Severe Thunderstorm Warning 474, NWS Memphis, TN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEMPHIS TN
312 PM CDT SUN SEP 17 2006

.DISCUSSION...19Z SURFACE ANALYSIS PLACES 1020 MB HIGH PRESSURE
ALONG THE MID ATLANTIC STATES AND A COLD FRONT EXTENDING FROM
MINNESOTA/WISCONSIN BACK THROUGH THE MIDDLE MISSISSIPPI VALLEY AND
SOUTHERN PLAINS. 12Z UPPER AIR PLOTS THIS MORNING SHOWED A RATHER
LARGE 850 MB MOISTURE GRADIENT BETWEEN BNA/LZK...BUT MOISTURE HAS
QUICKLY INCREASED IN THE LOW LEVELS AS UPPER LEVEL TROUGH AND
SURFACE REFLECTION INCHES CLOSER TO THE MID SOUTH. MAIN CONCERNS
THIS FORECAST PACKAGE IS CONVECTIVE CHANCES TONIGHT THROUGH MONDAY
NIGHT AND PRECIPITATION CHANCES TOWARDS NEXT WEEKEND.

TONIGHT THROUGH WEDNESDAY...SURFACE COLD FRONT WILL CONTINUE TO
APPROACH THE MID SOUTH TONIGHT...REACHING THE MISSISSIPPI RIVER BY
DAYBREAK MONDAY MORNING. MEANWHILE...NUMEROUS OUTFLOW BOUNDARIES AND
DAYTIME INSTABILITY HAVE FED ONGOING CONVECTIVE ACTIVITY ACROSS THE
MID SOUTH. LOW/MID LEVEL MOISTURE HAS QUICKLY INCREASED THIS
AFTERNOON AS THE TROPICAL REMNANTS FROM THE PACIFIC BEEN ABSORBED
INTO SOUTHWEST FLOW ALOFT AND A 35KT 850 MB LOW LEVEL JET ENTERS
WESTERN SECTIONS OF THE LOWER MISSISSIPPI VALLEY. THERE IS STILL
SOME DISAGREEMENT BETWEEN THE WRF/GFS WITH REGARDS TO TIMING. THE
WRF FAVORS A SLOWER FRONTAL PASSAGE AS DEPICTED IN THE LAST FEW
MODEL RUNS. MEANWHILE THE GFS HAS BEEN MUCH QUICKER AND A BIT
INCONSISTENT TIMING THE FRONT THROUGH THE FORECAST AREA. AS THE
SURFACE LOW ACROSS THE UPPER MIDWEST CONTINUES TO OCCLUDE...THINK
THAT A SLOWER GFS SOLUTION WITH THE FRONTAL PASSAGE IS BEST SOLUTION.

MODEL CONVECTIVE PARAMETERS PRODUCE MUCAPES DECREASING TO AROUND
1300 J/KG BY MONDAY MORNING WITH LI/S AROUND -3...AND 700 MB
DEWPOINT DEPRESSIONS APPROACHING 15C UPSTREAM. FAVORABLE NEARLY
UNIDIRECTIONAL WINDS ALOFT WOULD SUGGEST DEVELOPMENT OF
MULTICELLULAR LINE SEGMENTS. HOWEVER...DESPITE DECENT WIND PROFILES
WITH THE COLD FRONT...WEAK 700-500 MB LAYER MID LEVEL LAPSE RATES
AROUND 6 C/KM...A 50KT LOW LEVEL JET CONTINUING TO MOVE NORTHEAST OF
THE REGION...AND LIMITED SURFACE BASED INSTABILITY DUE TO THE
EXTENSIVE CLOUD COVER...THINK SEVERE THUNDERSTORM POTENTIAL OVERALL
WILL REMAIN ISOLATED AT BEST WITH POSSIBLY A DAMAGING WIND GUST.
PRECIPITABLE WATER VALUES WILL REMAIN HIGH AROUND 2 INCHES WITH
K-INDICIES AROUND 36 AND WILL MENTION HEAVY RAINFALL POTENTIAL AFTER
MIDNIGHT AND FOR MONDAY MORNING ACROSS PORTIONS OF THE MID SOUTH.

HIGH PRESSURE WILL BUILD IN BEHIND THE FRONT MONDAY NIGHT BRINGING
DRY WEATHER BUT BELOW NORMAL TEMPERATURES TO THE REGION UNTIL
ANOTHER SYSTEM APPROACHES BY NEXT WEEKEND.

.LONG RANGE...(THURSDAY THROUGH SUNDAY)...LONG RANGE MODELS FEATURE
A LONGWAVE TROUGH MOVING ACROSS THE REGION AT THE START OF THE
PERIOD AND FLOW TRANSITIONING BACK TO ZONAL FLOW ALOFT BY THE END OF
THE PERIOD. THE 00Z/06Z OPERATIONAL GFS SOLUTIONS BRING THE TROUGH
THROUGH THE AREA NEGATIVELY TILTED WHICH THE MAJORITY OF THE GFS
ENSEMBLE MEMBERS AND THE 00Z ECMWF DO NOT SUPPORT. NONETHELESS...A
COLD FRONT WILL MOVE THROUGH THE MID SOUTH ON SATURDAY WITH HIGH
PRESSURE BUILDING BACK IN ON SUNDAY. A WARM FRONT/SHORTWAVE EMBEDDED
WITHIN SOUTHWEST FLOW ALOFT WILL PASS THROUGH THE FORECAST AREA THE
LATTER HALF OF THURSDAY...AND HELD OFF ON INTRODUCING CHANCE POPS
UNTIL FRIDAY WITH THE APPROACH OF THE NEXT COLD FRONT.
&&

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

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE MEMPHIS TN
459 PM CDT SUN SEP 17 2006

ARZ008-009-017-018-026>028-035-036-048-049-058-MOZ113-115-
MSZ001>017-020>024-TNZ001>004-019>021-048>055-088>092-190000-
ALCORN-BENTON(MS)-CALHOUN-CARROLL-CHESTER-CHICKASAW-CLAY-COAHOMA-
CRAIGHEAD-CRITTENDEN-CROCKETT-CROSS-DESOTO-DECATUR-DUNKLIN-DYER-
FAYETTE-GIBSON-GREENE-HARDEMAN-HARDIN-HAYWOOD-HENDERSON-HENRY-
ITAWAMBA-LAFAYETTE-LAKE-LAUDERDALE-LAWRENCE-LEE(AR)-LEE(MS)-
MADISON-MARSHALL-MCNAIRY-MISSISSIPPI-MONROE-OBION-PANOLA-PEMISCOT-
PHILLIPS-POINSETT-PONTOTOC-PRENTISS-QUITMAN-RANDOLPH-SHELBY-
ST. FRANCIS-TALLAHATCHIE-TATE-TIPPAH-TIPTON-TISHOMINGO-TUNICA-
UNION-WEAKLEY-YALOBUSHA-
459 PM CDT SUN SEP 17 2006

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF EAST ARKANSAS...
THE MISSOURI BOOTHEEL...NORTH MISSISSIPPI...AND WEST TENNESSEE.

.DAY ONE...TONIGHT

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS NORTHEAST
ARKANSAS...THE MISSOURI BOOTHEEL...FAR WEST TENNESSEE...AND
NORTHWEST MISSISSIPPI THROUGH TONIGHT. SHOWERS AND THUNDERSTORMS
WILL CONTINUE ALONG AND AHEAD OF A COLD FRONT ENTERING THE LOWER
MISSISSIPPI VALLEY. A FEW THUNDERSTORMS MAY BECOME SEVERE WITH
DAMAGING WINDS AS THE PRIMARY SEVERE WEATHER THREAT. HEAVY
RAINFALL IS ALSO POSSIBLE ACROSS PORTIONS OF THE MID SOUTH.

.DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY

A COLD FRONT WILL MOVE THROUGH THE MID SOUTH ON MONDAY AND EXIT THE
REGION MONDAY NIGHT. SHOWERS AND THUNDERSTORMS ARE EXPECTED WITH A
THUNDERSTORM OR TWO POSSIBLY BECOMING SEVERE ALONG THE COLD FRONT.
DAMAGING WINDS WILL BE THE MAIN CONCERNS ALONG WITH HEAVY RAINFALL
POSSIBLE.

.SPOTTER INFORMATION STATEMENT...

SKYWARN SPOTTER ACTIVATION MAY BE NEEDED TONIGHT AND MONDAY.

JLH