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Feb. 18-20, 2012 Disco/Analysis


Poimen

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I'm too tired to add up the totals right now but the Euro has a changeover to snow early in the afternoon for northern NC including the Triad.

edit: verbatim the Euro has it snowing in the triad for ~18 hours.

18 hours is loooong time. Do you know how much QPF? I have a feeling that most of that 18 hours was very light or even flurries.

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18 hours is loooong time. Do you know how much QPF? I have a feeling that most of that 18 hours was very light or even flurries.

It was very light mostly. There were a couple 3 hours periods of 1"+ but most were around .5"

6z NAM went north, really nice band rolls through NC at the end though. Snowfall map says 4-5 for Triad, 1-3 for Triangle, 7-8 up near Mt. Airy. Mountains get not much, central NC gets some flakes stuff, coast and south (Charlotte) get nada. Asheville actually looks to get almost shutout too. Luckily it's the NAM so they don't have to worry.

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Blacksburg, VA

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...

-- Changed Discussion --

AS OF 400 AM EST SATURDAY... FIRST SIGNIFICANT WINTRY WEATHER SYSTEM OF THE SEASON EXPECTED SUNDAY INTO SUNDAY NIGHT. SIGNIFICANT DEFORMATION BAND WITH SLANTWISE CONVECTIVE MESOSCALE BANDS DEVELOPING WITHIN IT...WILL SET UP ALONG THE APPALACHIANS SUNDAY MORNING AND MOVE ACROSS OUR REGION BY MIDDAY SUNDAY INTO SUNDAY NIGHT. WITH A SOUTHERN SHIFT OF THE DEFORMATION BAND AND INCREASE IN QPF ELECTED TO EXPAND THE WATCH FURTHER SOUTH ALONG I-81 AND ACROSS NORTHWEST MOUNTAINS OF NORTH CAROLINA. BELIEVE THAT PRECIP RATES WILL BE ENOUGH TO GENERATE SNOW TO THE SFC WITH COLD AIR BEING PULLED DOWN FROM ALOFT BY THE PRECIP AS WELL AS IN FROM THE NORTH AS COLD SFC HIGH PRESSURE SLIDE ACROSS THE CENTRAL APPS DURING THE DAY...AND SFC LOW BEGINS TO DEEPEN AS IT APPROACHES THE COAST LATE SUNDAY. BEST BET FOR WARNING CRITERIA BEING MET WILL BE ACROSS THE HIGHEST ELEVATIONS AND THE WESTERN SLOPES...WHERE A MAX OF UP TO 10 INCHES...OR EVEN HIGHER IS POSSIBLE. ALLOWED FOR SOME SLEET WITH MODEL SOUNDINGS SUGGEST WEAK WARM NOSE WITH VERY WEAK SFC TROUGHING TRYING TO SLIDE UP THE WEST SIDE OF MOUNTAINS. THE COMBINATION OF A WARM GROUND AND MIX WITH RAIN AND SLEET MAY KEEP SNOW ACCUMS TO A MINIMUM THROUGH MIDDAY TO EARLY AFTERNOON. MORE SIGNIFICANT ACCUMS BY AFTERNOON WHEN COLDER AIR ARRIVES AND THINK BEST CHANCES FOR THE BANDING TO MOVE IN...BUT BY LATE DAY AND EARLY EVENING THE LOW WILL BE PULLING OUT AND DEFORMATION BAND WILL BE STARTING TO WEAKEN. USED A NON-DIURNAL CURVE ON SUNDAY AND SUNDAY NIGHT WITH TEMPERATURES FALLING SUNDAY AFTERNOON. BASED ON SLIGHTLY SLOWER TIMING OF SYSTEM EXITING...HAVE INCREASED POPS INTO SUNDAY NIGHT ACROSS THE EAST...AND SOME LIGHT SNOW ACCUMS ARE POSSIBLE EVEN DOWN TO NEAR VA/NC BORDER WHERE A WET INCH IS POSSIBLE...BUT NOT LIKELY ACCUMULATING ON ROADS. HOWEVER...WITH A SHIFT FURTHER SOUTH IN THIS TRACK...THESE AREAS COULD PICK UP MORE.

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Excellent duscussion as always from RAH:

REGARDING PRECIP TYPES/AMOUNTS: WITH EXPECTATIONS OF A COLDER COLUMN

WITH GREATER MOISTURE DEPTH... PARTIAL THICKNESSES AND THE TOP-DOWN

APPROACH BOTH SUPPORT AN EARLIER TREND TOWARD WINTRY PRECIP BY LATE

SUNDAY AFTERNOON AS THE STILL-MOIST LOWEST 10K FT COOLS... DOWN TO

AT OR JUST BELOW FREEZING IN THE TRIAD THROUGH ROXBORO BY 21Z

SUNDAY. THE RELATIVE LULL IN LIFT AND BRIEF DRYING ABOVE -4C BETWEEN

SHORTWAVE TROUGHS SUPPORT LIGHT RAIN/DRIZZLE IN LATE AFTERNOON/EARLY

EVENING TIME FRAME... WITH POSSIBLE FREEZING DRIZZLE IN THE FAR

NORTH... ALTHOUGH THE RECENT VERY WARM TEMPS WILL GREATLY LIMIT ANY

ICE ACCRUAL TO ELEVATED SURFACES AT MOST. THE AIR ABOVE -4C THEN

RE-MOISTENS WITH THE SURGE IN DYNAMIC FORCING ACCOMPANYING THE

ARRIVAL OF THE NORTHERN STREAM SHORTWAVE BY MID EVENING... AT WHICH

POINT THE ENTIRE COLUMN IS AT/BELOW FREEZING ROUGHLY ALONG/NORTH OF

I-85. WHILE THE BEST MID LEVEL FRONTOGENESIS IS EXPECTED TO OCCUR

OVER THE NC/VA BORDER REGION A BIT EARLIER... VERY LATE SUNDAY

AFTERNOON THROUGH MID EVENING ACCORDING TO THE NAM/GFS... THE

PROJECTED MID LEVEL DEFORMATION AND SATURATION AND ASCENT ALOFT

ALONG WITH THE DEEP NEAR-FREEZING ISOTHERMAL LAYER OVER THE FAR

NORTHERN PIEDMONT REMAINS SUFFICIENTLY HIGH TO SUPPORT SNOW BAND

DEVELOPMENT... MOST LIKELY SUNDAY EVENING INTO THE VERY EARLY

OVERNIGHT HOURS... ENDING LAST IN OUR NE (WARREN/HALIFAX COUNTIES)

BY 05Z-08Z. AMOUNTS ARE ALWAYS DIFFICULT TO PINPOINT PARTICULARLY AT

36-48 HOURS OUT... BUT AT THIS TIME... IT APPEARS THAT WE COULD SEE

AN INCH OR TWO OF ACCUMULATION NORTH OF THAT LEXINGTON-DURHAM-

HALIFAX LINE. AMOUNTS WILL BE GREATLY LIMITED BY THE WARM GROUND

TEMPS (4 INCH SOIL TEMPS ARE RUNNING IN THE UPPER 40S TO LOWER 50S

THIS MORNING). BUT IT MUST BE NOTED THAT IF PRECIP RATES BECOME

GREATER THAN EXPECTED... CERTAINLY POSSIBLE GIVEN THE STRONG SLOPED

FRONTOGENETIC ZONE EVIDENT ON NAM/ECMWF CROSS SECTIONS AT 850-700 MB

AND A PERIOD OF STEEPENING LAPSE RATES ALOFT... WE COULD SEE HIGHER

SNOW RATES IN OUR FAR NORTHEAST COUNTIES SUNDAY EVENING. AS THE

IMPACT OF THIS EVENT WOULD BE MOSTLY FELT IN THE 36-48 HOUR TIME

FRAME AND WITH LINGERING QUESTIONS OF AMOUNT AND PLACEMENT OF SUCH A

MESOSCALE BAND... WILL NOT POST A WINTER STORM WATCH AT THIS TIME...

BUT THIS WILL NEED TO BE STRONGLY CONSIDERED THIS MORNING AND

AFTERNOON... EFFECTIVE LATE SUNDAY AFTERNOON THROUGH SUNDAY NIGHT.

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Excellent duscussion as always from RAH:

BUT IT MUST BE NOTED THAT IF PRECIP RATES BECOME

GREATER THAN EXPECTED... CERTAINLY POSSIBLE GIVEN THE STRONG SLOPED

FRONTOGENETIC ZONE EVIDENT ON NAM/ECMWF CROSS SECTIONS AT 850-700 MB

AND A PERIOD OF STEEPENING LAPSE RATES ALOFT... WE COULD SEE HIGHER

SNOW RATES IN OUR FAR NORTHEAST COUNTIES SUNDAY EVENING. AS THE

IMPACT OF THIS EVENT WOULD BE MOSTLY FELT IN THE 36-48 HOUR TIME

FRAME AND WITH LINGERING QUESTIONS OF AMOUNT AND PLACEMENT OF SUCH A

MESOSCALE BAND... WILL NOT POST A WINTER STORM WATCH AT THIS TIME...

BUT THIS WILL NEED TO BE STRONGLY CONSIDERED THIS MORNING AND

AFTERNOON... EFFECTIVE LATE SUNDAY AFTERNOON THROUGH SUNDAY NIGHT.

GSP.....

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...

AS OF 330 AM FRIDAY...THE RACE IS ON BETWEEN THE ARRIVAL OF THE COLD

AIR FROM THE NORTH AND THE PRECIP FROM THE SW. THE TREND OF THE

MODELS CONTINUES TO BE SLIGHTLY FARTHER SOUTH AND SLIGHTLY COLDER AS

MORE OF THE COLDER AND DRIER AIR IS ALLOWED TO SPILL OVER THE NRN

MTNS ON SUNDAY. WE ARE REASONABLY CONFIDENT THAT A WIDESPREAD PRECIP

EVENT WILL HAPPEN ON SUNDAY...AND HIGH PRECIP CHANCES HAVE BEEN

PUSHED BACK EVEN LATER IN THE DAY AND INTO THE EVENING. TEMPERATURES

ARE LIKELY TO REACH AN EARLY HIGH AS COLDER AND DRIER AIR TRIES TO

WORK SOUTHWARD AFTER SUNRISE AS SURFACE HIGH PRESSURE MOVES OVER THE

GREAT LAKES AND THE SURFACE LOW REFORMS/DEEPENS OFF THE CAROLINA

COAST. FOLLOWED A BLEND OF GFS/NAM TEMPS WHICH BRINGS DOWN AIR COLD

ENOUGH TO CHANGE PRECIP OVER TO SNOW OVER THE NRN MTNS AND ADJACENT

BLUE RIDGE AS SNOW LEVELS DROP FROM 6K FEET TO 3K FEET DURING

MIDDAY. MODEL FCST SOUNDINGS AGREE THAT MOUNTAIN PEAKS ACROSS THE

NRN MTNS WILL BE SNOW AFTER SUNRISE...AND THAT MOST PLACES ABOVE 3K

FEET OVER THE NRN MTNS WILL CHANGE TO SNOW DURING THE MIDDLE PART OF

THE DAY. FOLLOWING THE QPF FROM THE HPC AND FACTORING IN SOME

ENHANCEMENT FROM THE EASTERLY FLOW...THERE IS THE POTENTIAL FOR

SIGNIFICANT SNOW ABOVE 3500 FEET OVER THE NRN MTNS SUNDAY AFTERNOON

AND EVENING. CONFIDENCE IS SLIGHTLY BETTER THAN 50/50...GIVEN THE

COOLER TREND WITH THE GUIDANCE. ALLOWING FOR SOME SLOP FACTOR AND

THE COOLER TREND...WILL ISSUE A WINTER STORM WATCH FOR THE NRN MTN

ZONES AND THE ADJACENT HIGH ELEVATION FOOTHILL ZONES...RUNNING FROM

NOON UNTIL MIDNIGHT. IF THE SNOW BEGINS EARLY ENOUGH...MT MITCHELL

AND GRANDFATHER MTN COULD GET OVER A FOOT. THE NEXT SHIFT WILL MAKE

THE CALL ABOUT ISSUING A WARNING OR ADVISORY THAT MIGHT BE ELEVATION

DEPENDENT. LESSER AMTS OF SNOW ARE FCST FOR THE REST OF THE MTNS...

FOOTHILLS...AND PIEDMONT OF NC. EVEN METRO CLT COULD SEE A HALF INCH

SUNDAY NIGHT. THIS WILL BE MENTIONED IN THE HWO. THE PRECIP SHOULD

TAPER OFF TO A BRIEF NW FLOW EVENT BEFORE SUNRISE MONDAY.

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almost reminds you of Christmas 2010. It was on off on off then on on on and on the 23rd off until the snarf I think showed snow and Robert kept saying it was going to happen. We all know the outcome. I guess we won't know until it does happen. i won't be surprised either way since the models have showed us a little bit of everything including some great accumulations down to nothing. Either way I think this is the start of a wintry pattern after a brief warm up next week

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GFS/NAM both still have a deformation band working through northern and central NC overnight Sunday. n fact, the 6Z NAM squeezes a .35 qpf max out of this band just west of Durham, and a stripe of at least .25" totals running across the northern piedmont of NC in assocation with this feature.

06znamp06thickpmsl_MA048.gif

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GSP.....

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...

AS OF 330 AM FRIDAY...THE RACE IS ON BETWEEN THE ARRIVAL OF THE COLD

AIR FROM THE NORTH AND THE PRECIP FROM THE SW. THE TREND OF THE

MODELS CONTINUES TO BE SLIGHTLY FARTHER SOUTH AND SLIGHTLY COLDER AS

MORE OF THE COLDER AND DRIER AIR IS ALLOWED TO SPILL OVER THE NRN

MTNS ON SUNDAY. WE ARE REASONABLY CONFIDENT THAT A WIDESPREAD PRECIP

EVENT WILL HAPPEN ON SUNDAY...AND HIGH PRECIP CHANCES HAVE BEEN

PUSHED BACK EVEN LATER IN THE DAY AND INTO THE EVENING. TEMPERATURES

ARE LIKELY TO REACH AN EARLY HIGH AS COLDER AND DRIER AIR TRIES TO

WORK SOUTHWARD AFTER SUNRISE AS SURFACE HIGH PRESSURE MOVES OVER THE

GREAT LAKES AND THE SURFACE LOW REFORMS/DEEPENS OFF THE CAROLINA

COAST. FOLLOWED A BLEND OF GFS/NAM TEMPS WHICH BRINGS DOWN AIR COLD

ENOUGH TO CHANGE PRECIP OVER TO SNOW OVER THE NRN MTNS AND ADJACENT

BLUE RIDGE AS SNOW LEVELS DROP FROM 6K FEET TO 3K FEET DURING

MIDDAY. MODEL FCST SOUNDINGS AGREE THAT MOUNTAIN PEAKS ACROSS THE

NRN MTNS WILL BE SNOW AFTER SUNRISE...AND THAT MOST PLACES ABOVE 3K

FEET OVER THE NRN MTNS WILL CHANGE TO SNOW DURING THE MIDDLE PART OF

THE DAY. FOLLOWING THE QPF FROM THE HPC AND FACTORING IN SOME

ENHANCEMENT FROM THE EASTERLY FLOW...THERE IS THE POTENTIAL FOR

SIGNIFICANT SNOW ABOVE 3500 FEET OVER THE NRN MTNS SUNDAY AFTERNOON

AND EVENING. CONFIDENCE IS SLIGHTLY BETTER THAN 50/50...GIVEN THE

COOLER TREND WITH THE GUIDANCE. ALLOWING FOR SOME SLOP FACTOR AND

THE COOLER TREND...WILL ISSUE A WINTER STORM WATCH FOR THE NRN MTN

ZONES AND THE ADJACENT HIGH ELEVATION FOOTHILL ZONES...RUNNING FROM

NOON UNTIL MIDNIGHT. IF THE SNOW BEGINS EARLY ENOUGH...MT MITCHELL

AND GRANDFATHER MTN COULD GET OVER A FOOT. THE NEXT SHIFT WILL MAKE

THE CALL ABOUT ISSUING A WARNING OR ADVISORY THAT MIGHT BE ELEVATION

DEPENDENT. LESSER AMTS OF SNOW ARE FCST FOR THE REST OF THE MTNS...

FOOTHILLS...AND PIEDMONT OF NC. EVEN METRO CLT COULD SEE A HALF INCH

SUNDAY NIGHT. THIS WILL BE MENTIONED IN THE HWO. THE PRECIP SHOULD

TAPER OFF TO A BRIEF NW FLOW EVENT BEFORE SUNRISE MONDAY.

I could be very wrong but my thinking and if you read Phil's write up above with the trend colder and more south each run I think all of wnc will change over to a heavy wet snow pretty quick sunday afternoon with a longer period of moderate to heavy snow Phil's 3-6 around Buncombe county looks pretty good sunday evening cause many many times I've seen this same set up before even though the models were holding back on the precip totals. WE'LL SEE.

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Reading in the Mid Atlantic forum and there was a post that the storm is currently 6-12 hours slower than progged by the models. If it is indeed slower we might be looking at another shift; probably south. More time for the cold to move in.

Always interesting to see when the real time storm doesn't match with what the model says....hmmmm :popcorn: At least it appears that I am now in the clear for the severe weather.....Shift to my south.....Now, maybe I can get Sears to deliver a rowboat when they bring the appliances this morning. :flood:

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Shocked GSP mentioned a half inch for CLT metro! Also if storm is twelve hours slower than currently shown that could have good implications.

yea with the trend of a slower storm each run this could mean more and more south and this storm could track in a very desirable direction for nc, blacksburg nws has already mentioned that with each model run there is a further south track of the storm and has said that DC and Maryland may be out of the heavy snow area. we'll see

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Just posted a discussion this morning......

Here you go!

The south trend slowing down on the models is a huge bummer Matthew. I see where GSP has our zone in a possible 1/2" of ip/SN. Just knowing from living in this location and climo, I have seen surprises before. Do you think that there is still a "decent" chance that if the storm slows down 6-12 hours that there could be a decent shot for the cold to become more entrenched and ala more of a wintry scenario for the CLT area? I know this is grasping at weenie straws, but the NAM and the GFS (to a lesser extent) still show us ending as snow. Your updates (as always) have been PRICELESS! A HUGE THANK YOU for your contributions!!

Jason

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Shocked GSP mentioned a half inch for CLT metro! Also if storm is twelve hours slower than currently shown that could have good implications.

When it comes to weather, we are always on the same page my friend (I see people roasting us as weenies-LOL...j/k). Anyway, GSP is one of if not the best NWS outlets, so maybe they are picking up on some data to know that the system may be slowing down. My question to you and/or one of the redtaggers...how do we look for the signs that the system may be slowing down? Radar? RUC? Any input is much appreciated! Now I am waiting with all the tenseness in the world for the 12z runs.

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Can somebody comment on potential dryslotting. If the energy transfers to a low off the coast, which areas are in trouble? Or are the upper air dynamics so great that secondary moisture will fill in behind the initial surge?

A met can correct me if I am wrong, but there is a steady transport of preci (deform axis) progged for central/north of NC. Also the east flow will nix that chance of moisture being robbed. If you live down around CLT, then it would behoove the def axis to be further south (ala the system slowing down = more time for cold air intrusion before he system rolls out to sea. I am hoping that second piece of energy rolling west to east helps the low intensify more and all of the Carolina's at least gets SOME TYPE of wintry precip to wet our appetites! :) :)

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Was surprised not to see reference to the 6z RGM. At 36 hours, quite a bit slower than 18z at 48hours.

Decent precip still going at 6z Monday in Eastern TN/WNC.

06_054_R1_north@america_I_4PAN_CLASSIC@012_048.jpg

.

Local mets here are very conservative right now and rightfully so. I'd give good money to know what they really think here in NE TN. All signs point to a very close call in the valleys. The lack of cold air already in place makes me nervous. I will say it's been nice to finally have something to discuss. SW VA and E KY should get slammed. Smokies also should have huge amounts. I don't think this is the last either.

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Been comparing last few runs of RUC to NAM -- don't see major differences with southern S/W or the northern energy. Only difference I can see is the RUC is digging the "Nebraska S/W" more than the NAM. At 3z Sunday, RUC runs has that s/w well down into Kansas -- NAM still has it on Nebraska/KS border.

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GFS/NAM both still have a deformation band working through northern and central NC overnight Sunday. n fact, the 6Z NAM squeezes a .35 qpf max out of this band just west of Durham, and a stripe of at least .25" totals running across the northern piedmont of NC in assocation with this feature.

06znamp06thickpmsl_MA048.gif

That's going to be the best chance for people outside of the mountains to get accumulating snow, with that piece of energy on the backside swinging around the Apps.

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That's going to be the best chance for people outside of the mountains to get accumulating snow, with that piece of energy on the backside swinging around the Apps.

Yep, absolutely right. All our snow hopes are in the evolution of this feature. The good news is it has been modeled by all the guidance for several runs now, the bad news is it really will be a nowcast event as far as determing who gets accumulating snow and who does not. If the NAM is in the ballpark, that would proabbly be an 1-3" accumulation under the band/comma head as it trecks across the northern piedmont. Perhaps 4" amounts in localized pockets.

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