Quantitative Precipitation Forecast
Issued by NWS

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FOUS30 KWBC 270155
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
954 PM EDT SUN APR 26 2015

...VALID 03Z MON APR 27 2015 - 00Z 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
10 N SRN 30 SW BPT 10 ESE 62H 30 NW 6R9 40 NNW DYS 30 S CDS
50 ESE PPA 20 S GAG 10 WSW END 15 SSW OKM 15 NNE LBR 15 E BAD
30 E ESF 15 NW ASD 35 NNE 1B7 20 NE AXO 10 N SRN.

MODERATE RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
40 WNW RPH 20 SW SPS 20 NW GLE 20 ENE TKI 10 S GVT 10 N LNC
10 NNW INJ 20 ESE SEP 30 WNW SEP 40 WNW RPH.


....SOUTHERN PLAINS AND LOWER MISSISSIPPI VALLEY...

THERE IS A WELL ADVERTISED BROAD SWATH OF MODERATE TO HEAVY
24-HOUR RAINFALL IN THE GLOBAL AND HIGH RESOLUTION MODELS THROUGH
28/00Z. THE MORE PREDICTABLE PORTION OF THIS SWATH IS IN THE MORE
STRONGLY FORCED REGION OF WESTERN OKLAHOMA AND THE EASTERN TEXAS
PANHANDLE...AT THE CENTER OF PERSISTENT UPPER LEVEL DIFLUENCE AND
STRONG EASTERLY LOW LEVEL INFLOW THROUGH EARLY MONDAY.
OBSERVATIONAL TRENDS SUGGEST THAT THE HEAVIEST CONVECTIVE RAINFALL
WILL BE DISPLACED...HOWEVER...TO THE SOUTHEAST OF THE STRONGEST
MID LEVEL FORCING. STORMS UP THROUGH 02Z ON MONDAY WERE MAINLY
SUPERCELLULAR....BUT HAD MANAGED TO TRAIN ON SMALL SCALES...AND
WITH WIDESPREAD INITIATION HAVING OCCURRED AND INCREASING
DEPTH/STRENGTH OF ASCENT...SOME UPSCALE GROWTH IS LIKELY
OVERNIGHT. PROPAGATION ALONG OUTFLOWS SHOULD TAKE ACTIVITY BETWEEN
ABILENE AND FORT WORTH TO THE EAST...AS CAPTURED BY THE 23Z AND
00Z HRRR RUNS. OF THE 12Z HIGH RESOLUTION MODELS THE WRF-NMM
SEEMED TO BEST FORECAST THE LATITUDE OF THIS DEVELOPING CLUSTER OF
STORMS / POTENTIAL MCS. ALTHOUGH MOISTURE PROFILES WERE
MARGINAL...THE COVERAGE AND SLOW EVOLUTION OF CONVECTION WILL LEAD
TO HIGHER PROBABILITIES OF EXCESSIVE RAINFALL FROM TRAINING CELLS.
WITH TIME...GULF MOISTURE WILL IMPROVE...CARRIED INTO NORTH TEXAS
ON A 30-40 KNOT LOW LEVEL JET. FLASH FLOOD GUIDANCE VALUES ARE IN
THE MID RANGE...AT GENERALLY 1.5 TO 2 INCHES IN 1 HOUR OR 2 TO 2.5
INCHES IN 3 HOURS. SOME LOCATIONS APPEAR LIKELY TO EXCEED THESE
VALUES...WITH GREATEST CONFIDENCE OVER THE MODERATE RISK AREA
THROUGH 09Z.

BEYOND THAT TIME...THE TANDEM OF STRONG INFLOW AND INCREASING MID
LEVEL ASCENT SHOULD SPREAD ALONG THE EDGE OF DEEPER RETURNING
MOISTURE OVER EAST TEXAS AND LOUISIANA...WHERE WE MAINTAINED A
SLIGHT RISK. WHILE THIS ACTIVITY SHOULD BE A BIT MORE
PROGRESSIVE...THE STRONG DYNAMIC FORCING ALONG A NARROW PLUME OF
1.5 INCH PLUS PWS COULD LEAD TO SOME POCKETS OF VERY HEAVY
RAIN...WITH SHORT TERM RAIN RATES OF 2 TO 3 INCHES IN AN HOUR OR
TWO.  WITH DOWNSTREAM BLOCKING PATRN HELPING TO HOLD HEIGHTS DOWN
ACRS THE ERN U.S. AND DRIER AIR EXTENDING INTO THE SE
STATES...EXPECT THE STGR STORMS ON MONDAY TO TRACK TOWARD THE
CENTRAL GULF COAST REGION...FINDING DEEP LAYERED E/W AXIS OF
SUB-TROPICAL MOISTURE ALONG THE NRN GULF OF MEXICO.

A SLIGHT RISK AREA ALSO EXTENDS BACK THROUGH WESTERN AND CENTRAL
OK...WHERE STRONG LIFT WILL MAINTAIN HEAVIER DOWNPOURS EMBEDDED
WITHIN A LARGER SCALE PRECIPITATION AREA DEVELOPING NORTH OF A
CLOSED MID LEVEL CENTER. ALTHOUGH LIFT AND EVEN LOW LEVEL INFLOW
WILL BE STRONGLY FAVORABLE FOR A LONG DURATION RAIN EVENT
HERE...LESSER INSTABLITY WILL LIKELY CAUSE HEAVIER RAIN TO OCCUR
WITHIN SMALLER SCALE UPDRAFTS LACKING ANY PARTICULAR FOCUS TO
INDUCE TRAINING OR LONGER TERM DURATION OF HEAVY RATES AT A GIVEN
POINT. 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.

BURKE/SULLIVAN
$$




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