Quantitative Precipitation Forecast
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000
FOUS30 KWBC 290812
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
411 AM EDT THU JUN 29 2017

...VALID 12Z THU JUN 29 2017 - 12Z FRI JUN 30 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
CWTA CWHY 1V4 10 NNE RUT RUT 25 ENE RME 20 SW ART 25 SW CXKE
CTCK.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
25 ESE KCRH 15 NNW KCRH 10 ENE KVBS LCH HEZ NMM 30 SSE 1M4
20 W GAD 25 NNE ALX TOI 15 ENE CEW 35 SSE NPA 15 NNW RAM.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 SW OKK 30 SSW PPQ 15 ESE CNU 30 SSW HUT 20 SSE HJH 10 SW HNR
25 W ALO 10 NNE EFT 15 NNE EKM 20 SW OKK.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
10 SSE RFD 10 SSE IGQ 10 NE TIP 25 ENE UIN 35 E UKL 25 NW EMP
10 W SDA 20 SW VTI 10 SSE RFD.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 SW SRN 10 ENE KCMB 30 WNW LFT 25 NW MCB 25 SSW MEI
55 WNW GZH 20 SW GZH PNS 25 SSW JKA 25 N KVKY.


...CENTRAL U.S....

AN ACTIVE NORTHERN STREAM WILL PRODUCE ORGANIZED BROAD SCALE
PRECIPITATION AREAS ALONG AN ADVANCING WARM FRONT / SURFACE LOW
TRACK THROUGH THE GREAT LAKES AND INTO NORTHERN NEW ENGLAND...MORE
CONVECTIVELY DRIVEN ALONG THE TRAILING COLD FRONT TOWARD THE
MID-LOWER  MISSOURI VALLEY...AND MORE SCATTERED IN NATURE ROLLING
OUT OF THE NORTHERN ROCKIES AND NORTHERN HIGH PLAINS. OVER THE
GREAT LAKES INTO THE NORTHEAST...MORE LIMITED ELEVATED DEEP-LAYER
INSTABILITY AHEAD OF THE WARM FRONT WILL LEAD TO A MORE LIMITED
RANGE WITH THE QPF AMOUNTS...THOUGH THE MODELS CONTINUE TO SHOW
MORE THAN SPREAD THAN DESIRABLE FOR A DAY 1 FORECAST IN TERMS OF
THE LOCATION OF MAX TOTALS. WPC OPTED FOR AN ENSEMBLE BLEND...LED
BY THE ECMWF...WRF-ARW...AND HREF MEAN. HIGHEST AREAL AVERAGE
TOTALS OVER THIS AREA... 0.50-1.0 INCH...WERE NOTED ACROSS UPSTATE
NY INTO NORTHERN VT/NH AND CENTRAL ME. PER THE HIGH-RES
CAMS...LOCALIZED AMOUNTS OF 1.5-2.0" ARE EXPECTED UNDERNEATH THE
STRONGER ELEVATED CONVECTIVE CORES.

FARTHER SOUTH AND WEST...ELEVATED CONVECTION CONTINUES TO GROW
UPSCALE ACROSS PORTIONS OF THE CENTRAL PLAINS INTO THE MID MS
VALLEY EARLY THIS MORNING...OWING TO THE STRENGTHENING LOW-LEVEL
JET INTO A QUASI-STATIONARY FRONTAL ZONE ALONG THE LEADING EDGE OF
THE THICKNESS DIFLUENCE. THE CONVECTION WILL THEN EXHIBIT TYPICAL
DIMINISHING TRENDS AFTER DAYBREAK AS THE NOCTURNAL LLJ WANES AND
THE ACTIVITY LOSES ITS ELEVATED CHARACTERISTICS. THIS WILL ALLOW
FOR A TEMPORARY REPRIEVE IN THE FLASH FLOOD THREAT...HOWEVER
ADDITIONAL  CONVECTION FIRING LATER IN THE AFTERNOON AHEAD OF THE
APPROACHING FRONT...BUOYED BY STRONG DEEP-LAYER DIURNAL
INSTABILITY (MIXED LAYER CAPES 2000-3500+ J/KG)...WILL BECOME
BETTER ORGANIZED AND AGAIN GROW UPSCALE LATER IN THE
EVENING/OVERNIGHT. THE MAIN CONCERN IS WHETHER OR NOT THIS
ACTIVITY WILL FALL ACROSS AREAS ALREADY BESIEGED BY THE HEAVY
RAINFALL WED NIGHT. SUSPECT AT LEAST A GOOD PORTION WILL
(ESPECIALLY ACROSS NORTHEAST KS-NORTHERN MO-SOUTHERN IA-WESTERN
IL)...HOWEVER PER THE WRF-ARW DEPICTION...THE LIKELY SOUTHWARD
PUSH IN AN OUTFLOW-REINFORCED QUASI WEST-EAST SURFACE BOUNDARY
WOULD EVENTUALLY FAVOR SOUTHERN KS INTO CENTRAL-SOUTHERN MO LATER
THU NIGHT.

IN TERMS OF THE EXCESSIVE RAINFALL OUTLOOK...WILL MAINTAIN THE
SLIGHT RISK OVER AREAS MOST VULNERABLE TO ADDITIONAL HEAVY
RAINFALL PER THE RECENT HEAVY RAINS/RESULTANT ANTECEDENT WET SOILS
AND LOWER FFG.


...CENTRAL GULF COAST...

A SHEAR AXIS OR 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. PERSISTENT LATENT
HEAT RELEASE FROM CONVECTION NEAR/AHEAD OF THE SHEAR AXIS MAY
OCCASIONALLY LEAD TO AN INCREASE OF MID LEVEL VORTICITY...FURTHER
ORGANIZING THE PRECIPITATION SHIELD...SUCH AS WAS SEEN OFFSHORE OF
LOUISIANA EARLY WEDNESDAY AFTERNOON. ONCE AGAIN...OUTSIDE OF THE
TYPICAL DIURNAL ENHANCEMENT FROM SEA/BAY BREEZES...THE MAIN
QUESTION WITH THIS FORECAST IS HOW MUCH OF THE CONVECTION NEAR THE
MID LEVEL TROUGH WILL MIGRATE ONSHORE TODAY. INSTABILITY WILL
REMAIN MAXIMIZED OFFSHORE...BUT THE GFS AND ECMWF INDICATE A
SUBTLE 250 MB JET STREAK THAT WILL BRUSH ACROSS THE GULF COAST
DURING THAT TIME FRAME...ENHANCING SOUTHERLY FLOW OFF THE
GULF...AND PULLING BOTH INSTABILITY AND FORCING MECHANISMS
NORTHWARD. SEVERAL HI-RES MODELS INDICATE PARTICULARLY HEAVY QPF
OVER SOUTHEAST LOUISIANA INTO SOUTHERN MS-AL DURING THE DAY 1
PERIOD...WHILE A GOOD CHUNK OF THE GLOBAL GUIDANCE SHOW HEAVIER
AMOUNTS DISPLACED FARTHER NORTH/INLAND AWAY FROM THE AXIS OF
STRONGEST DEEP-LAYER INSTABILITY. THERE ARE LARGE SCALE REASONS TO
EXPECT THE MID LEVEL TROUGH TO COME FARTHER ONSHORE...WITH
CONFLUENT LOW LEVEL FLOW INCREASING IN STRENGTH INTO LOUISIANA
ESPECIALLY. WPC FAVORED A  BLEND OF THE PREVIOUS WPC FORECAST AS
WELL AS THE 00Z HREF MEAN AND HIGH-RES VERSION OF WPC`S IN-HOUSE
ENSEMBLE.

HURLEY
$$





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