Quantitative Precipitation Forecast
Issued by NWS

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000
FOUS30 KWBC 210838
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
437 AM EDT WED SEP 21 2016

...VALID 12Z WED SEP 21 2016 - 12Z THU SEP 22 2016...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 S VTI 10 SE RDK 15 SSW AFK 30 SE HJH 25 WNW CNK 35 S HSI GRI
20 N BVN 15 WNW YKN 20 WNW FSD 15 NNW MML 10 N LJF 10 SSW PNM
15 WSW HYR 20 S IWD 25 E LNL 20 SE IMT 25 ENE SUE 25 E MTW
15 ENE ETB 20 W EFT 20 S VTI.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
DLN 35 E BTM 20 NW HLN 45 NNE 3DU 45 SE GPI 20 E GPI
25 SSW CWGM 15 SE CWGM 10 ENE 8S0 20 SSE CTB 35 NE GFA
55 ENE GFA 50 SE HVR 20 SSE CWAQ 25 ENE OLF 40 SSW JDN 25 N COD
40 ESE P60 35 NW BPI 20 ESE PVU 50 ESE U24 45 SE U24 10 NNE U24
30 SSE DPG 40 WNW U24 55 ESE ELY 35 SSE ELY 65 SSW ELY 20 NW TPH
60 NNW TPH 30 WNW P68 30 S 9BB 25 WSW 77M 10 W PIH 30 WNW IDA
30 ESE SUN 25 NW SUN DLN.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
100 ESE FFA 30 NE HSE 20 SSE EDE 15 SW EDE 15 W ASJ 10 NE EMV
15 WNW JGG MFV 25 SE WAL 40 ESE WAL 65 SE OXB 110 ESE OXB.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
30 WNW SUX 25 WNW ORC 20 SSE PQN 25 SSE MML GYL ANE 30 ENE EAU
AUW 10 SE PCZ 15 N UNU 15 ENE MRJ 25 ENE IIB 10 NE AMW
20 SSW MLE 25 ENE JYR 10 W OLU 30 WNW SUX.

MODERATE RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
25 S CMY 20 SE CAV CIN 10 NE DNS 25 NW DNS 25 ESE LRJ
20 SSE SHL 15 NNW SPW MJQ 15 NNE MKT LVN 10 SSW LUM 25 W MFI VOK
25 S CMY.



NORTHEAST NEBRASKA---NORTHERN TO CENTRAL IOWA---SOUTHERN MINNESOTA
INTO SOUTHWEST WISCONSIN

A SURFACE FRONTAL BOUNDARY EXPECTED TO REMAIN NEARLY STATIONARY
DURING THE UPCOMING FORECAST PERIOD FROM CENTRAL NEBRASKA---EAST
NORTHEASTWARD INTO THE VICINITY OF THE MN/IA BORDER---CENTRAL WI
AND THE NORTHERN PORTIONS OF THE U.P.  THIS BOUNDARY SHOULD REMAIN
THE FOCUS FOR ORGANIZED CONVECTION---HEAVY TO EXCESSIVE RAINFALL
AMOUNTS AS MOIST WEST SOUTHWESTERLY LOW LEVEL FLOW PERSISTS INTO
THE FRONT THIS PERIOD.  THE FIRST ROUND OF ORGANIZED CONVECTION
EARLY THIS MORNING AFFECTING SOUTHEAST MN---FAR NORTHEAST IA INTO
SOUTHWEST WI WILL LIKELY WEAKEN POST 1200 UTC AS IT SINKS FARTHER
SOUTHEASTWARD INTO NORTHERN ILLINOIS.  ADDITIONAL ORGANIZED
CONVECTION POTENTIAL LIKELY TO BEGIN BY OR SHORTLY AFTER 0000 UTC
THU AS THE STRENGTHENING SOUTHWEST LOW LEVEL FLOW REFOCUSES INTO
THE FRONT.  WITH PW VALUES EXPECTED TO INCREASE TO 1.75"+...2.5 TO
3 STANDARD DEVIATIONS ABOVE THE MEAN ALONG THIS FRONT AND
POTENTIAL FOR SLOW MOVING AND TRAINING OF CELLS ALONG THE
BOUNDARY---HEAVY TO EXCESSIVE RAINFALL AMOUNTS LIKELY IN THE
VICINITY OF NORTHEAST NEBRASKA---CENTRAL TO  NORTHERN
IA---SOUTHERN MN INTO SOUTHWEST WI.  WPC QPF LEANED TOWARD THE HI
RES ARW AND NSSL WRF WHICH WERE ON THE SOUTHWEST SIDE OF THE
GUIDANCE WITH RESPECT TO THE MAX AREA OF PRECIP.  MANY OF THE
OTHER NON CAM MODELS WERE FARTHER TO THE NORTHEAST WITH HEAVY
PRECIP INTO CENTRAL WISCONSIN.  THE NAM EXPERIMENTAL WAS CLOSER TO
THE ARW AND NSSL WRF---NOT AS FAR EAST NORTHEAST WITH HEAVY PRECIP
AS THE NAM CONEST.  A SLIGHT TO MODERATE RISK OF EXCESSIVE
RAINFALL AMOUNTS MAINTAINED FROM PREVIOUS WPC FORECASTS---WITH
ONLY A SLIGHT SOUTHWESTWARD SHIFT TO THE SLIGHT AND MODERATE AXES
TO REFLECT OUR PREFERRED ARW AND NSSL WRF AXES.

NORTHEAST NORTH CAROLINA INTO SOUTHEAST VIRGINIA

THE CLOSED LOW INITIALLY ALONG THE COASTAL NC/SC BORDER IS
EXPECTED TO BECOME INCREASINGLY SHEARED THIS PERIOD.  THIS SHOULD
RESULT IN WEAKENING OF THE ONSHORE EASTERLY FLOW TO ITS NORTH
WHICH HAS BEEN FOCUSING PERSISTENT MODERATE TO HEAVY RAINS OVER
NORTHEAST NC INTO SOUTHEAST VIRGINIA.  WHILE WEAKENING IS
EXPECTED---THIS AREA WILL STILL HAVE WELL DEFINED ONSHORE EASTERLY
FLOW---ESPECIALLY DURING THE BEGINNING OF THE FORECAST PERIOD.
THIS WILL SUPPORT ADDITIONAL MODERATE TO HEAVY TOTALS FOR
NORTHEAST NC INTO SOUTHEAST VA.  WITH RECENT HEAVY RAINFALLS
AMOUNTS OF 4-6"+ OVER PORTIONS OF NORTHEAST NC INTO SOUTHEAST
VIRGINIA---FFG VALUES HAVE LOWERED.  A MARGINAL RISK WAS
MAINTAINED OVER NORTHEAST NC INTO SOUTHEAST VIRGINIA FOR ISOLATED
RUNOFF ISSUES FROM THE EXPECTED ADDITIONAL MODERATE TO HEAVY
TOTALS.

EASTERN PORTIONS OF THE GREAT BASIN INTO THE NORTHERN ROCKIES

MODELS CONTINUE TO SHOW GOOD CONTINUITY AND AGREEMENT WITH THE
AMPLIFICATION OF THE UPPER TROF FROM THE PACIFIC
NORTHWEST---SOUTHWARD ALONG THE WEST COAST AND INLAND INTO THE
WESTERN PORTIONS OF THE GREAT BASIN.  THE MUCH ABOVE AVERAGE PW
VALUES THAT HAVE ALREADY PUSHED NORTHWARD INTO SOUTHERN
CALIFORNIA---THE SOUTHWEST AND THE SOUTHERN GREAT BASIN AHEAD OF
POST TROPICAL CYCLONE PAINE WILL CONTINUE TO PUSH NORTHEASTWARD
AHEAD OF THIS AMPLIFYING TROF ACROSS THE GREAT BASIN AND INTO THE
NORTHERN ROCKIES.  THIS WILL BE SUPPORTING INCREASING PRECIP
COVERAGE THROUGH THE GREAT BASIN INTO THE NORTHERN ROCKIES WITH
WIDESPREAD MODERATE TO LOCALLY HEAVY PRECIP TOTALS EXPECTED.  THE
THREE SMALL MARGINAL AREAS DEPICTED IN THE PREVIOUS DAY 2
EXCESSIVE RAINFALL POTENTIAL OUTLOOK WERE COMBINED INTO ONE
BROADER MARGINAL RISK AREA TO COVER THE MODEL SPREAD WITH RESPECT
TO THE MODERATE TO HEAVY RAINFALL POTENTIAL.

ORAVEC
$$





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