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Excessive Rainfall Discussion
 
(Latest Discussion - Issued 0655Z Apr 27, 2015)
 
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Abbreviations and acronyms used in this product
 
Geographic Boundaries -  Map 1: Color  Black/White       Map 2: Color  Black/White


EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
255 AM EDT MON APR 27 2015

...VALID 06Z MON APR 27 2015 - 12Z TUE APR 28 2015...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
30 SSW RKR 10 SSW BQP 25 S HBG 10 NNE JKA PAM 15 ESE AAF
40 S AAF 95 ESE KVOA 15 NNE KMDJ KVBS 20 ESE 11R 30 ESE PWG LUD
60 S CDS 35 S AMA 35 ENE TCC 20 WNW DHT 30 WSW GUY AVK
15 ENE SWO 30 SSW RKR.


....SOUTHERN PLAINS...LOWER MISSISSIPPI VALLEY...AND EASTERN GULF
COAST...

THE CLOSED UPPER LOW CURRENTLY PIVOTING INTO THE SOUTHERN HIGH
PLAINS WILL PUSH SLOWLY EAST TOWARD THE ARKLATEX BY TUE MORNING.
ROBUST FORCING FOR DEEP-LAYER ASCENT WILL CONTINUE OUT AHEAD OF
THE LOW...AS THE DIFFLUENT UPPER LEVEL FLOW AHEAD OF THE LOW
COUPLES WITH THE RIGHT-ENTRANCE REGION FORCING FROM THE UPPER
LEVEL CONFLUENT FLOW ACROSS THE NORTHERN TN/LOWER OH VALLEYS.
MEANWHILE...THE UPPER LOW WILL ALSO HELP TO PULL THE DEEP
SUBTROPICAL MOISTURE PLUME WITH PWS OF 1.5-2.0+ INCHES (2-2.5
STANDARD DEVIATIONS ABOVE NORMAL FOR LATE APRIL) NORTHWARD INTO
EAST TX...MUCH OF LA...AND SOUTHERN MS/AL LATER TODAY...WITH THE
FAVORABLE MOISTURE TRANSPORT AND PW AXIS SHIFTING EASTWARD TO
ALONG THE EASTERN GULF COAST OVERNIGHT INTO TUE AM. LOW-LEVEL
INFLOW AVERAGING 25-35 KTS WILL HELP DRAW IN THE
THERMODYNAMICALLY-RICH AIRMASS ALONG AND NORTH OF THE SURFACE
FRONTAL BNDRY... TAPPING A MODESTLY UNSTABLE AIRMASS WITH MUCAPES
AVERAGING 1500-3000 J/KG ALONG THE GULF COAST. THESE INGREDIENTS
COULD LEAD TO SCATTERED POCKETS OF VERY HEAVY RAIN...WITH SHORT
TERM RAIN RATES OF 2 TO 3 INCHES IN AN HOUR OR TWO. AREAL-AVERAGE
QPF ACROSS EASTERN TX EAST-SOUTHEAST ACROSS MUCH OF LA AND
SOUTHERN MA/AL WILL RANGE BETWEEN 1-2+ INCHES THROUGH 12Z
TUE...HOWEVER...AS NOTED FROM THE HIGHER RESOLUTION GUIDANCE THE
DYNAMICAL AND THERMODYNAMICAL SIGNAL IS THERE FOR MUCH HEAVIER
(POTENTIALLY EXCESSIVE) AMOUNTS...TO THE TUNE OF 3-6+ INCHES.

A SLIGHT RISK AREA ALSO EXTENDS BACK THROUGH WESTERN AND CENTRAL
OK ALONG WITH NORTH TX AND THE TX PANHANDLE...WHERE STRONG LIFT
WILL MAINTAIN HEAVIER DOWNPOURS EMBEDDED WITHIN A LARGER SCALE
PRECIPITATION AREA DEVELOPING NORTH OF A CLOSED MID LEVEL CENTER.
ALTHOUGH THE DEEP LAYER ASCENT AND LOW-LEVEL INFLOW WILL FAVOR A
LONG DURATION RAIN EVENT HERE...LESSER INSTABILITY WILL LIKELY
LIMIT SHORT TERM (1-3 HOURLY) RAINFALL RATES...THOUGH GIVEN THE
ALREADY WET ANTECEDENT SOILS AND (THUS) LOWERING OF FLASH FLOOD
GUIDANCE...THE FLASH FLOOD POTENTIAL HERE WILL EXIST MORE IN THE 3
TO 6 HOUR ACCUMULATION OF MODERATE AND LOCALLY HEAVY RAIN OVER ANY
PARTICULARLY FLASHY BASINS.

HURLEY