Quantitative Precipitation Forecast
Issued by NWS

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FOUS30 KWBC 271351
QPFERD

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

...VALID 15Z 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 80 ESE KVOA 15 N KIKT 10 W KMDJ 10 NNW GSM 10 NW KEIR
25 SSW SRN 35 S KVNP 20 SW KVNP 20 NW KVNP 25 NW 7R4 20 NNW LFT
35 E ACP 30 SSE ESF 20 NE ACP 15 NW ACP 10 SW POE 20 E JAS JAS
15 SSE LFK 20 WSW LFK 30 SE PSN 10 WSW PSN 15 ESE CRS 10 SSW LNC
10 SE GKY 10 W AFW 10 WNW 1F9 15 NNE RPH 30 NW RPH 55 SSW F05
50 SSE CDS 35 SW CDS 30 NNE PVW 35 SW 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...

AFTER LOOKING AT RECENT RADAR IMAGERY/TRENDS AND 12Z RAOBS..MADE
SOME CHANGES TO THE EXISTING EXCESSIVE AREA OVER PARTS OF
SOUTHEASTERN TX/SOUTHWESTERN LA..OTHERWISE MADE NO CHANGES
ELSEWHERE.  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.

TERRY
$$




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