386 
FXUS64 KBMX 091004
AFDBMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BIRMINGHAM AL
404 AM CST SUN DEC 9 2012

.DISCUSSION...

ANOTHER CLOUDY START TO THE DAY ACROSS CENTRAL ALABAMA. A DENSE FOG 
ADVISORY IS CURRENTLY IN EFFECT ACROSS ALL OF CENTRAL ALABAMA WITH 
MANY LOCATIONS REPORTING REDUCED VISIBILITIES. DUE TO THE FOG AND LOW 
CLOUDS...4 AM TEMPERATURES ARE STILL IN THE UPPER 50S AND LOW 60S
ACROSS THE AREA. THE FOG AND LOW CLOUDS ARE DUE TO THE CONTINUED
LOW LEVEL SOUTHERLY FLOW AND ISENTROPIC UPLIFT. AT UPPER
LEVELS...A BROAD SCALE TROUGH STRETCHES ACROSS A MAJORITY OF THE
CONUS WITH A SHORTWAVE TROUGH PIVOTING ACROSS THE ROCKY MOUNTAIN
REGION. AT THE SURFACE...A FRONT TO THE NORTH ACROSS TENNESSEE
STRETCHES WESTWARD TOWARDS A SURFACE LOW THAT HAS DEVELOPED ACROSS
THE TEXAS PANHANDLE. THIS UPPER LEVEL SHORTWAVE AND SURFACE FRONT
WILL BE THE MAIN WEATHER FEATURES OVER THE NEXT COUPLE OF DAYS.

TODAY...CLOUDS AND FOG WILL LINGER FOR MUCH OF THE MORNING. MODELS 
ARE SHOWING THAT THE CLOUDS WILL EVENTUALLY LIFT AND SOME BREAKS 
WILL BE POSSIBLE. THE MOISTURE IS NOT FORECAST TO BE AS DEEP AS IT 
WAS YESTERDAY WITH SHALLOWER MOISTURE ACROSS THE SOUTH. THEREFORE... 
EXPECT CLOUDS ACROSS THE SOUTH WILL BREAK UP MID LATE MORNING WITH 
SOME BREAKS IN THE CLOUDS FURTHER TO THE NORTH BY LATE MORNING TO 
EARLY AFTERNOON. MIXING WILL ALSO HELP CLOUDS BREAK UP AS SOUTHERLY 
WINDS WILL INCREASE THROUGHOUT THE DAY TODAY. NOT EXPECTING ANY 
THUNDERSTORMS TODAY AS UPPER LEVEL LAPSE RATES REMAIN RATHER WEAK 
AND MODEL SOUNDINGS ARE INDICATING A WEAK CAP SHOULD KEEP CONVECTION 
FROM FORMING. A STRAY SHOWER WILL BE POSSIBLE ACROSS THE NORTH LATE 
THIS MORNING WITH A BIT DEEPER MOISTURE AS NOTED EARLIER. 

TONIGHT...THE FOCUS SHIFTS TO THE COLD FRONT AND THE SHORTWAVE 
TROUGH APPROACHING FROM THE WEST. ONE OF THE MAIN FORECAST 
CHALLENGES IS WILL THERE BE ANY RAIN AHEAD OF THE FRONT DURING THE 
OVERNIGHT PERIOD. THE GFS IS THE MOST AGGRESSIVE WITH PRECIPITATION 
AHEAD OF THE FRONT WITH PW VALUES INCREASING TO 1.5 INCHES AROUND 
06Z. THE NAM IS MUCH DRIER DURING THE OVERNIGHT PERIOD WITH MAXIMUM 
PW VALUES AT 06Z AROUND 1.25 INCHES. THEREFORE...THERE IS STILL A 
LOT OF UNCERTAINTY WITH THE EVOLUTION OF THIS SYSTEM. 
ADDITIONALLY...THE GFS IS SHOWING A WEAK BUT MORE ROBUST SHORTWAVE 
TROUGH MOVING ACROSS THE FORECAST AREA DURING THE OVERNIGHT PERIOD. 
AT 12Z MONDAY...THE FRONT WILL BEGIN TO NUDGE INTO NORTHWESTERN 
PORTIONS OF THE FORECAST AREA. THEREFORE...INCLUDED DEFINITE POPS 
ACROSS THE WEST LATE TONIGHT WITH DECREASING POPS TOWARDS THE 
SOUTHEAST. THERE IS AN OUTSIDE CHANCE THAT STRONG TO SEVERE STORMS 
DEVELOP IN MISSISSIPPI AND MAKE IT INTO FAR NORTHWEST ALABAMA...NEAR 
THE FRONT...AFTER 4 AM...BUT HWO WILL KEEP THE CONFIDENCE FAIRLY LOW.

ON MONDAY...THE COLD FRONT WILL MOVE ACROSS THE FORECAST AREA AS THE 
MAIN UPPER LEVEL TROUGH LIFTS TO THE NORTHEAST. THE LOW LEVEL JET 
LOOKS TO STRENGTHEN EARLY IN THE DAY TO AROUND 45-50 KTS AND SHOULD 
PROVIDE ENOUGH FORCING FOR A LINE OF SHOWERS AND THUNDERSTORMS TO 
MOVE ACROSS THE FORECAST AREA DURING THE DAY MONDAY. THE FOCUS OF 
THE JET WILL BE ACROSS THE NORTH WHERE THE BETTER SHEAR LOOKS TO 
EXIST BASED ON THE MODELS. THE REAL QUESTION REMAINS HOW MUCH 
INSTABILITY WILL BE AVAILABLE. THE NAM REMAINS THE MOST AGGRESSIVE 
MODEL WITH INSTABILITY WITH SBCAPE VALUES RANGING FROM 300-500 J/KG. 
THE GFS AND ECMWF ARE NOT AS IMPRESSIVE WITH THE INSTABILITY WITH 
SBCAPE VALUES OF ONLY 100-300 J/KG AT BEST. ADDITIONALLY...THESE VALUES 
SHOW THAT THE CAPE IS GENERALLY LIMITED TO THE SOUTH WITH THE BETTER 
SHEAR TO THE NORTH. THEREFORE...THERE IS NOT A LOCATION OF A GOOD 
BALANCE BETWEEN THE INSTABILITY AND SHEAR. HOWEVER...BASED ON THE 
NAM FORECAST WILL CONTINUE A LOW END THREAT FOR STRONG TO SEVERE 
STORMS ON MONDAY. THE SHEAR WILL BE RATHER IMPRESSIVE...ESPECIALLY 
ACROSS THE NORTH...AND IF ANY CAPE CAN BE REALIZED THEN SEVERE 
STORMS WILL BE POSSIBLE. MODELS SHOW THAT SEVERE WEATHER PARAMETERS 
WILL ACTUALLY DECREASE THROUGHOUT THE AFTERNOON AND EVENING AND THE 
THE LINE OF SHOWERS AND THUNDERSTORMS SHOULD BE WEAKENING AS IT 
PUSHES ACROSS SOUTHEAST. THE MAIN THREATS WITH ANY STRONG TO SEVERE 
STORMS WILL BE DAMAGING WINDS AND HEAVY RAINFALL. SOME LOCATIONS 
COULD SEE RAINFALL AMOUNTS OF 1-2 INCHES. 

THE FRONT IS FORECAST TO EXIT THE AREA MONDAY NIGHT AND RAIN CHANCES 
WILL END AFTER 06Z TUESDAY ACROSS THE SOUTHEAST. COLDER AIR WILL 
MOVE IN BEHIND THE FRONT. TEMPERATURES ACROSS THE NORTHWEST ON 
TUESDAY MORNING WILL BE NEAR FREEZING. MODELS ARE INDICATING THAT 
THE FRONT MAY STALL OUT JUST TO THE SOUTHEAST OF THE FORECAST AREA. 
THEREFORE...NOT AS CONFIDENT THAT TEMPERATURES ACROSS THE SOUTHEAST 
WILL DROP OFF AS MUCH. ADDITIONALLY...MODELS ARE INDICATING A RATHER 
ROBUST TROUGH THAT WILL MOVE ACROSS THE AREA TUESDAY NIGHT INTO 
WEDNESDAY. DUE TO THIS ROBUST TROUGH AND LINGERING 
BOUNDARY...INTRODUCED POPS TO THE FORECAST ACROSS THE SOUTHEAST ON 
TUESDAY NIGHT INTO EARLY WEDNESDAY. SURFACE HIGH PRESSURE WILL BE 
LOCATED TO THE NORTHEAST OF THE FORECAST AREA LATE IN THE WORK WEEK 
SETTING UP A WEDGE ADVECTING IN COOLER TEMPERATURES ACROSS THE EAST. 
EVENTUALLY...THE SURFACE HIGH MOVES OFF TO THE EAST OVER THE WEEKEND 
AS THE NEXT SYSTEM APPROACHES FROM THE WEST WITH CHANCES FOR 
PRECIPITATION RETURNING TO THE FORECAST NEXT WEEKEND. 

MA

&&

.AVIATION...
06Z TAF DISCUSSION.

IFR CIGS CONTINUE TO SPREAD ACROSS CENTRAL ALABAMA LATE THIS 
EVENING...AND TERMINALS THAT HAVE YET TO OBSERVE LOW CLOUDS AND FOG 
SHOULD CONTINUE TO DETERIORATE OVER THE NEXT COUPLE OF HOURS. THE 
LOW STRATUS HAS ACTUALLY BEGUN TO LOWER TO THE SURFACE CREATING LIFR 
CIGS AND LIFR TO IFR VISIBILITIES AS WELL. UNFORTUNATELY...THESE 
TRENDS WILL CONTINUE THROUGH 15Z AT THE LATEST. A FEW FLUCTUATIONS 
IN CIGS AND VIS CAN BE EXPECTED...BUT PREVAILING CONDITIONS WILL 
CONTINUE LIFR TO IFR FOR ALL TERMINALS. AFTER 15Z...CIGS AND VIS 
WILL GRADUALLY IMPROVE ACROSS THE BOARD WITH VFR CONDITIONS 
EVENTUALLY EXPECTED FOR ALL TERMINALS BY 21Z. THE SOUTHERN SITES OF 
KMGM AND KTOI SHOULD CLEAR FIRST WITH A STRONG SOUTHERLY FLOW 
EXPECTED THAT SHOULD MIX OUT A MAJORITY OF THE LOWER CLOUD COVER. 
SOUTHERLY WINDS WILL PREVAIL THROUGH THE AFTERNOON HOURS AROUND 8-10 
KNOTS. 

56/GDG

&&

.PRELIMINARY POINT TEMPS/POPS...
GADSDEN     70  57  64  33  50 /  20  60 100  30  10 
ANNISTON    71  58  68  36  52 /  10  30 100  40  10 
BIRMINGHAM  70  61  65  34  51 /  10  60 100  30  10 
TUSCALOOSA  72  61  65  35  52 /  10  80 100  30  10 
CALERA      71  59  67  37  52 /  10  60 100  40  10 
AUBURN      71  57  71  43  54 /  10  20  80  50  10 
MONTGOMERY  75  59  74  42  56 /  10  30 100  50  10 
TROY        73  57  73  43  54 /  10  20  70  60  10 

&&

.BMX WATCHES/WARNINGS/ADVISORIES...
DENSE FOG ADVISORY UNTIL 9 AM CST THIS MORNING FOR THE FOLLOWING 
COUNTIES: AUTAUGA...BARBOUR...BIBB...BLOUNT...BULLOCK...
CALHOUN...CHAMBERS...CHEROKEE...CHILTON...CLAY...CLEBURNE...
COOSA...DALLAS...ELMORE...ETOWAH...FAYETTE...GREENE...HALE...
JEFFERSON...LAMAR...LEE...LOWNDES...MACON...MARENGO...MARION...
MONTGOMERY...PERRY...PICKENS...PIKE...RANDOLPH...RUSSELL...
SHELBY...ST. CLAIR...SUMTER...TALLADEGA...TALLAPOOSA...
TUSCALOOSA...WALKER...WINSTON.

&&

$$