Quantitative Precipitation Forecast
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135
FOUS30 KWBC 220055
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
854 PM EDT FRI JUL 21 2017

...VALID 01Z SAT JUL 22 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 40 WSW OLS 50 WSW TUS 45 W LUF 20 N IFP
45 SW SGU 20 WNW CDC 10 ESE MLF 25 NE U24 40 E SLC 20 W CMS
10 W RWL 10 NE CYS 15 SW AKO 10 ESE PUB 25 W TAD 25 N CQC
20 N ROW 30 WNW INK 15 N E38 85 SSW MRF 65 ENE MMCU.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
10 ESE CWCF 55 WNW CYRL 40 W CWCH 20 WNW JMR 15 NNW RPD
20 WSW SUE 15 N PTK 25 N ZZV LCK 15 SE MIE 10 N CMI 20 SSE MUT
15 ESE AWG 20 W IKV 10 NNW OMA 10 NE JYR 20 NW EAR 15 NNE BBW
25 WNW ORC PQN 30 NNW ABR 15 SW DVL 25 N CWEI 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 45 NNW GCN 35 SW 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
25 ENE IOW 20 ESE MIW 10 N BNW AXA KACQ 35 SE EAU MTW 10 SW LAN
10 W TDZ 15 S FDY 20 WSW AOH 15 N GUS IKK 15 S VYS 25 ENE IOW.

MODERATE RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
10 NW SQI 15 SSE MXO 20 WSW ALO 15 WSW CCY 10 S LSE 35 NNW DLL
ETB 15 ESE RAC 10 SW IGQ 10 NW SQI.


...01 UTC UPDATE...

A MARGINAL AREA OVER THE WRN MID-ATLANTIC HAS EXPIRED ALONG WITH
SUPPORTING CONVECTION. REMAINING THREAT AREAS OVER THE SWRN
US/CENTRAL GREAT BASIN/ROCKIES AND THE MIDWEST/GREAT LAKES REMAIN
ACTIVE AND WERE ONLY SLIGHTLY MODIFIED TO BETTER FIT LATEST
RADAR/SATELLITE/HRRR TRENDS AND LATEST WPC MESOSCALE PRECIPITTAION
DISCUSSIONS #527...#528 AND #529.

SCHICHTEL


18 UTC SPECIAL UPDATE...

WHILE DIFFERENCES IN THE DETAILS REMAIN...THE 12 UTC
GUIDANCE...INCLUDING THE HI-RES MODELS ARE IN GENERALLY GOOD
AGREEMENT SHOWING A CONVECTIVE COMPLEX DEVELOPING ACROSS IA THIS
AFTERNOON...MOVING EAST INTO SOUTHERN WI AND NORTHERN IL THIS
EVENING...WITH SOME POTENTIAL FOR TRAINING CELLS AS SOUTHWESTERLY
LOW LEVEL INFLOW CONTINUES TO CHANNEL DEEPER MOISTURE INTO THE
WESTERN FLANK OF THE ASSOCIATED OUTFLOW BOUNDARY.  THE OVERALL
MODEL TREND IN THE 12 UTC GUIDANCE WAS TOWARD A MORE SOUTHERLY
AXIS OF HEAVIER AMOUNTS...WHICH IS REFLECTED IN THE WPC QPF.
HEAVIEST AMOUNTS DURING THE AFTERNOON AND EVENING HOURS ARE
EXPECTED TO FOCUS FROM NORTHEASTERN IA INTO SOUTHERN WI AND
NORTHERN IL...WHERE SOME OF THE 12 UTC GUIDANCE IS INDICATING
LOCALLY HEAVY AMOUNTS OF 3-6 INCHES.  IN ADDITION TO SHIFTING
FURTHER TO THE SOUTH...ALSO EXTENDED SOME HEAVIER AMOUNTS IN THE
WPC QPF FURTHER TO THE EAST ACROSS LAKE MI INTO SOUTHWESTERN LOWER
MI AND NORTHERN IND WHERE SEVERAL OF THE LATEST GUIDANCE MEMBERS
SHOW STRONG CONVECTION DURING THE OVERNIGHT HOURS.  WITH THESE
CHANGES...THE SLIGHT AND MODERATE RISK WAS ADJUSTED FURTHER TO THE
SOUTH ACROSS SOUTHERN WI...NORTHERN IA AND NORTHERN IL.  THE
SLIGHT RISK WAS ALSO EXTENDED FURTHER TO THE EAST INTO
SOUTHWESTERN MI...NORTHERN IND AND NORTHWESTERN OH.

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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