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Weekend Threat 12/14-12/15


IsentropicLift

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Excellent breakdown form Upton

 

 

 

FROM SATURDAY THROUGH THROUGH SUNDAY NIGHT THERE ARE DIFFERENCES
BETWEEN THE MODELS IN THEIR HANDLING OF A COASTAL STORM. BECAUSE THE
GFS HISTORICALLY HAS HAD A BIAS OF BEING TO WEAK WITH AND TO QUICK
TO ERODE DAMMING HIGHS...AND GIVEN THAT EVEN IT KEEPS THE CORE OF
THE HIGH TO OUR N AND DOES NOT HAVE IT RETREATING - ANOTHER SIGN
THAT WORKS AGAINST ITS IDEA OF WEAKENING THE DAMMING OVER THE AREA.
BECAUSE OF THIS...THE GFS LOW TRACK IS TOO CLOSE TO THE COAST AS IT
DOES NOT ALLOW FOR SUFFICIENT BLOCKING OF ITS NORTHWARD PROGRESS BY
THE HIGH TO THE N.
FOR THIS REASON HAVE LEANED HEAVILY TOWARDS THE
ECMWF IN THIS TIME FRAME - IT ALSO HISTORICALLY DOES FAIRLY WELL
WITH DAMMING HIGHS IN ADDITIONS TO GENERALLY BEING THE BETTER
PERFORMING MODEL IN THIS TIME FRAME.

BASED ON THIS MODEL CHOICE HAVE THE POTENTIAL FOR A SIGNIFICANT
WINTER STORM TO IMPACT THE AREA FROM MAINLY SATURDAY AFTERNOON
THROUGH SUNDAY...WITH IT PASSING NEAR THE 40N/70W BENCH MARK DURING
THE DAY ON SUNDAY. MORE CONFIDENT OF ALL SNOW INLAND THAN AT THE
COAST
...WITH THE SURFACE WIND FORECAST TO GO E-ESE SATURDAY
AFTERNOON/NIGHT - USUALLY THIS WILL BRING MOST OF LONG ISLAND AND
NYC AS WELL AS AT LEAST COASTAL SE CT TO ALL RAIN. HOWEVER...THE
FACT THAT AN ARCTIC AIR MASS WILL BE IN PLACE AND RE-ENFORCED TO THE
N MEANS THAT IF THE FLOW IS BACKED MORE THAN CURRENTLY FORECAST DUE
TO ISALLOBARIC INFLUENCES - COULD END UP STAYING MAINLY SNOW OVER
COASTAL AREAS AS WELL
. STILL QUITE A BIT OF UNCERTAINTY ON TRACK OF
THE SYSTEM SO THIS FORECAST COULD VERY WELL CHANGE. FOR TEMPERATURES
SATURDAY-SUNDAY USED A BLEND OF ALL AVAILABLE GUIDANCE WITH ECMWF
2-METER TEMPERATURES - FOR NOW ECMWF 2-M TEMPERATURES APPEARED TOO
COLD - SO USED OTHER GUIDANCE TO TEMPER. EXPECT TEMPERATURES TO BE
BELOW NORMAL BASED ON THE ABOVE THINKING.
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This event is where you trust the Euro more than the gfs, it's a large scale storm, we're getting into that range where the Euro can be dead on, and it just makes better sense from a meteorological standpoint.

We want a more sheared out system, which is somewhat likely in a fast, progressive flow. Also, we want a faster transfer to the coastal system. It's a storm I have a feeling though has much better odds along I-90 than around the city. Inland areas could see a good amount of ice after snow initially, since the cold initial air won't leave at the ground with a weak, progressive system. The trends are better though for at least some initial accumulating snow for everyone.

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We want a more sheared out system, which is somewhat likely in a fast, progressive flow. Also, we want a faster transfer to the coastal system. It's a storm I have a feeling though has much better odds along I-90 than around the city. Inland areas could see a good amount of ice after snow initially, since the cold initial air won't leave at the ground with a weak, progressive system. The trends are better though for at least some initial accumulating snow for everyone.

Not true, you want a stronger system. In this case, a stronger system wouldn't necessarily bring rain, even to coastal sections. The 12z Euro yesterday was a good example. If the coastal ends up weaker you're just going to get a few hours of slop like yesterday.

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I dont look at 84 hr NAM surface temps , but 1.look at the CAD ,  2 .850s at Minus 3 , so temps that look to be 32- 34 at the onset

would fall , its not slop at 84 hrs - its snow . not saying its gona happen , but the model not saying slop  " yet "

nam_t2m_east_29.png

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