Severe Thunderstorm Warning 427, NWS Birmingham, AL

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BIRMINGHAM AL
313 PM CDT MON SEP 21 2009

.DISCUSSION...

WHAT LOOKED TO BE A FAIRLY BENIGN PATTERN HAS BECOME QUITE
INTERESTING OVER THE LAST 12-24 HOURS.  SYNOPTICALLY WE ARE IN A
VERY FAMILIAR WEATHER SETUP...UPPER LEVEL LOW PRESSURE OVER THE
SOUTH-CENTRAL PORTION OF THE COUNTRY THAT IS RESPONSIBLE FOR PULLING
LARGE AMOUNTS OF MOISTURE OUT OF THE GULF OF MEXICO AND DEPOSITING
IT IN THE ATMOSPHERE OVER ALABAMA.  THE COMBINATION OF PWS OVER 2
INCHES...ADEQUATE SURFACE CONVERGENCE LEADING TO 20-25 KTS OF
VERTICAL SHEAR...PLUS WHAT LOOKS TO BE MULTIPLE VORTICITY MAXIMA
RIDING ALONG THE SOUTHWESTERN 500MB FLOW OVER ALABAMA...HAVE LED TO
COPIOUS RAINFALL.  WHEN I SAY COPIOUS...I MEAN RAINFALL TOTALS SINCE
MIDNIGHT LAST NIGHT OF 4 TO 6 INCHES OVER MANY AREAS IN WEST-CENTRAL
ALABAMA WITH HIGHER TOTALS ESTIMATED FROM RADAR.  SOME AREAS COULD
HAVE SEEN TOTALS UPWARDS OF 10 INCHES.  THE OTHER PROBLEM THIS SET
UP HAS CAUSED...OR AT LEAST THE SHEAR HAS CAUSED...ROTATING
UPDRAFTS.  THIS HAS LED TO MULTIPLE WALL CLOUD SIGHTINGS...AS WELL
AS ONE UNCONFIRMED REPORT OF A TORNADO IN SUMTER COUNTY.   ANOTHER
TRIGGER MECHANISM FOR THE HELICITIES WE ARE EXPERIENCING COULD BE
THE RAIN/CLOUD COOLED BOUNDARY OVER SUMTER COUNTY...NOTICEABLE IN
THE VISIBLE SATELLITE IMAGERY. EITHER WAY...A BUSY DAY
METEOROLOGICALLY.

FOR THE REST OF THIS EVENING...RAIN SHOWERS AND ISOLATED
THUNDERSTORMS ARE LIKELY TO PERSIST...AT LEAST FOR A COUPLE OF HOURS
AFTER SUNSET.  EXPECT FOR THUNDERSTORM ACTIVITY TO DIMINISH
FIRST...WITH LINGER SHOWERS THROUGH MIDNIGHT.

IF ITS WET AND DREARY THAT YOU LIKE...YOU ARE IN FOR A TREAT FOR THE
NEXT COUPLE OF DAYS.  THIS SOUTHWEST FLOW PATTERN...CAUSED BY THE
COMBINATION OF THE DEEP CUTOFF UPPER LEVEL LOW OVER THE PLAINS
STATES...AND THE BERMUDA HIGH OVER THE WESTERN ATLANTIC...IS
EXPECTED TO REMAIN IN PLACE FOR THE NEXT COUPLE OF DAYS. THE
FORECAST CHALLENGE FOR THE NEXT COUPLE OF DAYS WILL BE HOW MUCH THE
RIDGE OVER THE ATLANTIC EXERTS ITS INFLUENCE ON THE LOW PRESSURE.
FOR NOW...EXPECT SCATTERED SHOWERS AGAIN ON TUESDAY AREA WIDE. THEN
ON WEDNESDAY...THE RIDGE BEGINS TO PUSH INLAND.  THIS WILL NOT
LIKELY DRY OUT THE ENTIRE CWA...BUT IT COULD DRY THINGS OUT FOR
FOLKS SOUTH OF INTERSTATE 20 ON WEDNESDAY AND THURSDAY.  HAVE
REDUCED POPS IN THESE AREAS ACCORDINGLY...THOUGH I ADMITTEDLY DIDNT
GO MUCH BELOW GUIDANCE.

CONVECTIVE ACTIVITY SHOULD PICK UP AREA WIDE AGAIN ON FRIDAY AS THE
CUTOFF LOW HELPS TO ERODE THE RIDGE OF HIGH PRESSURE OVER THE
SOUTHEAST.  THIS COULD LEAD TO MORE SHOWERS AND THUNDERSTORMS FOR
MOST OF CENTRAL ALABAMA THROUGH THE WEEKEND.

MODELS CONTINUE TO SHOW A DRYING TREND IN THE EXTENDED PORTIONS OF
THE FORECAST.  THE EURO AND THE GFS ARE IN PRETTY GOOD AGREEMENT
THAT SOME DRYING SHOULD BEGIN TAKING PLACE BY TUESDAY OF NEXT WEEK.

TEMPERATURES WILL REMAIN RIGHT AROUND NORMALS FOR THIS TIME OF
YEAR...THOUGH WE COULD SEE DAYTIME HIGH A COUPLE OF DEGREES WARMER
WITH THE RIDGE PUSHING INTO THE SOUTHEAST ON WEDNESDAY...BUT WERE
ONLY TALKING ABOUT COUPLE OF DEGREES.

ALSO...THE FLASH FLOOD WATCH THAT IS VALID UNTIL MIDNIGHT TONIGHT
WILL BE EXTENDED UNTIL 00Z WEDNESDAY AS ANY AMOUNT OF RAINFALL
TOMORROW WILL CAUSE PROBLEMS ONCE AGAIN.

&&

.AVIATION...18Z TAF DISCUSSION.

WE REMAIN IN A PATTERN WITH VERY LOW PREDICTABILITY BEYOND THE FIRST
COUPLES HOURS...AND AS A RESULT VERY LOW CONFIDENCE AFTER THAT.  THE
MAIN AREA OF CONCERN THIS MORNING...AND THROUGH AT LEAST 2100Z
TODAY...WILL REMAIN IN THE EET TO ANB CORRIDOR.  NUMEROUS SHOWERS
AND THUNDERSTORMS WILL FREQUENTLY REDUCE CEILINGS AND VISIBILITIES
TO BELOW 1 MILE AND BELOW 1000 FEET...RESPECTTIVELY.  TCL HAS
EMERGED INTO A BIT OF A CLEAR SPOT...WHICH MAY ALSO SOON REACH BHM.
BUT IF MORE RAIN DEVELOPS...THEN WILL HAVE TO ISSUE UPDATES TO TAKE
FORECASTS FOR THOSE LOCATIONS INTO A MORE PESSEMISTIC DIRECTION.
THE RAIN THUS FAR TODAY HAS STAYED WELL NORTH OF MGM AND TOI. GIVEN
SUCH LOW CONFIDENCE...I JUST WENT WITH A PERSISTENCE BASED FORECAST
FOR THOSE LOCATIONS...AND WILL ALSO UPDATE THEM IF/WHEN NECESSARY.

&&

.PRELIMINARY POINT TEMPS/POPS...
GADSDEN     70  86  69  88  71 /  60  60  30  50  20
ANNISTON    70  85  68  88  69 /  60  60  30  40  20
BIRMINGHAM  70  85  69  87  69 /  60  60  30  50  20
TUSCALOOSA  71  88  70  89  71 /  60  60  30  50  20
CALERA      70  85  69  87  70 /  60  60  30  40  20
AUBURN      69  85  69  86  69 /  50  40  20  30  20
MONTGOMERY  71  87  72  89  72 /  50  50  30  30  20
TROY        71  86  70  88  70 /  40  50  20  30  20

&&

.BMX WATCHES/WARNINGS/ADVISORIES...

FLASH FLOOD WATCH HAS BEEN EXTENDED UNTIL TUESDAY AT 7 PM FOR ALL
OF CENTRAL ALABAMA.

&&

27/61

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE BIRMINGHAM AL
1251 PM CDT MON SEP 21 2009

ALZ011>015-017>050-221200-
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-
1251 PM CDT MON SEP 21 2009

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

.DAY ONE...THIS AFTERNOON AND TONIGHT.

...FLASH FLOOD WATCH UNTIL MIDNIGHT..

A THREAT OF FLASH FLOODING WILL CONTINUE ACROSS ALL OF CENTRAL
ALABAMA THROUGH AT LEAST MIDNIGHT TONIGHT. THE AREA WITH THE
HIGHEST INITIAL THREAT THIS AFTERNOON WILL BE IN A BAND FROM
LAMAR...PICKENS...AND SUMTER COUNTIES...EASTWARD THROUGH TUSCALOOSA
AND METRO BIRMINGHAM...TO CHEROKEE...CLEBURNE...AND RANDOLPH
COUNTIES. THE HIGHEST THREAT MAY EXPAND OR MOVE NORTH OR SOUTH AS
ADDITIONAL SHOWERS AND STORMS DEVELOP.

IN ADDITION TO THE FLASH FLOODING...SEVERAL RIVERS ARE NOW IN
FLOOD...OR ARE FORECAST TO GO INTO FLOOD LATER TODAY.

.DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY.

RAIN CHANCES WILL REMAIN ABOVE NORMAL THROUGH AT LEAST TUESDAY...
CONTINUING A THREAT OF FLASH FLOODING.

RIVER FLOODING WILL REMAIN A CONCERN ON SEVERAL CENTRAL ALABAMA
RIVERS THROUGH AT LEAST FRIDAY.  PLEASE SEE THE LATEST RIVER FLOOD
STATEMENTS FOR DETAILS.

.SPOTTER INFORMATION STATEMENT...

ACTIVATION OF STORM SPOTTERS AND EMERGENCY MANAGEMENT WILL BE
NECESSARY FOR MANY AREAS THROUGH TONIGHT DUE TO FLOODING.

61

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BIRMINGHAM AL
333 PM CDT MON SEP 21 2009

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0900 AM     FLASH FLOOD      2 W VERNON              33.76N 88.15W
09/21/2009                   LAMAR              AL   EMERGENCY MNGR

            SEVERAL SECONDARY ROADS CLOSED JUST WEST OF VERNON NEAR
            HIGHWAY 18.

&&

88

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BIRMINGHAM AL
335 PM CDT MON SEP 21 2009

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0333 PM     HAIL             EPES                    32.69N 88.13W
09/21/2009  E0.88 INCH       SUMTER             AL   LAW ENFORCEMENT

            EXIT 23 ON I20 LIVINGSTON PDCHIEF REPORTING

&&

MBAER

PRELIMINARY LOCAL STORM REPORT...CORRECTED
NATIONAL WEATHER SERVICE BIRMINGHAM AL
350 PM CDT MON SEP 21 2009

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0333 PM     HAIL             EPES                    32.69N 88.13W
09/21/2009  E1.00 INCH       SUMTER             AL   LAW ENFORCEMENT

            EXIT 23 ON I20 LIVINGSTON PDCHIEF REPORTING. CORRECTED
            FOR 1 INCH.

&&

MBAER

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BIRMINGHAM AL
407 PM CDT MON SEP 21 2009

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0353 PM     HAIL             2 NW LIVINGSTON         32.62N 88.21W
09/21/2009  E0.50 INCH       SUMTER             AL   EMERGENCY MNGR

            DIME SIZE HAIL REPORTED ON EXIT 17 ON INTERSTATE
            20/59...WHICH IS THE INTERSECTION WITH STATE HIGHWAY 28.

&&

GGOGGINS

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