Quantitative Precipitation Forecast
Issued by NWS

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FOUS30 KWBC 191446
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1045 AM EDT SAT AUG 19 2017

...VALID 15Z SAT AUG 19 2017 - 12Z SUN AUG 20 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
45 ESE MTH 10 WSW MTH 35 WNW TMB 35 SW FPR FPR 15 NE PBI
35 E PMP.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
125 S GBN 60 ESE YUM 15 NNW GBN 20 SSW CGZ 20 N FHU 40 NNE DUG
65 NE SAD 45 SSW GNT 20 NE GNT 15 E SKX 40 N TCC 25 WSW CVS
20 E ATS 40 SSE GDP 50 W MRF 85 SW MRF.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 NNW BVN 20 N AUH OMA SDA 10 E BIE MHK 25 NE EWK 20 SE GBD
40 WSW HYS 45 SE GLD 30 NE GLD IML 20 S TIF 10 E VTN 35 NE ANW
20 NNW BVN.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
CGF 10 SW JHW 30 SSW ELM 30 W AVP 15 NNE UNV 10 ESE JST 2G4
20 W W22 15 NW PKB 45 SSE ILN 10 ENE LUK SGH CGF.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
85 SSE DUG 45 ENE DUG 20 NNW SVC 55 SSW ABQ 40 SE CQC 50 N ROW
ROW 25 W CNM 30 SSW GDP 85 WNW MRF 100 W MRF.



...15Z UPDATE...

OVERALL A RATHER QUIET PATTERN FOR EXCESSIVE RAINFALL, LOOKING
MORE SEPTEMBER/OCTOBER THAN AUGUST. THE ONLY SLIGHT THREAT REMAINS
THE RETURN OF MONSOONAL MOISTURE AND POSSIBLE SMALL SCALE VORT
LIFTING UP OR AT LEAST APPROACHING SOUTHERN NM BY THE END OF THE
FCST PERIOD. MEANWHILE ALL MARGINAL THREATS WERE KEPT AND ADJUSTED
SLIGHTLY BASED ON RADAR TRENDS AND LATEST GUIDANCE. WPC ALSO
INTRODUCED ANOTHER MARGINAL THREAT FROM OH INTO PA/NORTHERN WV. A
VIGOROUS UPPER DISTURBANCE ALOFT WILL SWEEP THROUGH THE GREAT
LAKES/OH VALLEY INTO THE NORTHEAST AND TRIGGER SCATTERED
SHOWERS/STORMS. THE SCATTERED AND NOT WIDESPREAD NATURE OF PRECIP
IS DUE TO MARGINAL MOISTURE CONTENT WITH PWS ONLY REACHING AN INCH
AND A QUARTER. THE GLOBAL MODELS AND HI-RES SUITE SUGGEST THE MOST
CONCENTRATED AREA BEING FROM OH INTO WESTERN PA WITH ISOLATED
HIGHER RAIN RATES AND A POSSIBLE FLASH FLOOD WARNING OR TWO.

MUSHER


...SOUTHWEST STATES...

DEEP LAYERED MOISTURE SHOULD BEGIN MOVING NORTHWARD FROM OLD
MEXICO LATER TODAY OR TONIGHT IN RESPONSE TO THE DEEPENING OF A
TROUGH LOCATED OFF CALIFORNIA.  THE MODELS DEPICT THE DEVELOPMENT
OF A VORT MAX SOUTH OF THE INTERNATIONAL BORDER WHICH EASES
NORTHWARD...PERHAPS THE RESULT OF CONVECTIVE FEEDBACK.
PRECIPITABLE WATER VALUES INCREASE FROM AROUND 1.25 INCHES THIS
MORNING TO OVER 1.5 INCHES DURING THE OVERNIGHT HOURS ACROSS PARTS
OF AZ.  WHILE THE PW VALUES DO NOT CLIMB AS MUCH OVER AZ...THE MID
AND UPPER LEVEL DYNAMICS ARE STRONGER OVER NM.  WILL CONTINUE A
SLIGHT RISK OVER PORTIONS OF NM CLOSE TO THE DYNAMICS...AND
EXTENDED THE MARGINAL RISK BACK WESTWARD ALONG THE SOUTHERN AZ
BORDER WHERE THE PRECIPITABLE WATER PLUME IS BETTER DEFINED. THIS
COULD BE THE BEGINNING OF A MULTI DAY PERIOD OF

...CENTRAL PLAINS...

KEPT A MARGINAL RISK IN PLACE OVER PORTIONS OF KS/NE AS SOUTHERLY
FLOW DEVELOPS LATER TONIGHT/EARLY SUNDAY...WHICH MAKES INCREASING
AMOUNTS OF MOISTURE AVAILABLE TO PRODUCE LOCALLY HEAVY RAINFALL
AMOUNTS AND RAINFALL RATES.  MODELS DEPICT SOUTH TO SOUTHWESTERLY
H85 FLOW AT 25 TO 35 KTS BY SUNDAY MORNING WHICH RESULTS IN
HALFWAY DECENT MOISTURE TRANSPORT INTO THE REGION AND AN UNSTABLE
ATMOSPHERE.  THE MODELS ONLY GET PRECIPITABLE WATER VALUES UP TO
AROUND 1.5 INCHES BEFORE THEY ARE SHUNTED EASTWARD...SO STILL SOME
UNCERTAINTY AS TO WHETHER OR NOT THE RAINFALL AMOUNTS WILL BE
THERE.  NOTED THAT THE 1 HOUR FFG ACROSS PARTS OF NEBR INVOF I-80
ARE BETWEEN 1.5 AND 2 INCHES...AND THESE RATES ARE NOT ENTIRELY
OUT OF THE REALM OF POSSIBILITIES.

...GULF COAST AND SOUTHEAST STATES...

DEEP MOISTURE REMAINS IN PLACE ALONG AND SOUTH OF A FRONTAL
BOUNDARY ASSOCIATED WITH A SYSTEM OVER/NEAR THE NORTHEAST STATES.
SHOWERS AND THUNDERSTORMS SOUTH OF THIS BOUNDARY WILL BE ABLE TO
TAP INTO THE DEEP MOISTURE AND BE FOCUSED/SUPPORTED BY THE FRONT
IN ADDITION TO LAKE/GULF BREEZE INTERACTIONS.  FLOW ACROSS THE
AREA IS GENERALLY LIGHT...WHICH SHOULD RESULT IN SLOW MOVING
STORMS.  FLASH FLOOD GUIDANCE VALUES ARE PRETTY HIGH...BUT THERE
HAS BEEN SOME LOCAL RAINFALL AMOUNTS IN THE 2 TO 3 INCH RANGE
DURING THE PAST 7 DAYS WHERE THE MODELS DEPICT THE POTENTIAL FOR
CONVECTION.  GIVEN THE FORECAST SOUNDING PROFILES...THINK ANY
CELLS COULD BE EFFICIENT RAINFALL MAKERS.

GRAPHICS AVAILABLE ON THE WEB AT WWW.WPC.NCEP.NOAA.GOV

BANN

$$




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