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February 8-9 Short range disco and Obs - STORM MODE


stormtracker

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Surface low currently in w TN, warm sector has dew points near 60 F. All models suggest some form of rapid development around 06z when low most likely to be in central Virginia to Chesapeake Bay. Cold air separation from low will be rapidly decreasing 06-09z. Would suggest to me that snowfall amounts will not be the primary concern for road maintenance towards morning rush, but flash freeze with small accumulations of snow making surfaces very slick. 

I continue to think it is feasible to see 2-4" around DC and BAL, 4 to 7" in n/c MD and noVA as rates will be very good for about 2-4 hours. But whatever the snowfall amounts turn out to be, I think this flash freeze and skating rink type conditions will be the big weather story by morning. 

Expect some thunder around 0400-0600h (EST) with this rapid development phase. 

With the current warmth and the dynamics of the developing low, sequence is likely to be complicated. I think you all stay in the warm sector of the developing low to about 06z, then parts of MD see backing of winds to SE then NE with winds near DC going calm for a time, then strong NE everywhere backing to NNW. It is during that phase that temps are likely to drop very quickly from maybe 50F at 06z to 33F at 09z and 28F at 12z. 

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27 minutes ago, caviman2201 said:

I'm not sure if anyone has been talking about this, but for areas to the south of I-70 that expect to see a significant amount of rain before temps crash, what are teh concerns about flash freezing of all that liquid after the temps do crash?  Will it be a non-issue with the sun?

Ground temps pal....

Minimal to no worries, except the normal bridge/overpass stuff.

Nut

 

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23 minutes ago, Roger Smith said:

Surface low currently in w TN, warm sector has dew points near 60 F. All models suggest some form of rapid development around 06z when low most likely to be in central Virginia to Chesapeake Bay. Cold air separation from low will be rapidly decreasing 06-09z. Would suggest to me that snowfall amounts will not be the primary concern for road maintenance towards morning rush, but flash freeze with small accumulations of snow making surfaces very slick. 

I continue to think it is feasible to see 2-4" around DC and BAL, 4 to 7" in n/c MD and noVA as rates will be very good for about 2-4 hours. But whatever the snowfall amounts turn out to be, I think this flash freeze and skating rink type conditions will be the big weather story by morning. 

Expect some thunder around 0400-0600h (EST) with this rapid development phase. 

With the current warmth and the dynamics of the developing low, sequence is likely to be complicated. I think you all stay in the warm sector of the developing low to about 06z, then parts of MD see backing of winds to SE then NE with winds near DC going calm for a time, then strong NE everywhere backing to NNW. It is during that phase that temps are likely to drop very quickly from maybe 50F at 06z to 33F at 09z and 28F at 12z. 

OK

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For documentation, and note the highlighted text.  AM snow may have a tough time sticking, but with a deepening low and significant cold air advection, the snow squalls could surprise a few spots.

Quote

000
FXUS61 KLWX 081948
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
248 PM EST Wed Feb 8 2017

.SYNOPSIS...Developing low pressure over the Tennessee valley
will gather strength as it tracks across central Virginia
tonight and off the Delmarva Thursday morning. High pressure and 
much colder temperatures will return Thursday night and Friday.

&&

.NEAR TERM /THROUGH THURSDAY/...After another day of record 
highs in the 70s, things will change drastically over the next 
24 hrs. Developig low pressure over the TN valley is expected to
gather strength as it moves across central VA and off the 
Delmarva Thu morning. Rain will overspread the region early 
this evening as heights aloft fall and upper trough over the 
wrn Great Lks takes on a negative tilt and upper difluence 
increases over the region. Rain will gradually change to snow 
overnight as colder air is drawn in, but exact timing of when 
p-type changes occur still differ somewhat in the models. Latest
ECWMF has trended warmer with sfc to 850 mb temps and track of 
850 mb low is across our area which is not conducive for 
significant snow accumulations especially considering temps are 
still in the upper 50s in Hagerstown. It does appear far 
northern areas of Carroll, Baltimore and Harford counties will 
see the highest snow totals outside of the upslope areas, but 
expect some melting of snow as it makes contact with warm 
ground. Overall, this is a moderate precip event with QPF totals
ranging from half to one inch. Snow will begin to taper off 
shortly after 12Z Thu as low pres pulls rapidly off the coast. A
brief break in the precip is expected late Thu morning into 
early afternoon, before additional shortwave energy moves across
and helps trigger snow showers and squalls. Strong NW flow, 
cold air advection and increasing low-mid level instability 
from steepening lapse rates will make atmosphere conducive to 
squalls some of which could be quite intense for brief periods 
of time. Expect an additional quarter to half inch of snow in 
most places and locally higher with any intense bands. These 
squalls could cause significant impacts to the Thu afternoon 
rush hour commute. Trof axis pushes east of the area around 00Z 
Fri with subsidence and drying building shutting down squalls. 

&&

.SHORT TERM /THURSDAY NIGHT THROUGH FRIDAY NIGHT/...Very cold
and brisk Thu night under building high pressure. Wind chills
may approach or exceed advzy criteria over the Potomac
highlands. Chilly Fri under high pressure. Moderating temps Fri
night under warm advection clouds and srly flow.

 

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Just now, caviman2201 said:

On Pivotal, the Kuchera is actually showing less snow than 10:1... 

all snow maps are overdone with this setup. i like posting them too but you can't take them at face value. look at temp profiles. DC is still at 34 when precip moves out of the area per 18z NAM. Do you really expect DC to pick up 1.3 of snow with that? 

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