That likely will lead to a rain/storm event that ends as snow.  But it will be that large storm that will crash us fully into the Polar Vortex influence.  I can see this happening between the 15th-20th.

Once the vortex takes over.  We join clipper land. :)  Several clippers will rotate through the area.  As usually the case, the ones that track just south/west of Louisville can give us a good 1-3" band of snow with banding features able to dump 6+".  This would especially be true if snow ratios are high...which with the extreme cold---would be likely.

After a period of time in the vortex, the indicies will dictate when we pull out of the pattern.  Once we do, the next storm that warms us up likely would be a big winter storm.  These make me nervous as ice storms become a huge threat in those setups.  Hopefully...anything that takes place in the transition back to warm will be minor.  But that is a long way off ---so I am getting ahead of myself :)

So there ya have it.  Long/wordy post---sorry.  But there is a lot to monitor in the coming weeks despite the warmer weather trend.

I just would not get excited about any snow chances until the last 10-12 days of the month.

We will keep you updated on this developing situation---expect adjustments.

 

Comments

[Chris]

One thing is for certain. So far, this winter has still been warmer than last winter. And last winter was a Top 10 Warmest winter. It will take several outbreaks of cold to move this winter even back to normal. Not saying it is impossible, but the first three weeks of December were extremely mild!