FXUS64 KBMX 011137
AFDBMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BIRMINGHAM AL
530 AM CST TUE DEC 1 2009

.UPDATE...AVIATION DISCUSSION.

&&

.SHORT TERM...TODAY THROUGH WEDNESDAY NIGHT.

BASED ON CURRENT WEATHER CONDITIONS OF MOSTLY CLEAR SKIES AND 
TEMPERATURES IN THE 30S...HARD TO BELIEVE THAT WE WILL BE DEALING 
WITH HEAVY RAINFALL AND SEVERE THUNDERSTORMS WITHIN THE NEXT 24 TO 
36 HOURS. HIGH CLOUDS ARE STREAMING NORTHEASTWARD TOWARDS ALABAMA AS 
STORM SYSTEM BEGINS TO TAKE SHAPE OFF THE TEXAS COAST. RAIN SHIELD 
ALREADY MOVING INTO THE LOUISIANA COAST. CLOUDS WILL GRADUALLY 
THICKEN TODAY AS MOISTURE INCREASES FROM TOP TO BOTTOM. DUE TO COLD 
START THIS MORNING AND EXPECTED CLOUD COVER TODAY...LOWERED HIGH 
TEMPERATURES A FEW DEGREES MOST AREAS. LIGHT RAIN SHOULD REACH 
SOUTHWEST COUNTIES BY SUNSET.

FOR TONIGHT...RAIN WILL OVERSPREAD CENTRAL ALABAMA DURING THE
EVENING HOURS AND SOUTHEAST WINDS WILL INCREASE TO 10 TO 20 MPH.
GFS MODEL STILL SHOWING A SURFACE LOW TRACK FARTHER EAST THAN
NAM/CANADIAN/ECMWF. FORECAST WILL BE BASED ON A TRACK CLOSER TO
THE NAM MODEL BASE ON CONSENSUS OF OTHER MODELS AND THE RUN TO RUN
CONSISTENCY OF THE NAM MODEL. THERE WILL LIKELY BE A LOW LEVEL
BAROCLONIC ZONE THAT WILL SET-UP ACROSS NORTHWEST FLORIDA AND
SOUTHEAST ALABAMA LATER TONIGHT AND WEDNESDAY MORNING. THIS BOUNDARY
WILL MOST LIKELY BE JUST NORTH OF SURFACE WARM FRONT...AND IT
WILL BE FOCUS FOR THE HEAVIEST RAINFALL. A FLASH FLOOD WATCH WILL
BE ISSUED FOR TONIGHT AND WEDNESDAY FOR AREAS ALONG AND SOUTH OF A 
WHITE HALL...TO ALEXANDER CITY...TO ROANOKE LINE. RAINFALL TOTALS 
WILL LIKELY BE IN THE ONE TO TWO INCH RANGE IN WATCH AREA...WITH UP 
TO ONE INCH ELSEWHERE. A LAKE WIND ADVISORY WILL LIKELY BE NEEDED FOR
MUCH OF THE SOUTHERN HALF OF THE COUNTY WARNING AREA... BUT WILL LET 
DAY SHIFT HANDLE ISSUANCE.

FOR WEDNESDAY...THE HEIGHT OF THE STORM WILL BE DURING THIS TIME
PERIOD. HEAVY RAINFALL WILL SPREAD OVER ALL OF CENTRAL ALABAMA BY
SUNRISE WEDNESDAY AND SURFACE WINDS WILL BE IN THE 15-25 MPH RANGE.
PREVIOUS NAM MODEL RUNS WERE SHOWING MID 60S DEWPOINTS ADVECTING
WELL NORTHWARD INTO CENTRAL ALABAMA. LATEST MODEL RUN SEEMS MORE 
PRACTICAL WITH 60 DEGREE DEWPOINTS GETTING AS FAR NORTH AS 
MONTGOMERY. THIS LINES UP PRETTY WELL WITH STORM PREDICTION OUTLOOK 
FOR DAY2. SEVERE THREAT WILL PRIMARILY BE IN THE 9 AM TO 3 PM TIME 
FRAME AS CONVECTIVE LINE SHOULD BE ENTERING WESTERN GEORGIA BY MID 
AFTERNOON. MAIN LIMITING FACTOR WILL BE WIDESPREAD RAIN AND CLOUD 
COVER. GIVEN HIGH SHEAR VALUES...AN ISOLATED TORNADO CANNOT BE RULED 
OUT. ANOTHER ONE TO THREE INCHES OF RAINFALL POSSIBLE ACROSS FLASH 
FLOOD WATCH AREA...WITH STORM TOTALS OF TWO TO FOUR INCHES. ISOLATED 
TOTALS NEAR SIX INCHES POSSIBLE.

FOR WEDNESDAY NIGHT...THE HEAVY RAINFALL AND STRONG CONVECTION
SHOULD BE OUT OF AREA BY SUNSET WEDNESDAY AS SURFACE LOW MOVES
RAPIDLY NORTHEAST AND PUSHES COLD FRONT THROUGH AREA. DUE TO
INTENSITY OF LOW LEVEL CYCLONE...THERE WILL BE PLENTY OF WRAP
AROUND CLOUDS ON BACK SIDE OF FRONT..AND CHANCES FOR LIGHT RAIN
WILL CONTINUE THROUGH THE OVERNIGHT HOURS WEDNESDAY AS UPPER LEVEL
TROF MOVES ACROSS AREA.

58/ROSE

.LONG TERM...THURSDAY THROUGH MONDAY.

IT APPEARS THAT AN ACTIVE SOUTHERN STREAM FLOW PATTERN WILL CONTINUE
DURING THIS PERIOD...WHICH MEANS CONFIDENCE IS LOW ON TIMING AND
INTENSITY OF EACH SYSTEM. MUCH COLDER AIR WILL MOVE INTO AREA
THURSDAY AND FRIDAY. MODELS ARE STRONGLY HINTING AT ANOTHER GULF
LOW FORMING ON FRIDAY AND MOVING RAPIDLY EAST NORTHEAST. THIS
SYSTEM COULD BRING SOME LIGHT PRECIPITATION TO SOUTH ALABAMA
FRIDAY NIGHT...BUT CONFIDENCE TO LOW AT THIS TIME TO INTRODUCE
PRECIPITATION..ESPECIALLY SINCE THICKNESS VALUES ARE COLD ENOUGH
TO SUPPORT FROZEN PRECIPITATION. ANOTHER WEAKER SYSTEM HAS BEEN
SHOWING UP EARLY NEXT WEEK..AND INCLUDED CHANCE OF RAIN ON MONDAY.

58/ROSE

&&

.AVIATION...12Z TAF DISCUSSION.

SOME PATCHY FOG WILL REMAIN POSSIBLE AT ALL SITES THROUGH SUNRISE 
LIMITING VSBYS TO NO LESS THAN 4 MILES. MID AND HIGH CLOUDS 
OVERSPREAD THE AREA FROM THE SOUTHWEST THROUGH 00Z...WITH A FEW 
SHOWERS APPROACHING MGM AND TOI SHORTLY THEREAFTER.  FROM 00Z TO 06Z 
AN AREA OF RAIN WILL SHIFT NORTHWARD ACROSS MGM AND TOI WITH 
CEILINGS 4000 TO 6000 FEET AND VSBYS 5 TO 6 MILES. AROUND 5 OR 6Z 
RAIN WILL OVERTAKE TCL...EET...BHM AND ANB WITH CEILINGS 4000 TO 
6000 FEET AND VSBYS 4 TO 6 MILES.  HEAVIER RAIN AND POSSIBLY 
THUNDERSTORMS RESULTING IN VISIBILITY AS LOW AS 2 MILES AND CEILINGS 
BETWEEN 500 AND 1000 FEET WILL IMPACT MGM AND TOI BY MIDNIGHT.  

WIND WILL STEADILY INCREASE TODAY AND TONIGHT FROM THE EAST. SPEEDS 
WILL REMAIN BELOW 10 KNOTS THROUGH 00Z AT BHM EET TCL AND ANB... AND 
BELOW 15 KNOTS AT MGM AND TOI.  OVERNIGHT SPEEDS WILL INCREASE TO 
BETWEEN 10 AND 20 KNOTS AREA WIDE WITH GUSTS IN EXCESS OF 25 KNOTS 
AT MGM AND TOI BY SUNRISE.  

12/SIRMON

&&

.BMX WATCHES/WARNINGS/ADVISORIES...FLASH FLOOD WATCH TONIGHT AND 
WEDNESDAY FOR SOUTHEAST COUNTIES.

&&

$$