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Excessive Rainfall Discussion
 
(Caution: Version displayed is not the latest version. - Issued 0107Z Aug 21, 2014)
 
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Abbreviations and acronyms used in this product
 
Geographic Boundaries -  Map 1: Color  Black/White       Map 2: Color  Black/White


EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
907 PM EDT WED AUG 20 2014

...VALID 03Z THU AUG 21 2014 - 00Z FRI AUG 22 2014...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 N DTL 15 N SAZ ROS RYV 20 ESE GSH 10 S FDY 20 WNW OSU
25 SW TZR 25 SSE ILN 15 SE LUK 30 WNW CVG 25 WNW EYE VYS MXO
30 SSE PQN 50 NE PIR 20 SSW MBG 40 WNW MBG 25 S KHZE N60
20 N MIB 20 SSW CYBR 15 SW KGAF 15 N DTL.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
10 NE SLK 25 SE SLK 15 NW GFL 20 WSW GFL 30 W SCH 10 S ITH
10 ENE ELM 25 SSE DSV 15 S DSV 15 WSW DSV 25 WNW DSV 25 WSW ROC
15 WNW ROC 20 SSW CWQP 10 S CYGK 15 SW CWGH 10 S CTCK 10 NE SLK.


03Z UPDATE...
ONLY SLIGHT CHANGES WERE MADE TO BOTH SLIGHT RISK AREAS.  ACRS THE
NRN PLAINS UPR MS VALLEY...TRIMMED WRN PORTION OF PREVIOUS OUTLOOK
AREA WERE EXCESSIVE THREAT HAS DIMINISHED WITH SLOW ADVANCE OF
COLD FRONT FROM THE WEST.  ALSO..PULLED AREA SLIGHTLY SWD ACRS SW
MN WITH PONTL FOR INCREASING WAA LIFT GENERATING CONVECTION N OF
WARM FRONT THAT COULD BECOME BETTER ORGANIZED ACRS THAT AREA
OVERNIGHT.  SLIGHT RISK AREA OVER NY WAS EXPANDED SLIGHTLY EAST TO
CAPTURE ONGOING HEAVIER ACTIVITY OVER CNTL NY.  INSTABILITY DROPS
OFF SIGNIFICANTLY FARTHER TO THE EAST WITH SLIGHTLY COOLER ELY
FLOW SO DO NOT ANTICIPATE STGR STORMS GETTING MUCH FARTHER EAST. 
OTHERWISE PREVIOUS FORECAST REASONING ACRS BOTH AREAS REMAINS
UNCHANGED.  SULLIVAN  PREVIOUS DISCUSSION FOLLOWS...


NORTHERN PLAINS---UPPER MS VALLEY--MID WEST INTO THE MID TO UPPER
OH VALLEY

MID TO UPPER LEVEL HEIGHT FALLS EJECTING EAST NORTHEASTWARD FROM
THE NORTHERN HIGH PLAINS TONIGHT INTO THE UPPER MS VALLEY DURING
THE DAY ON THURSDAY WILL SUPPORT INCREASING CONVECTIVE ACTIVITY
FROM THE NORTHERN PLAINS---SOUTHEASTWARD ALONG AND TO THE NORTH OF
A WARM FRONTAL BOUNDARY EXTENDING INTO THE UPPER MS VALLEY---MID
WEST INTO THE OH VALLEY REGION.  PW VALUES AHEAD OF THESE HEIGHT
FALLS AND IN THE VICINITY OF THIS FRONT WILL BE RISING TO MUCH
ABOVE NORMAL--- 2 TO 2.5+ STANDARD DEVIATIONS ABOVE THE MEAN AS
LOW LEVEL SOUTHERLY TO SOUTH WESTERLY FLOW STRENGTHENS INTO THIS
BOUNDARY.  OVERALL THERE IS FAIRLY GOOD AGREEMENT WITH THE QPF
AXES IN THE MODELS.  THE 1200 UTC AUG 20 ECMWF DID TREND SOUTHWARD
FROM ITS 0000 UTC RUN OVER THE UPPER MS VALLEY AND IS CLOSER NOW
TO THE FAVORED AXES OF THE HI RES ARW---NMM AND NSSL WRF WHICH
WERE USED PRIMARILY FOR QPF DETAILS.  HEAVY TO ISOLATED EXCESSIVE
PRECIPITATION TOTALS POSSIBLE IN A NARROW AXIS IN THE VICINITY OF
THIS WARM FRONT.  THE BIGGEST CONCERNS ARE FOR CHANGES IN THE
NARROW QPF AXIS WHICH IS POSSIBLE IF ANY ORGANIZED CONVECTION
PUSHES FARTHER TO THE SOUTH AND SOUTHEAST THAN EXPECTED AT THE
PRESENT TIME.  TRAINING OF CELLS ALONG AND NORTH OF THIS FRONT
POSSIBLE--ESPECIALLY EARLY THURSDAY MORNING WHEN THE LOW LEVEL
FLOW WILL BECOME MORE WEST SOUTHWESTERLY INTO THE FRONT--WITH
ISOLATED SHORT TERM PRECIPITATION TOTALS OF 2"+ POSSIBLE WHERE
TRAINING OCCURS. 

WESTERN TO NORTHERN NEW YORK STATE

CONCERNS FOR ISOLATED EXCESSIVE RAINFALL AMOUNTS WILL BE AHEAD OF
THE SURFACE FRONTAL BOUNDARY CURRENTLY MOVING THROUGH THE GREAT
LAKES THAT IS EXPECTED TO MOVE ONLY SLOWLY EASTWARD THIS PERIOD AS
IT ENCOUNTERS BLOCKING FLOW AHEAD OF IT ACROSS SOUTHEAST CANADA. 
HIGH PW VALUES---1.50-1.75"+--- AHEAD OF THIS SLOW MOVING FRONT
WILL SUPPORT HEAVY PRECIPITATION AMOUNTS FROM THE NORTHERN MID
ATLANTIC INTO THE SOUTHERN TIER OF NY AND NORTHERN NY.  THE SLOW
MOVEMENT OF THE FRONT WILL ALSO POSE RUNOFF ISSUES FOR PORTIONS OF
WESTERN NY/SOUTHERN TIER OF NY INTO NORTHERN NY WHERE THERE ARE
RELATIVELY LOW FFG VALUES.  SHORT TERM PRECIPITATION TOTALS OF
1-2"+ POSSIBLE IN AREAS OF SLOW MOVING CONVECTION.


ORAVEC