Quantitative Precipitation Forecast
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FOUS30 KWBC 092132
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
531 PM EDT WED AUG 09 2017

...VALID 2131Z WED AUG 09 2017 - 12Z THU AUG 10 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
25 S JWG 30 W CDS 25 SSE CVN 40 W TCC 15 WSW VTP LXV 20 NE HDN
20 SSW ARL LAR DEN 25 NNE LHX 20 W EHA 15 WNW LBL 45 N GCK
25 NNE HLC 40 WSW HJH 15 NNE MHK 10 NNW UKL 25 WNW CFV
20 ESE JWG 25 S JWG.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 WNW CWDV 25 S CWEC 25 N LNL 10 E RST 10 WNW CIN 20 SE OFK
25 N BVN 40 NE ONL 30 WSW BKX 15 SW K2D5 10 W RDR 10 NNW CWSU
45 SW CYHD 20 WNW CWDV.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
170 SE CHS 75 E SSI 30 SE SSI 10 NNW SGJ 15 WNW DAB 10 SSE LEE
30 WSW OCF 25 S 40J 30 ESE AAF 15 W AAF 10 E DTS 25 SE PQL
20 SW MSY 20 ENE KCRH 15 S KXIH 10 N IAH 15 ESE JSO 15 NE BAD
30 NNE GWO 35 NNW DCU 15 S CSV 25 WSW CEU 25 NW CAE 10 SE UDG
10 SE DPL 15 SSE MQI 80 E FFA 115 ENE HSE 90 SE HSE.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 WNW PNC 40 W CSM 30 N PVW 10 SE TCC 10 SE RTN 25 SE TAD
15 ESE CAO 25 SSW GUY 20 ESE LBL 30 N DDC 25 ESE HLC 20 S CNK
30 S MHK 45 WNW PPF 15 WNW PNC.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 NNW IWD 20 ESE RNH 10 SSW FBL 10 ESE JYG PQN 20 NNE BKX
15 SW FFM 10 W PKD 15 ENE FOZ 20 NE CKC 45 SE GNA 15 NNW IWD.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
130 S SUT 30 NE BQK 15 SW EZM 20 NNW LGC 25 SSW VPC 10 WSW WDR
20 S SSC 30 NE MRH 25 ENE HSE 45 E HSE 55 SSE HSE.


2130 UTC UPDATE

AMENDED THE ON GOING EXCESSIVE TO INTRODUCE A MARGINAL RISK FROM
THE SHASTA/SISKIYOU RANGE EASTWARD ACROSS THE GREAT BASIN.  THE
PRESENCE OF A WELL DEFINED VORT OVER FAR SOUTH CENTRAL/SOUTHEAST
ORE WILL CONTINUE TO AID THE DEVELOPMENT OF STORMS ACROSS THE
AREA.  WHILE STORMS MAY BE ABLE TO TAP MOISTURE IN THE MID
LEVELS...DEWPOINT DEPRESSIONS APPROACHING 50 DEGREES IN THE SUB
CLOUD LAYER SHOULD LIMIT WIDESPREAD PROBLEMS DUE TO HEAVY
RAINFALL.  EVEN SO...STORMS EARLY THIS AFTERNOON HAVE BEEN ABLE TO
PRODUCE ENOUGH RAINFALL FOR SOME PROBLEMS ESPECIALLY IN THE
COMPLEX TERRAIN.  REFER TO MESOSCALE PRECIPITATION DISCUSSION 661
ISSUED BY THE WEATHER PREDICTION CENTER FOR MORE DETAILS. THE RISK
OF EXCESSIVE RAINFALL SHOULD BE TAPERING OFF LATER THIS EVENING
WITH LOSS OF SOLAR HEATING.

ALSO TRIMMED THE NORTHERN/WESTERN PORTION OF THE SLIGHT RISK IN
THE CAROLINAS BASED ON SHORT TERM RADAR TRENDS.  STILL MAINTAINED
THE SLIGHT RISK ALONG AND AHEAD OF A SURFACE TROUGH...AND ONLY
MADE FAIRLY MODEST ADJUSTMENT TO THE MARGINAL RISK AREA WHICH
SURROUNDS THE SLIGHT RISK AREA.

BANN


1500 UTC UPDATE

THE ONLY CHANGE OF NOTE FROM THE PREVIOUS EXCESSIVE RAINFALL
POTENTIAL OUTLOOK WAS TO TRIM THE SOUTHERN EDGE OF THE SLIGHT RISK
AREA THAT WAS OVER FAR NORTHEAST NE---NORTHWEST IA AND FAR
SOUTHEAST SD TO A POSITION INTO SOUTHERN MN.  THIS WAS TO BETTER
FIT THE MAJORITY OF THE LATEST QPF GUIDANCE AND AFTER
COLLABORATION WITH WFO DMX.  ELSEWHERE---NO CHANGES MADE TO THE
PREVIOUS OUTLOOK.

ORAVEC

INITIAL DISCUSSION


EASTERN TX---LOWER MS VALLEY--SOUTHEAST---COASTAL CAROLINAS

WEAK HEIGHT RISES/EASTWARD EXPANSION OF THE SOUTHWESTERN U.S.
RIDGE WILL TAKE PLACE OVER THIS REGION WED-WED NIGHT AS SHORTWAVE
ENERGY PIVOTING S-SE ACROSS THE NORTHERN PLAINS AND UPPER MS
VALLEY. THIS WILL HELP PULL THE CURRENT QUASI-STATIONARY SURFACE
FRONT BACK NORTH ACROSS THE SOUTHERN PLAINS...LOWER MS VALLEY...TN
VALLEY...AND LOWER MID ATLANTIC REGION WED NIGHT. PW VALUES IN THE
VICINITY OF THIS BOUNDARY EXPECTED TO REMAIN ABOVE AVERAGE---2 TO
2.25+ INCHES OR 1 TO 1.5+ STANDARD DEVIATIONS ABOVE THE MEAN.
MODEL CONSENSUS IS FOR A CONTINUED POTENTIAL FOR MORE WIDESPREAD
MODERATE TO HEAVY PRECIP TOTALS IN THIS EXPANSIVE AREA OF ABOVE
AVERAGE PW VALUES---THOUGH TWO AREAS STAND OUT WITH POTENTIALLY
MORE FAVORABLE LARGE SCALE CONDITIONS FOR HEAVY RAINS. ONE IS
ACROSS PORTIONS OF THE SOUTHEAST FROM NORTHERN FL AND EASTERN GA
INTO SOUTHERN SC AND COASTAL AREAS OF NC...GIVEN THE LINGERING
SUBTLE RIGHT ENTRANCE REGION UPPER JET FORCING AND (THUS) A BIT
MORE FOCUSED LOW-LEVEL FRONTOGENESIS. THE SECOND...MORE DIFFUSE
SIGNAL IS IN THE VICINITY OF THE TX/LA BORDER WHERE A SLOW
MOVING/QUASI-STATIONARY MCV STUCK WITHIN THE COLL BETWEEN THE
RIDGE AXES W-E...NORTH OF T.S. FRANKLIN...AND SOUTH OF THE
WESTERLIES MAY FOCUS ADDITIONAL HEAVY RAINFALL ACROSS THE UPPER
COAST OF TX INTO LA. FOR QPF DETAILS---DAY 1 QPF AGAIN LEANED MORE
TOWARD THE NSSL WRF---ARW AND HI RES ENSEMBLES FOR THE  WIDESPREAD
MODERATE TO HEAVY PRECIP TOTAL POTENTIAL ACROSS THESE AREAS.


NORTHERN PLAINS INTO THE UPPER MS VALLEY

THE AFOREMENTIONED NORTHERN STREAM SHORTWAVE WILL WORK IN TANDEM
WITH THE LINGERING UPPER JET STREAK ACROSS SOUTHERN ONTARIO IN
GENERATING ROBUST DYNAMICAL FORCING (UPPER DIVERGENCE/DEEP-LAYER
ASCENT) WHILE ALSO CAUSING A SPIKE IN PWAT VALUES (1.25+ INCHES)
AND LOW-LEVEL MOISTURE FLUX AS SOUTHWESTERLY INFLOW INCREASES. A
MULTI-MODEL SIGNAL AMONG THE HIGH-RES GUIDANCE FOR A MCS WED
NIGHT-EARLY THU WAS ONCE AGAIN DEPICTED ACROSS MN INTO NORTHWEST
WI...THOUGH AT THE SAME TIME LATITUDINAL DIFFERENCES AND/OR A
BI-MODAL DISTRIBUTION OF THE HEAVY RAIN AXES WAS NOTED. BASED ON
THE PROJECTED INSTABILITY GRADIENT/N-S DISTRIBUTION
OVERNIGHT...THE WPC INCORPORATED SOME OF THE 00Z NSSL-WRF QPF
WHICH DID ILLUSTRATE A SECONDARY MAX OVER SOUTHERN MN. IN THIS
SCENARIO...THE CONVECTION FARTHER NORTH NEAR THE NORTHERN WI-N
BORDER WOULD BE HINDERED TO AN EXTENT AS THE SOUTHERN CONVECTION
TO SOME DEGREE OBSTRUCTS THE LOW-LEVEL INFLOW. DYNAMICS WILL BE
MORE FAVORABLE FARTHER NORTH (NORTHERN MN-FAR NORTHWEST
WI)...HOWEVER A MORE QUESTIONABLE THERMODYNAMIC ENVIRONMENT
(WEAKER INSTABILITY COMPARED TO AREAS SOUTH) WOULD LIKELY INHIBIT
THE POTENTIAL FOR EXCESSIVE SHORT-TERM RAINFALL RATES.


CENTRAL PLAINS INTO THE SOUTHERN HIGH PLAINS

A FARTHER SOUTHWARD CONVECTIVE MAX POSSIBLE DAY 1 ACROSS PORTIONS
OF THE CENTRAL PLAINS ASSOCIATED WITH SHORTWAVE ENERGY PUSHING
EASTWARD FROM THE LEE OF THE CENTRAL ROCKIES INTO THE CENTRAL
PLAINS. MODEL CONSENSUS IS FOR THE INITIAL AREA OF CONVECTION TO
CONTINUE TO DIVE SOUTH-SOUTHEASTWARD FROM IN THE VICINITY OF
NORTHEAST NM INTO NW TX TONIGHT EARLY THIS AM...  FOLLOWED BY A
SECOND AREA OF CONVECTION FORMING IN RESPONSE TO STRENGTHENING LOW
LEVEL SOUTHERLY FLOW ACROSS WESTERN TO CENTRAL KS AND NORTHERN OK
DURING THE DAY WEDNESDAY...THEN YET ANOTHER...MORE FOCUSED AREA OF
ELEVATED CONVECTION WED NIGHT INTO THU MORNING ACROSS THE TX-OK
PANHANDLES INTO NORTHERN OK AND SOUTHERN-EASTERN KS WHERE THE
INCREASING NOCTURNAL LOW-LEVEL INFLOW OVERRIDES THE LINGERING
OUTFLOW BOUNDARIES. IN THIS TYPE OF SETUP...THE SLIGHTLY FARTHER
SOUTHWARD SOLUTIONS OF THE NSSL WRF AND VERSION 2 OF THE WRF-ARW
WERE FAVORED WITH MODERATE TO HEAVY PRECIP TOTALS POSSIBLE.

HURLEY
$$





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