FXUS64 KHUN 231355 CCA
AFDHUN

AREA FORECAST DISCUSSION...CORRECTED
NATIONAL WEATHER SERVICE HUNTSVILLE AL
537 AM CST WED DEC 23 2009

.UPDATE...FOR 12Z TAFS

&&

.AVIATION...S/W NOW APPROACHING OUR CWA WILL BRING SOME LIGHT/SCT
SHRA MAINLY WEST OF I65 TODAY/EARLY EVENING. THEN EXPECT A SMALL
BREAK IN THE PCPN CHANCE ACROSS THE TN VALLEY FOR THE OVERNIGHT
HOURS. CONFIDENCE IN THIS FCST PACKAGE NOT REAL HIGH DUE TO THE
FACT THAT THE GFS IS MUCH MORE AGGRESSIVE WITH PCPN CHANCES THAN
THE NAM. FOR NOW WILL LEAN TOWARDS THE GFS. WILL KEEP VFR CONDITIONS 
AT BOTH MSL/HSV THRU THE PERIOD...BUT WOULD NOT BE SURPRISED FOR 
OCCASIONAL MVFR CONDITIONS DUE TO SCT SHRA ACTIVITY.

&&

.PREV DISCUSSION... /ISSUED 321 AM CST WED DEC 23 2009/ 

SYNOPSIS...A VERY ACTIVE PATTERN DOMINATES MUCH OF NORTH AMERICA. A 
POWERFUL TROUGH IS DIGGING OVER THE DESERT SOUTHWEST...RESULTING IN 
THE DEVELOPMENT OF A SUBTROPICAL JET ACROSS NORTHERN MEXICO AND THE 
SOUTHERN TIER STATES. THIS UPPER TROUGH WILL BE THE MAIN PLAYER FOR 
THE TN VALLEY ON CHRISTMAS EVE AND A PORTION OF CHRISTMAS DAY.

WITH THE APPROACH OF THIS SYSTEM...A WIND ADVISORY AND FLASH FLOOD 
WATCH HAVE BEEN ISSUED FOR CHRISTMAS EVE.

SHORT TERM (TODAY THROUGH FRIDAY NIGHT)...GENERALLY QUIET 
CONDITIONS TODAY AS MID TO HIGH CLOUDS BEGIN TO IMPINGE OVER THE 
AREA. SOME LOW CLOUDS WILL BEGIN TO ADVECT NORTHWEST AS A SHORTWAVE 
ASSOCIATED WITH THIS TROUGH LIFTS NORTHEAST ACROSS THE MS RIVER 
VALLEY. LIGHT SHOWER ACTIVITY IS POSSIBLE AS THIS SHORTWAVE LIFTS 
NORTHEAST MAINLY OVER NW AL. A WEDGE OF SOMEWHAT COOLER/DRIER AIR 
WILL LIKELY KEEP THE MAJORITY OF THE PRECIP TO THE WEST OF THE AREA 
FOR TODAY AND TONIGHT. NEVERTHELESS HAVE KEPT 50 POPS FOR NW AL. 
WITH THE SOUTHERLY FLOW/WAA IN PLACE...TEMPS WILL LIKELY RISE INTO 
THE MID TO UPPER 50S DESPITE THE CLOUD COVER. 

AS THE TROUGH SHIFTS EASTWARD...SFC CYCLOGENESIS OVER WEST TX WILL 
LIKELY SPREAD A MIX OF WINTRY PRECIP ACROSS THAT AREA WHILE SENDING 
LINES OF SHOWERS AND THUNDERSTORMS EASTWARD. THE VIGOROUS NATURE OF 
STRENGTHENING SFC LOW ALONG WITH THE POWERFUL JET STREAKS ASSOCIATED 
WITH THE TROUGH WILL CONTRIBUTE TO THE POSSIBILITY OF HIGH WINDS 
ACROSS ITS TRACK.

MEANWHILE...THE STRONG SOUTHERLY FLOW TONIGHT INTO THURSDAY IS 
EXPECTED TO CONTRIBUTE TO AMPLE MOISTURE AVAILABILITY AS THE 
TROUGH/SFC COLD FRONT ARRIVES. IN FACT...PWATS OF 1-1.25 INCH AND 
DEWPOINTS APPROACHING 50 DEGREES WILL CONTRIBUTE TO THE 
POSSIBILITY OF HEAVY RAINFALL. THE SFC LOW PRESSURE SWIFTLY LIFTS 
NORTHWARD ACROSS THE OZARKS...OCCLUDING AS IT LIFTS AND THE 
ACCOMPANYING COLD FRONT PUSHES EASTWARD ACROSS THE SOUTHEAST. WIND 
SHEAR IS QUITE HIGH WITH BULK SHEAR VALUES (0-3KM) AT 60 KTS AND 
0-3KM SRH RANGING FROM 300-1000 M2/S2 AHEAD AND BEHIND THE FRONT. 
WITH THE KINEMATICS/THERMODYNAMICS IN PLAY...WILL KEEP A SLIGHT 
CHANCE OF THUNDERSTORMS WITH HEAVY RAINFALL. HAVE ALSO DECIDED TO 
ISSUE A FLASH FLOOD WATCH FOR THURSDAY AFTERNOON THROUGH FRIDAY 
MORNING. ANOTHER CONCERN (AS STATED ABOVE) IS THE HIGH WIND ISSUE 
WITH AND WITHOUT THUNDERSTORMS. THE CONVECTION MAY ACTUALLY DRAW 
DOWN THE HIGH WINDS ALOFT...RESULTING IN DAMAGING WINDS AT THE SFC 
AS A QLCS PROGRESSES EASTWARD. HOWEVER...THE HIGH PRESSURE GRADIENT 
WILL ALSO CONTRIBUTE TO HIGH WINDS DURING THE SAME TIME PERIOD. WILL 
BE ISSUING A WIND ADVISORY FOR THE MORNING THROUGH LATE NIGHT 
CHRISTMAS EVE TO ACCOUNT FOR THE HIGH WINDS.

ONCE THE FRONT CLEARS ON EARLY FRIDAY MORNING...EXPECTING TEMPS TO 
ONLY SLOWLY RISE INTO THE UPPER 40S BEFORE FALLING QUICKLY FRIDAY 
NIGHT BELOW FREEZING. CLOUDS LOOK TO BRIEFLY CLEAR BEFORE MORE 
CLOUDS ADVECT EASTWARD OVER THE AREA FROM THE CLOSED UPPER LOW 
SLOWLY MEANDERING ACROSS THE GREAT LAKES AND OHIO RIVER VALLEY.

LONG TERM (SATURDAY THROUGH TUESDAY)...CLOUDS WILL BE SLOW TO 
DISSIPATE ON SATURDAY AS THE CLOSED LOW KEEPS MEANDERING AROUND THE 
NORTHERN TIER STATES. DESPITE THE CLOUD CLEARING UNCERTAINTY...TEMPS 
SHOULD STILL STRUGGLE TO REACH MUCH ABOVE THE LOW TO MID 40S DUE TO 
STRONG CAA. WINDS SHOULD STAY HIGH ENOUGH EARLY SATURDAY MORNING TO 
KEEP FOG/FZFG FROM BEING AN ISSUE.

NIGHTTIME LOWS SHOULD DROP BELOW FREEZING ONCE AGAIN ON SUNDAY 
MORNING. CLOUD CLEARING SHOULD THEN BEGIN TO OCCUR ON SUNDAY THROUGH 
TUESDAY...BUT DAYTIME TEMPS SHOULD STILL REMAIN IN THE 40S WITH 
NIGHTTIME LOWS NEAR IF NOT BELOW THE FREEZING MARK.

BY TUESDAY...THE ECMWF SHOWS A UPPER TROUGH CROSSING THE DESERT 
SOUTHWEST INTO TX...HINTING AT THE POSSIBILITY OF MORE PRECIPITATION 
LATER THAT WEEK.

&&

.HUN WATCHES/WARNINGS/ADVISORIES...
AL...WIND ADVISORY FROM 9 AM THURSDAY TO MIDNIGHT CST THURSDAY NIGHT FOR 
     THE FOLLOWING ZONES: COLBERT...CULLMAN...DEKALB...FRANKLIN 
     AL...JACKSON...LAUDERDALE...LAWRENCE...LIMESTONE...MADISON...
     MARSHALL...MORGAN.

     FLASH FLOOD WATCH FROM THURSDAY AFTERNOON THROUGH LATE THURSDAY 
     NIGHT FOR THE FOLLOWING ZONES: COLBERT...CULLMAN...DEKALB...
     FRANKLIN AL...JACKSON...LAUDERDALE...LAWRENCE...LIMESTONE...
     MADISON...MARSHALL...MORGAN.

TN...WIND ADVISORY FROM 9 AM THURSDAY TO MIDNIGHT CST THURSDAY NIGHT FOR 
     THE FOLLOWING ZONES: FRANKLIN TN...LINCOLN...MOORE.

     FLASH FLOOD WATCH FROM THURSDAY AFTERNOON THROUGH LATE THURSDAY 
     NIGHT FOR THE FOLLOWING ZONES: FRANKLIN TN...LINCOLN...MOORE.

&&

$$

007