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000
FXUS64 KMEG 201502
AFDMEG

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEMPHIS TN
1002 AM CDT MON MAY 20 2013

.UPDATE...

FORECAST IN GOOD SHAPE...WITH ONLY A MINOR TWEAK TO REMOVE THE
SHOWERS AND THUNDERSTORMS JUST A BIT EARLIER THAN PREVIOUS
THINKING ACROSS PORTIONS OF NE AR DUE TO CAPPING. WINDS ARE
STARTING TO BUILD FROM WEST TO EAST ACROSS THE REGION WITH GUSTS
CLOSE TO THE 20KT RANGE ALONG AND WEST OF THE RIVER. HIGHS SHOULD
STILL PUSH UPPER 80S OR CLOSE TO 90 ACROSS ENTIRE AREA. --ABS

&&

.PREV DISCUSSION... /ISSUED 620 AM CDT MON MAY 20 2013/

UPDATE...
UPDATED TO ADD 12Z AVIATION DISCUSSION.

PREV DISCUSSION... /ISSUED 453 AM CDT MON MAY 20 2013/

DISCUSSION...

A POTENT UPPER LEVEL LOW PRESSURE SYSTEM REMAINS NEARLY STATIONARY
OVER THE CENTRAL HIGH PLAINS EARLY THIS MORNING WITH A DOWNSTREAM
UPPER LEVEL RIDGE OF HIGH PRESSURE EXTENDING FROM THE DEEP SOUTH
ACROSS THE MID SOUTH INTO THE OHIO VALLEY. A LEAD SHORTWAVE
ROTATING THROUGH MISSOURI EARLY THIS MORNING CONTINUES TO LIFT
NORTHEAST WITH THUNDERSTORMS OVER MISSOURI CURRENTLY IN A
WEAKENING PHASE AS THE UPPER SUPPORT LIFTS NORTHEAST OF THE
REGION. THIS CONVECTIVE ACTIVITY WILL LIKELY LEAVE A CONVECTIVE
OUTFLOW BOUNDARY THAT WILL EXTEND ACROSS SOUTH CENTRAL MISSOURI
WESTWARD INTO NORTHEAST OKLAHOMA.

ACROSS THE MID SOUTH...THE UPPER LEVEL RIDGE OF HIGH PRESSURE WILL
KEEP DRY AND VERY WARM WEATHER IN PLACE TODAY. HUMID CONDITIONS
WILL ALSO PERSIST AS DEWPOINTS REMAIN IN THE UPPER 60S THROUGH THE
DAY. HIGH TEMPERATURES SHOULD TOP OUT AROUND 90 DEGREES IN MOST
AREAS. SOME LOW LEVEL STRATUS WILL OVERSPREAD THE REGION EARLY
THIS MORNING FROM THE SOUTH...BUT SHOULD MIX OUT FAIRLY QUICKLY
WITH MOSTLY SUNNY SKIES DEVELOPING BY LATE MORNING.

THE AFOREMENTIONED CONVECTIVE OUTFLOW BOUNDARY TO THE NORTH OF THE
FORECAST AREA WILL LIKELY BECOME A FOCUS FOR RENEWED THUNDERSTORM
DEVELOPMENT LATE THIS AFTERNOON INTO THIS EVENING AS ANOTHER MID
LEVEL SHORTWAVE EJECTS FROM THE SOUTHERN PLAINS INTO THE MID
MISSISSIPPI VALLEY TONIGHT. NUMEROUS THUNDERSTORMS SHOULD DEVELOP
ACROSS THE OZARKS OF SOUTHERN MISSOURI SOUTHWESTWARD INTO CENTRAL
OKLAHOMA BY THIS EVENING. INITIAL THUNDERSTORM MODE SHOULD BEGIN
AS SUPERCELLS BUT GRADUALLY TRANSITION INTO A QUASI-LINEAR
CONVECTIVE SYSTEM (QLCS) AS IT ADVANCES EAST-NORTHEASTWARD
OVERNIGHT. THIS LINE OF STORMS MAY ADVANCE ACROSS PORTIONS OF
NORTHEAST ARKANSAS AND THE MISSOURI BOOTHEEL AFTER MIDNIGHT. THE
AIRMASS AHEAD OF THIS CONVECTIVE COMPLEX SHOULD REMAIN
SUFFICIENTLY UNSTABLE WITH MLCAPES BETWEEN 1500-2500 J/KG...LI/S
AROUND -6C...AND MID LEVEL LAPSE RATES IN EXCESS OF 7.5 C/KM. IN
ADDITION...DEEP LAYER SHEAR BETWEEN 40-50 KTS WILL SPREAD ACROSS
NORTHWEST PORTIONS OF THE FORECAST AREA OVERNIGHT. THIS
COMBINATION OF SHEAR AND INSTABILITY MAY SUPPORT A CONTINUED
SEVERE THREAT AFTER MIDNIGHT INTO PORTIONS OF NORTHEAST ARKANSAS
AND THE MISSOURI BOOTHEEL. THE PRIMARY THREATS APPEAR TO BE
DAMAGING WINDS AND LARGE HAIL. AN ISOLATED TORNADO CANNOT BE RULED
OUT BUT SHOULD NOT BE THE PRIMARY SEVERE WEATHER HAZARD AS LOW
LEVEL WINDS VEER LATE TONIGHT. STORMS SHOULD EVENTUALLY WEAKEN
TOWARDS SUNRISE AS THEY APPROACH THE MISSISSIPPI RIVER AND
NORTHWEST TENNESSEE AS THE UPPER SUPPORT LIFTS TO THE NORTHEAST OF
THE CONVECTIVE ACTIVITY. THIS ACTIVITY SHOULD EVENTUALLY FIZZLE
LATER TUESDAY MORNING OVER NORTHWEST PORTIONS OF THE MID SOUTH.

THE UPPER RIDGE SHOULD TEMPORARILY REBUILD OVER THE MID SOUTH
DURING THE DAY TUESDAY BRINGING A LULL IN ANY CONVECTIVE ACTIVITY
AS THE CAPPING INVERSION STRENGTHENS AND INHIBITS CONVECTIVE
DEVELOPMENT. SKIES SHOULD SCATTER OUT WITH TEMPERATURES RISING
WELL INTO THE 80S BY TUESDAY AFTERNOON ALONG WITH CONTINUED HUMID
CONDITIONS AS DEWPOINTS REMAIN NEAR 70 DEGREES. A THIRD AND
STRONGER SHORTWAVE WILL EJECT FROM THE SOUTHERN PLAINS INTO THE
MID SOUTH BY TUESDAY EVENING. THIS SHORTWAVE SHOULD TAKE ON A
NEGATIVE TILT AS IT PROGRESSES ACROSS THE MID SOUTH TUESDAY NIGHT
INTO WEDNESDAY MORNING. AS THIS OCCURS...THE CAPPING INVERSION
WILL BEGIN TO ERODE ALLOWING FOR NUMEROUS THUNDERSTORMS TO DEVELOP
OVER WESTERN SECTIONS OF THE MID SOUTH LATE TUESDAY AFTERNOON.
THUNDERSTORMS SHOULD QUICKLY SPREAD NORTHEAST ACROSS THE REGION
TUESDAY NIGHT INTO WEDNESDAY MORNING. THE ATMOSPHERE SHOULD REMAIN
MODERATELY UNSTABLE THROUGH TUESDAY NIGHT WITH SBCAPE VALUES
RANGING FROM 1500-2500 J/KG...LI/S -6C TO -10C...AND MID LEVEL
LAPSE RATES GREATER THAN 7.0 C/KM. IN ADDITION...DEEP LAYER SHEAR
SHOULD STRENGTHEN AHEAD OF THE SHORTWAVE AS A 40-50 KT LOW LEVEL
JET OVERSPREADS THE AREA ALONG WITH AROUND 50 KTS OF MID LEVEL
FLOW. INITIAL THUNDERSTORM MODE SHOULD BE A MIX OF SUPERCELLS AND
BOWING LINE SEGMENTS EARLY IN THE CONVECTIVE EVOLUTION THROUGH
TUESDAY EVENING...EVENTUALLY TRANSITIONING TO AN EXPANSIVE QUASI-
LINEAR CONVECTIVE SYSTEM (QLCS). THE PRIMARY SEVERE THREATS WILL
BE DAMAGING WINDS AND LARGE HAIL. A TORNADO THREAT WILL EXIST
EARLY IN THE EVENT MAINLY ALONG AND WEST OF THE MISSISSIPPI RIVER
TUESDAY EVENING...ESPECIALLY WITH ANY DISCRETE SUPERCELLS THAT
DEVELOP. ANY TORNADO THREAT SHOULD DIMINISH LATER TUESDAY NIGHT AS
LOW LEVEL FLOW VEERS.

THE LINE OF THUNDERSTORMS SHOULD CONTINUE TO ADVANCE EAST OF THE
MISSISSIPPI RIVER LATER TUESDAY NIGHT INTO WEDNESDAY MORNING. THE
SEVERE WEATHER THREAT SHOULD GRADUALLY DIMINISH LATE TUESDAY NIGHT
INTO WEDNESDAY MORNING AS THE SHORTWAVE LIFTS NORTHEAST OF THE
REGION AND DEEP LAYER SHEAR WEAKENS. CHANCES FOR SHOWERS AND
THUNDERSTORMS SHOULD DIMINISH FROM WEST TO EAST DURING THE DAY ON
WEDNESDAY.

AS THE EARLY WEEK UPPER LEVEL LOW OVER THE CENTRAL HIGH PLAINS
MOVES EAST INTO THE GREAT LAKES BY THE END OF THE WEEK...ANOTHER
SHORTWAVE WILL EJECT SOUTHEAST FROM THE MIDDLE MISSISSIPPI VALLEY
THROUGH THE TENNESSEE VALLEY ON THURSDAY. THIS WILL HELP TO PUSH A
COLD FRONT ACROSS THE FORECAST AREA BY THURSDAY AFTERNOON.
ADDITIONAL SHOWERS AND THUNDERSTORMS MAY DEVELOP AHEAD OF THE
SOUTHWARD ADVANCING COLD FRONT. A FEW STORMS MAY BECOME STRONG AS
DEEP LAYER SHEAR RESTRENGTHENS ACROSS THE AREA. THE FRONT SHOULD PUSH
SOUTH OF THE REGION THURSDAY NIGHT WITH HIGH PRESSURE BUILDING IN.

HIGH PRESSURE SHOULD CONTROL THE MID SOUTH WEATHER FOR FRIDAY INTO
NEXT WEEKEND WITH A RETURN TO DRY AND LESS HUMID WEATHER.
TEMPERATURES WILL DROP BACK TO NEAR SEASONAL LEVELS FOR THE END OF
THE WEEK INTO NEXT WEEKEND.

JLH

AVIATION...
12Z TAF CYCLE

LOW STRATUS HAS ALREADY DEVELOPED ACROSS THE LOWER MISSISSIPPI
VALLEY EARLY THIS MORNING AND WILL SPREAD INTO ALL TAF SITES
BETWEEN 20/12-16Z. OTHERWISE...VFR CONDITIONS EXPECTED TO PREVAIL
THROUGH MUCH OF THE PERIOD AS CLOUDS MIX OUT BY LATE THIS MORNING
MORNING. SOUTH WINDS WILL INCREASE TO 10-16 KTS SUSTAINED WITH
GUSTS BETWEEN 18-26 KTS...ESPECIALLY AT JBR AND MEM. VCTS POSSIBLE AT
JBR MAINLY AFTER 21/08Z AS A SHORTWAVE TROUGH MOVES ACROSS
PORTIONS OF THE MIDDLE AND LOWER MISSISSIPPI VALLEYS.

CJC

&&

.PRELIMINARY POINT TEMPS/POPS...
MEM  89  74  88  69 /  10  10  30  70
MKL  88  72  88  69 /  10  10  30  70
JBR  89  69  86  66 /  20  40  60  90
TUP  89  71  89  70 /   0  10  20  40

&&

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

$$