COLD comes Tonight...Next Week's Storm Still Has Legs!

Man will Winter come in with a BLAST later this week.  In fact there was a 22 degree temp drop in PIT going from heavy rain and thunder to very heavy snow!  The idea I have presented in the last 2 blogs continues to hammer away the idea that winter will roar it's ugly head faster than many can imagine.  Here's a little advice for many of you.. Get the outside water turned off NOW!  Sitting in the weather office today and going over just the GFS X MOS data for New England brought a chill to my backbone.  Overnight low's 14 for the Hill Towns and Mountains to 22-26 for the valley's.  Lehigh valley, Pocono's, Blue Ridge mountains.. ALL very similar readings heading into next weeks over night low's.  This is a BIG change from the 50 degree day's and 30-40 degree night's!!

The image below is a comparison of the 8-10 day forecast from 2 of our long range computer models.. Both show a well developed negative NAO pattern with a sustained trough over the east coast.

 

 Overall the NAO itself has been mostly negative for a solid portion of the fall season.  With the Arctic Oscillation continuing to hold on to it's cold position; it has influenced the - NAO pattern to remain rather unchanged.  The difference now will be the density of colder air over the polar regions which will continue to pour down out of the Yukon and even as far west as Siberia. Before we cold air source remained help up under the influence of the Polar Jetstream.  With shorter day's changing synoptic patterns the cold air has nothing else to do but expand out and sink.  COLD AIR = MORE DENSE ///WARM AIR = LESS DENCE.  With the PNA still at a Negative to neutral phase (Trough out west..Ridging development over the South Atlantic coast of the US)  any "Real" cold air will stay bottled up towards the Northern Tier of the Nation.  This due in part to a less sharper trough for the east.

IMAGE SHOWS THE NAO TREND FROM LATE AUG.

 WHEN WILL IT SNOW?

While I am happy to see the Negitive NAO and the cold air back in play.. There is a PROBLEM.

We have thus far broken the NAO into a Positive Phase (warm) and Negitive Phase (cold).. We must next talk about two phases of the COLD phase.  

NAO development is weird in the sense that essentially it is dependent on Height Rise vs Fall's over the continent of Greenland.  When a Neg NAO develops we tend to see more ridging from the North Atlantic all the way into central Greenland which has a low developed underneath (which we refer to as the 50-50 low).  There are variations of such  - NAO developments.  We could have a more WEST based ridge that noses itself into the Davis Strait and Quebec or and East Based one which would bring the axis of the ridge more so over Ireland.  Different positions bring different storm tracks for the Mid Atlantic and New England. Since the axis of the ridge would change so does the low associated with it.  We call this low "The 50-50 Low".  The term "50-50 Low"   refers to the development or appearance of a strong or intense Low-pressure area both at the surface and in upper levels of the atmosphere -- usually at 500 MB -- over or near the positions of 50 degrees North Latitude and 50 degrees West Longitude.

Hence the 50-50 naming :-) ... Pretty easy HUH!

While this - NAO I am forecasting is welcomed news for COLD lovers.. The exact type is still unclear.  

The image here is taken from last nights GFS model run.  Note the Height extensions going from SE to NW direction.  This is a west based type of NAO development.  In this case we find a weaker 50/50 low with an upper level low trying to develop on the backside of the Ridge over Greenland.  This would be VERY problematic since this cut off low will develop an upper level trough over the North East.  SEE BELOW

 This better shows the Upper Level's and Jet Stream pattern.  Note the crushing trough over New England.  This type of scenario would keep the northern stream and southern stream apart and would force any appreciable storms to the south opposed to up the coast.

 The is however, a disagreement among our top 2 models.  The EURO model wants to toy with the idea of correcting the upper level low more east thus allowing to establish a stronger 50-50 low.  The below image is showing a 200 mi west shift then the GFS with a strong coastal storm trying to take shape.  While I am not saying this is the correct solution... The idea shouldn't be dismissed on either models.

 

HERE'S WHAT I KNOW.. AND NOW WHAT YOU KNOW!

-  IT GETS COLD THIS WEEKEND AND BEYOND (SHOCKER, RIGHT)

- THERE WILL BE A CLIPPER SATURDAY THAT WILL PUT DOWN A SURPRISE 2" SNOWFALL SOUTH OF THE MASON DIXON LINE.. BLUE RIDGE MTNS WILL GET INTO THAT.. EVEN DEEP CREEK 

- THERE WILL BE A STORM OFF THE COAST NEXT WEEK.. TRACK IS STILL UNCERTAIN!

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