Major National Winter Storm Dec 25-28

[am19psu]

A major winter storm is taking shape from Texas on Christmas to New England by Friday (potentially). Use this thread to discuss severe weather in the South and winter weather across the Midwest and Northeast.

[Srain]

While we are still a couple of days out and there remains some uncertainty in the eventual track of the Storm system, there are strong indications that both winter weather as well as a severe potential may well unfold across portions of E Texas extending E into the Deep South S of the I-20 Corridor. Further N into Eastern Oklahoma/Arkansas and on ENE in Mid West/Tennessee Valley within the cold sector, a variety of winter weather including snow and ice and very gusty winds and blowing snow creating the potential for a high impact event affecting travel as well as societal impacts during the busy Holiday period. The storm system is currently nearing the California Coast and should be onshore and in the RAOB network tomorrow. One concern we are following closely in the South is the Severe aspect of this dynamic Winter Storm. The SPC has outlined a Day 4 threat for severe storms in their Outlook. At this time the main threat appears to be damaging winds with a linear line of rapidly moving storms, but the tornado potential cannot be dismissed during the late Christmas Day time frame beginning in SE Texas and extending overnight into Southern Louisiana/Mississippi and Alabama on the 26^th.The severe potential may extend further E into GA/FL and SC on the 27^th.

[am19psu]

Should he noted that the low track above is for the pre-Christmas wave, not the main event that begins in Texas on Christmas

[Srain]

Should he noted that the low track above is for the pre-Christmas wave, not the main event that begins in Texas on Christmas

Excellent point Adam and the lead wave will play a pivotal role as to how things evolve for the Christmas Storm. A warm front will move N from the Western Gulf across Central/SE Texas into Louisiana during the day Christmas Eve setting the stage for the Severe potential outlined above. There are strong suggestions a Coastal Low/wave will develop along the Middle/Upper Texas Coast setting the stage for all the potential events that will follow. This appears to be a very dynamic storm complex with many implications for a large part of the Eastern half of the CONUS.

SHORT RANGE FORECAST DISCUSSION

NWS HYDROMETEOROLOGICAL PREDICTION CENTER COLLEGE PARK MD

239 AM EST SAT DEC 22 2012

VALID 12Z SAT DEC 22 2012 - 12Z MON DEC 24 2012

***STRONG LOW PRESSURE SYSTEM DEPARTING THE NORTHEAST U.S.***

***MORE BAD WEATHER FOR THE WEST COAST STATES***

***VERY COLD FOR THE NORTHERN PLAINS AND UPPER MIDWEST***

THE STRONG AREA OF LOW PRESSURE THAT AFFECTED MUCH OF THE CENTRAL

AND EASTERN U.S. OVER THE PAST COUPLE OF DAYS IS FORECAST TO MOVE

INTO EASTERN CANADA DURING THE DAY ON SATURDAY. SOME LINGERING

LIGHT SNOW SHOWERS ARE STILL POSSIBLE NEAR THE GREAT LAKES AND

INTO NORTHERN NEW ENGLAND THROUGH EARLY SUNDAY. THE HIGHER

ELEVATIONS OF THE CENTRAL APPALACHIANS WILL ALSO RECEIVE SOME

ADDITIONAL SNOWFALL. IN ADDITION, STRONG AND GUSTY WINDS ARE

LIKELY THROUGH SATURDAY WITH GUSTS UP TO 50 MPH POSSIBLE.

OVER THE WEST COAST STATES, STEADY RAIN AND HIGHER ELEVATION SNOW

IS EXPECTED TO CONTINUE AS ONSHORE FLOW CONTINUES UNABATED AHEAD

OF A FRONTAL TROUGH. THE HEAVIEST PRECIPITATION IS LIKELY FOR

CENTRAL AND NORTHERN CALIFORNIA, WITH A COUPLE INCHES OF RAIN FOR

COASTAL AREAS AND AT LEAST TWO FEET OF SNOW IN THE HIGHER

MOUNTAINS OF THE SIERRA NEVADA RANGE.

ELSEWHERE, BITTERLY COLD AIR WILL CONTINUE FOR THE NORTHERN PLAINS

AND UPPER MIDWEST THROUGH THE WEEKEND AND INTO EARLY NEXT WEEK.

OVER THE DEEP SOUTH AND INTO TEXAS, MUCH COOLER AND CONSIDERABLY

DRIER WEATHER HAS ARRIVED BEHIND THE COLD FRONT AND IT WILL FEEL

MORE LIKE DECEMBER.

[OUGrad05]

Ok folks forgive me, I'm pretty good at severe weather forecasting and prediction but I absolutely suck at reading models and interpretation for winter weather.

Anyone have specifics on how this will impact the Tulsa metro area and the timing of the various impacts?

The models don't seem to have a good grasp on this system yet, which isn't surprising since it won't really be over the data network for another 12 to 18 hours.

[Srain]

HPC Model Diagnostic Discussion for the 12Z suite of guidance:

...SFC LOW IMPACTING THE WEST COAST ON SUN...

PREFERENCE: 12Z NAM / 12Z ECMWF

CONFIDENCE: AVERAGE

REGARDING THE SFC LOW REACHING THE WEST COAST ON SUN...THE GFS

LOOKS FAST...AND THE 12Z ECMWF HAS SPED UP CLOSER TO THE CONSENSUS

BUT THE 12Z NAM AND 00Z EC MEAN ARE STILL A BIT BACK TOWARD THE

ENSEMBLE CONSENSUS...SLIGHTLY BEHIND THE 12Z ECMWF. GIVEN

DOWNSTREAM PREFERENCES...A 12Z NAM/ECMWF BLEND IS LIKELY BEST WITH

THE SFC LOW COMING INTO THE WEST COAST ON SUN GIVEN PLACEMENT IN

THE MIDDLE OF THE SPREAD...WITH CONSIDERATION OF SOME OF THE

FASTER GUIDANCE.

...SHRTWV ENERGY AMPLIFYING THROUGH THE INTERMOUNTAIN WEST ON MON

AND REACHING THE CNTRL/SRN PLAINS TUE...

PREFERENCE: 12Z ECMWF / 12Z UKMET

CONFIDENCE: BELOW AVERAGE

THE NAM IS ON THE WEAKER AND NRN SIDE OF THE MODEL SPREAD WITH

BOTH THE SHORTWAVE AND SFC LOW BY THE TIME THE SYSTEM REACHES THE

PLAINS. THE GFS HAS TRENDED QUICKER WITH THE SHORTWAVE EJECTING

OUT INTO THE PLAINS ON TUE AND IS ON THE FASTER SIDE OF THE

SPREAD. GIVEN THE 12Z CMC IS A BIT OUTSIDE OF THE

CONSENSUS...BLENDING THE 12Z ECMWF AND 12Z UKMET APPEAR THE BEST

WAY TO GO AND FALL RIGHT IN THE MIDDLE OF THE CONVERGING ENSEMBLE

SPAGHETTI LOW PLOTS...LOOKING OVER THE PAST 5 RUNS. THE 12Z ECMWF

LOOKS MOSTLY UNCHANGED FROM ITS 00Z RUN WITH THIS SYSTEM.

[Srain]

SPECIAL WEATHER STATEMENT

NATIONAL WEATHER SERVICE NORMAN OK

340 PM CST SAT DEC 22 2012

OKZ004>048-050>052-TXZ083>090-231200-

HARPER-WOODS-ALFALFA-GRANT-KAY-ELLIS-WOODWARD-MAJOR-GARFIELD-

NOBLE-ROGER MILLS-DEWEY-CUSTER-BLAINE-KINGFISHER-LOGAN-PAYNE-

BECKHAM-WA****A-CADDO-CANADIAN-OKLAHOMA-LINCOLN-GRADY-MCCLAIN-

CLEVELAND-POTTAWATOMIE-SEMINOLE-HUGHES-HARMON-GREER-KIOWA-JACKSON-

TILLMAN-COMANCHE-STEPHENS-GARVIN-MURRAY-PONTOTOC-COAL-COTTON-

JEFFERSON-CARTER-JOHNSTON-ATOKA-LOVE-MARSHALL-BRYAN-HARDEMAN-

FOARD-WILBARGER-WICHITA-KNOX-BAYLOR-ARCHER-CLAY-

INCLUDING THE CITIES OF...BUFFALO...ALVA...CHEROKEE...MEDFORD...

PONCA CITY...ARNETT...WOODWARD...FAIRVIEW...ENID...PERRY...

CHEYENNE...TALOGA...WEATHERFORD...CLINTON...WATONGA...

KINGFISHER...GUTHRIE...STILLWATER...ELK CITY...SAYRE...CORDELL...

ANADARKO...YUKON...EL RENO...MUSTANG...OKLAHOMA CITY...CHANDLER...

CHICKASHA...PURCELL...NORMAN...MOORE...SHAWNEE...SEMINOLE...

HOLDENVILLE...HOLLIS...MANGUM...HOBART...ALTUS...FREDERICK...

LAWTON...DUNCAN...PAULS VALLEY...SULPHUR...ADA...COALGATE...

WALTERS...WAURIKA...ARDMORE...TISHOMINGO...ATOKA...MARIETTA...

MADILL...DURANT...QUANAH...CHILLICOTHE...CROWELL...VERNON...

WICHITA FALLS...MUNDAY...KNOX CITY...SEYMOUR...ARCHER CITY...

HOLLIDAY...LAKESIDE CITY...HENRIETTA

340 PM CST SAT DEC 22 2012

...WINTER PRECIPITATION REMAINS POSSIBLE CHRISTMAS DAY...

WEATHER FORECAST MODELS CONTINUE TO DEPICT THE POTENTIAL FOR A

WINTER STORM TO AFFECT OKLAHOMA AND NORTHERN TEXAS CHRISTMAS EVE

NIGHT THROUGH CHRISTMAS NIGHT...WITH THE BEST CHANCES FOR

PRECIPITATION ON CHRISTMAS DAY. A BRIEF PERIOD OF A VERY LIGHT

WINTRY MIX WILL BE POSSIBLE CHRISTMAS EVE NIGHT ACROSS WESTERN

OKLAHOMA...WITH LIGHT RAIN POSSIBLE ACROSS SOUTHERN OKLAHOMA AND

WESTERN NORTH TEXAS. THE PRECIPITATION WILL THEN CHANGE OVER TO

SNOW ON CHRISTMAS. MODERATE TO STRONG WINDS COULD ALSO LEAD TO

SOME BLOWING AND DRIFTING OF THE SNOW IN SOME AREAS BUT BLIZZARD

CONDITIONS APPEAR UNLIKELY. THE SNOW IS EXPECTED TO END FROM WEST

TO EAST CHRISTMAS NIGHT.

THE AMOUNT OF SNOW AND WHERE THE HEAVIEST SNOWFALL WILL OCCUR

REMAINS UNCERTAIN...AS DIFFERENCES REMAIN BETWEEN THE SOLUTIONS

FROM THE COMPUTER MODELS. SOME MODELS CONTINUE THE TRACK OF HEAVIEST

SNOW ACROSS NORTHERN PORTIONS OF OKLAHOMA...WHILE OTHERS TAKE IT

ACROSS SOUTHERN OKLAHOMA INTO NORTHERN TEXAS. CONTINUING WITH A

CONSENSUS APPROACH...THE HIGHEST SNOW TOTALS ARE EXPECTED FROM WEST

CENTRAL OKLAHOMA INTO CENTRAL AND SOUTHEAST OKLAHOMA WHERE AMOUNTS

COULD AVERAGE THREE TO SIX INCHES.

WITH THE VARIATION IN FORECAST TRACKS AND SNOW AMOUNTS...EVERYONE

ACROSS THE STATE OF OKLAHOMA AND THOSE ACROSS NORTHERN TEXAS

SHOULD PAY CLOSE ATTENTION TO REFINED FORECASTS OVER THE WEEKEND.

IF YOU ARE PLANNING TO TRAVEL ACROSS THE SOUTHERN PLAINS FOR THE

UPCOMING HOLIDAY WEEK...HAVE A CONTINGENCY PLAN IN PLACE AND

PREPARE FOR WEATHER-RELATED DELAYS AND CANCELLATIONS.

SPECIAL WEATHER STATEMENT

NATIONAL WEATHER SERVICE TULSA OK

339 PM CST SAT DEC 22 2012

ARZ001-002-010-011-019-020-029-OKZ049-053>076-230945-

BENTON-CARROLL-WASHINGTON AR-MADISON-CRAWFORD-FRANKLIN-SEBASTIAN-

PUSHMATAHA-CHOCTAW-OSAGE-WASHINGTON OK-NOWATA-CRAIG-OTTAWA-PAWNEE-

TULSA-ROGERS-MAYES-DELAWARE-CREEK-OKFUSKEE-OKMULGEE-WAGONER-

CHEROKEE-ADAIR-MUSKOGEE-MCINTOSH-SEQUOYAH-PITTSBURG-HASKELL-

LATIMER-LE FLORE-

INCLUDING THE CITIES OF...ROGERS...BENTONVILLE...BERRYVILLE...

EUREKA SPRINGS...FAYETTEVILLE...SPRINGDALE...HUNTSVILLE...

VAN BUREN...OZARK...CHARLESTON...FORT SMITH...ANTLERS...CLAYTON...

HUGO...PAWHUSKA...BARTLESVILLE...NOWATA...VINITA...MIAMI...

PAWNEE...TULSA...CLAREMORE...PRYOR...JAY...BRISTOW...OKEMAH...

OKMULGEE...WAGONER...TAHLEQUAH...STILWELL...MUSKOGEE...EUFAULA...

SALLISAW...MCALESTER...STIGLER...WILBURTON...POTEAU

339 PM CST SAT DEC 22 2012

...CHRISTMAS DAY/NIGHT WINTER WEATHER POTENTIAL ACROSS EASTERN

OKLAHOMA AND NORTHWEST ARKANSAS...

A WINTER STORM WILL DEVELOP OVER THE SOUTHERN PLAINS CHRISTMAS DAY

WITH THE POTENTIAL FOR ACCUMULATING SNOW ACROSS MUCH OF EASTERN

OKLAHOMA AND NORTHWESTERN ARKANSAS. ALTHOUGH THE EXACT TRACK

REMAINS SOMEWHAT UNCERTAIN...MOST OF THE REGION WILL LIKELY RECEIVE

AT LEAST AN INCH OR TWO FROM THIS SYSTEM. THE STORM WILL LIKELY

LAY DOWN A HEAVIER BAND OF SNOW ACROSS A PORTION OF THE REGION.

LATEST DATA SUGGEST THE GREATEST SNOW POTENTIAL WILL OCCUR ALONG

AND SOUTH OF A EUFAULA TO EUREKA SPRINGS LINE. PEOPLE TRAVELING

ACROSS THE REGION CHRISTMAS DAY SHOULD CONTINUE TO MONITOR THE

LATEST FORECAST.

WE ARE CURRENTLY POSTING PRELIMINARY SNOW AMOUNT INFORMATION TO OUR

DECISION SUPPORT PAGE AT WWW.WEATHER.GOV/TULSA/DSP/DSP.PHP. THE

LOCATION AND MAGNITUDE OF ANY WINTER WEATHER IMPACTS WILL CONTINUE

TO BE REFINED AS THIS SYSTEM APPROACHES. GIVEN THE SYSTEM IS STILL

OFF THE NORTHWEST PACIFIC COAST...ANY SMALL DEVIATION IN THE STORM

TRACK COULD RESULT IN SIGNIFICANT FORECAST CHANGES EARLY NEXT

WEEK. THEREFORE...SNOW AMOUNTS WILL CONTINUE TO BE ADJUSTED AND

THE LOCATION OF THE HEAVIEST SNOW SWATH COULD SHIFT SEVERAL COUNTIES

IN ANY DIRECTION. PERSONS ACROSS SOUTHEAST OKLAHOMA AND NORTHWEST

ARKANSAS SHOULD BE PREPARED FOR ACCUMULATING SNOW CHRISTMAS DAY

INTO CHRISTMAS NIGHT. ROADS MAY BECOME SLICK AND HAZARDOUS CAUSING

TRAVEL DELAYS.

SPECIAL WEATHER STATEMENT

NATIONAL WEATHER SERVICE FORT WORTH TX

205 PM CST SAT DEC 22 2012

TXZ091>095-100>107-116>123-231200-

MONTAGUE-COOKE-GRAYSON-FANNIN-LAMAR-YOUNG-JACK-WISE-DENTON-COLLIN-

HUNT-DELTA-HOPKINS-PALO PINTO-PARKER-TARRANT-DALLAS-ROCKWALL-

KAUFMAN-VAN ZANDT-RAINS-

205 PM CST SAT DEC 22 2012

...WINTER WEATHER OUTLOOK FOR DECEMBER 25TH...

A STRONG STORM SYSTEM IS EXPECTED TO MOVE ACROSS THE REGION ON

CHRISTMAS DAY. BASED ON THE LATEST FORECAST DATA...THERE WILL BE A

GOOD CHANCE OF A COLD RAIN ON CHRISTMAS DAY ACROSS NORTH AND

CENTRAL TEXAS. ALONG AND TO THE NORTH OF I-20...ATMOSPHERIC

PROFILES WILL BECOME COLD ENOUGH FOR THE RAIN TO MIX WITH OR

CHANGE OVER TO SNOW DURING THE AFTERNOON AND EVENING HOURS. THE

LATEST MODEL GUIDANCE SUGGESTS SNOWFALL ACCUMULATIONS UP TO 2

INCHES ARE POSSIBLE CHRISTMAS AFTERNOON AND EVENING ALONG AND

NORTH OF A BOWIE TO EMORY LINE. SOUTH OF THIS LINE...LIGHT

ACCUMULATIONS OF SNOW ARE POSSIBLE.

AS THE CHANGE OVER TO SNOW OCCURS...NORTHWEST WINDS ARE EXPECTED

TO INCREASE IN SPEED TO 20 TO 30 MPH. ANY SNOW ACCUMULATIONS

WILL BLOW AROUND IN THESE WINDS...WHICH MAY REDUCE VISIBILITY IF

TRAVELING AFTER SUNSET ON CHRISTMAS DAY.

AS OF THIS AFTERNOON...THE UPPER LEVEL STORM SYSTEM WAS ENTERING

THE PACIFIC NORTHWEST. AT THIS TIME...THERE STILL REMAINS A GREAT

DEAL OF UNCERTAINTY REGARDING THE EXACT TRACK AND ANY ASSOCIATED

WINTRY PRECIPITATION FALLING OVER NORTH TEXAS ON CHRISTMAS DAY. IF

THE TRACK OF THE SYSTEM WERE TO SHIFT FARTHER SOUTH...THE

POTENTIAL FOR HIGHER SNOWFALL ACCUMULATIONS ACROSS THE REGION

WOULD INCREASE AND THE RAIN/SNOW LINE WOULD SHIFT FARTHER TO THE

SOUTH.

IN ADDITION TO THE WINTER PRECIPITATION POTENTIAL...THERE IS ALSO

A THREAT FOR SOME SEVERE STORMS EARLY CHRISTMAS MORNING AND

POSSIBLY INTO THE DAY ON THE 25TH. THE THREAT FOR SEVERE WEATHER

AT THIS TIME IS MAINLY SOUTH OF I-20 AND EAST OF I-35. THE

DETAILS OF THE SEVERE WEATHER POTENTIAL ARE JUST NOW COMING TO

FRUITION AND WILL ALSO BE REFINED OVER THE NEXT FEW DAYS.

BOTTOM LINE...WINTRY PRECIPITATION IS POSSIBLE MAINLY ALONG AND

NORTH OF THE I-20 CORRIDOR FOR THE AFTERNOON AND EVENING HOURS OF

CHRISTMAS DAY. SOME SNOW ACCUMULATIONS UP TO 2 INCHES ARE POSSIBLE

ALONG AND NORTH OF A BOWIE TO EMORY LINE. CHECK BACK FOR THE

LATEST FORECAST UPDATES IN THE COMING DAYS AS THESE DETAILS ARE

VERY LIKELY TO CHANGE WITH FUTURE FORECASTS.

SPECIAL WEATHER STATEMENT

NATIONAL WEATHER SERVICE SHREVEPORT LA

156 PM CST SAT DEC 22 2012

ARZ050-051-059>061-070>073-LAZ001>006-OKZ077-TXZ096-097-108>112-

124>126-136>138-231200-

BOSSIER-BOWIE-CADDO-CAMP-CASS-CLAIBORNE-COLUMBIA-FRANKLIN-GREGG-

HARRISON-HEMPSTEAD-HOWARD-LAFAYETTE-LINCOLN-LITTLE RIVER-MARION-

MCCURTAIN-MILLER-MORRIS-NEVADA-RED RIVER TX-SEVIER-SMITH-TITUS-

UNION AR-UNION LA-UPSHUR-WEBSTER-WOOD-

156 PM CST SAT DEC 22 2012

...WINTER WEATHER WILL BE POSSIBLE CHRISTMAS AFTERNOON AND NIGHT

MAINLY NORTH OF THE INTERSTATE 20 CORRIDOR...

A STRONG UPPER LEVEL STORM SYSTEM IS EXPECTED TO DEVELOP

CHRISTMAS DAY OVER OKLAHOMA...AS VERY COLD AIR DEEPENS AND BEGINS

TO PUSH SOUTHEAST BEHIND A COLD FRONT INTO SOUTHEAST OKLAHOMA

AND SOUTHWEST ARKANSAS CHRISTMAS AFTERNOON AND EVENING. SCATTERED TO

NUMEROUS SHOWERS AND A FEW THUNDERSTORMS WILL QUICKLY DEVELOP EARLY

CHRISTMAS MORNING ACROSS THE REGION AHEAD OF THE FRONT...AND PERSIST

THROUGH AT LEAST MIDDAY AS AN UPPER LEVEL DISTURBANCE LIFTS NORTHEAST

THROUGH THE AREA. TO THE NORTH OF THE AREA OVER CENTRAL AND EASTERN

OKLAHOMA WHERE THE SUBFREEZING TEMPERATURES ARE EXPECTED...AREAS OF

SNOW WILL DEVELOP AND GRADUALLY SPREAD EAST NEAR THE COLD CORE CENTER

OF THIS STORM SYSTEM. THE RAIN IS EXPECTED TO CHANGE OVER TO A RAIN

SNOW MIX BEFORE TRANSITIONING OVER TO ALL SNOW CHRISTMAS AFTERNOON

AND EVENING OVER PORTIONS OF EXTREME NORTHEAST TEXAS...SOUTHEAST

OKLAHOMA...AND SOUTHWEST ARKANSAS...MAINLY NORTH OF THE INTERSTATE 30

CORRIDOR AS THE COLDER AIR DEEPENS OVER THESE AREAS.

SOME SNOW ACCUMULATIONS WILL BE POSSIBLE CHRISTMAS AFTERNOON AND

EVENING MAINLY NORTH OF A MOUNT VERNON AND NEW BOSTON TEXAS...TO

HOPE ARKANSAS LINE. THESE POTENTIAL ACCUMULATIONS WILL BE

DEPENDENT ON THE TRACK OF THIS STORM SYSTEM...AND HOW QUICKLY THE

COLDER SUBFREEZING AIR IS ABLE TO PENETRATE SOUTHEAST INTO THE

AREA. A MORE SOUTHWARD STORM TRACK WOULD RESULT IN A POTENTIAL

INCREASE IN SNOW ACCUMULATIONS FARTHER SOUTH ACROSS THE AREA

CHRISTMAS AFTERNOON AND NIGHT.

AT THIS TIME...AREAS ALONG THE INTERSTATE 20 CORRIDOR OF NORTHEAST

TEXAS AND NORTH LOUISIANA MAY SEE A LIGHT RAIN SNOW MIX CHRISTMAS

NIGHT AS THIS STORM SYSTEM BEGINS TO PULL AWAY FROM THE AREA. NO SNOW

OR ICE ACCUMULATIONS ARE EXPECTED...AS SURFACE TEMPERATURES SHOULD

REMAIN ABOVE FREEZING.

UNCERTAINTIES STILL REMAIN AS TO THE TRACK...TIMING...AND DEPTH OF

THE COLDER SUBFREEZING AIR OF THIS STORM SYSTEM. RESIDENTS ACROSS

THESE AREAS SHOULD STAY TUNED TO THE LATEST STATEMENTS AND FORECASTS

IN THE FEW DAYS FROM THE NATIONAL WEATHER SERVICE IN SHREVEPORT

CONCERNING THIS POTENTIAL WINTER STORM.

SPECIAL WEATHER STATEMENT

NATIONAL WEATHER SERVICE LITTLE ROCK AR

243 PM CST SAT DEC 22 2012

ARZ003>007-012>016-021>025-030>034-037>047-052>057-062>069-231200-

ARKANSAS-BAXTER-BOONE-BRADLEY-CALHOUN-CLARK-CLEBURNE-CLEVELAND-

CONWAY-DALLAS-DESHA-DREW-FAULKNER-FULTON-GARLAND-GRANT-HOT SPRING-

INDEPENDENCE-IZARD-JACKSON-JEFFERSON-JOHNSON-LINCOLN-LOGAN-LONOKE-

MARION-MONROE-MONTGOMERY-NEWTON-OUACHITA-PERRY-PIKE-POLK-POPE-

PRAIRIE-PULASKI-SALINE-SCOTT-SEARCY-SHARP-STONE-VAN BUREN-WHITE-

WOODRUFF-YELL-

243 PM CST SAT DEC 22 2012

...WINTER WEATHER POTENTIAL ACROSS MUCH OF ARKANSAS CHRISTMAS DAY

AND CHRISTMAS NIGHT...

AN UPPER LEVEL STORM SYSTEM IS FORECAST TO TRACK INTO THE SOUTHERN

PLAINS STATES CHRISTMAS DAY. PRECIPITATION WILL BEGIN TO OVERSPREAD

THE STATE FROM THE SOUTH STARTING LATER MONDAY NIGHT AND CONTINUING

CHRISTMAS DAY.

AT THIS TIME...THE POTENTIAL FOR WINTER WEATHER EXISTS FOR MUCH OF

ARKANSAS. THE PRECIPITATION WILL START OFF MAINLY AS RAIN ACROSS

SOUTHERN AND CENTRAL PARTS OF THE STATE CHRISTMAS MORNING. WITH

COLDER AIR IN PLACE AT THE SURFACE...SOME SLEET OR SNOW COULD MIX

WITH THE RAIN AT THE ONSET AS IT ADVANCES NORTHWARD. OVER NORTHERN

ARKANSAS...IT APPEARS THAT MAINLY SNOW OR A PERIOD OF RAIN AND SNOW

WILL OCCUR TUESDAY.

AS THE STORM SYSTEM BEGINS TO MOVE EAST OF THE AREA CHRISTMAS

NIGHT...THE PRECIPITATION WILL TRANSITION TO ALL SNOW AS COLDER AIR

MOVES BACK INTO THE AREA. SIGNIFICANT ACCUMULATIONS OF SNOWFALL WILL

BE POSSIBLE ACROSS PARTS OF ARKANSAS. HOWEVER...WITH THE UNCERTAINTY

OF THE TRACK...THE LOCATIONS THAT WILL SEE THE MOST SIGNIFICANT

ACCUMULATIONS ARE UNKNOWN AT THIS TIME. PLEASE CONTINUE TO MONITOR

THE LATEST FORECAST AND STATEMENTS FROM YOUR NATIONAL WEATHER

SERVICE.

[Srain]

DAY 3 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

0205 AM CST SAT DEC 22 2012

VALID 241200Z - 251200Z

...NO SVR TSTM AREAS FORECAST...

...TX COASTAL PLAINS/LOWER MS VALLEY...

A PROGRESSIVE UPPER-LEVEL TROUGH IS FORECAST TO MOVE EWD ACROSS THE

INTERMOUNTAIN WEST ON MONDAY AND INTO THE ROCKIES. AHEAD OF THE

SYSTEM...MOISTURE WILL RETURN ACROSS THE TX COASTAL PLAINS AND LOWER

MS VALLEY. AS THE UPPER-LEVEL TROUGH MOVES INTO THE SRN PLAINS

MONDAY NIGHT AND LARGE-SCALE ASCENT INCREASES IN THE SRN

PLAINS...THUNDERSTORM DEVELOPMENT WILL BE POSSIBLE ACROSS THE SERN

THIRD OF TX EXTENDING EWD ACROSS SRN LA. AT THIS POINT...MODEL

FORECASTS SHOW SFC DEWPOINTS IN SE TX IN THE LOWER TO MID 60S F WITH

ABOUT 50 KT OF DEEP LAYER SHEAR. THIS ENVIRONMENT SHOULD SUPPORT A

SEVERE THREAT LATE MONDAY NIGHT AND ROTATING STORMS WILL BE POSSIBLE

ACROSS THE TX COASTAL PLAINS AFTER MIDNIGHT. IF THE UPPER-LEVEL

TROUGH IS A BIT SLOWER THAN FORECAST...THE BRUNT OF THE THUNDERSTORM

DEVELOPMENT COULD BE DELAYED UNTIL TUESDAY AFTER DAYBREAK. FOR THIS

REASON...WILL GO WITH A SEE TEXT FOR MONDAY NIGHT WITH THE POTENTIAL

TO UPGRADE TO SLIGHT RISK IN LATER OUTLOOKS.

..BROYLES.. 12/22/2012

[Ed Lizard]

If we get enough hail in Houston (glass quarter full optimistic) to turn the ground white, I will claim this as a White Christmas. Not a true snow miracle, ala 2004, but more like a team that is +5 winning outright.

[Ellinwood]

Some potential for tornadic activity along the Gulf Coast on Christmas... hodos are looking very nice, but the instability will be limited mostly to the southern Southeast. Doesn't look like the main threat will make it north of Birmingham. The low-level lapse rates are impressive on the forecast soundings.

A wind and maybe tornado threat could/should extend into the eastern Carolinas on the 26th. 55 kt. jet at 925 mb could make for a windy afternoon.

Both threats have been fairly consistent on the models.

[Srain]

Neutral trending to negative troughs/upper air disturbances (short wave) along with a potent upper jet raise an eyebrow for the severe potential in the warm sector.

[wxsmwhrms]

What makes me particularly nervous about the severe potential with this setup is that the lead wave moving through Monday will pull up quite a bit of moisture which will just be left behind as that wave moves off and everything waits for the big system Tuesday/Tuesday night. This will result in an unusually moist and unstable airmass (especially for late December) for an extremely potent weather system to work with.

[Srain]

Heh...

AREA FORECAST DISCUSSION...UPDATED

NATIONAL WEATHER SERVICE FORT WORTH TX

958 PM CST SAT DEC 22 2012

.UPDATE...

EVENING SURFACE OBSERVATIONS AND FORT WORTH SOUNDING INDICATE A

STEADY MOISTENING OF THE LOWER PARTS OF THE ATMOSPHERE OVER THE

LAST 24 HOURS. THIS IS IN RESPONSE TO INCREASING SOUTHERLY FLOW

AHEAD OF A WEAK DISTURBANCE WHICH WILL MOVE THROUGH THE PLAINS

LATE TOMORROW. A WEAK SURFACE LOW CURRENTLY OVER THE TX PANHANDLE

WILL MOVE EAST WITH THIS DISTURBANCE ON SUNDAY ALLOWING A COLD

FRONT FRONT TO APPROACH THE AREA. LATEST HIGH RESOLUTION GUIDANCE

INDICATES THAT THE FRONT WILL ACTUALLY ENTER OUR NORTHWEST

COUNTIES BY MIDDAY SUNDAY...SO HAVE LOWERED HIGH TEMPERATURES BY

SEVERAL DEGREES ACROSS THOSE AREAS. THIS COLD FRONT WILL CONTINUE

SOUTH SUNDAY EVENING WITH LOWS IN THE UPPER 20S AND LOWER 30S

ACROSS THE NORTHERN HALF OF THE AREA SUNDAY NIGHT.

THIS COLD AIR WILL NOT BE VERY DEEP ON MONDAY AND IS LIKELY TO BE

MIXED OUT TO SOME DEGREE IN RESPONSE TO INCREASING SOUTHERLY

WINDS AHEAD OF OUR NEXT SYSTEM OF INTEREST...WHICH WILL BE THE

CHRISTMAS DAY STORM. THERE IS SIGNIFICANT INTEREST IN THIS SYSTEM

FOR ITS POTENTIAL TO PRODUCE SOME HEAVY WINTRY PRECIP TOTALS

ACROSS PARTS OF THE SOUTHERN PLAINS AND MID SOUTH. AS IS OFTEN THE

CASE IN NORTH TEXAS HOWEVER...THE EXACT TRACK HAS MAJOR IMPACTS TO

PRECIPITATION TYPE ACROSS OUR AREA. A LOOK AT SEVERAL ANALOGS TO

THE CONSENSUS FORECAST FOR EARLY TUESDAY MORNING YIELDED A HANDFUL

OF EVENTS WITH SIMILAR SYNOPTIC SETUPS. ONE EVENT IN PARTICULAR

STANDS OUT FOR ITS STRIKING SIMILARITIES TO THE CURRENT FORECAST

PATTERN. IN EARLY DECEMBER 1989 A STRONG DISTURBANCE ENTERED THE

PACIFIC NORTHWEST MOVED SOUTHEAST ACROSS THE GREAT BASIN BEFORE

DIGGING ACROSS WEST TEXAS AND EVENTUALLY MOVING OVER NORTH TEXAS.

THIS SYSTEM DUG SLIGHTLY FARTHER SOUTH THAN THE CURRENT SYSTEM IS

FORECAST...HOWEVER SIMILAR SURFACE FEATURES DEVELOPED ACROSS

SOUTHEAST TEXAS BEFORE QUICKLY MOVING TO THE NORTHEAST. THE BULK

OF THE PRECIPITATION WAS LOCATED ACROSS EAST TEXAS AND LOUISIANA

WITH WRAP AROUND WINTRY PRECIP PRIMARILY ACROSS OKLAHOMA. THE ONE

DIFFERENCE WITH THIS SYSTEM...WAS SURFACE TEMPERATURES WERE

SEVERAL DEGREES WARMER THAN CURRENTLY FORECAST. SEVERAL OF THE

OTHER ANALOGS WITH SLIGHT DIFFERENCES IN TRACKS OF THE MAIN UPPER

TROUGHS YIELDED SIMILAR RESULTS. THIS INCREASES CONFIDENCE IN THE

CURRENT FORECAST OF PRIMARILY RAIN DEVELOPING INITIALLY AND MOVING

NORTHEAST WITH THE MAIN SURFACE LOW...AND A CHANGEOVER TO SOME

SNOW ON THE BACK SIDE OF THE SYSTEM. THE CURRENT FORECAST HANDLES

THIS WELL...AND FORECAST SOUNDINGS STILL SUPPORT A CHANGEOVER TO

SNOW ON CHRISTMAS AFTERNOON/EVENING AS THE COLDER AIR FILTERS IN.

WITH SUCH A FAST MOVING SYSTEM...AND STRONG WESTERLY WINDS ALOFT...

A SIGNIFICANT DRY SLOT WILL ADVANCE EASTWARD ON CHRISTMAS DAY AS

THE SYSTEM DEEPENS. THIS SHOULD ALLOW FOR A SHARP PRECIPITATION

GRADIENT ON THE BACK SIDE OF THE LOW AND FROM NORTH TO SOUTH WHERE

ANY WINTRY PRECIPITATION SHOULD OCCUR. THE CURRENT MENTION OF

NORTH OF THE I-20 CORRIDOR LOOKS GOOD FOR ANY POSSIBLE SNOW DURING

THE DAY ON TUESDAY.

[Ed Lizard]

GFS would be elevated in the HOU area, NAM has HOU near Southern end of rain, but suggestive of surface based storms. And, of course, everyone wonders who gets tagged hardest Christmas day in the interior Southern Plains and Mid-South.

[andyhb]

What makes me particularly nervous about the severe potential with this setup is that the lead wave moving through Monday will pull up quite a bit of moisture which will just be left behind as that wave moves off and everything waits for the big system Tuesday/Tuesday night. This will result in an unusually moist and unstable airmass (especially for late December) for an extremely potent weather system to work with.

Strongly agreed with this, that thing acts like a nearly ideal moisture pump, not too strong as to drop a cold FROPA into the Gulf, but not too weak as to have little/no influence on moisture trajectories.

[thewxmann]

Could someone add the severe threat into the thread title? Thank you!

[CUmet]

The darkness coupled with the fast 40-50 kt storm motions make for a potentially dangerous nocturnal tornado outbreak. The mid-level temps are quite cold, especially being so close to the Gulf Coast, and it's these cool mid-level events that tend to be particularly productive in the cool season. The shear vectors being oriented normal to the cold front are highly suggestive of cellular convective mode. The mid-level dry intrusion into the warm sector, particularly shown on the NAM and ECMWF, is quite impressive and may help in keeping the convection more discrete as well. Finally, in contrast to most southern tornado outbreak events, the threat in this case truly does extend all the way to the Gulf Coast, with the threat coming from supercells that initiate offshore as well.

[tornadotony]

What makes me particularly nervous about the severe potential with this setup is that the lead wave moving through Monday will pull up quite a bit of moisture which will just be left behind as that wave moves off and everything waits for the big system Tuesday/Tuesday night. This will result in an unusually moist and unstable airmass (especially for late December) for an extremely potent weather system to work with.

All the big systems seem to evolve like this. I'm about ready to sound the full alarm on this one. It's going to have better lapse rates in the warm sector, a MUCH WIDER unstable warm sector than the last system, plenty of moisture, and plenty of forcing for ascent over a broad area of the warm sector. The warm sector forecast soundings show hodographs bigger than William Howard Taft, with 50-60kt right off the deck at 850 hPa. Also of note, there's been a subtle but noticeable NW trend in the sfc low track, which easily places BHM and TCL in play and even starts to get HSV and even the Shoals into the discussion. I don't want to quite go full tilt into this, but the pieces certainly seem to be trying to line up for a nasty Christmas in Dixie.

[CUmet]

All the big systems seem to evolve like this. I'm about ready to sound the full alarm on this one. It's going to have better lapse rates in the warm sector, a MUCH WIDER unstable warm sector than the last system, plenty of moisture, and plenty of forcing for ascent over a broad area of the warm sector. The warm sector forecast soundings show hodographs bigger than William Howard Taft, with 50-60kt right off the deck at 850 hPa. Also of note, there's been a subtle but noticeable NW trend in the sfc low track, which easily places BHM and TCL in play and even starts to get HSV and even the Shoals into the discussion. I don't want to quite go full tilt into this, but the pieces certainly seem to be trying to line up for a nasty Christmas in Dixie.

It seems that over the past several runs of the GFS/ECMWF, the cyclogenesis starts a bit earlier and ends up being a bit stronger, which ends up pulling the warm front further north. I always get a bit hestitant about that around the Gulf Coast, because there have been a lot of times in the past where the precip along and north of the warm front tends to make the retreat of the warm front slower than what was progged. What makes this case different though is the strong cyclogenesis.

[andyhb]

It has that WSW/SW kick at H5 that seems to be characteristic of dynamic neutral-trending negatively tilted troughs...and yeah as Tony mentioned, the lift would be impressive in that case.

The upper level setup (H3 to H2) looks favorable as well, with some areas being in that left front of the incoming/right rear of the departing setup, especially on the GFS/Euro.

Also, good to see CUmet back.

[andyhb]

D2 already has some stronger wording for Christmas Eve.

DAY 2 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

1256 AM CST SUN DEC 23 2012

VALID 241200Z - 251200Z

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS CNTRL AND EAST TX...

...SRN PLAINS AND LOWER MS VALLEY...

AN UPPER-LEVEL TROUGH IS FORECAST TO AMPLIFY AND MOVE QUICKLY ESEWD

ACROSS THE ROCKIES ON MONDAY AND INTO THE SRN PLAINS MONDAY NIGHT.

AHEAD OF THE SYSTEM...MOISTURE WILL RETURN NWD ONTO THE TX COASTAL

PLAINS WHERE SFC DEWPOINTS SHOULD BE IN THE LOWER TO MID 60S F. THIS

SHOULD ALLOW FOR MODERATE DESTABILIZATION MONDAY EVENING FROM SCNTRL

TX EWD TO THE HOUSTON AREA. THE MOIST AND UNSTABLE AIRMASS COMBINED

WITH RAPIDLY STRENGTHENING DEEP LAYER SHEAR UPON THE APPROACH OF THE

EXIT REGION OF A POWERFUL MID-LEVEL JET...WILL RESULT IN THE

POSSIBILITY OF A SEVERE THREAT BETWEEN 06Z AND 12Z.

FORECAST SOUNDINGS IN THE HOUSTON AREA AT 09Z TO 12Z TUESDAY MORNING

SHOW MLCAPE AROUND 1500 J/KG WITH 0-6 KM SHEAR NEAR 60 KT. THIS

ENVIRONMENT COULD BE FAVORABLE FOR SUPERCELLS IF CELLS CAN REMAIN

DISCRETE AFTER INITIATION. IN ADDITION...SUBSTANTIAL LOW-LEVEL SHEAR

WITH 0-3 KM STORM RELATIVE HELICITIES OF AROUND 400 M2/S2 SHOULD BE

FAVORABLE FOR A TORNADO THREAT. IF A SQUALL-LINE QUICKLY ORGANIZES

ACROSS THE TX HILL COUNTRY AND MOVES QUICKLY EWD ACROSS EAST

TX...THEN THE WIND DAMAGE THREAT COULD BE THE GREATER THREAT LATE

MONDAY NIGHT. UNCERTAINTY STILL EXISTS CONCERNING THE TIMING OF THE

UPPER-LEVEL SYSTEM. IN SPITE OF THIS...AN UPGRADE TO SLIGHT RISK

APPEARS WARRANTED DUE TO THE POTENT SHEAR ENVIRONMENT WHICH IS

FORECAST TO COINCIDE WITH CONVECTIVE DEVELOPMENT AND AN UNSTABLE

AIRMASS.

FURTHER TO THE EAST...DESTABILIZATION IS FORECAST TO OCCUR ACROSS LA

AND CNTRL MS LATE MONDAY NIGHT AS MOISTURE RETURNS NWD. FORECAST

SOUNDINGS AT 09Z/TUE IN LA AND CNTRL MS GENERALLY SHOW WEAK

INSTABILITY BUT HAVE STRONG DEEP LAYER SHEAR PROFILES IN PLACE. IF

CELLS CAN INITIATE ALONG THE INSTABILITY AXIS...THEN THE ENVIRONMENT

COULD SUPPORT A MARGINAL SEVERE THREAT LATE MONDAY NIGHT.

..BROYLES.. 12/23/2012

[thewxmann]

It has that WSW/SW kick at H5 that seems to be characteristic of dynamic neutral-trending negatively tilted troughs...and yeah as Tony mentioned, the lift would be impressive in that case.

The upper level setup (H3 to H2) looks favorable as well, with some areas being in that left front of the incoming/right rear of the departing setup, especially on the GFS/Euro.

Also, good to see CUmet back.

Agreed on all accounts, especially the third line.

And yes -- there's tons of lift. The GFS adds fuel to the fire with dual jets aloft. I'm a little concerned that there will be too much convection, which may block moisture transport northward (or equivalently, might prevent the WF from reaching as far north as progged). I know CUmet mentioned strong surface cyclogenesis overcoming this, but it's still on the back of my mind.

That said, the strong windfields, broad-based trough, quality moisture trajectories, and cold mid-level temps of -15C are strong signals for what looks like the best significant tornado potential since Spring.

[andyhb]

D3:

DAY 3 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

0229 AM CST SUN DEC 23 2012

VALID 251200Z - 261200Z

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE SRN

PLAINS...LOWER MS VALLEY AND CNTRL GULF COAST STATES...

...GULF COAST STATES...

AN IMPRESSIVE UPPER-LEVEL SYSTEM IS FORECAST TO MOVE EWD INTO THE

SRN PLAINS EARLY TUESDAY MORNING AS THE EXIT REGION OF A POWERFUL

MID-LEVEL JET MOVES INTO THE GULF COAST STATES. AHEAD OF THE

SYSTEM...MOISTURE IS FORECAST TO RETURN NWD INTO THE LOWER MS VALLEY

AND CNTRL GULF COAST STATES WITH MODERATE INSTABILITY DEVELOPING

ACROSS THE SRN AND WRN PART OF THE SLIGHT RISK AREA EARLY IN THE DAY

ON TUESDAY. A CLUSTER OF THUNDERSTORMS OR SQUALL-LINE MAY BE ALREADY

DEVELOPED BY DAYBREAK ON TUESDAY ACROSS EAST TX WITH ADDITIONAL

STORMS POSSIBLY ONGOING ACROSS THE LOWER MS VALLEY. MODEL FORECASTS

INCREASE CONVECTIVE COVERAGE ACROSS THE LOWER MS VALLEY AND APPEAR

TO MOVE A WELL-DEVELOPED MCS EWD ACROSS THE REGION DURING THE DAY.

FORECAST SOUNDINGS AT MIDDAY TUESDAY IN THE LOWER MS VALLEY DEVELOP

AN IMPRESSIVE SHEAR ENVIRONMENT AS THE MID-LEVEL JET APPROACHES THE

REGION FROM THE WEST. NAM FORECAST SOUNDINGS VALID TUESDAY AT 21Z

JUST SOUTHWEST OF JACKSON MS SHOW MLCAPE VALUES AROUND 1500 J/KG

WITH ABOUT 60 KT OF DEEP LAYER SHEAR. THIS COMBINED WITH 0-3 KM

STORM RELATIVE HELICITIES AROUND 400 M2/S2 COULD BE FAVORABLE FOR

SUPERCELLS AND TORNADOES. IF MANY CELLS CAN REMAIN DISCRETE...THEN

CONDITIONS COULD ALSO BE FAVORABLE FOR STRONG TORNADOES AS THE

LOW-LEVEL JET MOVES EWD ACROSS THE CNTRL GULF COAST STATES FROM

TUESDAY MORNING INTO THE AFTERNOON. AT THIS POINT...THE POTENTIAL

FOR WIDESPREAD WIND DAMAGE APPEARS JUST AS VIABLE. THE MAGNITUDE OF

THESE THREATS MAY DEPEND UPON THE DOMINANT STORM MODE. IF THE

FAVORED MODE ENDS UP BEING LINEAR...THEN WIND DAMAGE COULD BE THE

GREATER THREAT.

FORECAST SOUNDINGS ACROSS THE LOWER MS VALLEY AND CNTRL GULF COAST

STATES TUESDAY INTO TUESDAY NIGHT SHOW POTENTIAL FOR A SUBSTANTIAL

SEVERE WEATHER EVENT. THE COMBINATION OF SHEAR AND INSTABILITY

COMBINED WITH A POTENT WEATHER SYSTEM SUGGESTS A 30 PERCENT

PROBABILITY AND SIGNIFICANT SEVERE HATCHED AREA ARE WARRANTED. THE

SEVERE THREAT SHOULD CONTINUE INTO TUESDAY EVENING AND POSSIBLY INTO

THE OVERNIGHT PERIOD AS THE UPPER-LEVEL TROUGH MOVES QUICKLY EWD

ACROSS THE GULF COAST STATES.

..BROYLES.. 12/23/2012

[Stebo]

I have been personally following this side of things along with the snow side of things, and I completely agree with what Tony and CUmet are saying. The key trend through out the day has been for this system to eject out a bit more NW. This would allow for a larger warm sector and more locations to be in play. The one main key with respect to this event is the strong low level shear and the flow straight out of the gulf, there will be instability in place with dew points potentially greater than 65 degrees. With the magnitude of the wind field over top this warm sector and the strength of lift associated with this system, it has a decently high ceiling.

[andyhb]

I also gotta point out, based on latest progs, this might not be done by the end of the 25th...when I look at the shear/instability combo into the Carolinas by Wednesday afternoon (as Ellinwood posted earlier).

[thewxmann]

Near Houston on the morning of Christmas

[andyhb]

Yeah, that too actually, especially looking at the thermodynamic profile with that sounding and also just the raw CAPE maps on twisterdata.

That wind vector in the mid/upper levels also favors right-moving cells as well potentially.

[Srain]

Could someone add the severe threat into the thread title? Thank you!

We are covering ALL aspects of this Winter Storm. That was the sole purpose of creating a Main Page thread to cover all the societal impacts of this dynamic Winter Storm.

[NavarreDon]

Great write up this am on the severe potential from MOB. I hope this really gets out to the "non-weather" public or a lot of people are going to get caught off guard.

[CHRISTMAS DAY]...

...SIGNIFICANT INCREASE IN SEVERE WEATHER WILL OCCUR FROM EARLY

CHRISTMAS MORNING THROUGH THE EVENING HOURS...

AN EXTREMELY POWERFUL UPPER LEVEL SHORTWAVE OVER NORTH TEXAS IN THE

MORNING WILL MOVE VERY QUICKLY TOWARD EAST THEN NORTHEAST...REACHING

WESTERN TENNESSEE BY MIDNIGHT. AN 80 TO 100 KNOT JET STREAK AT 500

MB WILL ACCOMPANY THIS SYSTEM...BUT MORE IMPRESSIVELY IS THE 50 TO

55 KNOT JET MAX AT 850 MB THAT WILL EXTEND FROM NEW ORLEANS TO

BIRMINGHAM BY LATE IN THE AFTERNOON.

AT THE SURFACE...A VERY STRONG SURFACE LOW CENTERED ACROSS TEXAS

WILL MOVE QUICKLY EAST-NORTHEAST OVER NORTHERN MISSISSIPPI BY LATE

AFTERNOON AND DEEPEN TO 998 MB...PLACING THE ENTIRE FORECAST AREA

WELL WITHIN THE WARM SECTOR. PLENTY OF MOISTURE WILL BE AVAILABLE TO

FEED INTO THE SYSTEM WITH 850 MB DEWPOINTS RANGING FROM 8C TO 11C

AND SURFACE DEWPOINTS IN THE LOWER 60S F ACROSS THE FORECAST AREA.

ATTENDANT STRONG COLD FRONT APPROACHING FROM THE WEST WILL REACH THE

MISSISSIPPI RIVER BY LATE AFTERNOON AND THEN QUICKLY SWEEP THROUGH

THE FORECAST AREA FROM MID EVENING THROUGH JUST AFTER MIDNIGHT.

CHRISTMAS DAY LOOKS TO HAVE ALL THE INDICATIONS OF A CLASSIC SEVERE

WEATHER EVENT SETTING UP. UNLIKE THE LAST EVENT WHICH EXHIBITED LOW

TOPPED / LOW LIGHTNING CONVECTION...THIS EVENT IS MORE CONDUCIVE TO

DEEP CONVECTION AS 500-300 MB LAPSE RATES WILL BE NEAR 8 C/KM AND

MUCAPES APPROACH 1600 J/KG. WE ARE EXPECTING A DUAL THREAT WITH

SUPERCELLS IMPACTING THE AREA DURING THE DAY AHEAD OF AN AREA OF LOW

PRESSURE AND COLD FRONT...AND THEN WITH BOWING RADAR STRUCTURES/LINE

ECHO WAVE PATTERNS IMPACTING THE AREA DURING THE EVENING ALONG AND

AHEAD OF THE COLD FRONT.

BRN INDICES GREATER THAN 10 AND SFC-3 KM STORM RELATIVE HELICITY

BETWEEN 300 AND 400 M^2/S^2 SUGGEST THAT SUPERCELLS ARE FAVORABLE.

IN ADDITION...MOST OF THIS HELICITY RESIDES IN THE SFC-1 KM LAYER

AND EHI VALUES ACROSS THE FORECAST WILL BE BETWEEN 1 (ONE) AND 3

(THREE)...SUGGESTING THE FORMATION OF STRONG CONVECTIVE SUPERCELLS

WITH EF-2 AND EF-3 TORNADOES POSSIBLE.

WITH THE DECREASED STABILITY...CLOUD TOPS ARE NOW PROJECTED TO BE

NEAR 50000 FEET AND MAXIMUM VERTICAL VELOCITIES NEAR 50 M/S. WITH

THIS...AND THE FACT THAT THE MODELS ARE NOW BRINGING A LAYER OF DRY

AIR INTO THE MID LEVELS...INDICATE THAT LARGE HAIL THROUGHOUT THE

DAY IS POSSIBLE WITH THE STRONGEST OF STORMS.

DUE TO EXTREMELY STRONG DEEP LAYER WINDS RESULTING IN STORMS MOVING

TOWARD THE NORTHEAST AT 50 TO 60 MPH...ANY STORMS DEVELOPING IN THIS

ENVIRONMENT HAVE A FAVORABLE CHANCE OF DAMAGING WINDS. ANY SEVERE

WEATHER THREATS WILL LIKELY HAPPEN VERY QUICKLY IF A WARNING IS

ISSUED UPSTREAM FROM YOU. DO NOT VENTURE OUTSIDE OR WAIT FOR A

THREAT TO APPEAR IMMINENT BEFORE TAKING ACTION. STAY TUNED TO

FURTHER DEVELOPMENTS AND INFORMATION AS THEY BECOME AVAILABLE.

HIGH TEMPERATURES MONDAY AND TUESDAY WILL RANGE FROM 68 TO 73

DEGREES. LOW TEMPERATURES MONDAY NIGHT WILL ONLY FALL INTO THE UPPER

50S NORTH TO MID 60S ALONG THE COAST. COOLER OVERNIGHT LOWS BEHIND

THE FRONT ARE EXPECTED TUESDAY NIGHT...FALLING INTO THE UPPER 30S TO

LOWER 40S NORTHWEST OF I-65...WITH MID 40 TO LOWER 50S TO THE

SOUTHEAST. /22

[Srain]

I also want to comment on the winter aspect of this storm in the cold sector. Depending on the eventual track, a trowal may develop dropping impressive snow totals for Arkansas/Southern Missouri/NW Tennessee/Western Kentucky. Should the trough deepen more than progged a track a bit further S, snow chances could increase across Northern Louisiana and NW Mississippi.