Quantitative Precipitation Forecast
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FOUS30 KWBC 211501
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1100 AM EDT FRI JUL 21 2017

...VALID 15Z FRI JUL 21 2017 - 12Z SAT JUL 22 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
85 NNW MMHO 60 SW OLS 35 WNW OLS 40 SE CGZ 10 NE SDL 25 NW PRC
65 SSE SGU 20 ENE CDC 40 ESE U24 35 E PVU 30 ENE FIR 10 W RWL
10 NE CYS 15 SW AKO 10 ESE PUB 15 W LVS 20 W 4CR 30 WNW GDP
30 W MRF 90 SSW MRF 80 E MMCU.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
10 ESE CWCF 55 NE CWII 35 NW INL 15 SSE HIB EGV 15 NW TVC
10 SW CFS 10 NNW MFD 20 SSW EKN LWB 20 NW 6V3 25 SW BMG
10 SE PIA IOW 20 W IKV 10 NNW OMA 10 NE JYR 20 NW EAR 15 NNE BBW
20 E YKN 35 SW BKX 40 NW HON 35 NNE BIS 35 NE CYEN 30 NNW CWIK.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
75 SSE OLS 20 SSE OLS 15 ESE DMA 40 ESE IWA 55 ESE PRC 30 S 40G
20 WNW GCN 60 ESE SGU 35 W PGA 25 SSE INW 25 N SOW 35 SSW RQE
20 WNW CEZ 10 SE EEO 40 SW LAR 10 NE BJC 10 ENE MNH 45 E MYP
25 W ALS 35 NNW SAF 45 WNW TCS 30 S DMN 115 ESE DUG.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 ENE IOW 15 WSW FOD 10 WSW EST 20 ESE MML 10 NNE HCD
10 NNE STP 10 E MFI 20 ESE ATW 20 N MKG 15 NNW FPK JYM 25 SE IRS
25 SSW SBN 25 NNE DNV 15 SW PNT 20 ENE IOW.

MODERATE RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 ENE SQI 10 NW MXO 15 E MCW 10 NW AEL 20 NE TOB 10 NE VOK MWC
15 E UGN 10 WNW MDW 15 ENE SQI.


15 UTC UPDATE...

MADE SOME ADJUSTMENTS ACROSS THE UPPER MIDWEST BASED UPON THE
LATEST FLASH FLOOD AND HI-RES NUMERICAL GUIDANCE.  THIS INCLUDED A
SLIGHT SOUTHWARD SHIFT IN THE SLIGHT/MODERATE RISK AREAS.  LATEST
RUNS OF THE HRRR HAVE BEEN FAIRLY CONSISTENT IN SHOWING CONVECTION
DEVELOPING ACROSS EASTERN SD THIS AFTERNOON...MOVING EAST ALONG
THE MN/IA BORDER WITH TRAINING CONVECTION DEVELOPING ALONG THE
WESTERN FLANK OF THE RESULTANT OUTFLOW.  THIS MAY CONTRIBUTE TO AN
AXIS OF HEAVY RAINFALL ACCUMULATIONS ACROSS PORTIONS OF NORTHERN
IA INTO SOUTHWESTERN WI.  WHILE THIS AXIS IS GENERALLY FURTHER
SOUTH THAN THE OVERNIGHT MODEL CONSENSUS...THE HRRR APPEARS TO AT
LEAST HAVE A BETTER HANDLE ON THE CURRENT CONDITIONS.  FURTHER
ADJUSTMENTS BASED ON THE 12 UTC MODEL SUITE MAY BE FORTHCOMING.

PREVIOUS DISCUSSION...

...NORTHERN PLAINS/UPPER MIDWEST SOUTHEASTWARD THROUGH THE OH
VALLEY...

...MDT RISK OF EXCESSIVE RAINS FOR PORTIONS OF SE MN..NE IA..SRN
WI AND EXTREME NRN IL...

A FAIRLY SIGNIFICANT HEAVY RAIN EVENT WILL LIKELY UNFOLD ACRS
PARTS OF THE UPPER MIDWEST WITH POTNL FOR FLASH FLOODING
ESPECIALLY LATE FRI INTO FRI NIGHT.  A WARM FRONT IS EXPECTED TO
RETURN NWD IN ADVANCE OF A LOW PRES SYSTEM THAT WILL PUSH EWD ACRS
THE ERN DAKOTAS.  THE LOW IS EXPECTED TO PROVIDE STG MSTR
TRANSPORT INTO AND NORTH OF THE BNDRY WITH PWS FCST TO INCREASE TO
BETWEEN 2 TO 2.25 INCHES.  FORECAST LIS ALONG AND SOUTH OF THE
FRONT ARE FCST TO INCREASE TO BETWEEN -8 TO -10 DURING PEAK
HEATING WHICH SHOULD ALLOW FOR RAPID EXPANSION OF CONVECTION ONCE
CAP IS BROKEN. PATRN WILL GENLY BE SUPPORTIVE OF CELL TRAINING
WITH MID/UPR FLOW GENLY PARALLEL TO THE SFC FRONT.  THUS..POTNL
WILL EXIST FOR RATHER WIDESPREAD 2 TO 3+" RAINS WITH LOCAL AMOUNTS
UP TO 6 INCHES.  GENL TRENDS OF THE LAST FEW MODEL CYCLES HAVE
SHOWN A SUBTLE SHIFT NWD TO THE MAIN PCPN AXIS.  IN THE CASE OF
THE GFS...IT IS A MUCH FARTHER N SOLN AND APPEARS A BIT OF AN
OUTLIER SOLN AT THIS TIME.  MOST OF THE 00Z HI RES RUNS..REMAIN ON
THE SRN SIDE OF THE GLOBAL GUIDANCE AND ARE GENERALLY
PREFERRED..WITH THE WRF ARW AND NAM CONEST GIVEN MORE WEIGHT.
OVERALL GIVEN THE SLIGHT NWD TRENDS IN THE MODELS...MANUAL QPF
HAVE SHIFTED THE HEAVIER QPF AXIS SLIGHTLY NWD FROM CONTINUITY.
STILL WITH THE MAIN HEAVY RAIN AXIS FORECAST TO OCCUR OVER AREAS
THAT HAVE EXPERIENCED SOME RECENT HEAVY RAINS...HAVE HIGHLIGHTED
MUCH OF SE MN..NE IA INTO SRN WI AND EXTREME NRN IL IN A MODERATE
RISK OF EXCESSIVE RAINS.  ADDITIONAL STORMS ARE LIKELY TO CONTINUE
TO SPREAD SEWD FROM EARLY MORNING COMPLEX ACRS PARTS OF THE
MIDWEST INTO THE OH VALLEY TOWARD THE CNTL APLCNS THIS AFTN.
WHILE NOT LIKELY TO PRODUCE WIDESPREAD HEAVY RAINS..NONE THE
LESS..STG INSTABILITY AND MDTLY HI MSTR COULD LEAD TO LOCALLY
HEAVY RAINS EWD INTO PARTS OF THE CNTL APLCNS FRI/FRI NIGHT AND
ISOLD FLASH FLOODING CAN NOT BE RULED OUT AND THEREFORE THIS AREA
HAS BEEN CONTAINED IN A MARGINAL RISK.    A WEAK 7H WAVE MOVING
ACROSS SOUTHERN CANADA AND THE DAKOTAS WILL SUPPORT AN AREA OF
CONVECTION AHEAD OF AN ASSOCD COLD FRONT FRI AFTN.  STG
INSTABILITY DVLPG AHEAD OF THE FRONT THRU NRN MN WILL LIKELY
SUPPORT SOME INTENSE CONVECTION..BUT CURRENT THINKING IS THAT WITH
DEEPER MSTR FOCUSING TO THE SOUTHEAST...THE VERY INTENSE AMOUNTS
FORECAST BY THE GFS APPEAR OVERDONE..BUT STILL COULD SEE LOCALLY
HEAVY DOWNPOURS FROM THE ERN DAKOTAS INTO NWRN MN GIVEN EXPECTED
HIGH INSTABILITIES FRI AFTN/EVENING.

...4 CORNERS REGION...

SOME SUBTLE DRYING IS EXPECTED THROUGH PARTS OF THE GT BASIN AS
WLYS TAKE A SLIGHT DIP SWD ACRS THE WEST COAST..HOWEVER FOR MUCH
OF THE 4 CORNERS REGION...PATRN WILL REMAIN MUCH THE SAME WITH
AREA WELL ENTRENCHED IN MONSOONAL CIRCULATION AROUND THE WESTERN
PERIPHERY THE STRONG UPPER RIDGE SITUATED OVER THE CNTL PLAINS/MID
MS VALLEY.  THE HIGH MSTR COMBINED WITH DAYTIME HEATING AND EMBDD
WEAK VORTS/MCVS ROTATING WITHIN THE WEAK ANTICYCLONIC CIRCULATION
WILL SUPPORT SOME LOCALLY HEAVY RAINFALL ACCUMULATIONS ALONG WITH
THE POTNL FOR FLASH FLOODING ESPECIALLY ACRS BURN SCAR AREAS AND
NEAR STEEPER TERRAIN.

PEREIRA/SULLIVAN
$$





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