Flash Flood Warning 15, NWS Huntsville, AL

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HUNTSVILLE AL
402 PM CDT FRI MAY 1 2009

.SYNOPSIS...
CONVECTIVE COMPLEX OF STRONG TO SEVERE THUNDERSTORMS CONTINUES TO
TO PUSH EAST ACROSS SOUTHERN MIDDLE TENNESSEE THIS AFTERNOON.
STRONG TO SEVERE STORMS HAVE ALSO DEVELOPED SOUTHWEST OF THIS
COMPLEX IN THE MORE UNSTABLE AIR OVER NORTHWESTERN ALABAMA IN
LAUDERDALE COUNTY. LARGE HAIL AND WINDS OVER 60 MPH WILL BE
POSSIBLE WITH ANY SEVERE STORMS. VERY HEAVY RAINFALL IS POSSIBLE
WITH THESE STORMS AS WELL.

.SHORT TERM...TONIGHT THROUGH MONDAY NIGHT...

FORECAST AREA WILL REMAIN VERY HUMID AND WARM THROUGHOUT THE
SHORT TERM...WITH DEWPOINTS IN THE MID TO UPPER 60S IN MOST
LOCATIONS. IMMEDIATE QUESTION IS WHEN WILL THE CURRENT CONVECTIVE
COMPLEX WEAKEN OR MOVE OUT OF THE AREA. RUC IS THE ONLY MODEL THAT
HAS REALLY PICKED UP ON THIS FEATURE WELL. DESPITE MODERATELY
UNSTABLE CONDITIONS WEST OF INTERSTATE 65 IN NORTHERN ALABAMA...NOT
SURE HOW FAR SOUTHWARD THIS CONVECTION WILL GET BEFORE WE LOSE THE
DAYTIME HEATING AND CONVECTION DIMINISHES. RUC WEAKENS THINGS
QUICKLY AFTER 00Z AND AND BY MIDNIGHT...HINTS THAT PRECIPITATION
MAY BE OVER. HOWEVER WILL KEEP HIGH CHANCE NORTH OF TENNESSEE
RIVER THROUGH 7 AM ON SATURDAY. STORMS SHOULD WEAKEN AS THEY PUSH
INTO NORTHEASTERN ALABAMA AND SOUTHERN MIDDLE TENNESSEE. FEEL THE
MAJORITY OF SEVERE WEATHER WILL REMAIN IN MORE UNSTABLE AIR WEST
OF INTERSTATE 65 THROUGH 7 AM. HOWEVER...A FEW SEVERE STORMS CANNOT
BE RULED OUT IN NORTHEASTERN ALABAMA OR SOUTHERN MIDDLE TENNESSEE.
POPS HAVE BEEN RAISED THIS EVENING TO ACCOUNT FOR CURRENT
CONVECTIVE ACTIVITY.

MODELS DEPICT ANOTHER SHORTWAVE PUSHING THOUGH THE FORECAST AREA
FROM WEST TO EAST DURING THE AFTERNOON HOURS ON SATURDAY. AT THIS
POINT...COULD BE UNDER ANOTHER SVR WATCH SATURDAY AFTERNOON...
HOWEVER BELIEVE MAJORITY OF STORMS WILL BE STRONG RATHER THAN
SEVERE WITH HEAVY RAINFALL...FREQUENT LIGHTNING...AND DAMAGING
WINDS POSSIBLE. THIS ACTIVITY SHOULD DIMINISH SATURDAY NIGHT.
AGAIN MODELS DIFFER ON EXACT LOCATIONS OF HEAVIER RAINFALL...
THEREFORE WILL KEEP HIGH CHANCE POPS EVERYWHERE EXCEPT IN SOUTHERN
MIDDLE TENNESSEE (WHERE POPS ARE LIKELY). HEAVY
RAINFALL...ESPECIALLY LAWRENCE COUNTY EASTWARD...WILL NEED TO BE
MONITORED CLOSELY FOR FLASH FLOODING THIS AFTERNOON AND
EVENING...SINCE BETWEEN 2 TO 3 INCHES OF RAINFALL ALREADY FELL IN
THOSE LOCATIONS EARLIER TODAY.

MODELS DRY THINGS OUT SUNDAY MORNING...BUT UNTIL THEN CANNOT RULE
OUT ADDITIONAL MESOSCALE WAVES PUSHING ACROSS THE STALLED FRONT AND
PRODUCING ADDITIONAL CONVECTIVE COMPLEXES OVER THE AREA. KEPT HIGH
CHANCE POPS THROUGH SUNDAY TO REFLECT THIS.

BY SUNDAY NIGHT...A STRONGER TROUGH AXIS BEGINS PUSHING EASTWARD
FROM WESTERN ARKANSAS TOWARD THE FORECAST AREA. THIS SHOULD
FINALLY KICK THE STALLED FRONTAL BOUNDARY TO THE EAST. THIS SHOULD
PRODUCE A BRIEF BREAK FROM SHOWER AND THUNDERSTORM ACTIVITY
SUNDAY EVENING...BEFORE ADDITIONAL DEVELOPMENT OCCURS AHEAD OF
THE FRONT AS IT APPROACHES NORTHWESTERN ALABAMA SUNDAY AFTER MIDNIGHT.

THIS WILL INCREASE LOW LEVEL SHEAR SUNDAY NIGHT INTO MONDAY.
SINCE THE ATMOSPHERE WILL REMAIN MODERATELY UNSTABLE...STRONG TO
SEVERE STORMS WILL BE POSSIBLE PARTICULARLY DURING THE DAY ON
MONDAY. LARGE HAIL...DAMAGING WINDS...AND ISOLATED TORNADOES COULD
DEVELOP WITH THIS FINAL ROUND OF STORMS. THE FRONT SHOULD PUSH
SOUTHEAST INTO CENTRAL ALABAMA BY MONDAY NIGHT. HOWEVER...LONGER
RANGE MODELS DIFFER...WITH THE ECMWF STALLING IT JUST SOUTH OR ON
TOP OF THE FORECAST AREA. GFS40 PUSHES IT MUCH FURTHER SOUTH. AT
THIS TIME HAVE KEPT CLOSE TO PREVIOUS THINKING IN THIS TIME
FRAME...SINCE CONFIDENCE IS LOW. KEPT DEWPOINTS ON THE HIGH SIDE
WITH AN EXPECTED SLOWER MOVEMENT OF THE FRONT.

.LONG TERM...TUESDAY THROUGH FRIDAY NIGHT.

REMAINDER OF THE EXTENDED MODELS ARE IN GOOD AGREEMENT PUSHING
ANOTHER STRONGER TROUGH AXIS EAST OF THE ROCKIES. MODELS DIFFER ON
PROGRESSION OF THIS FEATURE...WHICH WILL IMPACT THE AREA WITH
HIGHER RAIN CHANCES OCCUR IN THE EXTENDED. AT THIS POINT DUE TO
MODEL DIVERGENCE IN TIMING...HAVE JUST KEPT LOW CHANCE POP
WEDNESDAY THROUGH WEDNESDAY NIGHT...AS BOTH MODELS INDICATE WAVES
PUSHING THROUGH SOUTHWEST FLOW ACROSS AHEAD OF THIS FEATURE (WITH
LITTLE PRECIPITATION). BOTH MODELS AGREE THAT THE MAIN FORCING WILL
PUSH INTO THE AREA WITH THE TROUGH AXIS ON THURSDAY. AT THIS
POINT HAVE INCREASED POPS TO 40 PERCENT TO ACCOUNT FOR THIS.
THURSDAY NIGHT THROUGH FRIDAY MODELS STALL SURFACE FRONT
ASSOCIATED WITH THIS TROUGH AXIS OVER NORTHERN GA. HAVE KEPT SMALL
CHANCE OF SHOWERS AND THUNDERSTORMS DURING THIS TIME.

&&

.PRELIMINARY POINT TEMPS/POPS...
HUNTSVILLE    65  82  66  80  65 /  60  50  50  50  40
SHOALS        66  81  66  80  66 /  70  50  60  50  50
CULLMAN       64  82  65  78  65 /  50  40  40  40  30
FAYETTEVILLE  64  78  66  78  64 /  70  60  60  60  40
ALBERTVILLE   64  82  65  80  65 /  40  50  40  40  30
FORT PAYNE    63  79  66  79  64 /  40  50  40  40  30

&&

.HUN WATCHES/WARNINGS/ADVISORIES...
AL...NONE.
TN...NONE.
&&

20

HAZARDOUS WEATHER OUTLOOK...CORRECTED
NATIONAL WEATHER SERVICE HUNTSVILLE AL
244 PM CDT FRI MAY 1 2009

ALZ001>010-016-TNZ076-096-097-021000-
LAUDERDALE-COLBERT-FRANKLIN AL-LAWRENCE-LIMESTONE-MADISON-MORGAN-
MARSHALL-JACKSON-DEKALB-CULLMAN-MOORE-LINCOLN-FRANKLIN TN-
244 PM CDT FRI MAY 1 2009

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

.DAY ONE...THIS AFTERNOON AND TONIGHT...

A CLUSTER OF STRONG TO SEVERE THUNDERSTORMS WILL MOVE ACROSS THE
TENNESSEE VALLEY AREA THROUGH THE EVENING HOURS. THE STRONGER
THUNDERSTORMS WILL BE CAPABLE OF PRODUCING DAMAGING WIND GUSTS TO 60
MPH AND LARGE HAIL. LOCALLY HEAVY RAIN AND GUSTY OUTFLOW WINDS ARE
ALSO POSSIBLE WITH THE STRONGER THUNDERSTORMS. THE THUNDERSTORM
THREAT IS EXPECTED TO DIMINISH DURING THE OVERNIGHT HOURS.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY...

SCATTERED THUNDERSTORMS ARE POSSIBLE THROUGH THE PERIOD...WITH THE
BETTER CHANCES LOCATED OVER SOUTHERN TENNESSEE. SOME STORMS MAY BE
STRONG IN NATURE WITH THE POTENTIAL FOR GUSTY WINDS...SMALL HAIL AND
LOCALLY HEAVY RAINFALL. IN ADDITION...A FEW THUNDERSTORMS MAY
APPROACH SEVERE THRESHOLDS EARLY NEXT WEEK AS AN EASTWARD MOVING
COLD FRONT INTERACTS WITH PASSING UPPER LEVEL DISTURBANCES. THE
PRIMARY THREAT WITH ANY SEVERE STORMS THAT DEVELOP LOOKS TO BE
DAMAGING WIND GUSTS.

.SPOTTER CALL TO ACTION STATEMENT...

ACTIVATION OF STORM SPOTTERS AND EMERGENCY MANAGEMENT PERSONNEL IS
REQUESTED THIS AFTERNOON AND EVENING.

AK/CA/DL

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE HUNTSVILLE AL
407 PM CDT FRI MAY 01 2009

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

0406 PM     HAIL             GREEN HILL              34.97N 87.51W
05/01/2009  E0.88 INCH       LAUDERDALE         AL   TRAINED SPOTTER

&&

AMP

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE HUNTSVILLE AL
413 PM CDT FRI MAY 01 2009

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

0411 PM     HAIL             GREEN HILL              34.97N 87.51W
05/01/2009  E1.00 INCH       LAUDERDALE         AL   TRAINED SPOTTER

&&

AMP

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE HUNTSVILLE AL
507 PM CDT FRI MAY 01 2009

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

0359 PM     TSTM WND DMG     GREEN HILL              34.97N 87.51W
05/01/2009                   LAUDERDALE         AL   EMERGENCY MNGR

            TREES KNOCKED DOWN ALONG COUNTY ROAD 364 NEAR GREEN HILL.

&&

AMP

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