Special Weather Statement, NWS Birmingham, AL

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BIRMINGHAM AL
640 PM CDT SUN SEP 2 2012

.UPDATE...AVIATION DISCUSSION.

&&

.SHORT TERM...
TONIGHT THROUGH TUESDAY NIGHT.

THE LATEST WATER VAPOR IMAGERY INDICATES THAT THE REMNANTS OF ISAAC
HAVE SHEARED APART VERTICALLY...WITH UPPER LEVEL ENERGY SLOWLY
SHIFTING EAST AND SOUTH WHILE A MID AND LOW LEVEL CIRCULATION STILL
EXIST AND BEING ABSORBED BY A FRONTAL BOUNDARY OVER THE OHIO VALLEY
INTO THE LOWER MISSISSIPPI VALLEY. PRECIPITABLE WATER VALUES REMAIN 2
INCHES OR BETTER AREA WIDE WITH SURFACE DEW POINTS IN THE 70S. THE
ONLY CAVEAT HERE IS THAT THERE IS SOME DRY AIR CREEPING IN ALOFT...
PER THE LATEST WATER VAPOR IMAGERY. THIS REMNANT CIRCULATION WILL
INCREASE THE WIND FIELDS ABOVE THE SURFACE THE NEXT FEW DAYS...
CREATING AN ENVIRONMENT OF POTENTIAL SEVERE WEATHER DEVELOPMENT.

THE REMNANT OF ISSAC OPENS UP ALOFT AND SLOWLY PUSHES AN UPPER
TROUGH ACROSS THE AREA. THE VARIOUS MODEL SOLUTIONS REMAIN IN GOOD
AGREEMENT AND CONSISTENCY ALOFT. SEVERAL WAVES OF UPWARD VERTICAL
MOTION WILL AFFECT CENTRAL ALABAMA THROUGH LABOR DAY WITH NUMEROUS
SHOWERS AND THUNDERSTORMS DEVELOPING.

THE LATEST VISIBLE SATELLITE IMAGERY HAS 4 AREAS OF LOW LEVEL
CONVERGENCE...ONE ACROSS SOUTHEASTERN AREAS...ONE NEAR THE I-59
CORRIDOR...ONE IN FAR NORTHWESTERN ALABAMA...AND YET ANOTHER BACK
ACROSS WESTERN TENNESSEE. 0-1 KM BULK SHEAR AND SRH VALUES INCREASE
LATE THIS AFTERNOON AND EVENING AND JUMP TO 25-35 AND 200-250
RESPECTIVELY...ESPECIALLY NORTH. THIS TREND IS SUPPORTED BY THE
LATEST RUC ANALYSIS.

SO WITH ALL THIS SAID...THERE WILL BE A POTENTIAL OF SEVERE
THUNDERSTORMS GENERALLY NEAR AND NORTH OF THE I-20 CORRIDOR FROM 6
PM UNTIL MIDNIGHT. STORMS SHOULD DEVELOP ACROSS WESTERN TENNESSEE...
NORTHERN MISSISSIPPI AND NORTHWEST ALABAMA AND MOVE INTO CENTRAL
ALABAMA THIS EVENING. THE MAIN THREAT APPEARS TO BE DAMAGING STRAIGHT
LINE WINDS. BUT ATMOSPHERIC SHEAR VALUES WOULD SUPPORT A SMALL THREAT
FOR TORNADOES...ESPECIALLY IN ISOLATED CELLS. ADDITIONALLY...BRIEF
TORRENTIAL RAIN WILL ALSO BE POSSIBLE.

A SURFACE TROUGH MAY BE GENERATED BY NUMEROUS OUTFLOWS BUT THE
OVERALL ATMOSPHERE DOES NOT CHANGE APPRECIABLY DURING THE REMAINDER
OF THE SHORT TERM. WILL NOT MAKE ANY WHOLESALE CHANGES TO THE
CURRENT SHORT TERM AS IT APPEARS THE FORECAST REASONING HAS NOT
CHANGED AND THINGS ARE ON TARGET. BETTER THAN NORMAL RAIN CHANCES
ARE EXPECTED EACH PERIOD WITH HIGHS NEAR NORMAL AND
LOWS ABOVE NORMAL.

75

.LONG TERM...
WEDNESDAY THROUGH SUNDAY NIGHT.

FROM WEDNESDAY INTO NEXT WEEKEND... THE REMNANTS OF ISAAC LOOK TO BE
FINALLY SHEARED APART TO THE POINT IT IS NO LONGER DISCERNIBLE.
HOWEVER... AN UPPER LEVEL LOW NOW OVER THE SOUTHEAST COAST OF
FLORIDA SHOULD TRANSLATE SLOWLY NORTHWESTWARD TO THE GEORGIA/FLORIDA
BORDER BY WEDNESDAY AND THURSDAY. LOW LEVEL TROPICAL MOISTURE WILL
REMAIN IN PLACE ACROSS CENTRAL ALABAMA. SO THE HIGHEST PRECIP
CHANCES WEDNESDAY THROUGH FRIDAY WILL GENERALLY BE ACROSS
SOUTHEASTERN PORTIONS OF CENTRAL ALABAMA AS THE UPPER LEVEL LOW
SLOWLY EXITS EAST INTO THE ATLANTIC.

BY NEXT WEEKEND BOTH THE GFS AND THE ECMWF NOW SHOW A STRONG UPPER
TROUGH APPROACHING THE EASTERN CONUS. BOTH MODELS ALSO TAKE A FAIRLY
STRONG COLD FRONT THROUGH CENTRAL ALABAMA SATURDAY. THE GFS CLEARS
THE FRONT THROUGH THE AREA BEFORE THE BEST UPPER SHEAR CAN ARRIVE...
BUT THE ECMWF IS SLIGHTLY SLOWER WITH THE FRONTAL PASSAGE... WHICH
SUGGESTS THAT SOME DECENT SHEAR AND MORE ORGANIZED STORMS COULD BE
IN PLAY NEXT WEEKEND AHEAD OF OR ALONG THE COLD FRONT. NEEDLESS TO
SAY... TEMPS AND MOISTURE WILL BE MUCH LOWER BY NEXT WEEKEND IF THIS
FRONTAL PASSAGE VERIFIES. WILL CONTINUE TO MONITOR POSSIBLE SEVERE
POTENTIAL WITH UPCOMING FORECAST PACKAGES.

77/GLEASON

&&

.AVIATION...
00Z TAF DISCUSSION.

A SOLID LINE OF STRONG TO SEVERE TSTMS OVER NORTH ALABAMA WILL PUSH
SOUTHWARD THRU 04Z AND EFFECT THE NORTHERN TAF SITES. THE STRONGEST
PART OF THE LINE WILL LIKELY REACH KBHM AND KANB WITH VSBYS 1/2SM OR
LESS AND WIND GUSTS TO 35 KNOTS. WIND GUSTS WILL BE ADDED TO TAFS
ONCE TIMING OF CONVECTIVE LINE BECOMES MORE CERTAIN. MOST OF THE
CONVECTIVE ACTIVITY SHOULD BE GONE BY 04Z.  WITH AN OUTFLOW BOUNDARY
PUSHING THRU THE AREA WITH THE CONVECTIVE LINE...THIS FEATURE WILL
LIKELY DISRUPT THE SOUTHWEST LOW LEVEL INFLOW WHICH HAS BROUGHT LOW
CLOUDS INTO AREA AROUND SUNRISE THE PAST FEW MORNINGS. SINCE
ACTIVITY WILL BE ENDING BY 05Z...THERE WILL LIKELY BE ENOUGH TIME
FOR SOUTHWEST FLOW TO REDEVELOP OVERNIGHT AND BROUGHT LOW CLOUDS
BACK ACROSS AREA BY 11Z OR 12Z.

WITH RAIN FALLING AT KTOI THIS AFTERNOON...FOG WILL LIKELY BE AN
ISSUE OVERNIGHT AND INCLUDED LIFR FLIGHT CATEGORY BY 09Z.  AS WITH
PREVIOUS DAYS...LOW CLOUDS WILL LIFT AND BECOME SCATTERED BY 17Z.

58/ROSE

&&

.PRELIMINARY POINT TEMPS/POPS...
GADSDEN     72  86  72  85  71 /  70  70  60  60  30
ANNISTON    73  87  73  85  72 /  70  70  60  60  30
BIRMINGHAM  75  85  73  85  73 /  70  70  60  50  30
TUSCALOOSA  77  89  76  88  74 /  70  60  60  40  30
CALERA      74  87  73  87  74 /  70  60  60  60  30
AUBURN      72  87  73  86  72 /  40  60  60  60  40
MONTGOMERY  74  92  75  88  74 /  40  60  60  60  40
TROY        71  88  72  88  72 /  30  60  60  60  40

&&

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

&&

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE BIRMINGHAM AL
544 PM CDT SUN SEP 2 2012

ALZ011>015-017>050-031200-
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-
544 PM CDT SUN SEP 2 2012

THIS HAZARDOUS WEATHER OUTLOOK IS FOR THE COUNTIES SERVED BY THE
NATIONAL WEATHER SERVICE OFFICE IN BIRMINGHAM.

.DAY ONE...TONIGHT.

SEVERE THUNDERSTORMS ARE LIKELY THROUGH 11 PM ALONG AND NORTH OF A
LINE FROM MILLPORT...TO BIRMINGHAM...TO HEFLIN. DAMAGING WINDS ARE
THE PRIMARY THREAT. HOWEVER...ISOLATED TORNADOES ARE POSSIBLE...BUT
THE THREAT FOR TORNADOES SHOULD DIMINISH BY 8 PM.

.DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY.

SEVERE THUNDERSTORMS WILL BE POSSIBLE ON MONDAY ACROSS CENTRAL
ALABAMA...PRIMARILY DURING THE AFTERNOON AND EVENING HOURS. DAMAGING
WINDS ARE THE PRIMARY THREAT. CLOUD COVER MONDAY MORNING COULD
LIMIT INSTABILITIES AND THUNDERSTORM DEVELOPMENT...RESULTING IN A
LOWER CONFIDENCE IN SEVERE POTENTIAL.

.SPOTTER INFORMATION STATEMENT...

ACTIVATION OF STORM SPOTTERS AND EMERGENCY MANAGEMENT WILL BE
NEEDED TONIGHT AND POSSIBLY AGAIN ON MONDAY.

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