FXUS64 KBMX 072354
AFDBMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BIRMINGHAM AL
555 PM CST MON DEC 7 2009

.UPDATE...AVIATION DISCUSSION AND OVERNIGHT WEATHER.

&&

.DISCUSSION...

DID A QUICK UPDATE TO ZONES TO INCLUDE LIGHT RAIN IN THE NORTHWEST 
THROUGH THE EARLY EVENING HOURS. WEAK UPPER LEVEL ENERGY CONTINUES 
TO MAINTAIN A LARGE AREA OF LIGHT RAIN SHOWERS ACROSS PORTIONS OF 
THE AREA....GENERALLY NORTH OF I-20 AND WEST OF I-65. A FEW 
HUNDREDTHS OF AN INCH OF RAIN WILL BE POSSIBLE OVER THE NEXT SEVERAL 
HOURS.   

A BREAK IS RAIN ACTIVITY IS EXPECTED LATER TONIGHT BEFORE HEAVIER 
AND MORE ORGANIZED RAINFALL RETURNS TO THE AREA AFTER 3AM...AHEAD OF 
A DEEPENING STORM SYSTEM TO OUR WEST. 

NOT MUCH HAS CHANGED IN THE OVERALL THINKING REGARDING THE
FORECAST OVER THE NEXT 7 DAYS.

THE FIRST MAIN EVENT IS STILL FORECAST TO TRANSPIRE TUESDAY INTO
EARLY WEDNESDAY...AS A BIG SURFACE CYCLONE AND UPPER LEVEL
SHORTWAVE ENERGY PASS TO OUR NORTH. WE ARE STILL LOOKING FOR A BIG
SWATH OF RAIN TO PUSH THROUGH DURING THE DAY ON TUESDAY. AS WE
TRANSITION INTO TUESDAY NIGHT...AND THE UPPER SHORTWAVE MAKES ITS
CLOSEST APPROACH...WE ADD IN THE POSSIBILITY OF STRONG TO SEVERE
THUNDERSTORMS. LATEST MODEL RUNS HAVEN'T CHANGED MUCH IN EITHER
DIRECTION (PRO OR AGAINST THE POSSIBILITY OF SEVERE). AS IS OFTEN
THE CASE THIS TIME OF YEAR...THE LIMITING FACTOR IS THE AMOUNT OF
INSTABILITY AVAILABLE TO SUSTAIN UPDRAFTS SIGNIFICANT ENOUGH TO
NOT BE OVERWHELMED BY THE IMPRESSIVE AMOUNT OF SHEAR. WE WILL
MAINTAIN THE POSSIBILITY IN THE HAZARDOUS WEATHER OUTLOOK...
ALTHOUGH WITH A LOW CONFIDENCE. NAM IS STILL THE SLOWEST OF THE
MODELS...ALTHOUGH IT (RELUCTANTLY...IT SEEMS) IS FINALLY
SUCCUMBING TO THE FASTER TIMING SUGGESTED BY THE GFS AND ECMWF.
THUS...WILL BASE THE FORECAST FOR TUESDAY NIGHT AND WEDNESDAY
MORNING LARGELY ON THIS SLIGHTLY FASTER SOLUTION.

THE NEXT SYSTEM COMES IN HERE LATE IN THE WEEK...THIS TIME
COURTESY OF SEVERAL WEAK SHORTWAVE TROUGHS IN THE FAST MOVING
SOUTHERN STREAM. TEMPERATURES WILL BE COLD...LARGELY BECAUSE OF A
CAD-WEDGE STYLE HIGH PRESSURE SETUP. BUT IT DOES NOT APPEAR THAT
CONDITIONS WILL BE COLD ENOUGH TO PRODUCE ANY WINTRY WEATHER IN
OUR AREA -- BUT WILL WATCH LATER MODEL RUNS CLOSELY.

/61/

&&

.AVIATION...00Z TAF DISCUSSION.

AN AREA OF MVFR CIGS CONTINUES TO BLANKET AREAS ALONG AND NORTH OF 
I-59 NEAR ON ELEVATED WARM-FRONT.  SOUTH WINDS IN THE ELEVATED WARM 
SECTOR WERE ALSO PRODUCING LIGHT RAIN AND FOG WITH VSBYS BLO 3 
MILES.  WITH BOUNDARY LAYER WINDS BECOMING SOUTHEAST OVERNIGHT...IT 
IS LIKELY LOW CLOUDS AND RAIN WILL SHIFT SLOWLY NORTHWARD...AND MVFR 
CIGS AT KTCL AND KBHM MAY EVEN SCATTER BEFORE 03Z. HOWEVER...LOW 
CLOUDS WITH BASES OF 1000-2000 FEET AGL WILL LIKELY DEVELOP BETWEEN 
03Z AND 06Z AS LOW LEVELS SATURATE. THERE ARE STRONG INDICATIONS 
FROM MODELS AND MOS GUIDANCE THAT IFR CIGS WILL FORM BEFORE 12Z AND 
THIS IS INCLUDED IN TAFS.

CONFIDENCE IS LOW ON THE ARRIVAL OF SIGNIFICANT RAINFALL.  NEXT 
UPPER LEVEL IMPULSE WILL LIKELY ARRIVE INTO WEST ALABAMA AROUND 12Z. 
DO NOT EXPECT ANY THUNDERSTORMS WITH FIRST WAVE AS AIR MASS TO 
STABLE. RAIN SHOULD SPREAD OVER ALL TAF SITES AFTER 12Z EXCEPT KMGM 
AND KTOI.  WIDESPREAD RAIN SHOULD KEEP NORTHERN TAF SITES IN IFR 
CIGS THRU REMAINDER OF TAF PERIOD.

58/ROSE

&&

.BMX WATCHES/WARNINGS/ADVISORIES...NONE.

&&

$$