Special Weather Statement, NWS Memphis, TN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEMPHIS TN
834 PM CDT SUN SEP 2 2012

.UPDATE...

BRIEF UPDATE CONCERNING SEVERE WEATHER AND FLASH FLOODING CONCERNS.

&&

.DISCUSSION...

AS OF 830 PM...A LARGE LINE OF SHOWERS AND THUNDERSTORMS...SOME OF
WHICH WERE SEVERE AND HAVE SHOWN SOME SIGNS OF BRIEF
ROTATION...CONTINUE TO MOVE ACROSS NORTH MISSISSIPPI AND SHELBY
COUNTY TENNESSEE. THE TORNADO WATCH WAS JUST CANCELED FOR CHESTER
AND DECATUR COUNTIES. THE MAJORITY OF THE STORMS ARE MOVING ALONG
A BOUNDARY THAT STRETCHES ACROSS NORTH MISSISSIPPI AND SHELBY
COUNTY TENNESSEE. ANY POINTS BEHIND THIS BOUNDARY SHOULD BE IN THE
CLEAR WITH RESPECT TO SEVERE WEATHER. A FEW SHOWERS DEVELOPED IN
HARDEMAN...MCNAIRY AND HARDIN COUNTIES BUT THESE ARE NOT CLOSE TO
BECOME SEVERE. WILL LIKELY CANCEL THE REST OF THE TENNESSEE
PORTIONS OF THE TORNADO WATCH BEHIND THE BOUNDARY ONCE THE
THUNDERSTORMS MOVE OUT OF SHELBY COUNTY IN THE NEXT 30 MINUTES OR
SO.

FLASH FLOODING COULD BE A CONCERN FOR SOME AREAS THIS EVENING AS
MULTIPLE ROUNDS OF STORMS MOVE THROUGH. FLASH FLOOD WARNINGS ARE
CURRENTLY OUT OF SHELBY...DESOTO...MARSHALL...LEE AND ITAWAMBA
COUNTIES. WITH HEAVY RAINS MOVING TOWARD LEE AND ITAWAMBA
COUNTIES...WOULD EXPECT ANY FLASH FLOODING TO BECOME AGGRAVATED
AGAIN DUE TO HEAVY TROPICAL TYPE DOWNPOURS. THE FLOODING THREAT
SHOULD RELAX FARTHER NORTH AS THE STORMS MOVE OUT OF THE MEMPHIS
METRO AREA AND EXTREME NORTHWEST MISSISSIPPI.

&&

.PREV DISCUSSION... /ISSUED 657 PM CDT SUN SEP 2 2012/

UPDATE...
UPDATE FOR AVIATION.

PREV DISCUSSION... /ISSUED 408 PM CDT SUN SEP 2 2012/

DISCUSSION...19Z SURFACE ANALYSIS PLACES THE REMNANT LOW OF ISAAC
NEAR OLNEY ILLINOIS WITH THE UPPER LEVEL CIRCULATION CENTERED
ACROSS SOUTHERN INDIANA. WIDESPREAD CLOUD COVER THIS MORNING HAS
SINCE DISSIPATED ACROSS MUCH OF THE MID SOUTH. TEMPERATURES AS OF
3 PM CDT RANGE FROM THE 80S ACROSS WEST TENNESSEE NEAR THE
TENNESSEE RIVER AND UPPER 80S TO LOWER 90S ACROSS THE REMAINDER OF
THE MID SOUTH. STRONG TO SEVERE THUNDERSTORM POTENTIAL FOR THE
REMAINDER OF THIS AFTERNOON INTO THIS EVENING AND ALSO MONDAY
ACROSS PORTIONS OF THE MID SOUTH ARE THE MAIN FORECAST CONCERNS
IN THIS AFTERNOON/S FORECAST ISSUANCE.

SHORT TERM...(TONIGHT THROUGH WEDNESDAY)...A COUPLE OF SHORTWAVE
TROUGHS ASSOCIATED WITH THE REMNANT LOW /ISAAC/ ARE LOCATED ACROSS
SOUTHERN MISSOURI INTO KENTUCKY AND ANOTHER ONE CURRENTLY MOVING
THROUGH THE LOWER MISSISSIPPI VALLEY LATE THIS AFTERNOON.
VISIBLE SATELLITE TRENDS SHOW A DECENT CU FIELD DEVELOPING ALONG
THE I-40 CORRIDOR AND ACROSS PORTIONS OF NORTHEAST MISSISSIPPI.
KNQA/KGWX WSR-88D RADAR TRENDS OVER THE PAST HOUR HAVE SHOWN THE
DEVELOPMENT OF SCATTERED SHOWERS AND THUNDERSTORMS...PREDOMINANTLY
ACROSS NORTHEAST MISSISSIPPI.

LATEST SHORT TERM MESOSCALE TRENDS INDICATE SURFACE BASED CAPE
VALUES BETWEEN 3000-4000 J/KG...LI/S BETWEEN -6 TO -7...0-1 KM
STORM RELATIVE HELICITY VALUES AROUND 100 M2/S2 /FORECAST TO
INCREASE TO 150-200 M2/S2...AND PRECIPITABLE WATER VALUES AROUND 2
INCHES. THIS SUGGESTS ANY THUNDERSTORMS THAT REACH SEVERE LIMITS
WILL HAVE THE POTENTIAL TO PRODUCE DAMAGING WINDS AS THE PRIMARY
SEVERE WEATHER THREAT AND TORNADOES AS A SECONDARY SEVERE WEATHER
THREAT. LOCALIZED FLASH FLOODING FROM HEAVY RAINFALL WILL ALSO BE
POSSIBLE WITH THESE THUNDERSTORMS DUE TO AMPLE LOW LEVEL MOISTURE
ALREADY IN PLACE ACROSS THE LOWER MISSISSIPPI VALLEY. STILL THINK
THE BEST CHANCE FOR SEVERE THUNDERSTORMS WILL BE ACROSS NORTH
MISSISSIPPI.

SHORT TERM MODELS INDICATE THE REMNANT LOW WILL MOVE EAST
SOUTHEAST TOWARDS EAST TENNESSEE ON MONDAY. A SHORTWAVE TROUGH
ASSOCIATED WITH THE REMNANT LOW WILL MOVE ACROSS THE LOWER
MISSISSIPPI VALLEY ON MONDAY. THUS...A CHANCE FOR SHOWERS AND
THUNDERSTORMS WILL PERSIST...MAINLY COINCIDENT WITH DAYTIME
HEATING MONDAY AFTERNOON INTO MONDAY EVENING ACROSS NORTHEAST
MISSISSIPPI. A FEW OF THESE THUNDERSTORMS COULD BECOME STRONG TO
SEVERE WITH DAMAGING WINDS AS THE PREDOMINANT SEVERE WEATHER
THREAT. AN ISOLATED THUNDERSTORM THREAT MAY PERSIST INTO TUESDAY
AFTERNOON. HOWEVER...AT THIS TIME THINK MOST AREAS WILL REMAIN
RAIN FREE.

LONG TERM...(WEDNESDAY THROUGH SATURDAY)...12Z GFS LONG TERM
MODELS INDICATE CHANCES FOR SHOWERS AND THUNDERSTORMS WILL PERSIST
ACROSS THE MID SOUTH THROUGHOUT THE LONG TERM FORECAST AS A QUASI-
STATIONARY BOUNDARY DROPS INTO THE MID SOUTH TUESDAY NIGHT AND
WEDNESDAY AND A TRAILING COLD FRONT ARRIVES NEXT WEEKEND.
THUS...CONTINUED WITH SLIGHT CHANCE/CHANCE POPS THROUGH THIS
TIMEFRAME. AFTER THE COLD FRONT PASSES THROUGH THE MID SOUTH NEXT
WEEKEND...TEMPERATURES MAY FALL TO NEAR NORMAL TO SLIGHTLY NORMAL
VALUES FOR SEPTEMBER.

CJC

&&

.AVIATION...

00Z TAFS

TWO EAST/WEST CONVECTIVE LINES... ORIENTED WITH THE OUTER BANDS OF
ISAAC/S REMNANT LOW... WERE NOTED ON RADAR AND GOES IMAGERY AT 00Z.
THE NORTHERN CONVECTIVE LINE WAS JUST NORTH OF MEM AT 00Z TAF
ISSUANCE AND SHOULD PUSH A SURFACE BOUNDARY SOUTH THROUGH MEM BY
02Z...IF NOT A BIT SOONER. THIS WOULD TURN WINDS TO THE NORTH AT
MEM. THE BOUNDARY MAY PROVIDE A FOCUS FOR TSRA THROUGH 02Z.

THE SOUTHERN CONVECTIVE BAND WILL CONTINUE TO AFFECT TUP THROUGH
THE NEXT SEVERAL HOURS...WITH A FEW BREAKS. THE SOUTHERN
CONVECTIVE LINE MAY BE OVERTAKEN AND MERGE WITH THE LINE TO THE
NORTH. IT IS POSSIBLE TS MENTION FOR TUP MAY NEED TO BE PUSHED
BEYOND 04Z.

PWB

&&

.PRELIMINARY POINT TEMPS/POPS...
MEM  74  94  77  96 /  50  10  10  10
MKL  72  90  72  93 /  20  10  10  10
JBR  71  93  73  95 /  10  10  10  10
TUP  74  92  74  93 /  80  40  20  10

&&

.MEG WATCHES/WARNINGS/ADVISORIES...
AR...NONE.
MO...NONE.
MS...NONE.
TN...NONE.
&&

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