FXUS64 KBMX 241737
AFDBMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BIRMINGHAM AL
1135 AM CST THU DEC 24 2009

.UPDATE...FOR AVIATION.

&&

.DISCUSSION...

THE TIME IS UPON US TO BEGIN OUR SHIFT FROM NWP STUDY TO WATCHING 
WHAT IS REALLY EVOLVING OVER US AND UPSTREAM FROM US.  CURRENTLY 
LIGHT RAIN SHOWERS ARE MOVING SOUTH TO NORTH THROUGH OUR CWA.  NOT 
MUCH RAIN HAS BEEN MEASURED AT ANY OF OUR CLIMO SITES BUT THIS IS 
LIKELY DUE TO THE FACT THAT AN ALREADY DRY ATMOSPHERE IS TAKING 
AWHILE TO SATURATE AND ALLOW THESE RAINDROPS TO HIT THE GROUND.  
SATURATION WILL CONTINUE TO TAKE PLACE THROUGHOUT THE DAY ALLOWING 
FOR MORE OF THESE SHOWERS AHEAD OF THE FRONT TO REACH THE GROUND.

NOW FOR THE FRONT ITSELF.  CURRENTLY OVER THE MISSISSIPPI RIVER... 
THE CONVECTION SEEMS TO BE OUTRUNNING THE MODELS AT THIS POINT. SO 
WE HAVE HAD TO TWEAK THE ARRIVAL TIME OF THE MAIN AREA OF CONVECTION 
...TO SLIGHTLY EARLIER.  IT LOOKS LIKE OUR WESTERN COUNTIES SHOULD 
BEGIN TO LOOK FOR THIS MAIN AREA OF CONVECTION AROUND 2 PM CST...THE 
CENTRAL PORTIONS OF THE STATE BETWEEN 4 AND 7 PM...AND FOLKS IN THE 
EAST BETWEEN 6 AND 9 PM.

LAST NIGHT SPC ADVANCED THE SLIGHT RISK AREA A LITTLE FURTHER TO THE 
NORTH...AND WITH THE LATE MORNING UPDATE HAVE INCLUDED A MODERATE 
RISK FOR SEVERE WEATHER WELL TO OUR SOUTH AND WEST.  HERES THE GOOD 
NEWS...THOSE AREAS IN CENTRAL ALABAMA WE HAVE BEEN CONCERNED ABOUT  
STILL HAVE A LONG WAY TO GO TO GET THE NECESSARY DEW POINTS TO 
CREATE ENOUGH INSTABILITY TO KEEP THE CONVECTION GOING.  SINCE 
EARLIER THIS MORNING CTG LIGHTNING HAS DECREASED SIGNIFICANTLY WITH 
THE MAIN LINE...ESPECIALLY IN THE NORTHERN SECTIONS.  THIS BEING 
SAID...THERE WILL STILL BE A SMALL WINDOW FOR OUR SOUTHERN 
COUNTIES...ESPECIALLY THOSE SOUTH OF INTERSTATE 20 TO SEE AN 
ISOLATED SEVERE WIND GUST.  ADDITIONALLY... WITH THE AMOUNT OF WIND 
SHEAR IN THE ATMOSPHERE THERE IS A CHANCE THAT ROTATION COULD BE 
SEEN WITHIN THESE STORMS...SO I WOULDN'T BE SURPRISED TO SEE A 
TORNADO WATCH BE EXTENDED INTO SOUTHERN PORTIONS OF ALABAMA AT SOME 
POINT THIS AFTERNOON. 

THE MAIN THREAT TODAY CONTINUES TO BE THE PRESSURE GRADIENT WINDS 
AHEAD OF THE FRONT.  SUSTAINED WINDS OF 15-20 MPH WITH GUSTS TO 
30-35 MPH HAVE ALREADY BEEN SEEN AND THESE WINDS ARE EXPECTED TO 
INCREASE AS WE GO THROUGH THE DAY.  SOME OF THE HIGHER ELEVATIONS 
COULD POSSIBLY SEE WIND GUSTS TO 50 MPH.  PLEASE SEE OUR WIND 
ADVISORY PRODUCT FOR MORE INFORMATION.

27   

&&

.AVIATION...18Z TAF DISCUSSION.

MAIN CONCERN THIS AFTERNOON WILL CONTINUE TO BE THOSE WINDS ACROSS 
THE AREA. LOOK FOR WINDS TO CONTINUE TO INCREASE OVER THE NEXT FEW 
HOURS. ALREADY BEGINNING TO SEE GUSTS AROUND 25KT ACROSS 
TCL...BHM...AND EET. THIS WILL SLIDE OVER IN TO THE EASTERN TAF 
SITES BY 18 TO 19Z. WINDS WILL CONTINUE TO INCREASE OUT OF THE 
SOUTHEAST WITH SUSTAINED SPEEDS INCREASING TO 15 TO 25 KNOTS BY 19 
TO 21Z WITH GUSTS TO 35 KNOTS THROUGH REALLY 6Z. CROSS WINDS WILL 
MOSTLY IMPACT THOSE RUNWAYS THAT RUN SOUTHWEST TO NORTHEAST OR EAST 
TO WEST.  

THE FIRST BAND OF MOISTURE IS IMPACTING AREAS FROM EET TO ANB AND 
SOUTH TO MGM AND TOI. THIS BAND WILL MOVE NORTHEAST AND SLIDE EAST 
DURING THE AFTERNOON. GENERALLY BRIEF MVFR CEILINGS THROUGH 20Z ARE 
EXPECTED. RAINFALL WILL REMAIN LIGHT. CLOUDS WILL BECOME MVFR AFTER 
19 TO 20Z AS LOW LEVEL MOISTURE FINALLY INCREASES.  A LINE OF 
INTENSE RAINFALL PRODUCING LIFR CONDS WILL SWEEP RAPIDLY ACROSS 
CENTRAL ALABAMA BETWEEN 22Z AND 06Z.  THE SQUALL LINE WILL BE 
LOCATED AHEAD OF A STRONG COLD FRONT AND HAS THE POTENTIAL TO 
PRODUCE WIND GUSTS TO 50 KTS.

MVFR CEILINGS MAY CONTINUE WITH SCATTERED LIGHT RAIN THROUGH 18Z 
TOMORROW...WITH SOME IMPROVEMENT EXPECTED SOUTH AFTER THAT PERIOD. 

&&

.BMX WATCHES/WARNINGS/ADVISORIES...WIND ADVISORY FOR ALL OF CENTRAL 
ALABAMA UNTIL MIDNIGHT TONIGHT.

&&

$$