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Chill Storm Discussion and Obs


WinterWxLuvr

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For us close to metro folks it's bleak at best but not a frozen shutout. You can already see with hourly temps the hagerstown and winchester are running 5-10 degrees below folks closer to the beltways.

It's all going to come down to temps at onset. Stating the obvious of course but if you are 30 or below in the early morning hours you can pull off some frozen. Maybe some flakes...or pellets....or even a period of zr but we all know it's going to be a car washer for the most part.

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For us close to metro folks it's bleak at best but not a frozen shutout. You can already see with hourly temps the hagerstown and winchester are running 5-10 degrees below folks closer to the beltways.

It's all going to come down to temps at onset. Stating the obvious of course but if you are 30 or below in the early morning hours you can pull off some frozen. Maybe some flakes...or pellets....or even a period of zr but we all know it's going to be a car washer for the most part.

With these marginal temperature setups, I like the NAM forecast soundings at Twister. You can plot for your location. So I set the marker for N-central MD and for mid-afternoon tomorrow after the column is saturated and

the warm nose at 850 is more than just a bit intrusive.

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With these marginal temperature setups, I like the NAM forecast soundings at Twister. You can plot for your location. So I set the marker for N-central MD and for mid-afternoon tomorrow after the column is saturated and

the warm nose at 850 is more than just a bit intrusive.

I'm sure I'm doomed except something "interesting" on the front end. Prob not gonna last long at all imby.

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With these marginal temperature setups, I like the NAM forecast soundings at Twister. You can plot for your location. So I set the marker for N-central MD and for mid-afternoon tomorrow after the column is saturated and

the warm nose at 850 is more than just a bit intrusive.

The NAM still gives you a few inches before changing over.

I had completely forgotten/given up on this storm but the combination of EURO + GFS is promising, and the NAM is only marginally worse (and still gives us some snow).

DCA will only see a T (or an inch, at best), but I think IAD will record ~4".

Also of note is that NYC will see almost nothing at all, so I'm not sad about missing this storm up there (although I do love living above 40N because the line does indeed seem to be magical). The gradient will be entirely East-West as opposed to N/S.

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Have looked over the soundings for 18z. NAM is warmer, GFS is colder for the Shenandoah and Cumberland valleys. The warmer air seems to always come in aloft pretty fast, but the wind at the surface is NNE to almost due north so expect the cold air to remain trapped for a long time. May not get above freezing in many areas.

Freezing rain is the big issue with this, but could get a good thump of snow at the onset.

That's my 2 cents.

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With surface low pressure over Alabama right now in turn having the storm more south and east than modeled will this allow HP to funnel in more cooler air down to Southern VA or if storm goes more south and east will it be harder to scour out low level air? Just curious

Yes, you would continue have a N to NNE wind keeping in the cold air locked in at the surface.

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Common sense tells me mostly rain here....yesterday's storm kinda made my common sense waver....euro and gfs say we start frozen here...even nam says a little...don't think I'm buying it...my call is a bit of freezing rain turning to rain by 9am...very pessimistic on this one since yesterday over performed.

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Common sense tells me mostly rain here....yesterday's storm kinda made my common sense waver....euro and gfs say we start frozen here...even nam says a little...don't think I'm buying it...my call is a bit of freezing rain turning to rain by 9am...very pessimistic on this one since yesterday over performed.

we have been watching this so long I will be happy to see it come and go...the thing I am most interested in seeing is how far north it gets before moving east....even a 50 mile difference may mean holding the cold longer...I remember a few days ago when it was thought this would plow deep into Ohio as a 992

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Common sense tells me mostly rain here....yesterday's storm kinda made my common sense waver....euro and gfs say we start frozen here...even nam says a little...don't think I'm buying it...my call is a bit of freezing rain turning to rain by 9am...very pessimistic on this one since yesterday over performed.

I sense 2" of snow and sleet then a flip to ZR till around noon or so then to plain ole rain. Snowpack in the yard is still holding on nicely. Down to 34* now on my PWS

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the rainfall totals are going to be in record breaking territory (for the day, that is) so it (snow) will all be gone by 12Z Thursday for anyone in our area <2K' asl

12/26 record precip for the day is 1.31" and 12/27 is 1.21"

the only thing that may prevent breaking one of those records is that half, more or less, will fall before/after midnight on the 27th

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I sense 2" of snow and sleet then a flip to ZR till around noon or so then to plain ole rain. Snowpack in the yard is still holding on nicely. Down to 34* now on my PWS

The RAP agrees, the NAM says "Yeah, right, straight to sleet for you!, the HRRR agrees with the RAP. Interesting short-term model battle unfolding. My bet is slightly towards the HRRR/RAP idea.

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The nam is really way off from all other guidance now. Not saying its wrong. Perhaps with its higher res it can see something the others are missing but it blasts the warm layer way north of all other models early tomorrow. It doesn't matter as much here but in east central pa for instance it's the difference between 6-12" and almost nothing. Amazing. I remember one similar scenario with the v-day storm in 2007 and the nam was right with the warm layer getting way further north in pa then other guidance. We will see this time.

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I sense 2" of snow and sleet then a flip to ZR till around noon or so then to plain ole rain. Snowpack in the yard is still holding on nicely. Down to 34* now on my PWS

Big difference a few miles east of leesburg where nothing is left as of this morning. Only got a 1/2 inch here. Might be as close a difference tomorrow.

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Before bed thoughts on tomorrow:

Timing on the precip is everything tomorrow morning because by 1 pm we're all rain except for the Shenandoah Valley /I-81 corridor. I think even SE-DC/PG and Annapolis (and N) could start as a bit of sleet or snow before going to all rain by 10AM. Areas NW of I95 should start as snow before going to sleet and then rain. Areas S and E of IAD or MD200 should be all rain by 11:30AM. Leesburg/Fredrick/Westminster by 12:30 and everyone else outside of the Shenandoah by 1. I'm thinking .15 to .3" of QPF across the entire area by 1 PM.

Windy and Rainy the rest of the day.

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MODEL DIAGNOSTIC DISCUSSION

NWS HYDROMETEOROLOGICAL PREDICTION CENTER COLLEGE PARK MD

1121 PM EST TUE DEC 25 2012

VALID DEC 26/0000 UTC THRU DEC 29/1200 UTC

STORM MOVING ACROSS THE SOUTH AND EAST

======================================

PREFERENCE: NON-NAM COMPROMISE WITH AVERAGE CONFIDENCE

INITIALLY, THE 00Z NAM APPEARS TO BE 2-3C TOO WARM WITH ITS 850

HPA FREEZING LINE ACROSS VIRGINIA/MARYLAND AND THE UPPER OHIO

VALLEY. THE 00Z GFS PROBLEMS ARE CONSTRAINED TO A 2-3C ERROR IN

THE UPPER OHIO VALLEY. THESE 850 HPA TEMPERATURE ERRORS HAVE

POSSIBLE IMPLICATIONS FOR THEIR FORECAST WINTER WEATHER

PRECIPITATION TYPES EARLY ON. SEE WINTER WEATHER

GRAPHICS/PRODUCTS FROM HPC AND LOCAL FORECAST OFFICES FOR MORE ON

SNOW/SLEET/FREEZING RAIN EXPECTATIONS WITH THIS CYCLONE.

DURING THE SHORT RANGE PERIOD, THE 00Z NAM BECOMES A SLOWER THAN

THE REMAINDER OF THE GUIDANCE WITH THE SYSTEM MOVING THROUGH THE

NORTHEAST FROM LATE THURSDAY ONWARD, AND LIES NEAR THE SOUTHWEST

CORNER OF THE 12Z GLOBAL ENSEMBLE SPREAD WITH ITS ASSOCIATED

SURFACE LOW POSITION FRIDAY MORNING. TREND-WISE, THE GUIDANCE HAS

STRENGTHENED THIS SYSTEM OVER THEIR PAST DAY OF RUNS, BUT THE NAM

HAS STOPPED TRENDING QUICKER/NORTHEAST. WITH THE 21Z SREF/18Z

GEFS/12Z ECMWF ENSEMBLE MEANS SUPPORTING THE QUICKER NON-NAM

CONSENSUS, THE PREFERENCE IS FOR A NON-NAM COMPROMISE HERE WITH

AVERAGE CONFIDENCE CONSIDERING ITS PROGRESSIVE NATURE.

...MODEL TREND GRAPHICS AT www.hpc.ncep.noaa.gov/html/model2.shtml

...500 MB FORECASTS AT www.hpc.ncep.noaa.gov/h5pref/h5pref.shtml

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