Quantitative Precipitation Forecast
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FOUS30 KWBC 301410
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1010 AM EDT SUN APR 30 2017

...VALID 15Z SUN APR 30 2017 - 12Z MON MAY 01 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 WSW GVL 25 SSW MAI 30 N CYD 15 N KMYT 15 WNW KEIR 10 NE KVNP
30 WSW HEZ 20 WNW HEZ 15 SE BQP 15 N PBF 20 N HRO 30 SW SZL
30 S LWD 10 E CAV 10 NW ONA GRB 15 S CIU 30 WSW CWWX 15 SE CWSN
CGF 15 SSE MFD 25 SE JKL 15 WSW GVL.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
FFT 20 NNE 4A9 10 N TOI 10 E CEW 20 NNW KMIS 1B7 30 SE P92
15 W P92 BTR 25 ENE HEZ 15 SE TVR 35 S GLH 35 SSE SGT 20 NE SGT
20 ENE ARG 30 WSW FAM AIZ 15 NE DMO 15 NW UIN 25 WNW PWK
15 NNW BIV JYM FFT.

MODERATE RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
30 NE NMM 35 SSW TCL 45 WNW MXF 20 NW GZH 20 NW PQL 10 SSE HSA
10 SE NEW 10 W MSY 30 WNW MSY 20 W HDC 15 NNE MCB 20 S JAN
45 SSE GLH 20 ESE GLH 20 W UTA CIR 15 SSW FWC 20 ESE HSB
10 N OLV 15 NE GWO 50 WNW NMM 30 NE NMM.


15Z UPDATE...

CHANGES MAINLY REFLECT THE EASTWARD PROGRESSION OF FRONTAL
CONVECTIVE BAND EXTENDING FROM THE MID MS VALLEY SWD INTO THE
LOWER MS VALLEY.   FEEL THE HRRR HAS A GOOD HANDLE ON CURRENT
TRENDS WITH THE MORE ACTIVE CONVECTIVE BAND PUSHING OUT ACRS SRN
MS AND SE LA THIS MORNING AND EARLY AFTN AS PREFRONTAL SQLN TAPS
NARROW AXIS OF VERY HI MUCAPES AND HI PWS WORKING NWD FROM THE
NCNTL GULF OF MEX.  THIS LINE MAY TEND TO WEAKEN A BIT LATER THIS
MORNING BUT VORT LOBE ROTATING AROUND BASE OF PLAINS UPPER LOW
WILL LIKELY GIVE A BOOST TO CONVECTION LATER THIS AFTN/EVENING
ACRS PARTS OF SE LA/MS/AL.  WHILE FFG VALUES ARE RATHER HIGH ACRS
PARTS OF SRN MS/AL...RAIN RATES COULD BE QUITE HIGH WITH MULTIPLE
N/S CONVECTIVE BANDS LEADING TO POTNL HEAVY RAINFALL TOTALS OF 3
TO 5 INCHES IN SPOTS..SUPPORTING THE MDT RISK OF EXCESSIVE RAINS
ACRS THIS AREA.

...SOUTHERN U.S. FROM THE MISSOURI BOOTHEEL SOUTH AND EASTWARD...

THE THREAT OF ADDITIONAL FLOODING WILL MOVE DOWNSTREAM INTO THE
MID SOUTH AND THE TENNESSEE VALLEY TODAY. WITH STRONG FORCING AND
WIDELY AVAILABLE GULF MOISTURE AND INSTABILITY...THERE MAY BE VERY
LITTLE BREAK TO THE ACTION AT THE USUAL DIURNAL MINIMUM THIS
MORNING. AT 0830Z...CONVECTION HAD ORGANIZED IN TWO PRIMARY
AREAS...ONE BEING A LARGE ORGANIZED MCS OVER EASTERN
ARKANSAS...MIGRATING SLOWLY EASTWARD. THIS WAS FED BY THE MOST
INTENSE PORTION OF THE LOW LEVEL JET...AND DEVELOPMENT OF NEW
RAINFALL WILL OCCUR PREFERENTIALLY BACK ALONG THE SOUTHWEST
FLANK...TOWARD THE INSTABILITY AXIS STRADDLING THE MISSISSIPPI
RIVER. A SECOND MCS WAS BECOMING ESTABLISHED OVER LOUISIANA IN AN
AREA OF PERHAPS SOMEWHAT RICHER MOISTURE...SURFACE DEWPOINTS NEAR
75 DEGREES REPRESENTING TRULY TROPICAL AIR...AND WHERE UPPER LEVEL
DIFLUENCE WAS INCREASING AS THE SYNOPTIC SYSTEM BEGAN TO
ACCELERATE EASTWARD. THE HRRR WAS PICKING UP ON THIS MCS...AND WAS
USED TO ADJUST EXPECTATIONS...WITH PERHAPS THE SWATH OF HEAVIEST
RAIN OCCURRING IN BETWEEN NEW ORLEANS AND JACKSON THROUGH THE
FIRST HALF OF THE DAY.

IN VERY GENERAL TERMS...THE MODELS CARRY BOTH THESE CONVECTIVE
SYSTEM EASTWARD TODAY...AND ALTHOUGH THERE MAY BE A RELATIVE
MINIMUM IN BETWEEN THEM...CONFIDENCE IN THE DETAILS IS QUITE LOW.
THE SITUATION IS NOT AS CLEAR CUT AS IT WAS BEFORE THE WARM SECTOR
BECAME RIDDLED WITH OUTFLOWS. FOR THIS REASON AND FOR HYDROLOGIC
REASONS...A FEW DROUGHT AREAS AND HIGHER FLASH FLOOD GUIDANCE
VALUES...WE ATTEMPTED TO BE RESTRICTIVE WITH THE EASTWARD EXTENT
OF THE MODERATE RISK AREA. AT THE SAME TIME...UNUSUALLY RICH
MOISTURE AND STRONG FORCING WILL YIELD PARTICULARLY HEAVY SHORT
TERM RATES...SUCH THAT WE DID HAVE CONFIDENCE TO EXPAND THE
MODERATE RISK TO CAPTURE THE ONGOING MCS AND ITS EXPECTED
EVOLUTION OVER LA/MS THIS MORNING.


...OHIO VALLEY / MIDWEST / GREAT LAKES...

THROUGH A COMBINATION OF WARM ADVECTION...FRONTOGENESIS...AND
ASCENT ON THE SOUTHWEST FLANK OF A BROAD UPPER LEVEL JET
STREAK...RAIN MAY BE MORE OR LESS CONTINUOUS ACROSS WESTERN AND
CENTRAL MICHIGAN TODAY...INCLUDING ACROSS LAKE MICHIGAN TO
NORTHERN ILLINOIS. IT WILL BE DIFFICULT FOR MUCH INSTABILITY TO
DEVELOP HERE...BUT DEEPLY SATURATED PROFILES NORTH OF A WARM FRONT
WILL SUPPORT HEALTHY RAINFALL AMOUNTS IN THE 1.0 TO 2.5 INCH
RANGE...ON AVERAGE. SOME INSTABILITY WILL LIKELY DEVELOP A LITTLE
FARTHER SOUTH AND WEST...INTO WESTERN AND SOUTHERN ILLINOIS...AND
FEEDING UP INTO SOUTHEAST IOWA...JUST AHEAD OF A TRIPLE POINT LOW.
THE WPC QPF EMPHASIZES THIS AREA DURING PEAK HEATING EARLY THIS
EVENING. STRONG ASCENT WILL SUPPORT REASONABLY HEAVY RAINS DOWN
INTO KENTUCKY AND OVER INTO INDIANA AND PART OF OHIO
TODAY...ALTHOUGH THE STRONGER INSTABILITY AND HEAVIEST RAINS WILL
LIKELY OCCUR OVER THE SOUTHERN U.S. WPC USED HOURLY AND
THREE-HOURLY RAIN RATE FORECASTS FROM THE HI-RES MODELS...ALONG
WITH ANTECEDENT RAINFALL / SATURATED SOIL...TO DELINEATE MARGINAL
VERSUS SLIGHT RISK IN THESE AREAS.

BURKE/SULLIVAN
$$





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