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Weekend Snowfest/Rainfest/Mixed Mess?


showmethesnow

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1 minute ago, Interstate said:

With such a small stripe of the heaviest precip. This should make a lot of people nervous around the cities 

What? It's a uniform .4-.5 everywhere until you get east. There isn't a narrow zone at all. The color contours may give that impressive but QPF is pretty uniform. 

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30 minutes ago, mappy said:

can we reminisce about past storms in another thread please? 

I thought the reason Bob Chill brought up 12/2013 was to compare the surface temperature profile to the event tomorrow, not to reminisce. The lesson from that event was the models were too cold at the surface after the cold front...Hence the big forecast bust of a WSWarning verifying as 0.9" at DCA.  

Watching the surface temp drop tonight will be fairly important to the outcome tomorrow, IMO. As it is, the GFS is keeping inside beltway areas above freezing overnight tonight. 

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1 minute ago, gymengineer said:

I thought the reason Bob Chill brought up 12/2013 was to compare the surface temperature profile to the event tomorrow, not to reminisce. The lesson from that event was the models were too cold at the surface after the cold front...Hence the big forecast bust of a WSWarning verifying as 0.9" at DCA.  

Watching the surface temp drop tonight will be fairly important to the outcome tomorrow, IMO. As it is, the GFS is keeping inside beltway areas above freezing overnight tonight. 

I agree, but then followed up posts were those discussing it in detail. It diverts the discussion about this threat and can be discussed further elsewhere. 

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Pretty big model disagreement for within 24-hrs for the temp drop tonight. Euro and NAM get the metro areas safely below freezing overnight. As I said before, the GFS does not and is quite a bit warmer for the suburbs too. I think we'll have a pretty good idea of the accumulation situation for more urban areas by daybreak. If DCA is like 35F at 7 am, this will probably be like 12/5/09 in gradient with the Fall line being a very significant separation. 

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2 minutes ago, gymengineer said:

Pretty big model disagreement for within 24-hrs for the temp drop tonight. Euro and NAM get the metro areas safely below freezing overnight. As I said before, the GFS does not and is quite a bit warmer for the suburbs too. I think we'll have a pretty good idea of the accumulation situation for more urban areas by daybreak. If DCA is like 35F at 7 am, this will probably be like 12/5/09 in gradient with the Fall line being a very significant separation. 

Yep.  A lot of moving parts with this storm, but if temps bust high I cant see how we get more than a white rain event for most

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3 minutes ago, gymengineer said:

Pretty big model disagreement for within 24-hrs for the temp drop tonight. Euro and NAM get the metro areas safely below freezing overnight. As I said before, the GFS does not and is quite a bit warmer for the suburbs too. I think we'll have a pretty good idea of the accumulation situation for more urban areas by daybreak. If DCA is like 35F at 7 am, this will probably be like 12/5/09 in gradient with the Fall line being a very significant separation. 

i don't think the general idea has changed much since yesterday.  we need the rates and we need temps to drop accordingly overnight.  at minimum, it looks like we'll get snow tv.  if temps/rates work out, then we may end up with something to shovel.

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1 minute ago, gymengineer said:

Pretty big model disagreement for within 24-hrs for the temp drop tonight. Euro and NAM get the metro areas safely below freezing overnight. As I said before, the GFS does not and is quite a bit warmer for the suburbs too. I think we'll have a pretty good idea of the accumulation situation for more urban areas by daybreak. If DCA is like 35F at 7 am, this will probably be like 12/5/09 in gradient with the Fall line being a very significant separation. 

Need that baro to build in. Gotta have it like 30.20+ by 2pm or rain trouble brewing. Not worried about 37F+ in the afternoon if baro is  stout because if so dews will be low and evaporational  will be 33-50% of spread and not a tepid 20-25%

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12 minutes ago, BTRWx's Thanks Giving said:

Is this even considered a cad?

Insitu CAD meaning a cold/dry airmass is in place but by the time precip gets here there won't be a classic CAD HP to the N-NE funneling cold in. We have to make do with whatever is in place at onset. Evap cooling as precip begins and a decent column to start can be preserved well if there isn't strong southerly midlevel and surface winds and precip rates are good (which looks good for now). 

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I lost 6 degrees from evaporational cooling when precip started on 2/5.  As long as temps don't get above 38-39 early tomorrow, I expect snow to accumulate here pretty much from the onset. 

Mid-March last year was the only time since 2/15/2016 that I have recorded a snowfall >2" but I think tomorrow exceeds that in my yard.

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4 minutes ago, Bob Chill said:

Insitu CAD meaning a cold/dry airmass is in place but by the time precip gets here there won't be a classic CAD HP to the N-NE funneling cold in. We have to make do with whatever is in place at onset. Evap cooling as precip begins and a decent column to start can be preserved well if there isn't strong southerly midlevel and surface winds and precip rates are good (which looks good for now). 

Yeah, the one advantage here is that we don't have a wound-up system that is trying to drive the warm air north.  Low level winds are very light, and they aren't too bad in the lower mid-levels either.

5a8734d78d71e_2018021612_NAMNST_036_38.84-77.09_winter_sfc.thumb.png.3ddf9e6045ea86e7bfb71a5013e468be.png

 

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4 minutes ago, MN Transplant said:

Yeah, the one advantage here is that we don't have a wound-up system that is trying to drive the warm air north.  Low level winds are very light, and they aren't too bad in the lower mid-levels either.

 

 

Great post. Exactly what I was trying to say but a nice pretty sounding does it much better. Surface on up to 850 is solid for the most part to support snow. Euro has 850s tickling 0 to +1 for a time but it appears brief. Assuming precip doesn't come in tepid, that should work until you get S and E of DC. Flakes will probably take on many shapes tomorrow. Pretty at times and banged up at other times. lol. Northern tier should be pretty good across the board for dendrites. They never lose the column. Depending on 800mb temps, a period of sleet is very possible south of DC and up to my yard etc. Upper moco should be all snow. 

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