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February 12-13 Storm IV, Model Discussion


stormtracker

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Didnt see this posted yet

 

http://www.spc.noaa.gov/products/md/md0091.html

MESOSCALE DISCUSSION 0091   NWS STORM PREDICTION CENTER NORMAN OK   1242 PM CST WED FEB 12 2014   AREAS AFFECTED...VA...SE WV   CONCERNING...HEAVY SNOW    VALID 121842Z - 130045Z   SUMMARY...MODERATE TO HEAVY SNOW IS EXPECTED TO DEVELOP THIS   AFTERNOON FROM SERN WV EWD ACROSS MUCH OF VA. SNOWFALL RATES OF 1   INCH PER HOUR WILL BECOME COMMON WITH LOCALLY HIGHER RATES.   DISCUSSION...LATEST WATER VAPOR IMAGERY SHOWS AN UPPER-LEVEL TROUGH   IN THE MS VALLEY WITH A LEAD SHORTWAVE TROUGH EXTENDING FROM THE SRN   APPALACHIAN MTNS SEWD ACROSS SC. WIDESPREAD PRECIPITATION IS LOCATED   JUST AHEAD OF THIS FEATURE IN A BROAD ZONE OF WARM ADVECTION FROM   ERN GA NEWD INTO THE CAROLINAS. MODEL FORECASTS SUGGEST LARGE-SCALE   ASCENT ALONG THIS ZONE WILL MOVE NWD OVER THE NEXT FEW HOURS BECOME   INCREASINGLY ENHANCED ACROSS NRN NC AND VA LATE THIS AFTERNOON. THIS   WILL AID THE DEVELOPMENT OF MODERATE TO HEAVY SNOWFALL ACROSS VA AND   SERN WV LATE THIS AFTERNOON. THE 18Z SOUNDING FROM GREENSBORO NC   SHOULD BE REPRESENTATIVE OF THE AIRMASS IN VA...SHOWING THE PRIMARY   ZONE FOR DENDRITIC GROWTH BETWEEN 700 AND 500 MB. AS MOISTENING   CONTINUES TO OCCUR BELOW 850 MB...AN ISOTHERMAL LAYER SHOULD BE   FAVORABLE FOR HEAVY SNOW WITH RATES OF 1 INCH PER HOUR COMMON.   LOCALLY HIGHER RATES COULD OCCUR WITHIN THE MORE ORGANIZED BANDING.   ..BROYLES.. 02/12/2014   ATTN...WFO...AKQ...LWX...RNK...RLX...

obs thread is where this stuff should be 

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This is what I posted to the public - 

 

Final Call for DC Proper - 

8"-10"

Evolution: 

- Snow starts between 7-9pm, becomes heavy late evening and overnight
- Snow may mix with sleet at times toward dawn and perhaps change over around dawn
- Quasi - Lull mid-morning to mid-afternoon with light mixed precip, maybe even a little rain/freezing rain
- Snow redeveloping late afternoon, moderate at times, and tapering off to light snow/flurries after 9pm

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I still like CWG 5-10 for the city and less for me....more like 3-6 or 4-6.   I'm not sure of the rationale for lowering Annapolis as I don't see the surface temps being a big problem.  The warm layer will be aloft. 

 

Wes, very true.  We talked about this over the weekend at work, when this system was into the medium range via those runs of the EC/CMC/UK; I think we'd more likely see a cutoff in accums more so because of mid level dry slotting (above the -10C isotherm) than the BL or even an elevated warm layer (900-800 mb thermals).  Often times they go hand-in-hand, i.e. we don't get the additional diabatic cooling from precipitation rates within the dry slot, thus the drizzle/freezing drizzle or light sleet.

 

Either way, I see NO reason why forecasters cannot be bullish on the front end snowfall, given the antecedent thermal conditions, unless we get convective disruption early on in the process (offshore) that would lower our QPF through 12Z.  I still like the CWG's forecast from yesterday too, as well as yesterday afternoon's LWX map for areas along/east of I-95, while the latest forecast snowfall for areas west of I-95.  In other words, yes, I like the idea of boosting amounts w-nw, but not at the expense of lowering totals east toward the Bay. Low level thermals will not be a problem through 12-15Z.

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Bob…I looked at 12z NAM profiles and didn't see a layer that looked unstable around us.  But CSI bands wouldn't show up on that and with the rockin' frontogenesis over us, we will likely see that.  

 

 

There's gotta be CSI all over the place with rates being forecast.  I wouldn't be surprised at a rumble or two.

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This is what I posted to the public - 

 

Final Call for DC Proper - 

8"-10"

Evolution: 

- Snow starts between 7-9pm, becomes heavy late evening and overnight

- Snow may mix with sleet at times toward dawn and perhaps change over around dawn

- Quasi - Lull mid-morning to mid-afternoon with light mixed precip, maybe even a little rain/freezing rain

- Snow redeveloping late afternoon, moderate at times, and tapering off to light snow/flurries after 9pm

 

FWIW (extremely little, i know), I agree with every single bit of this.  8-10 seems like the sweep spot for DC.  6-8, followed by lull, followed by 2-3. 

 

The lull will be a nice chance to get outside with the kids and do some sledding.  I've got a 3 and 4.5 year old who have never been on a sled ride.  Looking forward to changing that.

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I want HM or Coastal to stop back by and tell me that my expectations of +TSSN somewhere in our area is not just a weenie wishcast.

 

It is not a weenie wishcast. It is very legit. The "secondary circulation" on this frontogen machine is going to steamroll you guys tonight. I could see DC seeing double digit totals easily. 

 

There's gotta be CSI all over the place with rates being forecast.  I wouldn't be surprised at a rumble or two.

Deep-layer CSI forecasts from NAM look supportive of your statement but I haven't done an official check of stability through cross-sections (to rule out CI etc). Given the timing of this maturing cyclone, the synoptic setup and frontogen, I'm going to assume it's all CSI all night. :)

I'm really happy for you guys in DC!

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