Severe Thunderstorm Warning 162, NWS Birmingham, AL

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BIRMINGHAM AL
643 PM CDT MON APR 13 2009

.UPDATE...FOR 00Z AVIATION.

&&

.DISCUSSION...

ALTHOUGH A BREAK IN THE WEATHER IS EXPECTED EARLY THIS
AFTERNOON...THINGS WILL BE QUICKLY CHANGING AS THE ATMOSPHERE
BEGINS TO DESTABILIZE ONCE AGAIN. CURRENT THINKING IS THAT THIS
WILL BE A TWO ROUND EVENT. FIRST ROUND WILL BE ISOLATED
THUNDERSTORMS WITH THE SECOND ROUND BEING A SQUALL LINE. LETS GO
AHEAD AND FOCUS ON THE FIRST ROUND OF SEVERE WEATHER.

ISOLATED THUNDERSTORMS WILL BEGIN TO TRIGGER AS EARLY AS 3 PM
ACROSS AREAS ALONG THE MISSISSIPPI AND ALABAMA STATE LINE.
COVERAGE IS EXPECTED TO INCREASE ACROSS WEST CENTRAL ALABAMA. BY 5
PM...SCATTERED THUNDERSTORMS SHOULD BE PRETTY ACTIVE ACROSS AREAS
WEST OF INTERSTATE 65. AIRMASS WILL CONTINUE TO DESTABILIZE ACROSS
THE EASTERN PARTS OF INTERSTATE 65 WHICH ALLOW THUNDERSTORM
DEVELOPMENT TO OCCUR AFTER 5 PM. ALL OF THESE STORMS WILL HAVE THE
POTENTIAL TO PRODUCE VERY LARGE HAIL AND DAMAGING WINDS. ALTHOUGH
CONDITIONS ARE NOT QUITE PRIME FOR A TORNADO OUTBREAK...THERE
COULD BE ENOUGH SHEAR TO PRODUCE A FEW ISOLATED TORNADOES. BUFKIT
NAM DATA SHOWS THAT EHI AND HELICITY WONT BE QUITE AS HIGH. LOW
LEVEL SHEAR WILL BE UNIDIRECTIONAL...BUT PLENTY OF SPEED SHEAR.
ALTHOUGH UNIDIRECTIONAL SHEAR IS NOT USUALLY CONDUCIVE OF TORNADIC
ACTIVITY...STORM INTERACTION WITH A BOUNDARY AND RIGHT OR LEFT
MOVERS COULD COMPLETELY CHANGE THE ENVIRONMENT OF THESE STORMS
AND THUS ALLOW THEM TO QUICKLY PRODUCE A TORNADO. THESE STORMS
COULD LAST WELL INTO THE EVENING HOURS.

THE SECOND ROUND OF STORMS WILL BE IN THE FORM OF A SQUALL LINE.
MODELS INDICATE THAT THIS LINE WILL DEVELOP ACROSS EASTERN
MISSISSIPPI AND WILL QUICKLY RACE TOWARDS THE EAST TOWARDS THE
FORECAST AREA. BASED ON THE LOCAL HIGH RESOLUTION WRF...THE LINE
COULD BEGIN TO APPROACH THE STATE AS EARLY AS 8 PM AND ARRIVING TO
THE INTERSTATE 65 CORRIDOR NEAR 11 PM. THE MAIN THREAT WITH THIS
LINE WILL BE DAMAGING WINDS AND LARGE. THE TORNADO THREAT WILL BE
A LITTLE LESS WITH THIS LINE BUT COULD NOT BE DISREGARDED. THE
THREAT OF SEVERE WEATHER COULD EXTEND AS LATE AS 4 AM...ESPECIALLY
FOR LOCATIONS WEST OF INTERSTATE 65. THERE IS STILL SOME QUESTION
MARK WHETHER OR NOT INSTABILITY WILL REMAIN PAST MIDNIGHT FOR
AREAS EAST OF 65. HOWEVER...MODELS HINTING AT A LOW LEVEL JET
DEVELOPING ALONG THE LINE OF STORMS WHICH COULD HELP SUSTAIN THE
LINE WELL INTO THE OVERNIGHT HOURS AND WELL INTO AREAS EAST OF
INTERSTATE 65.

AFTER THIS EVENT IS OVER...WE SHOULD BE PRETTY QUITE AT LEAST
THROUGH THE REST OF THE WEEK. NEXT STORM SYSTEM COULD MOVE IN OVER
THE WEEKEND.

&&

.AVIATION...00Z TAF DISCUSSION.

SCATTERED SHOWERS AND THUNDERSTORMS ARE DEVELOPING ACROSS WEST
ALABAMA AHEAD OF A SLOW MOVING COLD FRONT. AT THIS POINT...THE
STORMS ARE TOO ISOLATED TO INCLUDE IN THE TAFS BUT WILL WATCH THE
TRENDS AS THERE IS SOME POTENTIAL FOR A BKN SQUALL LINE TO DEVELOP
AND PUSH THROUGH THE AREA TONIGHT.

MVFR CEILINGS WILL REMAIN IN PLACE ACROSS MGM AND TOI THROUGH THE
OVERNIGHT WITH DEVELOPING/LOWERING CEILINGS ACROSS THE NORTH. IFR
CONDITIONS WILL BE POSSIBLE THROUGH MID MORNING WITH CLEARING BY
NOON.

WINDS ARE SOUTH TO SOUTHEAST AND WILL SHIFT TO WEST AND NORTHWEST
BEHIND THE FRONT.

&&

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

&&

10/88

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE BIRMINGHAM AL
116 PM CDT MON APR 13 2009

ALZ011>015-017>050-141816-
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-
116 PM CDT MON APR 13 2009

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

.DAY ONE...THIS AFTERNOON AND TONIGHT.

TWO WAVES OF SEVERE WEATHER WILL BE POSSIBLE THIS AFTERNOON AND INTO
THE OVERNIGHT HOURS.

THE FIRST ROUND WILL BE ASSOCIATED WITH ISOLATED SUPERCELLS THAT MAY
DEVELOP AHEAD OF A COLD FRONT. AREAS WEST OF I 65 WILL HAVE THE BEST
CHANCE AT SEEING THIS ISOLATED CONVECTION AS EARLY AS 3 PM.
WHILE AREAS EAST OF I 65 WILL SEE A BETTER CHANCE AFTER 5 PM. WITH
THESE ISOLATED SUPERCELLS...LARGE HAIL...DAMAGING WIND...AND
TORNADOES WILL ALL BE POSSIBLE.

THE SECOND WAVE WILL BE ASSOCIATED WITH THE COLD FRONT THAT WILL
LIKELY DEVELOP IN EASTERN MISSISSIPPI THIS EVENING. LOOK FOR
DAMAGING WINDS AND LARGE HAIL TO IMPACT THE WESTERN PORTIONS OF
CENTRAL ALABAMA AS EARLY AS 8 PM. AN ISOLATED TORNADO CAN NOT BE
RULED OUT. THIS SQUALL LINE WILL TRAVERSE THE STATE LASTING WELL INTO
THE OVERNIGHT HOURS. THE LINE SHOULD SHOW SIGNS OF WEAKENING OVER
EASTERN ALABAMA BY 4 AM.

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

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

ACTIVATION OF STORM SPOTTERS AND EMERGENCY MANAGEMENT WILL LIKELY
BE NEEDED LATE MONDAY AFTERNOON THROUGH MONDAY NIGHT.

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE BIRMINGHAM AL
712 PM CDT MON APR 13 2009

ALZ011-012-140045-
LAMAR-MARION-
712 PM CDT MON APR 13 2009

...SIGNIFICANT WEATHER ALERT FOR LAMAR AND MARION COUNTIES UNTIL 745
PM CDT...

AT 710 PM CDT...THE NATIONAL WEATHER SERVICE IS TRACKING A STRONG
THUNDERSTORM 6 MILES SOUTH OF WESTON...OR 7 MILES SOUTHWEST OF
HAMILTON...MOVING NORTHEAST AT 50 MPH.

PEA SIZE HAIL AND WINDS UP TO 40 MPH ARE EXPECTED WITH THIS STORM.

* LOCATIONS IN OR NEAR THE PATH INCLUDE...
  BYRD.
  RANKIN FITE AIRPORT.
  HAMILTON.
  BRINN.
  HACKLEBURG.
  BEAR CREEK.

STAY TUNED TO NOAA WEATHER RADIO...COMMERCIAL RADIO...OR YOUR LOCAL
TELEVISION STATIONS FOR LATER STATEMENTS AND POSSIBLE WARNINGS
CONCERNING THIS WEATHER SITUATION.

27