Deep South Winterwx Discussion 2015-2016

[MississippiWx]

Euro is basically the GFS solution.

[timmeister]

12Z CMC-GDPS now has wintry precipitation further south with snow in New Orleans.

[SeGaBob]

I think our NWS office will take out our 20% chance of snow in the evening update if models keep lining up with the GFS... It's all on the NAM now.

[BigB0882]

Well the good news is there is plenty of time for them to change and come back further north.

[SeGaBob]

I was wrong about them taking our 20% chance out... they increased it to 50%

[timmeister]

18Z NAM showing Snow, Sleet and Freezing Rain from Texas to North Carolina

[SeGaBob]

Rather long piece of the afternoon discussion from the NWS office in Charleston,SC for my area.

TUESDAY....THINGS BEGIN TO GET EXTREMELY TRICKY TUESDAY AS
CYCLOGENESIS INITIATES OVER THE GULF OF MEXICO AND TRACKS ACROSS
CENTRAL FLORIDA TO A POSITION OFF THE SOUTH CAROLINA/GEORGIA COAST
TUESDAY NIGHT. THE GFS/ECMWF/GEM AND NAM ALL OFF A VARIETY OF TRACK
SOLUTIONS WITH INHERENT MOISTURE/QPF AND P-TYPE PROBLEMS. THE
NAM/GEM APPEAR TO BE TOO WET/COLD WHILE THE OPERATIONAL GFS/ECMWF
LOOK TOO FAR OFFSHORE/DRY. THE OPERATIONAL GFS/ECMWF ARE CERTAINLY
THE OFFSHORE OUTLIERS COMPARED TO THEIR ENSEMBLE COUNTERPARTS AND
PREFER A WETTER/COLDER SOLUTION CLOSER TO THE GEFS MEAN WHICH TAKES
LOW PRESSURE TO POSITION THAT IS MORE CLIMATOLOGICALLY FAVORABLE FOR
P-TYPE PROBLEMS ACROSS SOUTHEAST SOUTH CAROLINA AND SOUTHEAST
GEORGIA. OUR CURRENT THINKING IS THAT RAIN ASSOCIATED WITH POWERFUL
JET DYNAMICS ALOFT WILL BEGIN TO OVERSPREAD THE REGION FROM
SOUTH-NORTH AS COLD/DRY AIR FILTER SOUTH IN RESPONSE TO THE
LOW-LEVEL FLOW BACKING NORTH AS LOW PRESSURE APPROACHES. AS DIABATIC
PROCESSES TAKE HOLD...THE COLUMN WILL COOL RAPIDLY AS PRECIPITATION
RATES INTENSIFY. THIS WILL ALLOW A FAIRLY STEADY TRANSITION OF
RAIN-SNOW FROM NORTH-SOUTH TUESDAY AFTERNOON. HIGHS WILL OCCUR
FAIRLY EARLY IN THE DAY...LOWER-MID 40S THEN DROP TO BELOW FREEZING
DURING THE AFTERNOON HOURS. POPS WILL BE INCREASED TO 30 PERCENT
MOST AREAS.

TUESDAY NIGHT...THE POTENTIAL EXISTS FOR SIGNIFICANT WINTER WEATHER
DURING THIS TIME AS ADEQUATE LIFT AND COLD AIR LOOK TO BE IN PLACE
FOR ACCUMULATING SNOWFALL. FORECAST SOUNDINGS OFF THE GFS/ECMWF AS
WELL AS OTHER PIECES OF INTERNAL GUIDANCE ALL AGREE THAT FAVORABLE
LIFT/MOISTURE WILL BE PRESENT THROUGHOUT THE DENDRITIC GROWTH ZONE
BY TUESDAY NIGHT WITH A SUFFICIENT AMOUNT OF COLD/DRY AIR TO THE
NORTH TO SUPPORT SNOW. CLIMATOLOGICAL SNOW RATIOS OF 7:1 WITH MODEST
QPF AMOUNTS COULD SUPPORT WARNING LEVEL SNOW AMOUNTS...BUT ITS STILL
A BIT TOO EARLY TO NARROW DOWN SPECIFIC VALUES THIS FAR OUT. PLAN TO
INCREASE POPS TO 50 PERCENT FOR MOST AREAS TUESDAY NIGHT WITH A
MENTION OF SNOW ALL AREAS...EXCEPT A BRIEF MENTION OF RAIN/SNOW MIX
ALONG THE GEORGIA COAST WHERE IT MAY TAKE A FEW HOURS AFTER SUNSET
THE LOWEST LEVELS OF THE TROPOSPHERE TO COOL ENOUGH TO SUPPORT ALL
SNOW. LOWS WILL RANGE FROM THE LOWER-MID 20...EXCEPT UPPER 20S
ACROSS THE GEORGIA COAST. STIFF NORTH WINDS WILL MAKE CONDITIONS
FEEL MUCH COLDER WITH WIND CHILLS IN THE 10-15 DEGREE RANGE. IT
SHOULD BE NOTED THAT CONFIDENCE IS STILL LOW ON EXACTLY WHICH P-TYPE
WILL DOMINATE THIS EVENT. IF THE NAM WERE TO VERIFY...A DANGEROUS
ICE STORM WOULD OCCUR. IT IS BEST FOR ALL TO CONTINUE TO MONITOR THE
LATEST FORECASTS FROM THE THIS OFFICE.

WEDNESDAY...SNOW WILL GRADUALLY END FROM SOUTHWEST-NORTHEAST AS LOW
PRESSURE PULLS AWAY AND HIGH PRESSURE BUILDS INTO THE REGION. HIGHS
WILL WARM INTO THE MID-UPPER 30S...BUT THIS IS CONTINGENT ON ANY
POTENTIAL SNOW COVER. LOWS WILL RANGE FROM THE LOWER-MID 20S...AGAIN
CONTINGENT ON SNOW COVER.

[cycloneye]

Here is a closeup view of the 18z NAM. Icestorm despicted but still there are differences between the operational GFS/ECMWF and their ensembles.

[cycloneye]

Here is the latest HPC discussion.

...GULF COAST/SOUTHEAST/FL...

THE MODELS ARE IN RATHER POOR CORRELATION WITH THE QPF...CERTAINLY
MORE SO COMPARED TO THEIR MASS FIELD DIFFERENCES. THE MAIN
DIFFERENCE DEALS WITH TO WHAT DEGREE THE SRN STREAM WILL BECOME
INVOLVED IN TERMS OF BOTH THE DISTRIBUTION OF THE PCPN (I.E. HOW
FAR N INTO THE GULF COAST/SOUTHEAST/SOUTHERN MID-ATLANTIC REGION
THE PCPN WILL GET) AS WELL AS AMOUNTS...PARTICULARLY NEAR THE GULF
COAST. THE NAM TRENDED MUCH WETTER AT 12Z COMPARED TO PRIOR
RUNS...INDICATIVE OF A MORE PROGRESSIVE SRN STREAM WAVE AND THUS A
BROADER EXPANSION OF WAA/OVERRUNNING PCPN...HOWEVER THE 18Z NAM
HAS SINCE BACKED OFF ON THIS IDEA CONSIDERABLY (ESPECIALLY WITH
RESPECT TO THE NRN EXTENT). HOWEVER...GIVEN THE LACK OF
CONSISTENCY WITH THE NAM (AND THE SREF MEAN FOR THAT MATTER)...WPC
STAYED FAIRLY CLOSE TO A BIAS-CORRECTED GEFS MEAN...WHICH IS STILL
SOMEWHAT WETTER THAN THE OPERATIONAL GFS/UKMET/ECMWF...BUT
NEVERTHELESS INCORPORATES THE IDEA OF MORE SRN STREAM INTERACTION
TOWARD THE END OF DAY 3...WHICH IS WHERE THE OPERATIONAL ECMWF IS
TRENDING (THOUGH AGAIN...NOT TO THE BULLISH EXTENT AS THE NAM OR
SREFMEAN). EXPECT A LLVL BOUNDARY (INVERTED SFC TROUGH) TO GET
FRONTOGENETIC SUPPORT VIA THE RIGHT ENTRANCE REGION OF THE UPPER
LEVEL JET STREAK...ANY SRN STREAM SUPPORT WOULD ONLY AMPLIFY THE
FORCING AND EXTEND THE OVERRUNNING PCPN FARTHER N INTO THE COLDER
AIR. FOR FURTHER DETAILS REGARDING THE WINTER WEATHER
PROBABILITIES ASSOCIATED WITH THIS SYSTEM...PLEASE REFER TO THE
WPC'S SUITE OF WINTER WEATHER PRODUCTS... INCLUDING THE LATEST
QPFHSD DISCUSSION.

http://www.hpc.ncep.noaa.gov/discussion ... isc=qpfpfd

[South Texas Storms]

Where did you get that image from cycloneye?

[cycloneye]

Where did you get that image from cycloneye?

From Levi Cowan's site.

http://www.tropicaltidbits.com/analysis/models/

[South Texas Storms]

I can't find out how to get a close up view of the SE US and how to get the winter precipitation simulated radar product that you have though.

[cycloneye]

:uarrow:
I can't find out how to get a close up view of the SE US and how to get the winter precipitation simulated radar product that you have though.

http://www.tropicaltidbits.com/analysis ... /namconus/

[South Texas Storms]

Yeah I know how to get that image, but I don't know how to get the pink/blue colors that show freezing rain and snow on the image like you have gotten a few posts up.

[BigB0882]

That would be quite a bit of ice, wouldn't it? Does anyone have QPF totals for the NAM?

[cycloneye]

:uarrow:
Yeah I know how to get that image, but I don't know how to get the pink/blue colors that show freezing rain and snow on the image like you have gotten a few posts up.

He posted that one on another site. But here is the 18z GFS ensemble mean run.

[South Texas Storms]

Oh ok thanks yeah I saw where he posted it now, it's not on his public site yet. The models are still having trouble with this potential system as it's currently over data sparse regions.

[northjaxpro]

JUst checking in herfe at work, and my the 18Z NAM really showing a potential nasty icestorm. This is getting more interesting by the hour. The WFO in Charleston, SC is really jumping onboard for a potential significant winter storm event across their forecast area after reading their AFD. The WFO in Tallahassee is beginning to lean bullish with this potential storm as well.

Ill check the runs later this evening, but this situation is looking very interesting to say the least as we get closer to the event.

[cycloneye]

00z NAM is a dream for many folks in the deep south.

[BigB0882]

NAM seems further south with the main precip, at least for Louisiana.

Actually it is further south in general. I hope this isn't the beginning of a trend to agreement with the GFS.