Quantitative Precipitation Forecast
Issued by NWS

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FOUS30 KWBC 170836
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
435 AM EDT MON JUL 17 2017

...VALID 12Z MON JUL 17 2017 - 12Z TUE JUL 18 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
30 N CWEC 20 E CWEC 45 NW CMX 20 SE DYT 20 W MML 50 SE PHP
20 SE BFU 55 NNW GCC 40 WNW 2WX 50 NNE D07 30 NNE JMS 20 S FGN
25 SE CYHD 45 SE CYXL.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
KBBF 15 E 5R5 10 NNE BPT 20 NW BTR 30 ENE NMM 35 WNW MLJ
15 SSE CAE 10 ESE CTZ 20 E FFA 45 ENE HSE 40 SSW SUT 20 WSW SSI
25 W DAB 20 SE MCO 50 ENE PGD 15 ENE PGD 20 ENE SRQ 20 SW VVG
30 NE CTY 25 WSW 40J 55 SSW AAF 20 S KIPN.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
CWVY 30 ESE CWHV 20 NW LEW 20 N BAF 20 SE MPO GAI 30 S SHD
25 ENE HSP 10 SSE CBE 35 NE FIG 20 WNW FZY 15 ESE CTCK CWVY.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
115 WSW OLS 50 SW GBN 10 W BLH 45 ENE NXP DRA 95 NW SGU
35 WNW MLF 20 NE MLF 15 NNE BCE PGA 65 ESE PGA 10 E 4BL 30 S GJT
20 N GUC 40 SE MYP 25 NNW RTN 15 ENE LVS CQC 15 W 4MY 25 E GNT
50 SSW GNT 50 NW SVC 80 S DMN 145 SSE DUG 105 NE MMCN.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 WSW CNK GBD 40 NNE GCK 35 ENE GLD 25 SW BBW 20 SSW BVN
20 N HJH 20 WSW CNK.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
70 SW OLS 75 W OLS 35 SSW CGZ 30 ENE IWA 35 ESE PRC 30 SE IGM
20 NE IGM 55 W GCN 25 N FLG 30 SSE INW 25 ESE SOW 50 NNE SAD
10 N SAD 35 SSE SAD 60 ESE DUG 75 SE DUG 90 S DUG.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
10 E RME 10 ESE CWFQ 25 NNW BML 15 NNE 1P1 15 ESE ALB 35 SW AVP
IPT 25 ESE ELM 10 E RME.


...SOUTHWEST U.S...

MONSOONAL CONVECTION WAS A LITTLE SLOW TO GET STARTED SUNDAY BUT
HAD PROMPTED A FEW FLASH FLOOD WARNINGS DURING THE EVENING AND
NIGHTTIME HOURS. OBSERVED RAIN RATES WERE IMPRESSIVE WITH SOME
REPORTS OF AROUND 0.75 INCHES IN 30 MINUTES OVER CENTRAL ARIZONA.
INSTABILITY IS FORECAST TO RECOVER TO SIMILAR LEVELS ON
MONDAY...BUT THERE ARE SOME NEGATIVE FACTORS AS WELL...WITH MODEL
QPF SHOWING A SLIGHT DOWNWARD TREND AND THE RIDGE CENTER SETTLING
FARTHER INTO ARIZONA. THE TRADE-OFF WILL BE STORMS THAT ARE LESS
ORGANIZED DUE TO LESS SHEAR AND STEERING FLOW...BUT WILL ALSO
THEREFORE BE VERY SLOW MOVING. RELYING ON THE HI-RES MODELS AND
THE UNIVERSITY OF ARIZONA WRF...IT APPEARS MONDAY WILL SEE THE
HIGH TERRAIN MORE FAVORED FOR HEAVY RAINFALL...WITH OUTFLOWS
BECOMING LESS PRODUCTIVE IN GENERATING NEW CELLS AS THEY MOVED TO
LOWER ELEVATIONS. MOISTURE AND INSTABILITY REMAIN SUPPORTIVE OF
BRIEF INTENSE RAIN RATES CAPABLE OF PRODUCING FLASH FLOODING.
WHETHER THE NUMBER OF OBSERVED EVENTS WILL WARRANT A SLIGHT RISK
OF EXCESSIVE RAINFALL IS UNCLEAR...BUT AFTER COORDINATING WITH
LOCAL OFFICES IT WAS DECIDED TO MAINTAIN A SLIGHT RISK AREA IN THE
HIGHER TERRAIN.

MARGINAL RISK WILL EXTEND WESTWARD INTO PARTS OF CA/NV. THE NCEP
GUIDANCE IS TYPICALLY TOO DRY WITH WESTWARD EXTENT DURING THE
MONSOON. THERE WERE CLUSTERS OF CONVECTION SUNDAY NEAR LAS
VEGAS...AND IF ANYTHING...THE PW PLUME CONTINUES TO EXPAND WEST ON
MONDAY...COINCIDENT WITH SOME BETTER QPF SIGNAL IN THE U. OF AZ
WRF.


...NORTHEAST U.S...

AN UPPER LOW WILL MOVE INTO PA/NY AND NEW ENGLAND...PRODUCING A
SWATH OF CONVECTION. THE UPPER LOW...TOPPING THE DEVELOPING BROAD
CENTRAL U.S. RIDGE...WILL BE SEPARATED FROM SUB-TROPICAL
MOISTURE...WITH PW VALUES AVERAGE FOR SUMMER. PROGRESSIVE STORM
MODES WILL ALSO HELP KEEP THE ODDS OF EXTREME LOCAL RAINFALL AT
TOLERABLY LOW LEVELS. AREAL AVERAGE OF AROUND AN
INCH...HOWEVER...ALONG WITH ISOLATED HEAVIER DOWNPOURS...MAY LEAD
TO SOME FLASH FLOODING...ESPECIALLY WITH LOWER GUIDANCE VALUES
OVER NEW YORK / NEW ENGLAND.


...PLAINS...

A SMALL VORT MAX REMAINS EMBEDDED IN THE RIDGE POSITION...AND IS
BEING DRAGGED VERY SLOWLY EASTWARD THROUGH KANSAS AND NEBRASKA.
SMALL SCALE BUT HEAVY...THUNDERSTORM CLUSTERS ARE EXPECTED WHERE
THIS FEATURE OVERLAPS WITH SOUTHERLY INFLOW AND A RELATIVE
INSTABILITY AXIS...ESPECIALLY IN BETWEEN INTERSTATES 70 AND 80
FROM OAKLEY / HAYS TO NORTH PLATTE KEARNEY. WHILE WPC
DETERMINISTIC QPF IS CONSERVATIVE HERE...THIS FEATURE IS PRODUCING
SOME OF THE HEAVIEST RAIN IN THE HI-RES MODELS THAT IS SEEN ACROSS
THE NATION ON DAY 1...SPECIFICALLY 4-PLUS INCH AMOUNTS IN THE NSSL
WRF AND NAM CONUS NEST. WIND PROFILES MAY ALLOW FOR SOME UPDRAFT
ROTATION / DEVIANT MOTION...RESULTING IN NEAR ZERO MOTION AT
TIMES...BUT COVERAGE AND EVEN CONFIDENCE IN THIS OCCURRING ARE NOT
SUFFICIENT FOR SLIGHT RISK PROBABILITIES...THUS THE AREA IS
ENCAPSULATED IN A MARGINAL RISK. IT IS WORTH NOTING THAT THE HRRR
OUT THROUGH 00Z IS NOT NEARLY SO SUGGESTIVE OF HEAVY RAINFALL WITH
THIS FEATURE.


...SOUTHEAST...

THE DEEPEST SUB-TROPICAL MOISTURE IS SOUTH OF THE CENTRAL U.S.
RIDGE POSITION...AND WILL AGAIN SUPPORT WIDESPREAD DIURNAL
CONVECTION...INCLUDING ALONG SEA BREEZES. ISOLATED DOWNPOURS MAY
CAUSE FLASH FLOODING IF THEY OCCUR OVER SUSCEPTIBLE BASINS OR
CITIES. PREDICTABILITY APPEARS VERY LOW...HOWEVER...WITH LESS
ORGANIZATION EXPECTED ON MONDAY AS WIDESPREAD OVERTURNING HAD
STABILIZED PARTS OF THE CAROLINAS AND THE UPPER TROUGH WILL
STRETCH OUT MORE POSITIVELY TILTED...PRODUCING MOST OF ITS DEEP
LAYER LIFT JUST OFFSHORE OF THE EAST COAST.

BURKE
$$





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