Quantitative Precipitation Forecast
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FOUS30 KWBC 242337
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
737 PM EDT FRI APR 24 2015

...VALID 00Z SAT APR 25 2015 - 00Z SUN APR 26 2015...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
35 SSE 3T5 40 WSW VCT 40 NW ALI 25 WSW COT UVA 20 S 6R9
25 NNW 05F 15 W NFW 10 ENE GLE 45 NNE PRX 20 N LRF 20 SE MKL
25 W CHA 30 SSW RHP 25 SW CEU 15 N 3J7 20 S LZU 20 ESE ANB NMM
25 NNW HEZ 35 NE OCH 35 SE PSN 15 NE 11R 35 SSE 3T5.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 SSW AFK 20 N CSQ 20 WSW IOW 25 ESE MLI 25 SSW LAF BMG
10 S AJG 20 NE BLV 35 NW SUS 20 NNW SZL 20 ENE UKL EWK 10 E RSL
20 WNW CNK 15 SSW AFK.


...SOUTHERN PLAINS EWD ACRS PORTIONS OF THE LOWER MS AND TN
VALLEYS...

HEIGHT FALLS ASSOCIATED WITH THE UPPER LOW THAT WAS LIFTING INTO
THE CENTRAL PLAINS WILL INTERACT WITH A VERY MOIST PLUME OF
MOISTURE...PW VALUES GREATER THAN 1.7 INCHES...LEADING TO
WIDESPREAD MODERATE TO HEAVY CONVECTIVE RAINS FROM TEXAS EASTWARD.
EXPECTATIONS FOR HEAVY RAIN ARE ESPECIALLY FOCUSED THIS EVENING
FROM NORTHEAST TEXAS INTO ADJACENT AR/LA AND EXTREME SE OK...WHERE
THE NOSE OF THE LOW LEVEL JET CROSSES TO THE COOL SIDE OF AN
OUTFLOW BOUNDARY AND WARM FRONT. THE UPPER LOW WAS OPENING AND
EJECTING...WHICH WILL ALLOW THE COUPLET OF LOW LEVEL INFLOW / MID
LEVEL ASCENT TO PROGRESS STEADILY EASTWARD...BUT CONVECTION MAY BE
SUSTAINED OVER A GIVEN LOCATION FOR 2-3 HOURS PRIOR TO SEEING AN
APPRECIABLE DECREASE OF INTENSITY. THE HEAVY RAIN SIGNAL IN THE
MESOSCALE MODELS IS CONSISTENT IN THE SHORT TERM...ALTHOUGH THEY
DIVERGE IN PLACEMENT FARTHER DOWNSTREAM TOWARD MORNING. A STRIPE
OF HEAVY RAIN WHICH FELL EARLY FRIDAY IN NE TX AND ADJACENT STATES
LOWERED FLASH FLOOD GUIDANCE VALUES...MAKING IT SOMEWHAT LIKELY
THAT AT LEAST A FEW LOCATIONS WILL SEE RAINFALL EXCEEDING FFG.

MODELS ALSO AGREE ON A SECONDARY MAXIMUM OF PRECIPITATION THIS
EVENING IN SOUTH TEXAS AS CONVECTION ROLLS EAST OFF THE SIERRA
MADRES. ORGANIZED CONVECTION IN THIS REGION SHOULD BE A BIT MORE
PROGRESSIVE OWING TO A LACK OF FOCUSED INFLOW AND GREATER
DOWNDRAFT CAPE...BUT THE ANOMALOUSLY MOIST ENVIRONMENT...PW VALUES
AGAIN GREATER THAN 1.7 INCHES...WILL FAVOR LOCALLY INTENSE RAIN
RATES IN AN AREA ALREADY SATURATED BY A RECENT WET WEATHER
PATTERN. THE MAXIMUM 3-HOUR PRECIPITATION FROM THE SREF IS
PARTICULARLY HIGH OVER SOUTH TEXAS...AT JUST UNDER 3 INCHES IN THE
MODEL.

FARTHER TO THE EAST...UNCERTAINTY INCREASES...BUT OUR RISK AREA
CAPTURES A SWATH OF HEAVY PRECIPITATION FORECAST BY WPC AND
SEVERAL HI-RES MODELS SUCH AS THE 12Z WRF-ARW AND GEM REGIONAL.
THIS SWATH EXTENDS ACROSS NRN MS/AL/GA AND SRN TN...ALONG AND JUST
SOUTH/SOUTHEAST OF THE NOSE OF THE LLJ...AS IT IS DRIVEN EASTWARD
BY THE SHARP EJECTING SHORTWAVE...WITH LESS DEPENDENCE ON THE
DIURNAL CYCLE. A MAXIMUM OF LOW LEVEL MOISTURE TRANSPORT AND PW
ANOMALIES WILL ACCOMPANY THE LLJ...AND THIS PATTERN SOMETIMES
LEADS TO 2-3 HOUR PERIODS OF TRAINING ON SMALLER SCALES IN THE
SOUTHEAST U.S.


...CENTRAL PLAINS / KS EASTWARD TO IL/IN...

IN THE 00Z UPDATE WE EXPANDED THE EXISTING SLIGHT RISK AREA WEST
TO EAST. A SUBTLY DEFINED HEAVY RAIN EVENT IS POSSIBLE FRI
NIGHT/SAT. STRONGER FORCING AND STEEP LAPSE RATES MAY COMPENSATE
FOR SLIGHTLY LESSER INSTABILITY COMPARED TO AREAS FARTHER SOUTH.
EVEN WITH THE THRUST OF GULF MOISTURE SHIFTING SOUTH AND EAST OF
THIS REGION...A RIBBON OF PW VALUES APPROACHING 1.25 INCHES IS
FORECAST TO BE INGESTED BY AND WRAP AROUND THE TIGHT MID LEVEL
CIRCULATION HEADING INTO THIS REGION FROM WESTERN KS. CONVECTION
WILL BE LESS APT TO FORWARD PROPAGATE...GIVEN A WILL BE SLIGHTLY
ELEVATED...AND DRIVEN MORE BY STRONG LOW LEVEL INFLOW AND MID
LEVEL ASCENT RATHER THAN COLD POOL FORCING. SOME SLOW MOVING CELLS
PRODUCING HEAVY RAIN WERE ALREADY DEVELOPING IN NORTHERN KS AT
23Z...AND ARE LIKELY TO FORM AGAIN AS FORCING GRADUALLY SHIFTS
DOWNSTREAM TO THE EAST OVERNIGHT. MODELS SHOW SOME ELEVATED
INSTABILITY WITHIN A DEVELOPING WARM CONVEYOR BELT...INCLUDING
WELL DOWNSTREAM OF THE SURFACE WARM FRONT INTO PARTS OF
MIDWEST/MID MS VALLEY. THE POTENTIAL FOR FOCUSED LOCALLY HEAVY
RAIN SHOULD LINGER THROUGH MIDDAY SATURDAY BEFORE THE MID LEVEL
SYSTEM UNDERGOES RAPID SHEARING UNDER DOWNSTREAM REX BLOCK SET UP.
 WHILE WELL REMOVED FROM DEEPER MSTR TO THE SOUTH...MODEST PWS AND
SLOW MOVEMENT OF THE MID LEVEL CIRCULATION ITSELF COULD LEAD TO A
STRIPE OF 1 TO 2 INCH PLUS RAINS IN THE COMMA HEAD AND NEAR MID
LEVEL COLD POOL. ISOLD HEAVIER AMOUNTS WILL BE POSSIBLE...LEADING
TO A SLIGHT RISK OF EXCESSIVE RAIN.

BURKE/SULLIVAN
$$




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