Quantitative Precipitation Forecast
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FOUS30 KWBC 220049
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
849 PM EDT FRI APR 21 2017

...VALID 01Z SAT APR 22 2017 - 12Z SAT APR 22 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
10 SSW I16 15 WSW HLX 20 ESE 1A5 30 ENE CHA 15 NNE MDQ 10 W MSL
45 NW GWO 10 NNE LLQ 10 NE TXK 20 SW LBR 20 NNW GVT 15 E GYI
10 WSW MLC 15 SW GMJ 15 NE GMJ 15 NW SGF 40 WSW TBN 10 NNE FAM
15 S CUL 25 SSE FTK 30 NNE SME 35 N LNP 10 SSW I16.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 SE LRF 20 N MWT 10 N RKR 10 SW FYV 15 E ROG 45 E SGF
35 WSW FAM 20 SW FAM 35 SW EHR 25 WNW BWG 30 E CKV 55 ENE MKL
20 NE OLV 15 NNE SGT 20 SE LRF.


...01 UTC UPDATE...

ADJUSTED THE PREVIOUS WPC SLIGHT AND MARGINAL EXCESSIVE RAINFALL
THREAT AREAS FOR LATEST SATELLITE/RADAR AND HRRR TRENDS.

SCHICHTEL


...SOUTHERN PLAINS...LOWER-MID MISSISSIPPI VALLEY...TENNESSEE
VALLEY...LOWER OHIO VALLEY...

A SLOWLY EVOLVING UPPER TROUGH...ONE THAT WILL ELONGATE WITH TIME
AS IT BECOMES INCREASINGLY CONSTRICTED BY MID LEVEL RIDGES TO ITS
NORTH AND SOUTH...WILL COMBINE WITH FAVORABLE UPPER JET DYNAMICS
IN THE FORM OF COUPLED JET STREAKS TO GENERATE ADDITIONAL HEAVY
RAINFALL NORTH OF A SURFACE STATIONARY FRONT.

LARGELY LEFT THE BROAD SLIGHT RISK OF EXCESSIVE RAINFALL IN TACT
FROM THE OVERNIGHT SHIFT.  THE NORTHERN PORTION OF THE SLIGHT RISK
IS IN A REGION WHERE INSTABILITY WILL GENERALLY BE ALOFT THAT
RESULTS IN ONLY MODEST RAINFALL RATES.  THE CONCERN HERE IS THAT
THE FLASH FLOOD GUIDANCE VALUES ARE CLOSE TO 1.5 INCHES PER HOUR
FROM SOUTHEAST KS INTO SOUTHERN MO...WITH VALUES CLOSER TO AN INCH
PER HOUR IN AND NEAR THE OZARKS.  THIS AREA SHOULD RECEIVE ONE
PERIOD OF RAIN THIS MORNING FOLLOWED BY AT LEAST ONE OTHER ROUND
LATER TODAY OR TONIGHT AS A WAVE DROPS OUT OF THE WESTERN HIGH
PLAINS.  THINKING IS THAT SEVERAL ROUNDS OF RAIN WILL RESULT IN
LOWERING OF THE FFG WITH TIME.

INSTABILITY AND ASSOCIATED HIGHER RAINFALL RATES ARE MORE LIKELY
TO OCCUR ACROSS THE SOUTHERN PORTION OF THE SLIGHT RISK
AREA...INITIALLY BEGINNING OVER PARTS OF THE SOUTHERN PLAINS AND
LOWER MISSISSIPPI VALLEY THAT SPREADS INTO THE TN LATER TONIGHT.
CAPES ARE EXPECTED TO PEAK AROUND 2000 J PER KG AND LOW LEVEL FLOW
INCREASES TO 50 KTS OR MORE AHEAD OF AN AREA OF LOW PRESSURE
APPROACHING FROM THE WEST.

SHORT TERM RADAR TRENDS SUGGEST THAT CONVECTION OVER SOUTHERN KS
INTO SOUTHWEST OK AS OF 14Z IS PROPAGATING EASTWARD MORE QUICKLY
THAN EARLIER FORECAST. WHILE THIS MAY ULTIMATELY LIMIT RAFL AMOUNT
DESPITE THE ENHANCED HOURLY RAINFALL RATES...THE SLOWLY-EVOLVING
SYNOPTIC PATTERN AND RESULTANT MULTIPLE ROUNDS OF CONVECTION OVER
THE SAME AREAS WILL INCREASE SOIL MOISTURE/LOWER FFGS WITH TIME.

BANN

$$





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