River Flood Warning 54, NWS Memphis, TN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEMPHIS TN
653 AM CDT WED MAR 30 2016

.UPDATE...

12Z AVIATION UPDATE.

&&

.PREV DISCUSSION... /ISSUED 408 AM CDT WED MAR 30 2016/

A BUSY NEXT FEW DAYS IS IN STORE FOR THE MID-SOUTH WITH MULTIPLE
PERIODS OF STRONG TO SEVERE THUNDERSTORMS AND HEAVY RAINFALL
LIKELY. THERE ARE 3 MAIN CONCERNS THROUGH THURSDAY
NIGHT...OUTLINED BELOW:

1) STRONG TO SEVERE THUNDERSTORM POTENTIAL WEDNESDAY AFTERNOON
THROUGH WEDNESDAY NIGHT WITH LARGE HAIL...DAMAGING WINDS AND
A FEW TORNADOES POSSIBLE.

2) HEAVY RAINFALL/FLASH FLOODING...MAINLY WEDNESDAY EVENING
THROUGH EARLY THURSDAY MORNING. FLASH FLOODING IS POSSIBLE MAINLY
ALONG AND SOUTH OF I-40 WHERE 2-4 INCHES OF RAINFALL IS LIKELY
WITH LOCALLY HIGHER AMOUNTS UP TO 6 INCHES.

3) SEVERE THUNDERSTORM POTENTIAL THURSDAY...MAINLY EAST OF THE
MISSISSIPPI RIVER WHERE TORNADOES...LARGE HAIL...AND DAMAGING
WINDS ALL APPEAR POSSIBLE.

CURRENTLY...A DEEP LONGWAVE TROUGH WAS DIGGING ACROSS THE WESTERN
CONUS WITH A DEVELOPING LEE CYCLONE LOCATED IN NW KS/SW NE. A
VERY DRY AIRMASS WAS STILL IN PLACE ACROSS THE MID-SOUTH WITH
DEWPOINTS CURRENTLY IN THE MID 30S TO LOW 40S. A STRONG LOW LEVEL
JET WAS LOCATED WEST OF THE MID-SOUTH WITH SIGNIFICANT
TEMP/MOISTURE ADVECTION OCCURRING ALONG ITS AXIS...ALTHOUGH NOT
YET EXTENDING INTO THE MID-SOUTH.

THERE IS UNANIMOUS AGREEMENT AMOUNT GLOBAL AND HI-RES MODELS THAT
AN EXCEPTIONAL MOISTURE FLUX WILL TAKE PLACE THROUGH THE MORNING
AND EARLY AFTERNOON HOURS WITH SURFACE DEWPOINTS MAKING REMARKABLE
RECOVERIES FROM THE UPPER 30S TO THE LOW AND AND MID 60S BY LATE
AFTERNOON. ELEVATED INSTABILITY WILL FIRST INCREASE ACROSS THE
MID-SOUTH WITH SUFFICIENT ELEVATED CAPE PRESENT TO GENERATE
THUNDERSTORMS BY 18Z. THIS IS WHERE THE FORECAST BECOMES MORE
UNCERTAIN. HI RES MODELS/CAM SOLUTIONS CONTINUE TO DEPICT A
PSEUDO-WARM FRONTAL STRUCTURE DEVELOPING SW TO NE FROM PBF TO JUST
SOUTHEAST OF JBR. AHEAD OF THIS FEATURE...SIGNIFICANT SURFACE
HEATING OCCURS...BUT NORTHWEST...STRONG THETA-E ADVECTION SHOULD
KEEP CLOUDS/PRECIP AROUND...EFFECTIVELY REINFORCING THIS BOUNDARY.
IF ENOUGH SURFACE-BASED INSTABILITY CAN BE GENERATED ALONG AND
SOUTH OF THE BOUNDARY...THE SEVERE THREAT WOULD MARKEDLY INCREASE
FOR MUCH OF EAST ARKANSAS...NORTHWEST MISSISSIPPI AND WEST
TENNESSEE. AS OF NOW...AN ENHANCED RISK FOR SEVERE THUNDERSTORMS
EXTENDS UP TO THE MEG CWA WITH A SLIGHT RISK COVERING THE MAJORITY
OF THE MID-SOUTH. THE EVOLUTION OF THESE MESOSCALE FEATURES WILL
NEED TO BE WATCHED CLOSELY TODAY...AS IT WOULD NOT TAKE MUCH OF AN
INCREASE IN INSTABILITY FOR THE TORNADO THREAT TO BECOME MUCH MORE
SIGNIFICANT.

DURING THE LATE AFTERNOON HOURS...A SIGNIFICANT COMPLEX OF
SHOWERS AND THUNDERSTORMS SHOULD EVOLVE FROM NEAR THE ARKLATEX AND
SPREAD NORTHEAST...PERHAPS ALONG THE AFOREMENTIONED WARM-FRONTAL
FEATURE. IT REMAINS TO BE SEEN HOW ORGANIZED THIS CLUSTER WILL
BECOME...WITH SOME CAM SOLUTIONS DEPICTING A WELL ORGANIZED
..FORWARD-PROPAGATING MCS...AND SOME DEPICTING A TRAINING
CONVECTIVE EVENT. THE NCAR HI-RES ENSEMBLE SHOWS A CLUSTERING OF
UPDRAFT HELICITY TRACKS AMONGST ITS MEMBERS PROGRESSING THROUGH
THE MID-SOUTH DURING THE OVERNIGHT HOURS. WHILE INSTABILITY WILL
BE MEAGER...THE SEVERE THREAT DOES LOOK TO PERSIST OVERNIGHT AS A
SIGNIFICANT SUB-TROPICAL IMPULSE EJECTS ACROSS THE REGION. INTENSE
LOW LEVEL SHEAR SHOULD PROMOTE CORRIDORS OF DAMAGING WIND...WITH
SOME QLCS TORNADO POTENTIAL APPARENT THROUGH MUCH OF THE OVERNIGHT
HOURS.

THIS IS ALSO THE PERIOD WHEN THE THREAT FOR HEAVY RAINFALL WILL
MAXIMIZE. 00Z MODEL GUIDANCE HAS ONLY SHOWN AN INCREASE IN THE
FORECAST PW VALUES...WITH THE GFS SHOWING REMARKABLE VALUES OF
1.7 TO 1.9 INCHES...ALMOST CERTAIN CLIMATOLOGICAL RECORDS FOR THIS
TIME OF YEAR. THE AXIS OF HEAVIEST RAINFALL IS STILL
UNCERTAIN...BUT GIVEN THE CONVECTIVE NATURE...AND TRAINING
POTENTIAL...A WIDESPREAD 2-4 INCHES IS EXPECTED ALONG AND SOUTH OF
THE I-40 CORRIDOR...WITH AMOUNTS NEARING 6 INCHES WHERE THE
HEAVIEST AXIS SETS UP.

IN THE WAKE OF WEDNESDAY NIGHT CONVECTION...ATTENTION WILL QUICKLY
TRANSITION TO THURSDAY'S SEVERE POTENTIAL. THERE IS GROWING
CONCERN THAT A MORE HIGH-END TYPE SEVERE THREAT MAY
MATERIALIZE...BUT SIGNIFICANT UNCERTAINTY REMAINS. THE SLOWING
TREND OF THE LONGWAVE TROUGH/SURFACE FRONTAL PASSAGE...DEPICTED
WELL BY THE GEFS ENSEMBLE MEMBERS...LOOKS TO BE COMING TO
FRUITION. AIRMASS RECOVERY DURING THE DAY ON THURSDAY IS LOOKING
MORE AND MORE LIKELY WITH THE SURFACE FRONTAL BOUNDARY HANGING
BACK TO THE WEST. ANOTHER MOISTURE SURGE IS DEPICTED AHEAD OF
ANOTHER SUB-TROPICAL IMPULSE EJECTING INTO THE MID-SOUTH...WITH
THE 4-KM NAM SHOWING MID TO UPPER 60S RECOVERING TO AT LEAST THE
MISSISSIPPI RIVER. A SLIGHT...TEMPORARY WEAKENING OF FLOW FIELDS
IS ALSO SHOWN IN THE WAKE OF THE DEPARTING SHORTWAVE DURING THE
DAYTIME HOURS...WITH A REINTENSIFICATION SHOWN TOWARD 00Z.
EFFECTIVE HELICITY VALUES INCREASE TO GREATER THAN 200 M2/S2
COINCIDENT WITH AN IMPRESSIVE THERMODYNAMIC PROFILE ALONG AND EAST
OF THE MISSISSIPPI RIVER...WHERE 2000 TO 3000 J/KG OF SBCAPE IS
FORECAST. MUCH STRONGER UPPER LEVEL FLOW WILL OVERSPREAD THE
REGION ON THURSDAY WHICH WILL BOOST EFFECTIVE SHEAR VALUES INTO
THE 50 TO 60 KT RANGE. RENEWED...ROBUST CONVECTIVE DEVELOPMENT
WILL LIKELY HOLD OFF UNTIL THE LATE AFTERNOON HOURS ON
THURSDAY...WITH A MIXED-MODE OF SUPERCELLS AND BOWING LINE
SEGMENTS POSSIBLE. ALL MODES OF SEVERE WEATHER APPEAR POSSIBLE.
THE POTENTIAL FOR SIGNIFICANT TORNADOES IS UNCLEAR AT THIS
TIME...BUT ONE OF THE MAIN THREATS THAT MAY EVOLVE IS SIGNIFICANT
HAIL...2 INCHES OR GREATER...GIVEN SUBSTANTIAL INSTABILITY PRESENT
WITH VERY STEEP MID-LEVEL LAPSE RATES. THIS ROUND OF CONVECTION
WILL BE SLOW TO CLEAR SOUTHEAST PORTIONS OF THE CWA...BUT BY
FRIDAY MORNING...THE MID-SOUTH SHOULD BE PRECIP FREE.

.LONG-TERM...

THE WEEKEND THROUGH THE LONG-TERM SHOULD FEATURE A
MUCH QUIETER WEATHER PATTERN WITH COOLER AND DRIER CONDITIONS
PREVAILING. NO SIGNIFICANT SYSTEMS ARE PRESENT IN THE LONG-TERM
PERIOD OF THE FORECAST AT THIS TIME.

TVT

&&

.AVIATION...

12Z TAF SET

VFR CIGS/VSBYS TO START THE PERIOD WILL GRADUALLY LOWER TO MVFR
LATER THIS AFTERNOON AND EVENING AS SCATTERED TO NUMEROUS SHOWERS
AND THUNDERSTORMS DEVELOP AND MOVE EAST ACROSS THE TAF SITES.
SHOWERS AND THUNDERSTORMS WILL BECOME WIDESPREAD OVERNIGHT WITH
HEAVY RAINFALL POSSIBLE AT TIMES ALONG WITH REDUCED CIGS/VSBYS TO
IFR.

SOUTHEAST WINDS WILL GRADUALLY INCREASE TODAY...BECOMING STRONG
AND GUSTY BY LATER THIS AFTERNOON. STRONG SOUTH WINDS SHOULD
PERSIST THROUGH THE OVERNIGHT HOURS IN ADVANCE OF AN APPROACHING
STORM SYSTEM.

JLH

&&

.MEG WATCHES/WARNINGS/ADVISORIES...
AR...FLASH FLOOD WATCH FROM 1 PM CDT THIS AFTERNOON THROUGH THURSDAY
     EVENING FOR CRITTENDEN-LEE AR-PHILLIPS-ST. FRANCIS.

MO...NONE.
MS...FLASH FLOOD WATCH FROM 1 PM CDT THIS AFTERNOON THROUGH THURSDAY
     EVENING FOR ALCORN-BENTON MS-CALHOUN-CHICKASAW-COAHOMA-
     DESOTO-ITAWAMBA-LAFAYETTE-LEE MS-MARSHALL-MONROE-PANOLA-
     PONTOTOC-PRENTISS-QUITMAN-TALLAHATCHIE-TATE-TIPPAH-
     TISHOMINGO-TUNICA-UNION-YALOBUSHA.

TN...FLASH FLOOD WATCH FROM 1 PM CDT THIS AFTERNOON THROUGH THURSDAY
     EVENING FOR CHESTER-DECATUR-FAYETTE-HARDEMAN-HARDIN-HAYWOOD-
     HENDERSON-MADISON-MCNAIRY-SHELBY-TIPTON.

&&

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE MEMPHIS TN
922 AM CDT WED MAR 30 2016

ARZ008-009-017-018-026>028-035-036-048-049-058-MOZ113-115-
MSZ001>017-020>024-TNZ001>004-019>022-048>055-088>092-311215-
ALCORN-BENTON MS-BENTON TN-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-
922 AM CDT WED MAR 30 2016

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

.DAY ONE...TODAY AND TONIGHT

FLASH FLOODING AND SEVERE WEATHER ARE BOTH POSSIBLE TODAY AS A
STRONG STORM SYSTEM MOVES INTO THE MID-SOUTH. SHOWERS AND
THUNDERSTORMS WILL DEVELOP DURING THE AFTERNOON HOURS ON
WEDNESDAY...WITH LARGE HAIL...DAMAGING WINDS AND A FEW TORNADOES
POSSIBLE THROUGH THE LATE EVENING. THE SEVERE WEATHER THREAT WILL
LAST THROUGH THE NIGHT...INTO THE EARLY MORNING HOURS ON THURSDAY.

HEAVY RAINFALL AND FLASH FLOODING ARE ALSO LIKELY...ESPECIALLY
DURING LATE WEDNESDAY EVENING THROUGH THURSDAY MORNING. 2 TO 4
INCHES OF RAINFALL IS POSSIBLE WITH LOCALLY HIGHER AMOUNTS...UP TO
6 INCHES...POSSIBLE.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY

A SEVERE THREAT MAY BE ONGOING THURSDAY MORNING AS A COMPLEX OF
SHOWERS AND THUNDERSTORMS CONTINUES TO PROGRESS ACROSS PORTIONS OF
THE MID-SOUTH. ANOTHER ROUND OF SEVERE WEATHER IS EXPECTED
THURSDAY AFTERNOON AND THURSDAY NIGHT...WITH TORNADOES...LARGE TO
VERY LARGE HAIL...AND DAMAGING WINDS ALL POSSIBLE DURING THIS
PERIOD. LOCALLY HEAVY RAINFALL IS ALSO POSSIBLE WITH ANY
THUNDERSTORMS.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE NEEDED IN SUPPORT OF SEVERE WEATHER
OPERATIONS LATER THIS AFTERNOON INTO TONIGHT AND AGAIN THURSDAY AND
THURSDAY NIGHT.