Special Weather Statement, NWS Huntsville, AL

AREA FORECAST DISCUSSION...CORRECTED
NATIONAL WEATHER SERVICE HUNTSVILLE AL
543 AM CST THU DEC 20 2012

.UPDATE...
FOR 12Z TAFS

&&

.DISCUSSION...
/ISSUED 214 AM CST THU DEC 20 2012/
FOCUS OF THIS DISCUSSION WILL BE ON THE MESOSCALE THIS MORNING...AND
THE GRADIENT WIND/COLD ADVECTION THRU TONIGHT. FEW CHANGES ARE BEING
MADE TO THE EXTENDED FORECAST ATTM WHICH STILL REMAINS QUITE ACTIVE
NEXT WEEK...BUT CONFIDENCE REMAINS LOW IN THE EXACT MODEL SOLUTIONS
AND TRACK OF THE STRONG STORM/LOW CHRISTMAS DAY AND BEYOND.

THE CURRENT WINTER STORM IS GOING ABOUT AS PLANNED WITH A 993MB LOW
BETWEEN MCI- SGF IN MO AND A COLD FRONT SLICING SWD THRU AR INTO ERN
TX. WHILE THUNDERSNOW AND A BLIZZARD ARE TAKING HOLD OF IA...A
STRONGLY FORCED SQLN WITH MULTIPLE LEWP FEATURES HAS DEVELOPED AHEAD
OF THE COLD FRONT WITHIN THE WARM SECTOR OVER NERN AR THRU NWRN LA.
THE 60F ISODROSOTHERM WAS INTERSECTING THIS LINE IN THE VCNTY OF
LITTLE ROCK...WITH M-U60S DEW POINT VALUES IN SRN MS/LA ADVECTING
NWD. LOCALLY...DEW POINTS REMAINED IN THE L-M40S WITH A MORE SELY
FETCH AT THIS HOUR. THE GRADIENT WAS TIGHTENING AND A MORE SOUTHERLY
FLOW WILL DEVELOP OVER THE NEXT FEW HOURS AS A STRONG LLJ OF 60-70KT
BEGINS TO SHIFT EWD INTO MIDDLE TN AND NRN AL. BASED ON MODEL
SOUNDINGS...OUR HIGHEST RIDGES MAY EXPERIENCE A SUDDEN UPSWING IN
WINDS BY SUNRISE...AND WILL HAVE TO WATCH THESE SPEEDS CLOSELY AS THE
MODELS SUGGEST 50+ MPH WINDS.  WDSPREAD SHRA HAVE BROKEN OUT IN THE
MOISTURE TRANSPORT AND WARM ADVECTION ZONE ACROSS ACROSS MS AND
WRN/CNTRL AL. A FEW STORMS MAY BEGIN TO POP UP IN THIS AREA DUE TO
ELEVATED INSTABILITY (SI'S BECOMING SLIGHTLY NEGATIVE). A STRONG
INVERSION THAT IS DEVELOPING ~2KFT IS THE BIG QUESTION MARK ON
INHIBITION OF ANY DAMAGING CONVECTIVE DOWNDRAFTS DEVELOPING THIS
MORNING WITH THESE PRE-FRONTAL CELLS. THE SFC WARM SECTOR SHOULD
REMAINED PINCHED OFF TO OUR S FOR MUCH OF EARLY THIS MORNING...WITH
ONLY A BRIEF WINDOW JUST AHEAD OF THE SQLN WHEN 55-60F DEW POINTS
COULD REACH PORTIONS OF NRN AL. THE GREATEST RISK OF THIS OCCURRING
WOULD BE OVER NERN AL FROM 15-18Z. IN THE MEANTIME...THE INVERSION
MAY SERVE AS A STRONG DUCT FOR ANY GRAVITY WAVES THAT CAN DEVELOP TO
PROPAGATE AND PRODUCE PERIODIC GUSTY WINDS. IN ANY CASE...TIMING OF
THE SQLN LOOKS LIKE 12-15Z IN NWRN AL...AND 15-18Z ACROSS NC/NERN AL
AND SRN TN. THE THREAT OF SEVERE WINDS APPEARS MARGINAL GIVEN THE
STRONG INVERSION...BUT WE WILL CONTINUE TO HIGHLIGHT THE POSSIBILITY
IN THE HWO.

THE MAIN CONCERN TODAY WILL BE THE GRADIENT WINDS/GUSTS THAT WILL
PERSIST BEHIND THE COLD FRONT. THE LOW-MID-UPPER JETS LINE UP WELL
AS THE PRESSURE RISE CENTER MOVES ACROSS WITH STRONG SUBSIDENCE. WE
WILL MAINTAIN A WIND ADVISORY THRU TODAY...BUT AM CONTEMPLATING
CUTTING THE ADVISORY OFF AT 00 OR 06Z THIS EVENING AS THE GRADIENT
SUBSIDES. STRONG COLD ADVECTION WILL SEND TEMPS PLUMMETING INTO THE
20S TONIGHT (WIND CHILLS IN THE TEENS). WE WILL HAVE TO WATCH
MOISTURE AND CLOUD DECKS THAT DROP SEWD INTO MIDDLE TN AND THE
CUMBERLAND PLATEAU. ATTM...MOST IF NOT ALL OF THIS MOISTURE WILL
REMAIN JUST TO OUR NE...BUT THE SEWANEE AREA COULD BE CLIPPED AND
FLURRIES WOULD BE POSSIBLE. WE'LL BE FORTUNATE TO REACH THE M40S ON
FRIDAY WHILE OUR HIGHEST ELEVATIONS ABOVE 1600 FT ONLY HITTING THE
U30S.

AK

&&

.AVIATION...
FOR 12Z TAFS...GENERALLY POOR AVIATION CONDITIONS ARE XPCTED THROUGH
THE MORNING HRS...AS A STRONG COLD FRONT APPROACHES FROM THE W.
WIDESPREAD SHRA...ALONG WITH AN EMBEDDED SQLN PUSHING EWD ACROSS WRN
TN/NRN MS...ARE XPCTED ALONG/AHEAD OF THE FRONT...BEFORE PRECIP TAPERS
OFF FROM W TO E AFTER 18Z WITH THE EXITING FRONT. SFC WINDS THOUGH
ARE XPCTED TO REMAIN STRONG/WINDY...WITH SLY WINDS AOA 25KT WITH
GUSTS NEAR 35KT POSSIBLE THIS MORNING BEFORE SFC FLOW SHIFTS TO THE
W THIS AFTERNOON. WIND SPEEDS ARE XPCTED TO GRADUALLY DIMINISH THIS
EVENING AND OVERNIGHT...AS CLOUD COVER LIFTS/SCT.

09

&&

.HUN WATCHES/WARNINGS/ADVISORIES...
AL...WIND ADVISORY UNTIL MIDNIGHT CST TONIGHT FOR ALZ001>010-016.

TN...WIND ADVISORY UNTIL MIDNIGHT CST TONIGHT FOR TNZ076-096-097.

&&

FOR MORE INFORMATION PLEASE VISIT OUR WEBSITE
AT WEATHER.GOV/HUNTSVILLE.

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