Flash Flood Warning 90, NWS Memphis, TN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEMPHIS TN
346 AM CDT THU MAY 15 2008

.DISCUSSION...

AN UPPER LEVEL SHORTWAVE TROUGH POSITIONED OVER THE SOUTHERN
PLAINS THIS MORNING WILL CONTINUE TO MOVE NORTHEAST AND
DEAMPLIFY...AS WEAK SURFACE LOW PRESSURE OVER NORTH TEXAS MOVES
INTO THE MID SOUTH LATER TODAY. NUMEROUS SHOWERS AND THUNDERSTORMS
HAVE ALREADY DEVELOPED EARLY THIS MORNING OVER THE LOWER
MISSISSIPPI VALLEY AND THIS ACTIVITY WILL CONTINUE TO DEVELOP AND
MOVE OVER OUR FORECAST AREA THROUGH THE MORNING HOURS. THIS
ACTIVITY IS PRIMARILY A RESULT OF A BROAD LOW LEVEL WARM ADVECTION
REGIME OVER THE LOWER MISSISSIPPI AND TENNESSEE VALLEY REGIONS.
THE POTENTIAL FOR HEAVY RAIN APPEARS TO BE FOCUSED FURTHER TO THE
SOUTH...SO HAVE TRIMMED BACK THE FLASH FLOOD WATCH TO EMCOMPASS
ONLY SOUTHERN COUNTIES IN THE CWA. CONFIDENCE ON WHETHER OR NOT A
HEAVY RAIN EVENT WILL OCCUR ACROSS ANY OF OUR REGION CONTINUES TO
WANE...BUT SOUTHERN AREAS HAVE THE GREATEST POTENTIAL AS A LOW
LEVEL JET MAX NOSES INTO THIS REGION AND FOCUSES LOW LEVEL LIFT.
LATER SHIFTS CAN DETERMINE IF THE THREAT STILL EXISTS AND WHETHER
TO CANCEL THE REMAINING WATCH AREA.

AS FOR THE SEVERE POTENTIAL...IT APPEARS THAT EARLY TO MID DAY
CLOUDS AND WIDESPREAD PRECIPITATION ALONG WITH MEAGER MID LEVEL
LAPSE RATES MAY LIMIT INSTABILITY AND THE ATMOSPHERES ABILITY TO
RECOVER LATER THIS AFTERNOON. MODELS DO CONTINUE TO INDICATE THAT
SOME RECOVERY OF INSTABILITY...WITH SBCAPES BETWEEN 1000-1500J/KG
AND LI/S BETWEEN -2C AND -4C...WILL OCCUR BEHIND THIS MORNINGS
ACTIVITY...ESPECIALLY ACROSS NORTHERN MISSISSIPPI IN ADVANCE OF A
WEAK COLD FRONT. AT THIS TIME...IT APPEARS THAT FORECAST MODELS
MAY BE OVERDOING THE INSTABILITY AND THE SEVERE THREAT SHOULD REMAIN
LIMITED LATER TODAY. AT THIS TIME...PLAN TO REMOVE SLIGHT RISK WORDING
FROM THE MORNING HWO. WILL CONTINUE TO MENTION THE POSSIBILITY FOR
STRONG STORMS LATER THIS AFTERNOON...JUST IN CASE STRONGER INSTABILITY
DOES DEVELOP AND BETTER RECOVERY OCCURS AHEAD OF THE SURFACE COLD
FRONT.

THE COLD FRONT WILL SWEEP SOUTHEAST ACROSS THE MID SOUTH THIS
EVENING WITH DRIER CONDITIONS MOVING IN AS SURFACE HIGH PRESSURE
BUILDS SOUTHEAST OVER THE AREA. NORTHWEST FLOW ALOFT SHOULD
DEVELOP FOR THE WEEKEND AND INTO THE FIRST PART OF NEXT WEEK AS
THE FORECAST AREA BECOMES POSITIONED ON THE SOUTHWEST EDGE OF
STRONGER MID LEVEL FLOW ALOFT. MEDIUM RANGE MODELS HINT AT A
SERIES OF UPPER LEVEL DISTURBANCES MOVING ACROSS AND IMPACTING THE
REGION DURING THIS PERIOD. LOW LEVEL MOISTURE RECOVERY AND TIMING
OF INDIVIDUAL DISTURBANCES STILL REMAINS IN QUESTION THIS
MORNING...SO WILL KEEP POPS OUT OF THE FORECAST FOR THIS TIME
PERIOD UNTIL TIMING AND POSITIONING BECOME BETTER DETERMINED.

MEDIUM RANGE MODELS DIVERGE QUITE A BIT BEYOND EARLY NEXT WEEK
WITH THE GFS MAINTAINING THE EASTERN TROUGH AND FAST NORTHWEST
FLOW ALOFT...WHILE THE LATEST ECMWF LIFTS THE EASTERN TROUGH OUT
TO THE EAST AND BUILDS AN UPPER RIDGE OVER THE REGION. WITH SUCH
LARGE MODEL SPREADS...HAVE MADE FEW CHANGES TO THE END OF THE
EXTENDED FORECAST PERIOD.

&&

.PRELIMINARY POINT TEMPS/POPS...
MEM  78  56  74  58 /  70  20  10  10
MKL  72  55  71  50 /  70  20  10  10
JBR  71  53  72  52 /  70  10  10  10
TUP  77  59  74  53 /  90  40  10  10

&&

.MEG WATCHES/WARNINGS/ADVISORIES...
AR...NONE.
MO...NONE.
MS...FLASH FLOOD WATCH THROUGH THIS EVENING FOR CALHOUN-CHICKASAW-
     COAHOMA-ITAWAMBA-LAFAYETTE-LEE MS-MONROE-PANOLA-PONTOTOC-
     QUITMAN-TALLAHATCHIE-UNION-YALOBUSHA.

TN...NONE.
&&

JLH