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Area Forecast Discussion

000
FXUS64 KMEG 150223
AFDMEG

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEMPHIS TN
923 PM CDT THU MAY 14 2009

.DISCUSSION...

A MOIST AND UNSTABLE AIRMASS IN PLACE ACROSS MUCH OF THE MID
SOUTH...ESPECIALLY ACROSS NORTH MISSISSIPPI WHERE SBCAPES RANGE
FROM 1500 TO 2500 J/KG AND LIFTED INDEX VALUES ARE -3C TO -7C.
AFTERNOON HEATING PRODUCED A FEW THUNDERSTORMS LATE IN THE DAY AND
THEIR OUTFLOW BOUNDARIES CONTINUE TO RESULT IN NEW DEVELOPMENT
ACROSS MAINLY NORTH MISSISSIPPI. COVERAGE HAS ACTUALLY INCREASED
SLIGHTLY OVER THE PAST HOUR SO WILL GO AHEAD AND ADD SMALL POPS
IN FOR THE REST OF TONIGHT FROM I-40 SOUTH SINCE THE RUC AND NAM
BOTH HOLD ON TO THIS ISOLATED CONVECTION UNTIL AFTER MIDNIGHT.
REMAINDER OF FORECAST LOOKS GOOD. UPDATE OUT SHORTLY.

SJM

&&

.PREV DISCUSSION... /ISSUED 627 PM CDT THU MAY 14 2009/

DISCUSSION...

UPDATED FOR 00Z AVIATION DISCUSSION.

PREV DISCUSSION... /ISSUED 303 PM CDT THU MAY 14 2009/

DISCUSSION...

A STATIONARY FRONTAL BOUNDARY REMAINS STRETCHED ACROSS SOUTHERN
MISSOURI INTO WESTERN KENTUCKY THIS AFTERNOON WITH AN OLD CONVECTIVE
OUTFLOW BOUNDARY POSITIONED ACROSS NORTH MISSISSIPPI. STRONG
DAYTIME HEATING WILL CONTINUE THIS AFTERNOON AND HELP TO
DESTABLIZE THE AIRMASS WITH SCATTERED THUNDERSTORMS EXPECTED LATE
THIS AFTERNOON...ESPECIALLY FOCUSED ALONG ANY BOUNDARIES. A FEW OF
THESE STORMS COULD BECOME STRONG WITH GUSTY WINDS AND SMALL
HAIL...BUT NOT ANTICIPATING SEVERE STORMS AT THIS TIME. THE BEST
CHANCES FOR STORM DEVELOPMENT AND STRONG STORMS SHOULD BE ACROSS
NORTH MISSISSIPPI. ANY SCATTERED CONVECTION THAT CAN DEVELOP
SHOULD DIMINISH QUICKLY THIS EVENING WITH THE LOSS OF DAYTIME
HEATING.

THE STATIONARY FRONT SHOULD LIFT BACK NORTH AS A WARM FRONT ON
FRIDAY WITH WEAK HIGH PRESSURE BUILDING OVERHEAD. ANTICIPATE THE
ENTIRE AREA WILL BE WARM SECTORED WITH TEMPERATURES RISING WELL
INTO THE 80S AND DEWPOINTS APPROACHING 70. THESE VERY WARM AND
HUMID CONDITIONS WILL ALLOW THE ATMOSPHERE TO BECOME VERY UNSTABLE
BY FRIDAY AFTERNOON WITH SURFACE BASED CAPES RANGING FROM
3000-4000J/KG...LI/S BETWEEN -6C AND -8C...AND MID LEVEL LAPSE
RATES AROUND 6.5C/KM. EXPECT MAINLY UNORGANIZED DIURNAL CONVECTION
TO DEVELOP DURING THE PEAK HEATING OF THE DAY AS THE AIRMASS
SHOULD ONLY BE WEAKLY CAPPED. ALTHOUGH DEEP LAYER SHEAR WILL BE
WEAK...THE STRONG INSTABILITY SHOULD REMOVE ANY WEAK CAPPING AND
ALLOW FOR SLOW MOVING THUNDERSTORMS TO DEVELOP. CONSIDERING THE
MAGNITUDE OF EXPECTED INSTABILITY...CURRENTLY ANTICIPATE A FEW OF
THE PULSE STORMS TO BECOME SEVERE...WITH DAMAGING WINDS AND LARGE
HAIL POSSIBLE. ANY THUNDERSTORMS THAT DEVELOP SHOULD QUICKLY
DIMINISH WITH THE LOSS OF DAYTIME HEATING AND PEAK INSTABILITY.

A NORTHERN STREAM SHORTWAVE TROUGH WILL MOVE EAST ACROSS THE
MISSISSIPPI VALLEY ON SATURDAY HELPING TO ADVANCE A COLD FRONT
SOUTHEAST ACROSS THE MID SOUTH SATURDAY AFTERNOON AND NIGHT.
STRONG HEATING IN ADVANCE OF THIS FRONT WILL ALLOW FOR MODERATE TO
STRONG INSTABILITY TO AGAIN DEVELOP BY SATURDAY
AFTERNOON...ESPECIALLY ALONG AND SOUTH OF INTERSTATE 40. AS STRONG
CONVERGENCE ALONG THE FRONT PUSHES THROUGH THE UNSTABLE AIRMASS
EXPECT NUMEROUS SHOWERS AND THUNDERSTORMS TO DEVELOP. STORMS MAY
ORGANIZE INTO A LINEAR LINE AHEAD OF THE FRONT WITH A THREAT FOR
SEVERE STORMS CAPABLE OF DAMAGING WINDS AND LARGE. THE FRONT
SHOULD MOVE SOUTH OF THE REGION ON SUNDAY WITH SURFACE HIGH
PRESSURE BUILDING IN.

SURFACE HIGH PRESSURE ALONG WITH BUILDING UPPER LEVEL RIDGING
SHOULD KEEP DRY WEATHER IN PLACE FOR MUCH OF NEXT WEEK.
TEMPERATURES SHOULD INITIALLY REMAIN BELOW AVERAGE FOR THE
BEGINNING OF NEXT WEEK WITH TEMPERATURES WARMING BACK TO ABOVE
SEASONAL AVERAGES FOR THE MIDDLE TO END OF NEXT WEEK. SOME OF THE
MEDIUM RANGE FORECAST GUIDANCE IS HINTING AT A POSSIBLE
SUBTROPICAL OR TROPICAL SYSTEM FORMING OFF THE EAST COAST OF
FLORIDA AND MOVING WESTWARD TOWARDS THE END OF NEXT WEEK. THIS MAY
SPREAD INCREASING MOISTURE INTO THE MID SOUTH AND INCREASE
CONVECTIVE CHANCES DURING THIS PERIOD. HAVE LEFT OUT ANY MENTION
OF THIS IN THE EXTENDED FORECAST AS MODELS STILL DO NOT AGREE ON
THE OVERALL PATTERN.

JLH

&&

.AVIATION...

VFR CONDITIONS WILL PERSIST FOR NEXT 24 HOURS. SOME ISOLATED
THUNDERSTORMS ARE POSSIBLE FOR NEXT COUPLE OF HOURS BUT SO FAR
THERE IS LITTLE ACTIVITY OVER THE FORECAST AREA. WINDS WILL REMAIN
LIGHT AND VARIABLE TONIGHT THEN BECOME SOUTH AT 5 TO 10 KNOTS ON
FRIDAY. SOME SCATTERED THUNDERSTORMS WILL BE FOUND ACROSS THE
FORECAST AREA ON FRIDAY BUT COVERAGE IS NOT ENOUGH TO MENTION IN
TAFS AT THIS TIME.

ARS

&&

.PRELIMINARY POINT TEMPS/POPS...
MEM  68  86  71  82 /  20  40  10  70
MKL  65  85  68  81 /  20  40  10  80
JBR  65  85  69  78 /  10  40  10  70
TUP  67  85  68  83 /  20  40  10  80

&&

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

$$