Damaging Wind in Alabama, April 26, 2011

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HUNTSVILLE AL
1225 AM CDT TUE APR 26 2011

.UPDATE...QUICK UPDATE TO ADD SVR THUNDERSTORM WATCH UNTIL 5 AM FOR
OUR WRN AL ZONES OF LIMESTONE...LAWRENCE...LAUDERDALE...COLBERT...AND
FRANKLIN.

&&

.DISCUSSION...LINE OF STRONG TO SEVERE STORMS...AHEAD OF AN UPPER TROF...
ARE JUST NOW APPROACHING OUR WRN ZONES. AS A RESULT...A SEVERE
THUNDERSTORM WATCH HAS BEEN ISSUED FOR THE ABOVE COUNTIES IN NW AL.

.AVIATION...FOR 06Z TAFS.

NO MAJOR CHANGES FROM PREVIOUS AVIATION DISCUSSION...EXCEPT TO ADJUST
FOR THE TIMING OF STORMS.

&&

.PREV DISCUSSION... /ISSUED 1008 PM CDT MON APR 25 2011/

UPDATE...EVENING UPDATE TO PUBLIC FORECAST.

DISCUSSION...
PRIMARY CONCERN FOR THE OVERNIGHT PERIOD REVOLVES AROUND EVOLUTION OF
SEVERE MCS CURRENTLY MOVING INTO SW TENNESSEE/NW MISSISSIPPI. A
STRONG COLD POOL HAS DEVELOPED BEHIND THIS FEATURE AND SHOULD ENABLE
IT TO ACCELERATE EASTWARD...POSSIBLY AFFECTING THE FAR NORTHWESTERN
COUNTIES OF THE FORECAST AREA AS EARLY AS MIDNIGHT-3 AM...I-65
CORRIDOR BETWEEN 3-6 AM...AND NE ALABAMA BETWEEN 6-9 AM. WILL
INCREASE POPS ACCORDINGLY AND MENTION POTENTIAL FOR STRONG STORMS IN
ZFPHUN. HWO AND GRAPHICAST HAVE ALREADY BEEN UPDATED TO REFLECT
QUICKER MOVEMENT OF SQUALL LINE TO THE EAST. OTHER ELEMENTS OF FIRST
PERIOD FORECAST APPEAR TO BE ON TRACK AND WILL NOT REQUIRE CHANGES AT
THIS TIME.

70/DD

PREV DISCUSSION... /ISSUED 702 PM CDT MON APR 25 2011/

UPDATE...FOR 00Z AVIATION FORECAST.

AVIATION...
AVIATION WEATHER CONDITIONS WILL BEGIN TO DETERIORATE ACROSS THE AREA
OVERNIGHT...LIKELY BETWEEN 26/05-08Z...AS A STRENGTHENING SSW LOW-
LEVEL JET ADVECTS A BKN MVFR STRATUS DECK NORTHWARD. THIS JET WILL
ALSO RESULT IN STRONG LLWS IN THE 1-3 KFT LAYER. CONDITIONS WILL
DECLINE FURTHER AS A COMPLEX OF STRONG/SEVERE TSRA MOVES EASTWARD
FROM NORTHERN MISSISSIPPI. EXPECT TSRA TO BEGIN IMPACTING MSL AS
EARLY AS 26/08Z...AND HAVE INCLUDED VCTS/CB WITH TEMPO GROUP FOR
PREVAILING MVFR CONDS IN TSRA BETWEEN 26/08-12Z. SIMILAR CONDS ARE
EXPECTED AT HSV...BUT DELAYED ONSET OF TSRA THREAT BY A COUPLE OF
HOURS. SCATTERED SHRA/TSRA MAY REMAIN INVOF EACH TERMINAL THRU THE
AFTERNOON...BUT FEEL THIS ACTIVITY WILL NOT BE AS WIDESPREAD AS
ACTIVITY EARLIER IN THE MORNING. PREVAILING WINDS WILL REMAIN IN THE
10-15 KNOT RANGE THRU THE PERIOD...WITH SSE FLOW OVERNIGHT VEERING TO
SSW LATE TOMORROW MORNING.

70/DD

&&

.HUN WATCHES/WARNINGS/ADVISORIES...
AL...FLASH FLOOD WATCH FROM 7 AM CDT THIS MORNING THROUGH WEDNESDAY
     EVENING FOR THE FOLLOWING ZONES: COLBERT...CULLMAN...DEKALB...
     FRANKLIN AL...JACKSON...LAUDERDALE...LAWRENCE...LIMESTONE...
     MADISON...MARSHALL...MORGAN.

TN...FLASH FLOOD WATCH FROM 7 AM CDT THIS MORNING THROUGH WEDNESDAY
     EVENING FOR THE FOLLOWING ZONES: FRANKLIN TN...LINCOLN...MOORE.

&&

007

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE HUNTSVILLE AL
1159 PM CDT MON APR 25 2011

ALZ001>010-016-TNZ076-096-097-261015-
LAUDERDALE-COLBERT-FRANKLIN AL-LAWRENCE-LIMESTONE-MADISON-MORGAN-
MARSHALL-JACKSON-DEKALB-CULLMAN-MOORE-LINCOLN-FRANKLIN TN-
1159 PM CDT MON APR 25 2011

THIS HAZARDOUS WEATHER OUTLOOK IS FOR NORTH ALABAMA AND PORTIONS
OF SOUTHERN MIDDLE TENNESSEE.

.DAY ONE...TONIGHT...
A SEVERE THUNDERSTORM WATCH HAS BEEN ISSUED FOR LAUDERDALE...
COLBERT...FRANKLIN...LIMESTONE...AND LAWRENCE COUNTIES IN
NORTHWESTERN ALABAMA THROUGH 500AM THIS MORNING.

A LINE OF SHOWERS AND THUNDERSTORMS WILL PUSH INTO NORTHWESTERN
ALABAMA BETWEEN MIDNIGHT AND 300 AM...CROSS THE INTERSTATE 65
CORRIDOR BETWEEN 300 AM AND 600 AM...AND WILL PUSH INTO NORTHEAST
ALABAMA BETWEEN 600 AM AND 900 AM. THESE THUNDERSTORMS MAY BE
CAPABLE OF PRODUCING SEVERE WEATHER...INCLUDING DAMAGING
WINDS...ISOLATED TORNADOES...AND LARGE HAIL. IN ADDITION...VERY
HEAVY RAINFALL ASSOCIATED WITH THE THUNDERSTORMS MAY LEAD TO A FEW
INSTANCES OF FLASH FLOODING.

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

THUNDERSTORMS WILL LIKELY BE ONGOING ACROSS THE AREA ON TUESDAY
MORNING...BUT MAY HAVE A TENDENCY TO WEAKEN DURING THE LATE MORNING
INTO THE AFTERNOON. HOWEVER...FURTHER REDEVELOPMENT OF SHOWERS AND
STORMS IS POSSIBLE DURING THE DAY. THUNDERSTORMS DURING THIS PERIOD
WILL STILL HAVE THE POTENTIAL TO PRODUCE SEVERE WEATHER...ALTHOUGH
THE MAIN THREAT MAY EVOLVE INTO A FLASH FLOODING SITUATION WITH
SHOWERS AND STORMS CONTINUING TO DEVELOP OVER THE SAME LOCATIONS.

THE POTENTIAL EXISTS FOR A SIGNIFICANT SEVERE WEATHER OUTBREAK
BEGINNING EARLY WEDNESDAY MORNING AND ESPECIALLY WEDNESDAY AFTERNOON
AND EVENING AS A COLD FRONT FINALLY PUSHES ACROSS THE AREA. THE
PRIMARY THREATS WILL BE DAMAGING WINDS...LARGE HAIL...AND TORNADOES.

IN ADDITION...HEAVY RAINFALL FROM THESE THUNDERSTORMS AND PRECEDING
ACTIVITY ON TUESDAY IS EXPECTED TO CAUSE THE POTENTIAL FOR WIDESPREAD
FLASH FLOODING. PLEASE REFER TO THE FLASH FLOOD WATCH FOR FURTHER
INFORMATION ON THIS THREAT. ALSO...THE WINDS OUTSIDE OF ANY
THUNDERSTORM ACTIVITY MAY REACH WIND ADVISORY CRITERIA ON WEDNESDAY.

THERE IS ANOTHER CHANCE FOR THUNDERSTORMS LATE THIS WEEKEND.

.SPOTTER CALL TO ACTION STATEMENT...

ACTIVATION OF STORM SPOTTERS AND EMERGENCY MANAGEMENT PERSONNEL IS
REQUESTED IN THE WATCH AREA...AND IS POSSIBLE AGAIN LATER TUESDAY
MORNING ACROSS THE AREA. ACTIVATION WILL AGAIN BE LIKELY MAINLY LATE
TUESDAY NIGHT INTO WEDNESDAY.

KDW/CA