The Big One - Forecast & Discussion

[deltadog03]

I actually hope to get a little freezing rain or drizzle so that it covers everything and will make it hang around longer. Plus when I had my 10 inches a few years ago, the little bit of freezing rain/drizzle I got made everything that much prettier.

 

the 12z gfs now has freezing temperatures making it all the way into eastern alabama to the west of atlanta by 12z Wed! And that's right ahead of the heaviest precipitation. You don't  see freezing temps from a wedge make into alabama very often.

Chris, GFS, and now NAM are soooo dang close to dropping over 1" of ZR here.  Its showing like .30" ZR as it is.

[Berlin1926]

NWS Wakefield sounds like this ends up wet north of the Triangle and east to the coast.

&&

.LONG TERM /THURSDAY NIGHT THROUGH SUNDAY/...

MODELS IN BETTER AGREEMENT NOW WITH NRN STREAM AND SRN STREAM ENERGY

PHASING INTO A POTENT SHORTWAVE OVER THE GULF STATES LATE WEDS INTO

THURS. STRONG SPEED MAX WILL ROUND THE BASE OF THE

SHORTWAVE...EJECTING THE FEATURE NEWD THURS MORNING. CYCLOGENESIS

WILL BE ONGOING TO BEGIN THE EXTENDED PERIOD AS THE SFC LOW

STRENGTHENS ALONG A TRAILING COLD FRONT OFF THE SE COAST. SFC LOW

WILL LIFT ALONG THE SE AND MID-ATLANTIC COASTS WED NIGHT INTO THURS

MORNING. BEST/DEEPEST MOISTURE WILL REMAIN OFFSHORE IN STRONGEST

RETURN FLOW...BUT EXPECT MORE THAN SUFFICIENT MOISTURE TO GO ALONG

WITH UVM PROVIDED BY INCREASING FLOW ALOFT (DIVERGENCE) AND HEIGHT

FALLS (SHORTWAVE). HAVE INTRODUCED LIKELY POPS GENERALLY ALONG AND

EAST OF INTERSTATE 95 WED NIGHT-THURS MORNING AS CONFIDENCE IS

INCREASING...BUT WILL MAINTAIN CHANCE POPS WEST OF INTERSTATE 95.

WHILE THE ECMWF THERMAL PROFILE IS WARMER THAN ITS GFS

COUNTERPART...A BLEND OF LOW LEVEL THICKNESSES REVEAL A MIXED BAG OF

PTYPES OVER THE REGION. TO BACK UP WARMER GUIDANCE...SFC HIGH

PRESSURE WILL PUSH OFF THE NE COAST (RESULTING IN ONSHORE FLOW) AS

LOW-LEVEL THICKNESSES ACTUALLY RISE OVERNIGHT WED NIGHT-THURS

MORNING (TEMPS WILL INCREASE OVERNIGHT AS WELL). EXPECT THE COAST TO

REMAIN RAIN WHILE INLAND WILL TRANSITION FROM SNOW TO RAIN-SNOW WITH

SOME SLEET TO ALL RAIN BY THURS AFTERNOON. STILL TO EARLY TO

DETERMINE ANY POTENTIAL ACCUMULATIONS...BUT ANY ACCUMULATION WEDS-WEDS

NIGHT WILL LIKELY MELT THURS. SFC LOW WILL RAPIDLY INTENSIFY AND LIFT

NEWD AWAY FROM THE REGION LATE THURS...ALLOWING PRECIP TO COME TO AN

END OVER MOST OF THE REGION. WILL HANG ON TO SLIGHT CHANCE POPS FOR

A WINTRY MIX OVER THE NE THRU THURS NIGHT.

[Lookout]

Chris, GFS, and now NAM are soooo dang close to dropping over 1" of ZR here.  Its showing like .30" ZR as it is.

The thing is if they are just off by 1 degree your ice totals will be 2 or 3x higher.

 

12z canadian has some insane totals across central ga between 48 and 60 hours. Canadian continues hit everyone hard

 

 

 

[Poimen]

The GGEM is really juiced by hour 60...heavy precip into southern VA by that hour.

[deltadog03]

Sure does...puts you in the game for sure. As i just mentioned the gfs is now showing freezing temps all the way into alabama. The nam is also doing it but because of it's stronger waa aloft, it warms them back above freezing slightly before going back to freezing with the back end snow. However I doubt temps will rise there if it gets below freezing with steady precip. So the models might finally be getting a better handle on the low level cold with this. And it wouldn't surprise me to see it trend colder and further south/west even more.

I fully agree!!  CMC (global) is also colder at 2m as well.  I think they might be starting to see the colder 2m temps...It usually happens in 48hr and under with them.   I agree...I think the NAM bumping them back above is bogus.  

[FallsLake]

RDU folks, I actually like the 12z runs. The 12z NAM shifted back east from the 6z, the GFS looks like a major snow to sleet storm with the 30 degree dew point line never making it west of Raleigh. It's still going to be a mixed bag of everything, but now it looks like rain will not be one of them(except for maybe late on Thursday).

 

By the way, my wife's shopping in Wake Forest and said it was snowing. NWS has increased the chance of snow for the Raleigh area for this afternoon and tonight.

[Shawn]

Modeling is all pretty much leveling KCAE with ZR.  Some have more snow and sleet than others.. but overall at least 1 inch+ of ZR looks probable.

[Stormsfury]

I fully agree!!  CMC (global) is also colder at 2m as well.  I think they might be starting to see the colder 2m temps...It usually happens in 48hr and under with them.   I agree...I think the NAM bumping them back above is bogus.  

I'm not surprised with the wedge depictions making it to even AL now.  ***IF** there's that much thump of snow in NE GA, Upstate SC and points like CLT, and into the normally favored CAD regions, that stiff NE wind will effectively transport the low level cold SW across that snowpack.

[tarheelwx]

FWIW, there will not be any snowpack from the triad to RDU north and east until later on Wednesday late afternoon/evening.  I"m not sure how far north/northeast you have to go to get snowpack, but there will be a fair geographical area without snowcover until Wednesday evening sometime.  I think as you get north of VA, there is plenty of snow.  Not sure how this might impact those much further south.  Probably some, but may be insignificant as there is plenty at the source of the hp.  I figure the more the better.

TW

[buckeyefan1]

CAE updated the short term  

 

.NEAR TERM /THROUGH TONIGHT/...
A COLD FRONT WILL MOVE THROUGH THE FORECAST AREA THIS AFTERNOON.
LITTLE MOISTURE IS ASSOCIATED WITH THIS FRONT. A WEDGE-RIDGE
PATTERN WILL OCCUR BEHIND THE FRONT TONIGHT. THE NAM INDICATES
WEAK ISENTROPIC LIFT WITH AN INCREASE IN MOISTURE OVERNIGHT. THERE
MAY BE ENOUGH MOISTURE AND LIFT FOR PRECIPITATION. EXPECT THIS
PRECIPITATION WILL BE LIGHT BECAUSE OF THE WEAK SUPPORT. MODEL
TIME-HEIGHT DISPLAYS SUPPORT A MIX OF RAIN...SLEET AND SNOW FROM
COLUMBIA NORTHWARD...AND RAIN AND POSSIBLY A LITTLE SLEET SOUTH
OF COLUMBIA. THE GUIDANCE CONSENSUS SUPPORTS LOWS IN THE LOWER 30S
NORTH...AND MIDDLE TO UPPER 30S FROM COLUMBIA SOUTHWARD. WITH
TEMPERATURES COOLING TO NEAR FREEZING TRAVEL PROBLEMS ARE NOT OUT
OF THE QUESTION DESPITE EXPECTED LIGHT AMOUNTS NORTH OF COLUMBIA
BY RUSH HOUR TUESDAY MORNING.

[Shawn]

For reference, I expect one of these to be what's used to refer to this system when all is said and done:

 

The WPC basically says the midlands, athens, etc will probably see a "historic" storm... already.

 

SECS: Significant East Coast Snowstorm
MECS: Major East Coast Snowstorm
HECS: Historic East Coast Snowstorm

[RevDodd]

Soundings on the 12z GFS for FAY 12/12 pm show more IP and less ZR. That would be a welcome trend, without messing up the snow fest in the Foothills.

[RaleighWx]

12z GFS soundings look mostly snowy for RDU changes to sleet/freezing rain towards end.

[AUProud]

Spann just tweeted

 

James Spann ‏@spann  3m

New model data in, NWS considering an upgrade to a winter storm warning for North-Central AL. Mostly ice, some snow http://www.alabamawx.com 

[packfan98]

The UKIE and Canadian looks West to me. Looks like a track inside of the outer banks which would push the mixing issues further west.  Can anyone confirm or provide any analysis that has better maps than me?  Thanks!

[RaleighWx]

Maybe this was posted earlier but from WPC

 

THEN FINALLY ON WED... THE DIGGING UPSTREAM DYNAMICS OVER THE

CENTRAL PLAINS WILL RAPIDLY CATCH UP WITH THE SRN STREAM DYNAMICS

TO POTENTIALLY PHASE OVER THE SERN PORTION OF THE COUNTRY. THIS

WILL ALLOW A SIGNIFICANT INCREASE IN MOISTURE ADVECTION FROM THE

GULF OF MEXICO AND ATLANTIC TO INTERACT WITH THE DEVELOPING

COASTAL LOW ALONG THE SOUTHEAST COAST... WHILE ONE OF THE MORE

IMPRESSIVE CONFLUENT ZONES ALOFT KEEPS THE ARCTIC AREA OF HIGH

PRESSURE ENTRENCHED OVER THE EAST. A TRUE BAROCLINIC LEAF PRECIP

SHIELD WILL EVOLVE FEATURING CONTINUED ICING FROM EAST OF ATL

TOWARD CAE THEN SHIFTING NORTH TOWARD RDU AND A VERY HEALTHY

DEFORMATION ZONE OF BANDING SNOWFALL FROM SWRN NC/NWRN SC NEWRD TO

SWRN/CENTRAL VA BEFORE POSSIBLY FLIRTING WITH THE DC/BALT METRO

AREAS. THE ICE ACCUMULATIONS REMAIN POSSIBLY PARALYZING IF NOT

HISTORICAL WITH ADDITIONAL .50 TO .75 INCH AXIS FROM AHN TO CAE TO

RDU AND 8 TO 10 INCHES OR SNOW FROM AVL/GSP TO ROA/LYH/CHO. WPC

CONTINUED THE COMPROMISE OF THE GFS/ECMWF WITH SUPPORT FROM THE

SREF MEAN... THOUGH MUCH MORE OF THE ENSEMBLE SUPPORT IS BEGINNING

TO CLUSTER CLOSER TO THE ECMWF ON A FULL FLEDGED PHASED COASTAL

WINTER STORM.

[buckeyefan1]

Bufkit for the nam/gfs at cae.....wow

 

 

 

[ncskywarn]

12z GFS soundings look mostly snowy for RDU changes to sleet/freezing rain towards end.

Agreed and thank you Allen. If you're in the triangle area you're going to like this.

KRDU 12Z GFS

[CaryWx]

12z GFS soundings look mostly snowy for RDU changes to sleet/freezing rain towards end.

Thanks Allan. Sounding like less of an ice storm in the Triangle from that run. Zr trailing out as the system moves away hopefully will not accrue too much beyond .25

[rduwx]

12z GFS soundings look mostly snowy for RDU changes to sleet/freezing rain towards end.

 

That's encouraging.  I was looking at the soundings on plymouth and there was a warm nose between hrs 60 and 66.  At 66 we were above freezing between 800 and 900 layer.  Has the bulk of the precip already fallen by then?

[deltadog03]

Chris, Mike,  12z gfs, via the meteogram generator has .85" of ZR showing up on it from the 12z gfs run.  6z run had .20"

[ScottL]

Chris, GFS, and now NAM are soooo dang close to dropping over 1" of ZR here.  Its showing like .30" ZR as it is.

 

Just to clarify, is that QPF equivalent or accumulation?  What would be a typical ratio of QPF to accumulation (if there is such a quick ratio to use a la 10:1 with snow accumulation)?

 

Thanks!

[deltadog03]

Just to clarify, is that QPF equivalent or accumulation?  What would be a typical ratio of QPF to accumulation (if there is such a quick ratio to use a la 10:1 with snow accumulation)?

 

Thanks!

ZR accumulation..sorry

[BullCityWx]

Look at this SICK comma head on the ukie: 

[strongwxnc]

Cobb data off the 12 GFS puts down

7.1" in Kctl,

6.2" in KGSP

6.0" in KHKY

13.1" on KAVL

8.2" in KGSO

[max100]

Georgia Power states they are pulling in crews from multiple states to assist.

 

 

 Kirk Mellish on WSB radio ATL, is leaning towards this being an "epic and historical storm", said his confidence is high. Have never heard his voice shaky and sounds extremely very concerned. 

[Wow]

Look at this SICK comma head on the ukie:

Nam really gives us a ton of snow from that feature. A ton of energy is moving through the base of the through to really keep it going down here.

[atlweatherman]

Atlanta Mayor and Georgia Governor press conference currently being held concerning preparations for the storm hitting Atlanta:

 

http://www.wsbtv.com/s/news/live/?breaker3time=1150

[oconeexman]

Cobb data off the 12 GFS puts down

7.1" in Kctl,

6.2" in KGSP

6.0" in KHKY

13.1" on KAVL

8.2" in KGSO

Gfs looks to be the lightest amounts for now which still look pretty dang good. Hopefully that's as low as it will go and be used for the conservative side of the model blend.

[RaleighWx]

Well waited long enough. Here is my first map and a brief discussion.

 

Well this is as difficult a map as I have ever had to make due to the many zones of p-type issues and also the model uncertainty, but this is my best guess.

Synopsis

A complicated setup as we see several s/w in the southern branch of the jet stream interact with each other while the northern branch of the jet stream delivers a fresh supply of cold polar/arctic air into the Great Lakes and Northeast. The high pressure is not too strong, around 1032-1035mb, but it is in a classical CAD position as the storm begins and transitions to a hybrid setup as the storm wears on. Diabatic processes will help intensify the damming and drive it well into South Carolina and Georgia.

Right now, I feel like low pressure along the Gulf Coast will consolidate into a stronger area of low pressure east of Savannah/Charleston by Wednesday morning. By Wednesday afternoon a trough will capture this storm and begin to strengthen it rapidly while turning it north east of Hatteras. I do not expect the low pressure center to track up the coastal plain but to stay off shore. This fits historical events, climo, takes into account model biases, and the current synoptic pattern with the wedge locked in east of the mountains.

Best Chance for Heavy Snow

I see the area from NE Georgia into upstate South Carolina, western NC, and central Va as standing the best chance to receive very heavy snow. I have 8-12 inches there right now, but if the storm does indeed bomb and hug the coast amounts in excess of a foot are possible. This includes Greenville, SC, Asheville, Hickory, Greensboro into Roanoke.

Best Chance for Severe Ice

This zone is hard to pinpoint as we have an unusually wide transition zone with this Miller A type storm. Right now from central Georgia into central SC and into east-central NC stand the best chance of seeing 0.5 to 0.75 inches of freezing rain accrual. It is possible some areas could see up to 1 inch of ice accrual, but this would be an unusually severe case. This includes areas like Athens, Columbia, Fayetteville, and Raleigh. It is possible there could be a changeover to rain Wednesday night along the I-95 corridor and east in NC, but it could be brief or hold east of I-95. As of now, I do not think Raleigh-Durham changes to plain rain.

There are many transition zones and mixed precipitation areas, so look at the map and that will tell you what I think for your area. I will update this as data changes. Confidence is still somewhat low but increasing some.