Severe Thunderstorm Warning 467, NWS Jackson, MS

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE JACKSON MS
1225 PM CDT THU JUL 30 2009

.UPDATE...
EXPANDED FFA TO INCLUDE TENSAS AND CATAHOULA PARISHES. LATEST TRENDS
IN RADAR DATA SHOWING LEAD OUTFLOW BOUNDARY GRADUALLY BECOMING NE/SW
ORIENTED AND SLOWING. THIS COMBINED WITH LATEST OUTPUT FROM 12Z NAM
AND ASSOCIATED LOCAL WRF ENSEMBLE OUTPUT...SUGGESTS THAT AN AXIS OF
HEAVIER RAIN NEXT 12-18 HOURS COULD SET UP FROM S OF KTVR TO NEAR
KGTR. AT LEAST NORTHERN PORTIONS OF CATAHOULA AND TENSAS PARISHES
HAVE RECEIVED VERY HEAVY RAINFALL LAST FEW WEEKS AND ARE PRONE TO
FLASH FLOODING FROM ANY EXCESSIVE RAINFALL NEXT 24 HOURS.  LATEST
GUIDANCE DOES SUGGEST THAT ORGANIZED CONVECTION WILL EVENTUALLY
SHIFT INTO SOUTHERN ZONES LATER THIS EVENING OR FRIDAY MORNING...BUT
WILL NEED TO REEVALUATE THIS MORE WITH AFTERNOON PACKAGE. NO CHANGES
TO FORECAST OTHER THAN THE FFA EXPANSION.                       /08/

REST OF PREVIOUS DISCUSSION...

SHORT TERM UPDATE...LATEST SATELLITE IMAGERY SHOWS SOME IMPRESSIVE
FLOW AROUND A MIDLEVEL SHORT WAVE THIS MORNING OVER THE ARKLATEX
REGION. SHV SOUNDING SHOWED SOME LOW LEVEL WINDS OF 30 TO 40 KNOTS.
THIS TROUGH WAS UNDER THE ENTRANCE REGION OF AN INTENSIFYING UPPER
JET STREAM OVER THE PLAINS. LOCAL WRF MEMBERS 8 OUT OF 10 SHOW AN
IMPRESSIVE LINE OF HEAVY STORMS MOVING INTO THE DELTA REGION LATE
THIS AFTERNOON THROUGH THIS EVENING...WHICH WILL BREAK OUT SOME
SEVERE STORMS. EXPECT SHOWERS AND THUNDERSTORMS TO DEVELOP BY EARLY
THIS AFTERNOON. STRONG STORMS WILL BE POSSIBLE IN THE NORTHWEST
DELTA REGION BY EARLY AFTERNOON. SO WILL KEEP HIGH END POPS FOR THE
NORTHWEST HALF. HEAVY RAINS WILL AGGRAVATE MOIST SOIL CONDITIONS
OVER MOST OF THE REGION. SO WILL KEEP FLASH FLOOD WATCH OVER THE
SAME AREA...WHICH HAS HAD PREVIOUS DAYS OF HEAVY RAINFALL. WITH THIS
IN MIND WILL KEEP CURRENT FORECAST ON TRACK.          /17/

HAZARD WEATHER UPDATE...
UPDATE...WITH REGARD TO HAZARDOUS WEATHER NEXT 24 HOURS...BECOMING
INCREASINGLY CONCERNED ABOUT SIGNIFICANT FLASH FLOOD POTENTIAL...
PARTICULARLY FOR THE ARKLAMISS DELTA THIS AFTERNOON...AND EVENTUALLY
EXPANDING ENE INTO THE GOLDEN TRIANGLE REGION THIS EVENING AND INTO
THE OVERNIGHT. VERY ANOMALOUS SETUP FOR JULY ACROSS REGION THIS
MORNING...WITH 30-40 KT 850 MB LLJ SHOWN BY PROFILERS/VWP ACROSS
AR/LA/E TX. THIS IS FEEDING 16-17C 850 MB DEWPOINTS AND A SWATH OF 2
INCH PW VALUES INTO THE REGION. COMBINATION OF STG LLJ AND EXTREME
MOISTURE LEADS TO MOISTURE TRANSPORT VALUES IN EXCESS OF 300 G/KG
FOCUSED INTO THE ARKLAMISS BY LATER TODAY...AND ACROSS MUCH OF NRN
MS TONIGHT. SFC ANALYSIS SHOWS A SUBTLE BOUNDARY LYING FROM THE
ARKLATEX ENE INTO NRN AL. EXPECT THIS TO BE THE FOCUS FOR HEAVY
CONVECTIVE RAINS THIS AFTERNOON INTO TONIGHT AS UPPER WAVE CURRENTLY
DRIVING MCS OVER ARKLATEX APPROACHES. WIDESPREAD RAINFALL AMOUNTS OF
1-3 INCHES LOOK LIKELY ACROSS THIS REGION BY 12Z FRI...BUT LOCALIZED
TOTALS OF 5 TO 10 INCHES LOOK POSSIBLE WHERE TRAINING OCCURS GIVEN
EFFICIENT RAINFALL AND POTENTIAL FOR BACK BUILDING GIVEN VERY WEAK
CORFIDI VECTORS WITH SOME ORIENTATION ALONG THE FLOW PARTICULARLY
TONIGHT. 06Z RUN OF LOCAL WRF ENSEMBLE SHOWS PROBABILITIES GREATER
THAN 50 PCT OF SOME 5 INCH RAINFALL TOTALS OVER THE DELTA...WITH
10-20 PCT PROBS OF SPOTS GREATER THAN 10 INCHES.

FFG VALUES ARE EXTREMELY LOW ACROSS ALL OF THE REGION N OF
I-20...AND SOME SPOTS COULD SEE SIGNIFICANT FLASH FLOODING. FARTHER
S...ORGANIZED HEAVY RAINFALL SEEMS LESS LIKELY...AND FFG VALUES ARE
MUCH HIGHER GIVEN RECENT DRY WEATHER. HOWEVER...SOME LOCALIZED
PONDING ISSUES COULD BE A CONCERN WHERE CONVECTION DEVELOPS.

WHILE FLASH FLOODING IS THE BIGGEST CONCERN...SEVERE WEATHER IS ALSO
AN ISSUE...PARTICULARLY FOR THIS AFTERNOON AND EVENING. WELL
ORGANIZED MCV MOVING THROUGH E TX AS THE PRESENT TIME AS SHOWN BY 50
KT REAR INFLOW JET AT 850 MB AS SHOWN A PALATINE TX PROFILER. AREA
SOUNDINGS SHOW SBCAPE VALUES OF 3500 TO 4500 J/KG BY AFTERNOON GIVEN
TEMPS NEAR 90F AND DEWPOINTS IN MID 70S. COMBINED WITH ENVIRONMENTAL
500 MB FLOW OF 20-35 KT..EXPECT SOME ORGANIZATION TO CONVECTION
WITH LINES AND POSSIBLY A FEW HP SUPERCELLS AS DISCUSSED BY SPC.
THIS SHOULD LEAD TO SOME WET MICROBURSTS...AND WITH SUPERCELLS A LOW
RISK FOR MARGINALLY SEVERE HAIL AND POSSIBLY A TORNADO GIVEN
MODERATE VALUES OF LOW LEVEL HELICITY AND VERY LOW LCL HEIGHTS.

HWO COVERS SETUP QUITE WELL...BUT DID TWEAK THE HAZARD GRIDS TO
INCREASE THE FLASH FLOOD AND SEVERE POTENTIAL VALUES JUST A BIT
GIVEN LATEST OBSERVATIONAL AND MODEL TRENDS.             /08/

&&

.AVIATION...
MAIN FOCUS WILL BE CONVECTIVE POTENTIAL. EXPECT GREATEST RISK FOR
PERSISTENT MVFR/IFR CONDITIONS IN PRECIP TO BE AT KGWO/KGTR THROUGH
THE NEXT 24 HOURS...WITH KGLH...KJAN AND KMEI ALSO LIKELY TO
EXPERIENCE SUCH CONDITIONS AT TIMES. KHBG LOOKS TO HAVE MORE OF A
DIURNAL CONVECTIVE RISK THIS AFTERNOON...AND WILL INDICATE
ACCORDINGLY IN TAFS. LATEST GUIDANCE DOES SUGGEST THAT ORGANIZED
CONVECTION WILL EVENTUALLY SPREAD INTO KHBG...AND HAVE SHOWN
PREDOMINANT TSRA THERE TOWARD MORNING. BEHIND THIS CONVECTIVE
SETUP...WINDS WILL SHIFT MORE TO NW AND BECOME LIGHT LATE TONIGHT AT
NORTHERN/CENTRAL ZONES...LIKELY ALONG WITH IFR/LIFR CONDITIONS GIVEN
DRY AIR ALOFT OVERSPREADING EXTREMELY MOIST LOWER LEVELS GIVEN
RECENT AND ADDITIONAL RAINFALL.

&&

.JAN WATCHES/WARNINGS/ADVISORIES...
MS...FLASH FLOOD WATCH THROUGH FRIDAY MORNING FOR MSZ018-019-025>050.

LA...FLASH FLOOD WATCH THROUGH FRIDAY MORNING FOR LAZ007>009-015-016-
     023>025.

AR...FLASH FLOOD WATCH THROUGH FRIDAY MORNING FOR ARZ074-075.

&&

08/17

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE JACKSON MS
603 AM CDT THU JUL 30 2009

ARZ074-075-LAZ007>009-015-016-023-MSZ018-019-025>050-311115-
ASHLEY-CHICOT-MOREHOUSE-WEST CARROLL-EAST CARROLL-RICHLAND-
MADISON LA-FRANKLIN LA-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-WARREN-HINDS-RANKIN-SCOTT-
603 AM CDT THU JUL 30 2009

THIS HAZARDOUS WEATHER OUTLOOK IS FOR EXTREME SOUTHEAST
ARKANSAS...NORTHEAST LOUISIANA...AND CENTRAL MISSISSIPPI.

.DAY ONE...TODAY AND TONIGHT

THUNDERSTORMS WITH VERY HEAVY RAINFALL ARE EXPECTED TODAY AND
TONIGHT AS AN UPPER LEVEL DISTURBANCE APPROACHES FROM THE WEST. DUE
TO THE VERY MOIST GROUND...FLASH FLOODING WILL BE POSSIBLE IN AREAS
AFFECTED BY THUNDERSTORMS AND A FLASH FLOOD WATCH IS IN EFFECT
THROUGH TONIGHT. PLEASE REFER TO THE FLASH FLOOD WATCH PRODUCT FOR
DETAILS.

A FEW THUNDERSTORMS COULD BE STRONG TO SEVERE WITH 40 TO 60 MPH WIND
GUSTS AND HAIL. THE SEVERE WEATHER RISK WILL BE DETERMINED BY HOW
MUCH DAYTIME HEATING CAN OCCUR AS WIDESPREAD CLOUD COVER MAY LIMIT
HEATING AND INSTABILITY. HOWEVER...UNSEASONABLY STRONG WINDS ALOFT
MAY HELP TO ORGANIZE STORMS INTO A LINE AND THIS WOULD INCREASE THE
POTENTIAL FOR LOCALIZED WIND DAMAGE. IT SHOULD ALSO BE NOTED THAT ONE
OR TWO TORNADOES WILL BE POSSIBLE IF SEVERE STORMS CAN
DEVELOP...ESPECIALLY DURING THE LATE AFTERNOON AND EARLY EVENING
HOURS.

.DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY

THE PROBABILITY OF 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 TODAY AND TONIGHT.

LAZ024>026-MSZ051>066-072>074-311115-
CATAHOULA-TENSAS-CONCORDIA-NEWTON-LAUDERDALE-CLAIBORNE-COPIAH-
SIMPSON-SMITH-JASPER-CLARKE-JEFFERSON-ADAMS-FRANKLIN MS-LINCOLN-
LAWRENCE-JEFFERSON DAVIS-COVINGTON-JONES-MARION-LAMAR-FORREST-
603 AM CDT THU JUL 30 2009

THIS HAZARDOUS WEATHER OUTLOOK IS FOR NORTHEAST LOUISIANA AND SOUTH
CENTRAL MISSISSIPPI.

.DAY ONE...TODAY AND TONIGHT

ISOLATED STRONG TO SEVERE THUNDERSTORMS COULD DEVELOP IN THE DAYTIME
HEATING...WITH THE GREATEST COVERAGE AND POTENTIAL DURING THE MID TO
LATE AFTERNOON. THE STRONGEST STORMS WOULD BE CAPABLE OF PRODUCING
WIND GUSTS OF 40 TO 60 MPH...SMALL HAIL...AND A QUICK ONE TO TWO
INCHES OF RAINFALL.

.DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY

THE PROBABILITY OF 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...IS NOT ANTICIPATED.

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

EC

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE JACKSON MS
1258 PM CDT THU JUL 30 2009

LAZ024-026-MSZ060-301845-
CATAHOULA LA-CONCORDIA LA-ADAMS MS-
1258 PM CDT THU JUL 30 2009

...STRONG THUNDERSTORMS MOVING INTO CATAHOULA AND CONCORDIA
PARISHES...

A STRONG THUNDERSTORM CAPABLE OF PRODUCING 40 TO 50 MPH WINDS WAS
LOCATED 6 MILES WEST OF ACME AT 1258 PM CDT...MOVING NORTHEAST AT 30
MPH. OTHER DEVELOPING STRONG STORMS WERE NEAR JONESVILLE AND
HARRISONBURG.

VERY HEAVY RAIN ALONG WITH FREQUENT CLOUD TO GROUND LIGHTNING ARE
ALSO POSSIBLE WITH THESE STORMS.

PEOPLE IN NORTHWESTERN ADAMS COUNTY...AND CONCORDIA AND CATAHOULA
PARISHES SHOULD MONITOR THIS STORM CLOSELY.

AEG

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