Quantitative Precipitation Forecast
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FOUS30 KWBC 290019
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
819 PM EDT WED JUN 28 2017

...VALID 01Z THU JUN 29 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
40 SSE KMZG 30 E KMIU 15 ENE KMIU 30 NNW KMZG 15 NW LBX
35 E IAH 20 SSW DRI 20 SSE DRI 15 WNW BTR 20 S HBG 50 NNE MOB
30 ESE GZH 30 S OZR PAM 60 SSW PAM 60 ESE KVOA.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
25 NNW LNK 15 NW CSQ 15 ESE IKV 20 WNW MIW 20 SSW AUM
15 ENE RNH 10 S EVM 10 N BJI 20 NE TVF 15 SW ROX 15 SSE FGN
30 NNE INL 35 SSE CWCH 30 SW CYQT 40 WNW CMX 40 NNW SAW 25 N ERY
40 NNE DRM 25 NE CYZE 35 WSW CWWX 35 SW OSC 10 W AZO 10 SW SBN
15 WNW IKK 20 SSE C75 10 SSE UIN 30 NE LXT 15 N MHK 35 WNW CNK
10 WNW HDE 20 ENE LXN 30 N EAR 15 NNE GRI 25 NNW LNK.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
DLL 15 NW UNU 10 NW SBM 15 SW LDM 25 SSE LDM 20 SSW RQB
15 NW LWA 10 WNW LOT 10 NNW C75 15 ESE EOK 25 WNW UIN 15 SW IRK
25 NNW CDJ 30 SW LWD 15 S CSQ 10 S OXV 30 ENE PEA 15 WNW CID
15 ESE IIB 20 S OVS DLL.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
25 S KVBS 15 SSW KVBS 15 SE LCH 10 E ARA 15 NE GAO KDLP KMDJ
25 NW QT9.


01Z UPDATE...
CHANGES TO THE PREVIOUS FORECAST AREAS AND REASONING WERE
RELATIVELY MINOR.  ACROSS THE UPPER MS VALLEY...HAVE TRIMMED
WESTERN PORTIONS OF THE PREVIOUS SLIGHT RISK AREA WITH STRONGER
AND MORE ORGANIZED STORMS CONTINUE TO PROGRESS EWD TOWARD ERN/SRN
PORTIONS OF IA...EXTREME NRN MO AND SRN WI..WITH THESE STORMS
CONTINUING TO FEE OFF OF AREA OF GREATER THAN 2 THSD J/KG MLCAPES
EXTENDING NEWD FROM MO  INTO SRN WI. NORTHERN PORTION OF THIS AREA
WAS ALSO REDUCED GIVEN LACK OF INSTABILITY..THOUGH SOME ELEVATED
STOMRS MAY DVLP ACRS NRN PORTIONS OF THE L.P. OF MI LATE TONIGHT.
 MAIN CONCERN WITH THIS AREA IS WITH THE MULTIPLE LINE SEGMENTS
SOME OF WHICH HAVE BECOME ALIGNED WITH THE MEAN WLY MID LEVEL FLOW
LEADING TO SOME TRAINING CONCERNS ESPECIALLY THE SLOWER ACTIVITY
ALONG THE SRN EDGE OF THE STRONGER WLYS OVER SRN IA/NRN MO.  ACRS
THE GULF COAST...MADE A SLIGHT SHIFT EWD TO THE SLIGHT RISK ACRS
LA BUT OTHERWISE NO MAJOR CHANGES IN FORECAST RATIONALE.  HRRR
GUIDANCE HAS BEEN TOO QUICK TO DVLP HEAVIER RAINS ACROSS SRN LA
GIVEN CLOUD COVER AND LACK OF INSTABILITY...BUT RECENT SATL
IMAGERY DOES SEEM TO SHOW A SLIGHT NWD TREND TOWARD THE COLDER
CLOUD TOPS TOWARD THE SE LA COAST AND THE HRRR SIM REFLECTIVITY
SUPPORTS THIS EWD SHIFT OF THE POTNL HEAVIER RAINS THERE
OVERNIGHT.    SULLIVAN   PREVIOUS DISCUSSION FOLLOWS...



...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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