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Central PA & The Fringes - Early March 2015


MAG5035

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EURO round 1:

 

18 - 0.01-0.1 for all, no temp issues

21 - 0.1-0.25 UNV North, then NE along 81, 850s cutting through UNV

24 - 0.1-0.25 all except around PA/MD border w/ 0.25-0.5 northern tier, 850s around Voyager-land on NW, 32 still W+S of all

27 - Same except drop the 0.25+, 850s north of PA, 32 UNV-MDT on east

30 - 0.1-0.25 in western half, 0.01-0.1 otherwise, 32 to far NEPA

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3Z SREF came in at 8.2" vs 5.65" @ 21z & 4.92" @ 15z.

The 6z NAM is still stubborn setting up the sleet band of death through the LSV and having one go from 12" of snow to 3" of sleet & 2" snow in a manner of 10 miles

7993d5af0414bc41170c3b6a7a7581f5.jpg

bdc62e9660881e09f14c61d27f339d5e.jpg

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Looking at the 700 mb wind field from the 06z NAM, you can see how there is a significant ageostrophic component to the flow over the southern portion of PA. That ageostrophic flow is essential to bringing moisture into the cold side of the front. It is also symptomatic of the large area of frontogenesis associated with the strengthening upper-level jet streak.

 

WND700nam212F48.png

 

There seems to be pretty good agreement among guidance that this feature will be present to provide mesoscale lifting and transport of moisture into the cold air. However, it remains to be seen how far this intense region of snowfall extends to the NW. At the moment it certainly looks most favorable for the southeast third of the state. We are still ~48-54 hours out so slight changes in the relative magnitudes of the midwest/great plains CAA and the southeast WAA could shift where the ageostrophic circulation associated with the jet streak sets up.

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Looking at the 700 mb wind field from the 06z NAM, you can see how there is a significant ageostrophic component to the flow over the southern portion of PA. That ageostrophic flow is essential to bringing moisture into the cold side of the front. It is also symptomatic of the large area of frontogenesis associated with the strengthening upper-level jet streak.

 

 

There seems to be pretty good agreement among guidance that this feature will be present to provide mesoscale lifting and transport of moisture into the cold air. However, it remains to be seen how far this intense region of snowfall extends to the NW. At the moment it certainly looks most favorable for the southeast third of the state. We are still ~48-54 hours out so slight changes in the relative magnitudes of the midwest/great plains CAA and the southeast WAA could shift where the ageostrophic circulation associated with the jet streak sets up.

:clap:  These are types of posts that justify my hours of continuous lurking here.  

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Looking like this could be our biggest event of the year.

 

i'm thinking we could start as snow today for a brief period, Whats your thoughts?

I think not likely... by the time the heavier precip arrives to get through the dry air and reach the ground we will already have the warmer air aloft in place.  The leading nose of the warm air is moving in around 800-750 mb as was expected according to the 12z soundings to our south and west.  I am thinking some sleet but changing to rain.  Don't think we see much sleet accumulation here.  Even with freezing rain the areas that get significantly warm aloft I just don't see much icing occurring (except for where the rain causes ponding) with the layer with temps below freezing likely ending up fairly thin.  The NAM has stayed on the extreme side of the models with trying to drive the warm layer close to +10C which would be way too warm for good accretion if it actually occurred.

 

below is the 12z sounding from Wilmington, OH

ILN.gif

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I think not likely... by the time the heavier precip arrives to get through the dry air and reach the ground we will already have the warmer air aloft in place.  The leading nose of the warm air is moving in around 800-750 mb as was expected according to the 12z soundings to our south and west.  I am thinking some sleet but changing to rain.  Don't think we see much sleet accumulation here.  Even with freezing rain the areas that get significantly warm aloft I just don't see much icing occurring (except for where the rain causes ponding) with the layer with temps below freezing likely ending up fairly thin.  The NAM has stayed on the extreme side of the models with trying to drive the warm layer close to +10C which would be way too warm for good accretion if it actually occurred.

 

good post, Thank you. When i looked earlier, i didn't honestly think we would have significant snow, i just thought it looked like we would have a little of everything, start as snow and quickly changing to sleet, frzn and then plain rain, with minimal impact.

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