Quantitative Precipitation Forecast
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FOUS30 KWBC 281403
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1002 AM EDT WED JUN 28 2017

...VALID 15Z WED JUN 28 2017 - 12Z THU JUN 29 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
10 NE OWA 10 SW JMR 15 SSW FSE 15 WNW TVF 15 SW ROX 15 SSE FGN
30 NNE INL 30 ENE ELO 20 SW CMX 25 N ERY 40 NNE DRM 25 NE CYZE
35 WSW CWWX 15 W MOP C09 10 S UIN 30 NE DMO 25 SW IXD 35 E HLC
25 ESE LBF 20 NE BBW 25 ENE JYR 10 NNE OMA FOD 10 NE OWA.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
40 SSE KMZG 30 E KMIU 25 NNE KMIU 15 ENE KRP 20 NNE PKV
15 NNW SGR 30 SSW JAS 15 WNW BTR 20 S HBG 50 NNE MOB 30 ESE GZH
30 S OZR PAM 60 SSW PAM 60 ESE KVOA.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 NW VYS 15 SSW EOK 35 NNW SZL 10 NE TOP 40 SW FNB ICL IKV
10 SSE DEH 10 SSE MDZ 10 NNW ESC 20 WSW CIU 20 ENE DRM CWNL
10 SSE APN 15 ESE LDM 10 SSW UGN 15 NW VYS.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
25 S KVBS 20 SW KVBS 25 W KVBS 10 SSW BPT 10 NE BPT 10 NW LCH
10 ENE ARA 15 NE GAO KDLP KMDJ 25 NW QT9.


...UPPER MISSISSIPPI VALLEY INTO THE UPPER GREAT LAKES...

THE SLIGHT RISK IN THE MIDWEST AND GREAT LAKES APPEARS WELL
PLACED...AND WAS EXPANSIVE ENOUGH THAT THERE DID NOT APPEAR TO BE
REASON TO EXPAND IT. SOME OF THE BETTER PERFORMING GUIDANCE AS OF
THIS MORNING...THE NAM CONUS NEST AND 00Z WRF-ARW...PRODUCE QPF
THAT ALIGNS WELL WITH THE SLIGHT RISK AREA. THERE IS SOME
CONCERN...AS BOTH OF THESE MODELS DEPICT...THAT PERSISTENT LOW
LEVEL CONFLUENCE AT THE TAIL END OF THE EXITING SHORTWAVE THIS
EVENING...COULD LEAD TO A SLOWLY SAGGING MCS PRODUCING VERY HEAVY
RAIN OVER SOUTHERN IOWA / NORTHERN MISSOURI...SO THERE ARE PERHAPS
GREATER ODDS OF FLASH FLOODING IN THOSE LOCATIONS.

SOME THOUGHT WAS ALSO GIVEN TO EXPANDING THE MARGINAL RISK
WESTWARD...ANTICIPATING THAT THE HIGH PLAINS WILL REMAIN
CONVECTIVELY ACTIVE WITHIN POST FRONTAL UPSLOPE...BENEATH
ENERGETIC WESTERLY FLOW ALOFT. THE QPF SIGNAL IS NOT MUCH TO LOOK
AT...BUT WE SUSPECT THERE WILL BE SCATTERED STRONG STORMS WITH
HEAVY RAIN RATES. THEY MAY BE TOO SPARSE AND/OR QUICK MOVING TO
WARRANT MUCH OF AN OUTLOOK...BUT WE DID EXPAND THE MARGINAL RISK
TO COVER THE RECENT RAIN FOOT AND SATURATED GROUND ACROSS CENTRAL
NEBRASKA. CAPE INCREASES BACK INTO THIS AREA DRAMATICALLY AFTER
00Z.


...GULF COAST...

A WEAKNESS IN THE MID LEVEL HEIGHT FIELD EXISTS ALONG THE GULF
COAST...SITTING ATOP A STALLED SURFACE FRONTAL BOUNDARY FROM
NORTHERN FLORIDA TO COASTAL TEXAS. THE SITUATION IS FAVORABLE FOR
DIURNALLY ENHANCED SEA BREEZE ACTIVITY NEAR THE COAST AND BROADER
AREAS OF RAIN JUST OFFSHORE AND AHEAD OF THE WEAKLY DEFINED TROUGH
AXIS. THIS IS ESPECIALLY TRUE OVER THE WESTERN GULF /
TEXAS...WHERE THE HI-RES MODELS HAVE SOME INDICATION OF CONVECTION
AND LATENT HEAT RELEASE BEING SUFFICIENT TO FEEDBACK ONTO THE MID
LEVEL FLOW...DEVELOPING A BROAD CIRCULATION. ANY SHOWERS MAY
PRODUCE LOCALLY HEAVY DOWNPOURS...BUT THE BULK OF THE MORE
ORGANIZED RAINFALL WEDNESDAY SHOULD OCCUR IN ASSOCIATION WITH SEA
BREEZES OVER THE CENTRAL GULF COAST AND THEN DURING THE OVERNIGHT
HOURS OFFSHORE OF TEXAS AND LOUISIANA NEAR THE DEVELOPING LOW
CENTER. SOME OF THIS HEAVY NOCTURNAL RAINFALL MAY MIGRATE
ONSHORE...ESPECIALLY INTO LOUISIANA.

WED NIGHT INTO EARLY THU...THE MODELS DEPICT A SLIGHT NORTHWARD
SHIFT WITH THE MID-LEVEL SHEAR AXIS/VORT LOBE...BECOMING DRAPED
ALONG THE CENTRAL-EASTERN GULF COAST AS THE WESTERN U.S. TROUGH
AMPLIFIES AND THE SOUTHEAST RIDGE SLIDES A LITTLE FARTHER EAST. AS
A RESULT...EXPECT MORE OF THE CONVECTION OVER THE GULF TO COME
ASHORE ACROSS THE WESTERN AND ESPECIALLY CENTRAL PORTIONS OF THE
GULF COAST. HIGHEST AREAL-AVERAGE TOTALS (2-2.5") WERE NOTED IN A
RELATIVELY NARROW CORRIDOR CLIPPING SOUTHERN LA...THOUGH SOME OF
THE HIGH-RES CAMS CONTINUED TO DEPICT SOME RATHER PRODIGIOUS
TOTALS (4-8+ INCHES) JUST OFFSHORE.

IN TERMS OF THE EXCESSIVE RAINFALL THREAT...WPC INCLUDED A NARROW
SLIGHT RISK AREA OVER FAR SOUTHERN LOUISIANA GIVEN THE
AFOREMENTIONED WETTER TRENDS IN THE GUIDANCE. A HIGHLY-FAVORABLE
THERMODYNAMIC ENVIRONMENT CHARACTERIZED BY PWS AOA 2.25" ALONG
WITH A DEEP...NARROW DISTRIBUTION OF INSTABILITY (MUCAPES
1500-2000 J/KG JUST OFFSHORE) WILL MAKE FOR ROBUST WARM RAIN
PROCESSES AND HIGHLY-EFFICIENT SHORT-TERM RAINFALL
RATES...POSSIBLY EXCEEDING 2.5"/HOUR UNDERNEATH THE HEAVIEST
CORES.

HURLEY/BURKE
$$





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