Severe Thunderstorm Warning 397, NWS Jackson, MS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JACKSON MS
1000 AM CDT WED AUG 4 2010

.UPDATE...

LOW TEMPERATURES THIS MORNING WERE INCREDIBLY WARM...PARTICULARLY IN
THE "DELTA" REGION WHERE SOME LOCATIONS DID NOT GET BELOW 84 DEG F.
HEAT INDICES AT GLH/MLU WERE ALREADY 105 AS OF 9 AM. THE CURRENT
FORECAST FOR TODAY IS IN GOOD SHAPE REGARDING TEMPERATURES/HEAT INDICES
AND IN SHOWING THE HOTTEST READINGS OVER NW HALF...BUT WOULD NOT BE
SURPRISED TO SEE IT GET A LITTLE HOTTER BASED ON THE VERY WARM START.

APPARENT RESIDUAL CONVECTIVE BOUNDARIES FROM YESTERDAY HAVE
INITIATED A CLUSTER OF SHOWER/TSTMS OVER SW MS THIS MORNING...BUT
EXPECT THIS WILL MIX OUT LATER THIS MORNING AS IT MIGRATES WWD INTO
ERN LA. MORNING AREA SOUNDINGS INDICATE THE POTENTIAL TO APPROACH
5000 J/KG SFC CAPE AND 1500 J/KG DCAPE WITH STEEP LOW TO MID LEVEL
LAPSE RATES. EXPECT THAT A REPEAT OF YESTERDAY'S CONVECTIVE ACTIVITY
WILL OCCUR WITH GREATEST COVERAGE SOUTHEAST HALF. THE IMPRESSIVE
COMBINATION OF CAPE AND DCAPE SHOULD YIELD MORE ISOLATED DAMAGING
MICROBURTS THIS AFTN/EARLY EVNG. /EC/

&&

.PREV DISCUSSION... /ISSUED 355 AM CDT WED AUG 4 2010/

...DANGEROUS HEAT WAVE WILL CONTINUE ACROSS THE REGION...

SHORT TERM...THE VERY HOT CONDITIONS AND RIDICULOUS HEAT INDICES
WILL CONTINUE TO BE THE MAIN WEATHER STORY AND FOCUS OF THE
FORECAST. HOWEVER...STEADILY INCREASING CONVECTIVE POTENTIAL EACH
DAY HAS BEEN RESULTING IN STRONG/SVR STORMS AND NOW HAS BECOME
ANOTHER PRIMARY CONCERN IN THE FORECAST.

THE LINGERING STOUT UPPER RIDGE REMAINS A MAJOR PLAYER IN OUR
FORECAST...BUT THIS FEATURE HAS PEAKED AND WILL BEGIN TO CENTER
ITSELF TO OUR W TODAY. EVEN AS THIS OCCURS...LOW LEVEL TEMPS WILL
REMAIN EXTREME AND SUPPORTIVE OF MORE TRIPLE DIGITS. THE HOTTEST
READINGS WILL AGAIN OCCUR ALONG AND N/NW OF I-20 WITH READINGS
PEAKING BETWEEN 101-105 DEGREES. SFC DEWPTS WILL AGAIN REMAIN HIGH
AS LOW LEVEL MOISTURE HOLDS AT OPPRESSIVE LEVELS. THE RESULTING HEAT
INDICES (HI'S) WILL PEAK FROM 110-118 LIKE PREV DAYS. AS A
RESULT...HAVE EXPANDED THE EXCESSIVE HEAT WARNING FOR ALL AREAS
TODAY.

BY THU...FORECAST MODELS CONTINUE TO SHOW THAT LOW LEVEL TEMPS WILL
REMAIN HIGH...BUT JUST A TAD LOWER THAN WHAT HAS BEEN SEEN. DUE TO
THIS...ALONG WITH THE PRESENCE OF MORE CLOUDS/PRECIP...HIGH TEMPS
LOOK TO BE A TAD LOWER THAN WHAT HAS BEEN EXPERIENCED. MOS GUID
SEEMED GOOD AND HIGHS RANGED FROM 97-102. LOW LEVEL MOISTURE WILL
AGAIN REMAIN HIGH AND RESULTING HI'S WILL PEAK BETWEEN 106 AND 113
DEGREES. HOWEVER...LOCATIONS S OF I-20 SEEM TO REMAIN IN THE 105-110
HI RANGE...WHILE THE REST OF THE AREA HITS THE 109-113 RANGE. DUE TO
THIS...WILL KEEP THE HEAT ADV GOING FOR THE S PORTION AND EXTEND THE
EXCESSIVE HEAT WARN FOR AREAS ALONG AND N OF I-20 FOR THU.

AS FOR POPS/WX/STORM POTENTIAL...I DROPPED THE BALL YESTERDAY AND
DID NOT EXPRESS THE SVR RISK PROPERLY. STORMS WERE MORE VIGOROUS ON
TUE AND I SEE NO REASON IT WILL BE ANY DIFFERENT TODAY AND POSSIBLE
THU. WE ACTUALLY WILL HAVE SOME LIFTING FEATURE MOVING INTO THE S
HALF OF THE CWA TODAY. THIS FEATURE IS NOTED ON WV AND IS TRACKING
ACROSS AL/GA. THE KEY TO THESE STORMS BEING GOOD WIND PRODUCERS IS
THE FACT THAT THEY ARE OCCURRING IN +100 DEGREE HEAT.
ADDITIONALLY...MOISTURE IN THE 850-700MB LAYER HAS BEEN HIGH AND
ALLOWING FOR STRONGER UPDRAFTS AS THE STORMS INTERACT WITH EVOLVING
SFC BOUNDARIES. WITH CLOUD BASES 7-8 KFT...THERE CONTINUES TO EXIST
A LOT OF AREA UNDER CLOUD BASE FOR EVAP COOLING. ALSO...DCAPE VALUES
OFF OBSERVED SOUNDINGS HAVE BEEN 1100-1800 J/KG! DUE TO THIS...WILL
INCLUDE THE SVR WIND RISK IN THE FORECAST. MAIN TIMEFRAME FOR
STRONG/SVR STORMS (2-8PM)...AND FOR AREAS MAINLY ALONG AND S OF A
DEKALB TO JACKSON TO ST. JOE LINE. STORMS SHOULD PROPAGATE TO THE
SW/S. GUID POPS WERE NOT TOO BAD...BUT I DID INCREASE ALL AREAS
TODAY. OVERALL...POP VALUES ARE NOT REAL HIGH...10% IN THE N...20%
CENTRAL AND 40% ACROSS THE SOUTH. I DID MAKE MORE ADJ FOR TONIGHT AS
GUID WAS OFFERING 30-40% FOR ALL AREAS. THAT DOES NOT SEEM TO FIT
THE EVOLUTION OF THINGS LATELY. HOWEVER...THERE WILL STILL BE
ACTIVITY UNTIL 02Z...SO I CARRIED MOSTLY 20%. ON THU...GUID
CONTINUED THE TREND OF HAVING BETTER CHANCES ACROSS THE BOARD AND
THAT SEEMED REASONABLE. I STAYED WITH THE DIURNAL TIMING OF
THINGS...BUT LEFT SOME OVERNIGHT CHANCES GOING THU NIGHT ACROSS THE
NORTH. THERE DOES EXIST SOME CHANCE FOR A NOCTURNAL STORM CLUSTER TO
GET GOING AND MOVE OUT OF AR/NORTHERN MS. NOT SURE THAT WILL
EVOLVE...BUT SOME LOW END CHANCE EXISTS FOR THAT TO OCCUR. /CME/

LONG TERM...FRIDAY THROUGH TUESDAY...THE GOOD NEWS IS THAT WE
SHOULD SEE INCREASED RAIN CHANCES AND TEMPERATURES NOT IN THE 100S.
THE BAD NEWS IS THAT TEMPERATURES WILL NOT DROP THAT MUCH IN THE
LONG TERM AND WARM AND MUGGY CONDITIONS CONTINUE.

MODELS CONTINUE TO BE IN GOOD AGREEMENT OF LOW PRESSURE DEVELOPING
EARLIER IN THE WEEK OVER CANADA AND DIGGING A TROUGH OVER THE
EASTERN HALF OF THE COUNTRY. WHILE THIS OCCURS THE UPPER RIDGE
CONTINUES TO BREAK DOWN SOME AND RETROGRADE TO THE WEST. AS THE LOW
MOVES EAST ACROSS CANADA....THIS SHOULD SEND A FRONT TOWARD THE REGION FOR
FRIDAY. THERE CONTINUES TO BE SOME DISAGREEMENT WITH HOW FAR INTO
THE CWA THIS BOUNDARY MAKES IT. IT LOOKS LIKE BOTH THE GFS AND ECMWF
BRING IT TO AT LEAST THE CENTRAL PORTION OF THE CWA BEFORE STALLING
IT. WITH PLENTY OF MOISTURE POOLING AHEAD OF THIS BOUNDARY...THIS
SHOULD HELP FOCUS A HIGHER CHANCE FOR SCATTERED SHOWERS AND
THUNDERSTORMS FRIDAY INTO THE WEEKEND FOR MOST OF THE CWA AND
ESPECIALLY AREAS ALONG AND SOUTH OF THE BOUNDARY. STRONG TO SOME
SEVERE STORMS MAY BE POSSIBLE FRIDAY AS LAPSE RATES DONT LOOK TOO
BAD AND AROUND 26-27VT ALONG WITH COOLER 500MB TEMPS OF -5 TO -6C.
WITH ABUNDANT MOISTURE IN PLACE...PW VALUES FORECAST TO BE STILL IN
EXCESS OF 2 INCHES...AND LIGHT FLOW...HEAVY RAINFALL/PONDING COULD BECOME
AN ISSUE. THIS WILL CONTINUE TO BE MONITORED IN THE COMING DAYS.

IN ADDITION TO SOME INCREASED RAIN CHANCES...THE STALLED
BOUNDARY...AND ADDITIONAL CLOUD COVER WILL ALSO LEAD TO SLIGHTLY
COOLER TEMPS...BUT STILL GENERALLY IN THE MID TO UPPER 90S. ON
FRIDAY THE HIGHEST TEMPERATURES SHOULD REMAIN GENERALLY NORTH OF
I-20 WHERE THE THERMAL RIDGE WILL LINGER JUST LONG ENOUGH TO MOST
LIKELY BRING SOME UPPER 90S....BUT LIKELY REMAIN SHY OF 100. THE
FURTHER SOUTH YOU GO...THE LOW LEVEL TEMPS ARE COOLER AND WE SHOULD
SEE SFC TEMPS IN THE MID 90S. WHILE TEMPS WILL BE COOLER THAN WE
HAVE BEEN SEEING...DEWPOINTS WILL STILL REMAIN HIGH AND THUS
ALLOWING HEAT INDICES TO REMAIN ELEVATED. LOCATIONS ACROSS AT LEAST
THE NW DELTA...IF NOT THE HIGHWAY 82 CORRIDOR...COULD SEE HEAT
ADVISORY CRITERIA AT THE VERY LEAST(BUT MAY STILL BE ENOUGH FOR HEAT
WARNING). SATURDAY WILL ALSO BE SIMILAR WITH SLIGHTLY COOLER TEMPS
EVERYWHERE BUT STILL INTO THE MID 90S BEFORE AFTERNOON CONVECTION
SHOULD BEGIN AND INCREASED CLOUDS LIMIT INSOLATION. WITH THE COOLER
TEMPS...HEAT INDICES WILL STILL REMAIN UNCOMFORTABLE BUT HEAT
WARNING CRITERIA NOT LIKELY TO BE MET.

BY SUNDAY...THE BRIEF RELIEF FROM THE HEAT WILL BE SHORT LIVED AS
500MB HEIGHTS START TO RISE AGAIN GIVEN THE UPPER TROUGH MOVING OUT OVER
THE EAST COAST/ATLANTIC WATERS AND THE UPPER RIDGE THAT HAD
RETROGRADED WEST...MOVES BACK TO THE EAST. MODELS ARE IN GOOD
AGREEMENT THAT THE UPPER RIDGE WILL TAKE HOLD OF THE REGION ONCE
AGAIN THROUGH ABOUT TUESDAY OR MAYBE WEDNESDAY. 500MB HEIGHTS DO NOT
REACH AS HIGH AS THEY ARE IN THIS CURRENT HOT SPELL SO THAT SHOULD
HOLD TEMPS BELOW THE 100 DEGREE MARK BUT READINGS SHOULD STILL BE
ABLE TO ACHIEVE THE UPPER 90S. SOME LOCATIONS MAY FALL SHORT
DEPENDING ON HOW MUCH SOIL MOISTURE WE CAN SCROUNGE THIS WEEKEND.
HOWEVER THE BUILDING RIDGE SHOULD LIMIT RAIN CHANCES AND RIGHT NOW
ONLY THE SOUTH MIGHT SEE SOME RAIN.

ANOTHER INTERESTING FEATURE THAT BOTH THE GFS AND ECMWF DEPICT IS AN
UPPER LOW/INVERTED TROUGH GENERALLY OVER FLORIDA COME TUESDAY. THEY
DEPICT THIS FEATURE MOVING WESTWARD ACROSS THE CENTRAL GULF. THIS
MAY ALSO BE ENOUGH TO BREAK THE RIDGE AND NOT ALLOW FOR TEMPERATURES
TO GET REALLY HIGH AND ALSO INCREASE RAIN CHANCES FOR THE END OF THE
LONG TERM PERIOD AND BEYOND. WILL BE SOMETHING TO WATCH FOR ANY
POTENTIAL DEVELOPMENT IN COMING MODEL RUNS. /28/

&&

.AVIATION...

HOT WEATHER FLYING CONDS WL PERSIST FOR THE NEXT FEW DAYS AS STRONG
HI PRES REMAINS OVR THE REGION. SFC WINDS WL REMAIN LGT THIS
MORNING...BCMG OCSNLY GUSTY THIS AFTN AS SHWRS/TS DEVELOP. SHWRS/TS
SHOULD BE MOST ACTIVE ACROSS SRN/SERN AREAS...AND STRONG SFC
WINDS/WND SHEAR CAN BE XPCTD INVOF THIS ACTIVITY. 5-6SM BR PSBL
ACROSS SRN AREAS TOMORROW MORNING. /BK/

&&

.CLIMATE...THE AREA REMAINS IN THE MIDDLE OF A HEAT WAVE AND VERY
HOT CONDITIONS WILL CONTINUE ACROSS THE REGION FOR A FEW MORE DAYS.
MORE RECORD HIGH WERE BROKEN ON TUESDAY WITH ADDITIONAL RECORDS
POSSIBLY FALLING BETWEEN TODAY AND THURSDAY. BELOW IS A TABLE THAT
LISTS THE NEW RECORDS FROM PREV DAYS ALONG WITH RECORDS HIGHS AND
FORECAST VALUES THROUGH THURSDAY...AUG 5TH.

DATE: 8/1 SUNDAY    ** NEW RECORDS **
   SITE      MAX TEMP    OLD RECORD
   GLH       104         103 (1980)
   GWO       101          99 (1986)
   TVR       102         102 (1986)

DATE: 8/2 MONDAY    ** NEW RECORDS **
   SITE      MAX TEMP    OLD RECORD
   GLH       104         103 (2008)
   GWO       103          98 (2008)
   HBG       103          98 (1998)
   JAN       105         102 (1947)
   MEI       102         102 (1999)
   TVR       103         100 (1952)

DATE: 8/3 TUESDAY   ** NEW RECORDS **
   SITE      MAX TEMP    OLD RECORD
   GLH       105         103 (1930)
   GWO       102         100 (1987)
   HBG       100          99 (1999)
   JAN       103         103 (1952)
   MEI       102         100 (1954)
   TVR       104          99 (1954)

DATE: 8/4 WEDNESDAY
   SITE        RECORD      FORECAST
   GLH       103 (1924)       104
   GWO       102 (1964)       104
   HBG       101 (1951)        99
   JAN       102 (1897)       103
   MEI       101 (1981)       101
   TVR        98 (2006)       103

DATE: 8/5 THURSDAY
   SITE        RECORD      FORECAST
   GLH       103 (1924)       102
   GWO       100 (2006)       102
   HBG        99 (1951)        99
   JAN       102 (1902)       100
   MEI       102 (1951)       100
   TVR       101 (1964)       101

&&

.PRELIMINARY POINT TEMPS/POPS...
JACKSON      103  77 100  77 /  21  19  25  18
MERIDIAN     101  75 100  74 /  22  19  25  18
VICKSBURG    103  77 101  76 /  13  18  24  18
HATTIESBURG   99  76  99  77 /  39  27  45  18
NATCHEZ       99  77  97  76 /  24  25  42  18
GREENVILLE   104  78 102  77 /  10  16  17  29
GREENWOOD    104  77 102  75 /  10  17  18  30

&&

.JAN WATCHES/WARNINGS/ADVISORIES...
MS...EXCESSIVE HEAT WARNING UNTIL 7 PM CDT THURSDAY FOR MSZ018-019-
     025>052.

     EXCESSIVE HEAT WARNING UNTIL 7 PM CDT THIS EVENING FOR
     MSZ053>066-072>074.

     HEAT ADVISORY FROM 7 PM THIS EVENING TO 7 PM CDT THURSDAY FOR
     MSZ053>066-072>074.

LA...EXCESSIVE HEAT WARNING UNTIL 7 PM CDT THURSDAY FOR LAZ007>009-
     015-016-023.

     EXCESSIVE HEAT WARNING UNTIL 7 PM CDT THIS EVENING FOR
     LAZ024>026.

     HEAT ADVISORY FROM 7 PM THIS EVENING TO 7 PM CDT THURSDAY FOR
     LAZ024>026.

AR...EXCESSIVE HEAT WARNING UNTIL 7 PM CDT THURSDAY FOR ARZ074-075.

&&

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