Tornado and Flash Flooding in Mississippi, April 20 to 21, 2011

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JACKSON MS
1050 PM CDT TUE APR 19 2011

.UPDATE...NO CHANGES MADE TO THE FORECAST. LATEST RADAR DATA SHOWS
HEALTHY CONVECTION JUST UPSTREAM OF NWRN ZONES. EVENING RAOBS AND
FORECAST SOUNDINGS INDICATE THAT CONVECTION THIS EVENING WILL BE
ELEVATED WHICH SUPPORTS PREVIOUS FORECAST THINKING THAT HAIL AND
WIND WILL BE PRIMARY CONCERNS. LATEST HIGH RES MODELS HAVE PULLED
BACK ON SPEED AND INTENSITY OF CONVECTION. BEST CHANCES FOR
STRONG...POSSIBLY SEVERE...WILL REMAIN ACROSS NRN TIERS OF FORECAST
AREA FOR THIS EVENING.

&&

.DISCUSSION...CHALLENGING FORECAST FOR TONIGHT...WED AND INTO WED
NIGHT AS UNCERTAINTY EXISTS IN HOW THE ACTIVITY TO OUR NW/N THIS
EVENING WILL EVOLVE. EVEN WITH THIS UNCERTAINTY...MODEL GUID IS
SUGGESTING THE POTENTIAL FOR SEVERE STORMS AND POSSIBLE HEAVY
RAINFALL. THIS WILL BE THE PRIMARY FOCUS OF THE FORECAST. FROM
THU/FRI AND INTO THE WEEKEND...A WARM/HUMID PATTERN WILL BE IN PLACE
WITH NO REAL SHOT AT PRECIP UNTIL SOMETIME NEXT WEEK.

CURRENTLY IT IS WARM AND WINDY/BREEZY ACROSS THE CWA. STORMS HAVE
FIRED UP ACROSS THE SOUTHERN PLAINS AND NOW THE MIDWEST. LOOK FOR
THIS ACTIVITY TO QUICKLY GROW IN COVERAGE AND BECOME MORE ORGANIZED
LATE THIS AFTERNOON AND EVENING. THE CHALLENGE IN THE FORECAST IS
JUST HOW QUICKLY THIS WILL EVOLVE AND HOW MUCH OF THE ORGANIZED LINE
CAN MAKE IT INTO THE NW/N CWA LATER TONIGHT. ALSO...IF THE CAP
REMAINS STRONG...THEN WE COULD SEE SOME REMNANT OUTFLOW BOUNDARY
SURGE SOUTH AND FOCUS THE SFC BOUNDARY ACROSS AREAS OF THE CWA
FURTHER SOUTH THAN CURRENTLY ANTICIPATED. I WILL START BY SAYING
MODEL SOLUTIONS ON THE EVOLUTION ARE A BIT ALL OVER THE PLACE. THE
GLOBAL GUID KEEPS THE SFC BOUNDARY STALLED ACROSS THE N PORTION OF
THE CWA WHILE THE HI-RES RUNS OFFER DIFFERING SOLUTIONS AS WELL.
THERE IS A SOLUTION THAT LEANS MORE TOWARD...THE OPS RUNS THAT KEEP
ACTIVITY IN THE NORTH...OTHERS ARE FASTER AND PUSH THE SFC BOUNDARY
FURTHER SOUTH. ALL IN ALL...LOW CONFIDENCE IN THE EVOLUTION OF
THINGS.

SO FOR TONIGHT...THERE WILL BE A RISK FOR DMG WINDS AND HAIL ACROSS
THE NORTH FROM ANY LINE THAT MAKES A STRONG SURGE SOUTHWARD. TIMING
IS A BEAR...IT COULD BE ANYTIME FROM NEAR MIDNIGHT TO 6-7 IN THE
MORNING.

FOR WED INTO WED NIGHT...MUCH WILL HINGE ON HOW/WHERE THE LINE IS IN
THE MORNING AND WHERE ANY OUTFLOW/SFC BOUNDARY WILL STALL FOR LATER
IN THE DAY. ONE THING ALL THE GUID SUGGESTS IS THAT THERE WILL BE
VERY STEEP LAPSE RATES AND UNSTABLE CONDITIONS AS WE WARM JUST A
BIT. WITH THAT SAID...VERTICAL TOTALS WILL BE 28-30C AND MLCAPE WILL
BE AROUND 3000 J/KG. IT IS VERY HARD NOT TO GET SEVERE STORMS WITH
THAT ENVIRONMENT IN PLACE. SOME LIMITING FACTORS WILL BE THE LACK OF
ANY S/WV FOR MID/DEEP LAYER LIFT. ALSO...MID LEVEL HEIGHTS WILL BE A
BIT ON THE HIGH SIDE. THE DRIVING FORCE FOR ANY ACTIVITY TOMORROW
WILL BE LOW LEVEL CONVERGENCE ALONG THE STALLED BOUNDARY AND THERMO
PROCESSES. THERE WILL BE DECENT FLOW ALOFT...MAINLY ABV 500 MB...SO
THE MODE APPEARS TO BE MULTI-CELL CLUSTERS. THE PRIMARY RISKS WILL
BE DMG WIND AND LARGE HAIL. MOST OF THE HAIL SHOULD BE LESS THAN
GOLF BALL...BUT WITH SUCH STEEP LAPSE RATES...ANY WELL ORGANIZED
STORM COULD POSSIBLY PRODUCE LARGER HAIL.

DEPENDING ON HOW THE STALLED BOUNDARY GETS ORIENTED...THIS ACTIVITY
COULD WAIT AND FIRE LATER IN THE DAY AND BE MORE IN THE EVENING. DUE
TO THIS...WILL GO WITH HIGHER POPS FOR WED AFTERNOON AND KEEP THE
GUID VALUES FOR THE EVENING.

THERE WILL ALSO EXIST A RISK FOR LOCALLY HEAVY RAIN. THE POTENTIAL
ORIENTATION OF THE STALLED SFC BOUNDARY COULD LEAD TO REPETITIVE
STORMS. IF THIS OCCURS...THEN QUITE A BIT OF RAIN COULD OCCUR FOR
SOME AREAS. WE HAVE THOUGHT ABOUT A FLASH FLOOD WATCH...BUT WILL
HOLD OFF AND WAIT UNTIL WE HAVE A BETTER HANDLE ON WHERE THE SFC
BOUNDARY WILL STALL. FOR NOW...THE NORTHERN AREAS SEEM TO HAVE THE
GREATEST FOR EXCESSIVE RAINFALL.

LOOK FOR WARM CONDITIONS TO EXIST INTO THE WEEKEND AND GUID VALUES
FOR TEMPS SEEMED PRETTY CLOSE. /CME/

&&

.AVIATION...THUNDERSTORMS WILL DEVELOP ALONG A COLD FRONT WELL OFF
TO THE NORTHWEST AND TRY TO PUSH INTO PORTIONS OF THE REGION
NORTH OF INTERSTATE TWENTY MAINLY LATE TONIGHT. THOSE STORMS COULD
BE CAPABLE OF HAIL...GUSTY WINDS AND SEVERE TURBULENCE. OTHERWISE
TONIGHT...EXPECT MVFR CEILINGS PUSHING UP FROM THE SOUTH WELL AFTER
MIDNIGHT. TOMORROW MVFR CONDITIONS DUE TO LOW STRATUS SHOULD END BY
10 AM OR SO WITH SCATTERED SHOWERS AND THUNDERSTORMS GRADUALLY
DEVELOPING ALONG AND NORTH OF THE INTERSTATE TWENTY CORRIDOR DURING
THE MIDDAY AND AFTERNOON HOURS. SURFACE WINDS WILL AGAIN BE FROM THE
SOUTH TO SOUTHWEST...ALTHOUGH NOT AS STRONG AND TENDING TOWARD
VARIABILITY UP NORTH ALONG THE HIGHWAY 82 CORRIDOR. /BB/

&&

.JAN WATCHES/WARNINGS/ADVISORIES...
MS...NONE.

LA...NONE.

AR...NONE.

&&

CME/BB
03

HAZARDOUS WEATHER OUTLOOK...CORRECTED
NATIONAL WEATHER SERVICE JACKSON MS
336 PM CDT TUE APR 19 2011

LAZ015-016-023>026-MSZ047>066-072>074-202045-
RICHLAND-MADISON LA-FRANKLIN LA-CATAHOULA-TENSAS-CONCORDIA-WARREN-
HINDS-RANKIN-SCOTT-NEWTON-LAUDERDALE-CLAIBORNE-COPIAH-SIMPSON-
SMITH-JASPER-CLARKE-JEFFERSON-ADAMS-FRANKLIN MS-LINCOLN-LAWRENCE-
JEFFERSON DAVIS-COVINGTON-JONES-MARION-LAMAR-FORREST-
336 PM CDT TUE APR 19 2011

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL MISSISSIPPI
AND NORTHEASTERN LOUISIANA ALONG AND SOUTH OF THE INTERSTATE TWENTY
CORRIDOR.

.DAY ONE...TONIGHT AND WEDNESDAY

THE POTENTIAL FOR A FEW STRONG TO SEVERE THUNDERSTORMS AND
TORRENTIAL DOWNPOURS WILL INCREASE WEDNESDAY AFTERNOON AND CONTINUE
INTO THE EVENING IN THE VICINITY OF A STALLED FRONTAL BOUNDARY DRAPED
ACROSS THE REGION. THE PRIMARY SEVERE WEATHER RISKS WILL BE LARGE
HAIL TO THE SIZE OF HALF DOLLARS AND DAMAGING WIND GUSTS OF UP TO 60
MPH. THE RISK OF SEVERE WEATHER SHOULD BE LEAST ALONG AND SOUTH OF
HIGHWAY 84.

.DAYS TWO THROUGH SEVEN...WEDNESDAY NIGHT THROUGH MONDAY

THE PROBABILITY FOR WIDESPREAD HAZARDOUS WEATHER IS LOW.

.SPOTTER CALL TO ACTION STATEMENT...
THE ACTIVATION OF STORM SPOTTERS...HAM RADIO OPERATORS...AND
EMERGENCY MANAGEMENT PERSONNEL IN SUPPORT OF SEVERE WEATHER
OPERATIONS...MAY BE NEEDED ON WEDNESDAY.

ARZ074-075-LAZ007>009-MSZ018-019-025>046-202045-
ASHLEY-CHICOT-MOREHOUSE-WEST CARROLL-EAST CARROLL-BOLIVAR-
SUNFLOWER-LEFLORE-GRENADA-CARROLL-MONTGOMERY-WEBSTER-CLAY-LOWNDES-
CHOCTAW-OKTIBBEHA-WASHINGTON-HUMPHREYS-HOLMES-ATTALA-WINSTON-
NOXUBEE-ISSAQUENA-SHARKEY-YAZOO-MADISON MS-LEAKE-NESHOBA-KEMPER-
336 PM CDT TUE APR 19 2011

THIS HAZARDOUS WEATHER OUTLOOK IS FOR EXTREME SOUTHEASTERN ARKANSAS
AND PORTIONS OF NORTHEASTERN LOUISIANA AND CENTRAL MISSISSIPPI NORTH
OF INTERSTATE TWENTY.

.DAY ONE...TONIGHT AND WEDNESDAY

STRONG TO SEVERE THUNDERSTORMS ARE POSSIBLE LATE TONIGHT...MAINLY
FROM MIDNIGHT THROUGH DAYBREAK ALONG AND NORTH OF THE HIGHWAY 82
CORRIDOR...AS A COLD FRONT APPROACHES FROM THE PLAINS. THE MAIN
RISKS WITH THIS ACTIVITY WILL BE LARGE HAIL TO THE SIZE OF HALF
DOLLARS AND WIND GUSTS IN EXCESS OF 60 MPH...ALTHOUGH AN ISOLATED
TORNADO CANNOT BE RULED OUT NORTHWEST OF A GRENADA MISSISSIPPI TO
BASTROP LOUISIANA LINE. IN ADDITION...TORRENTIAL DOWNPOURS IN SOME
AFFECTED AREAS COULD RESULT IN PONDING OF WATER ISSUES BEFORE
DAYBREAK.

THE PREVIOUSLY MENTIONED COLD FRONT MOVING INTO THE REGION AND
STALLING EARLY WEDNESDAY WILL SET THE STAGE FOR A RISK OF SCATTERED
STRONG TO SEVERE THUNDERSTORMS IN ALL AREAS ALONG AND NORTH OF
INTERSTATE TWENTY TOMORROW INTO WEDNESDAY EVENING. THE MAIN RISK
WILL ONCE AGAIN BE HAIL TO THE SIZE OF HALF DOLLARS AND WIND GUSTS IN
EXCESS OF 60 MPH. HOWEVER...AN INCREASING CONCERN WILL BE THE
CONTINUED RISK OF TORRENTIAL DOWNPOURS...ESPECIALLY ALONG AND NORTH
OF THE HIGHWAY 82 CORRIDOR IN MISSISSIPPI WHERE FLASH FLOODING WILL
BE POSSIBLE IN AT LEAST ISOLATED LOCATIONS. IN THESE LATTER AREAS
TOTAL RAINFALL AMOUNTS BY EARLY THURSDAY MAY REACH OR EXCEED 2 TO 3
INCHES.

.DAYS TWO THROUGH SEVEN...WEDNESDAY NIGHT THROUGH MONDAY

THE PROBABILITY FOR WIDESPREAD HAZARDOUS WEATHER IS LOW.

.SPOTTER CALL TO ACTION STATEMENT...
THE ACTIVATION OF STORM SPOTTERS...HAM RADIO OPERATORS...AND
EMERGENCY MANAGEMENT PERSONNEL IN SUPPORT OF SEVERE WEATHER
OPERATIONS...MAY BE NEEDED LATE TONIGHT AND WEDNESDAY.

FOR MORE INFORMATION PLEASE VISIT OUR WEBSITE AT
WWW.SRH.NOAA.GOV/JAN. THIS INCLUDES THE GRAPHICAL HAZARDOUS
WEATHER OUTLOOK.

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