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DTWXRISK

ABOUT FRIDAY/ SATURDAY DEC 5-6

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The Friday night Saturday system seems to be ideal for a heavy rain going over to snow event especially on the   12z WED    EURO  solution.  Even if we assume that the European solution here is correct   -- it may not be  -- and the actual track of the LOW  is further to the East and it is  going to move off the coast  earlier than what the previous  runs of the  Euro were showing .  the problem is the lack of low-level cold air.


 At 9z  SAT  the  12z  EURO has the LOW in Hampton Roads   --  I have drawn in the  0c  850mb  isotherm in Orange and the 32 degree temperature line at the surface in purple.  NOW if this was the middle of winter this heavy rain would be changing over to snow in the entire Shenandoah Valley as well as the mountains of Western North Carolina Southwest Virginia and pretty close to the Washington DC area certainly northwest Virginia     as well as interior Southeastern Pennsylvania.
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Indeed looking at the  72 hrs  euro  valid 12z   SAT   it is  clear that the 0c  850mb  isotherm has been pulled into the coast as the Nor'easter is developing off the Delmarva. And again if this was the middle of winter…  the rain could possibly change the snow as far south as Richmond and east of Washington D.C Baltimore and Philadelphia.   ( if my Grandmother had balls she would be my  Grandfather….)

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But as the image on the right shows the low-level temperatures are simply too warm to support any snow except for perhaps the Shenandoah Valley./    western   MD   south central PA.   But even there  temperatures of 35 and 37 degrees  are not going to allow for any kind of accumulation even if it does end as snow. 

 

The   500mb pattern seems to be ideal Friday night going into Saturday morning. The two short waves clearly phase in the pre-dawn hours of Saturday which allows the southeast LOW to undergo significant intensification and bomb out as the shortwave goes negative off the Middle Atlantic Coast on Saturday morning 

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The operational European goes kablooie with the system and as a monster raging Nor'easter Saturday afternoon evening. This is clearly an elevation snow which was what the precipitation type surface  maps are clearly depicting. Even if you look at the surface temperatures for late Saturday afternoon Boston is still in the mid 30s es as is all of Southeastern Massachusetts Rhode Island and most of coastal and interior  CT. 412359050_download(2).thumb.png.6d41bbc3e75af73c9afc2edde1939acf.png


The snowfall accumulation map from the operational European on both weathermodelS and weatherbell are simply  BULLSHIT 

It is  clear that they continue to measure mixed precipitation --which is what much of the precipitation in central or western Massachusetts will be ---as all snow.

 Moreover if you compare the more accurate and far more reasonable snowfall maps from    eurowx.com   you can see that their  snow algorithm is far more reasonable and makes accurate   and makes sense given the  Upper air  pattern and the model surface development of this Coastal storm. The differences in the snowfall amounts in Central and Western Massachusetts is astronomical.

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in summary this event for Friday night into Saturday is a classic East Coast Nor'easter and   supports   adage that early December is very difficult to get a major pure East Coast snow storm because of the still relatively  mild sea  surface water temperatures.  Not impossible just difficult

The choice is up to you. I'm sure some of you rather have the ridiculous over-amped over done snowfall maps from the European or the GFS. It seems that the operational European so far this cold season is way over doing the snowfall amounts as we saw with the Ohio Valley storm last week and now this one.   This event is only 72 hours away so usually the European model Gets a Clue at this point rather than going bonkers with the snowfall  totals.. 

Of course if the European model is acting funny this cold season and is over doing the snowfall amounts and this is going to be a  forecast problem.    The only way in my opinion to get around this is to check these ridiculous snowfall amounts from these other websites with the snowfall maps from EURO   WX.COM ….   which seems to be   far superior to anything on whether Bell or weather models.

ecmwf-deterministic-neng-t2m_f-7202000.png

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Thread title needs an edit (Friday and Saturday would be Dec 4-5). 

This disturbance in the Gulf coast region came through my part of the world on Monday and we got about 2" of powder snow from it then.

The speed with which the upper level energy then raced into the Gulf of Mexico was impressive. Whether anything else about it will be impressive remains to be seen, I agree with this cautious approach. Looks very prone to mixing, RGEM freezing line is not in a particularly good spot either at 48h. 

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