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February 8 Storm Obs/Discussion


NoVaWx

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72403 IAD Sterling Observations at 12Z 08 Feb 2012

-----------------------------------------------------------------------------

PRES HGHT TEMP DWPT RELH MIXR DRCT SKNT THTA THTE THTV

hPa m C C % g/kg deg knot K K K

-----------------------------------------------------------------------------

1014.0 93 0.2 -2.5 82 3.15 0 0 272.3 281.0 272.8

1002.0 184 2.0 -4.0 64 2.85 56 5 275.0 283.0 275.5

1000.0 199 2.2 -3.8 65 2.90 65 6 275.4 283.5 275.8

995.0 240 2.6 -3.4 65 3.00 75 8 276.1 284.6 276.6

987.0 305 2.6 -4.1 61 2.87 90 11 276.8 284.9 277.3

984.0 330 2.6 -4.4 60 2.82 90 11 277.0 285.0 277.5

950.3 610 0.5 -5.9 62 2.60 95 13 277.7 285.1 278.1

925.0 827 -1.1 -7.1 64 2.44 110 11 278.2 285.2 278.6

920.0 870 -1.5 -7.5 64 2.38 110 10 278.2 285.1 278.6

914.9 914 -1.8 -6.8 69 2.52 110 9 278.3 285.6 278.8

906.0 992 -2.3 -5.6 78 2.79 124 8 278.6 286.6 279.1

880.4 1219 -3.5 -6.6 79 2.67 165 4 279.6 287.3 280.1

872.0 1295 -3.9 -6.9 80 2.63 175 6 280.0 287.6 280.4

850.0 1496 -4.7 -5.7 93 2.95 200 11 281.2 289.7 281.7

849.0 1505 -4.7 -5.6 93 2.98 205 12 281.3 289.9 281.8

847.0 1524 -4.7 -5.6 93 2.99 215 14 281.5 290.2 282.0

826.0 1722 -4.3 -5.5 91 3.09 234 17 283.9 292.9 284.5

814.9 1829 -3.9 -7.1 78 2.78 245 19 285.5 293.7 286.0

811.0 1866 -3.7 -7.6 74 2.67 245 19 286.1 294.0 286.5

791.0 2064 -3.5 -6.5 80 2.99 245 21 288.3 297.2 288.9

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It's hard to get excited by the event with temps starting out this warm. The 06Z nam has dc around 40 at 00Z. It's now warmer than the gfs. The warm layer remains pretty shallow when you throw in the dewpoints. I like the CWG forecast from yesterday but think the trace amounts for the city are more likeley than the 1".

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It's hard to get excited by the event with temps starting out this warm. The 06Z nam has dc around 40 at 00Z. It's now warmer than the gfs. The warm layer remains pretty shallow when you throw in the dewpoints. I like the CWG forecast from yesterday but think the trace amounts for the city are more likeley than the 1".

I wouldn't get excited for accumulations in DC itself even if temps were in the 20s...

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FDK sitting exactly at the 32/30 mark. Won't be much wet-bulbing going on, but at least temperatures are cooperating.

yea, my temp is up to 37 already. Probably won't go much higher but it's already high enough to cause inherent probs at precip onset.

I do have a met question though. Warm layer is pretty shallow. It's gets subfreezing pretty quickly as you go up. We're not going to get much evap cooling help with this system. However, does snowfall bring down the cold air from above like rain does? I would think rain is much more efficient at it but snow does do it too right?

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Smells like snow, looks like snow, will have to see if it actually will snow. 34.7 currently in my back yard. It will be interesting to see if FCPS lets out early or not if it does start when expected. We have some very hilly back roads that the busses travel as well as up the Catoctins and up near the PA line.

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yea, my temp is up to 37 already. Probably won't go much higher but it's already high enough to cause inherent probs at precip onset.

I do have a met question though. Warm layer is pretty shallow. It's gets subfreezing pretty quickly as you go up. We're not going to get much evap cooling help with this system. However, does snowfall bring down the cold air from above like rain does? I would think rain is much more efficient at it but snow does do it too right?

That's actually a good question and I wish I could answer it :lol: I'm not a forecasting met by any stretch of the imagination, so others will be better qualified to answer. However, anytime you have a precipitation event there will be a certain amount of mixing in the lower atmosphere. With such a shallow warm layer, I woudn't think that it would take much to mix down the colder air.

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yea, my temp is up to 37 already. Probably won't go much higher but it's already high enough to cause inherent probs at precip onset.

I do have a met question though. Warm layer is pretty shallow. It's gets subfreezing pretty quickly as you go up. We're not going to get much evap cooling help with this system. However, does snowfall bring down the cold air from above like rain does? I would think rain is much more efficient at it but snow does do it too right?

if it's snowing heavily, the melting of the snowflakes can cause cooling. Lance Bosart did a paper on such a case but melting is much less efficient than evaporation so in this case, it probably won't help much unless the precip is heavier than forecast.

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Sounds good.

36 in Columbia. dp 27.

Ouch! -- but not surprised. At 4:00am it was 32.0 IMBY and by 5:15 it was 32.4.

Looking forward (NOT!) to the craziness on the roads this afternoon coming north from DC.

Sticking with my call yesterday afternoon -- Up to 2" for N&N-central MD, dwindling down to a coating-1" just NW of I-95. Not that this is a profound prediction.

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