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Excessive Rainfall Discussion
 
(Caution: Version displayed is not the latest version. - Issued 0119Z Aug 20, 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
919 PM EDT TUE AUG 19 2014

...VALID 03Z WED AUG 20 2014 - 00Z THU AUG 21 2014...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
45 SSW PUC 15 E BCE 40 SSE CDC 10 SE SGU 50 NW SGU 10 NNW U24
30 ESE DPG 10 N SLC HIF 20 SSE LGU 25 NW EVW 10 NNE EVW
10 SSE FIR 30 SSE FIR 35 NNE PUC 20 SW PUC 45 SSW PUC.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 S AFJ 20 WSW BVI 25 NW HZY 15 E CXDI 10 E CYTZ 15 WSW CWNC
20 NW ELZ 25 NE FIG 15 NE AOO 25 E CBE 25 SSE 2G4 20 S AFJ.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
30 WSW CWKO 35 SSW CXBK 20 SW CWWF CYEN 40 ESE CYEN 20 ENE K08D
30 SE K08D 20 SE N60 40 ENE BIS 45 SSW JMS 15 NNE MBG 30 NW MBG
55 NNE D07 15 SE D07 35 NW PHP 20 E RCA 15 E RCA 35 N RCA
25 SSE 2WX 35 WNW 2WX 35 WSW BHK 15 NNE MLS 35 ESE JDN
30 NNE GGW 30 WSW CWKO.


SOUTHWEST INTO THE GREAT BASIN

REDUCED SLIGHT RISK AREA FROM PREVIOUS ISSUANCE WHILE STILL
MAINTAINING SLIGHT RISK FOR AREAS STRADDLING THE WASATCH RANGE.
DIFFLUENT FLOW PATRN AHEAD OF UPR LOW OVER CAWILL CONTINUE TO
SUPPORT INCREASED THREAT OF CONVECTION OVER ERN NV THIS EVENING
THAT SHOULD SLOWLY SPREAD EWD INTO UT OVERNIGHT. THOUGH OVERALL
ORGANIZED THREAT OF EXCESSIVE RAINS SHOULD CONTINUE TO DIMINISH AS
PIECE OF S/WV ENERGY LIFTS NEWD FROM THE CNTL GT BASIN...CAN NOT
RULE OUT SOME SPOTTY STG STORMS THAT COULD BE CAPABLE OF PRODUCING
SOME LOCALLY HEAVY TO EXCESSIVE RAINS..PARTICULARLY OVER STEEPER
TERRAIN.

NORTHERN PLAINS

THE WELL DEFINED HEIGHT FALLS AND ASSOCIATED AXIS OF ABOVE AVERAGE
PW VALUES WILL BE PRESSING INTO THE NORTHERN PLAINS WEDNESDAY. 
MODEL CONSENSUS IS FOR THE HEAVY PRECIPITATION POTENTIAL TO
DEVELOP WEDNESDAY OVER THE NORTHERN PLAINS WITH THE ORGANIZING
CONVECTION WEDNESDAY AFTERNOON IN A REGION OF FAIRLY UPPER
DIFFLUENT FLOW AND STRENGTHENING LOW LEVEL INFLOW INTO THE WARM
FRONTAL BOUNDARY FORECAST OVER THE NORTHERN PLAINS.  WITH FFG
VALUES RELATIVELY LOW OVER THE NORTHERN PLAINS---RUNOFF ISSUES MAY
DEVELOP FROM EASTERN MT---INTO WESTERN ND AND NORTHWEST SD.  
THERE IS A FAIRLY LARGE SPREAD IN THE MODELS WITH RESPECT TO WHERE
THE HEAVIEST RAINS OVER THE NORTHERN PLAINS MAY BE TOWARD THE END
OF THE FORECAST PERIOD---LEADING TO LOW CONFIDENCE IN DETAILS. 
HOWEVER---THERE IS A SIGNAL IN MOST OF THE GUIDANCE FOR THE
POTENTIAL FOR HEAVY TO ISOLATED EXCESSIVE AMOUNTS ACROSS THESE
AREAS.  A BLEND OF THE 1200 UTC HI RES ARW--ALONG WITH THE IN
HOUSE PSEUDO BIAS CORRECTED MEANS USED FOR QPF DETAILS.


EASTERN GREAT LAKES INTO THE CENTRAL APPALACHIANS---UPPER OH VALLEY

A SURFACE FRONTAL BOUNDARY WILL BE PUSHING EASTWARD FROM THE
EASTERN LAKES INTO THE NORTHERN MID ATLANTIC-CENTRAL
APPALACHIANS/UPPER OHIO VALLEY REGION THIS PERIOD.  AN AXIS OF
1.5-1.75"+ PW AMOUNTS ALONG AND AHEAD OF THIS FRONT IN A REGION OF
UPPER DIFFLUENCE IN THE VICINITY OF THIS FRONT WILL SUPPORT
POTENTIAL FOR ORGANIZED FRONTAL CONVECTION ACROSS THESE AREAS. 
HEAVIEST TOTALS LIKELY DURING THE AFTERNOON WEDNESDAY FROM EASTERN
OH---WESTERN NY---WESTERN PA INTO FAR WESTERN MD AND ACROSS THE
NORTHERN AND EASTERN PANHANDLE OF WV.  MODERATE TO HEAVY
PRECIPITATION TOTALS DEPICTED ACROSS THESE AREAS IN THE .50-1"
RANGE---WITH LOCALLY HEAVY TOTALS AND ISOLATED RUNOFF ISSUES
POSSIBLE.

CNTL PLAINS/MID MS VALLEY

SOME CONCERN HERE DURING THE OVERNIGHT ACRS PARTS OF NEBRASKA INTO
IA/NRN MO AS LOW LEVEL JET INCREASES TO OVER 30 KTS INTO E/W
FRONTAL BOUNDARY NEAR THE KS/NEB BORDER.  MODELS SHOW MSTR
DEEPENING ALONG AND NORTH OF THE BNDRY OVERNIGHT WITH PWS
INCREASING TO OVER 1.50 INCHES IN A NW/SE AXIS ACRS ERN NEBRASKA
BY 06Z..NEAR 5H RIDGE CREST AXIS.  THIS COULD LEAD TO INCREASING
ELEVATED TSTMS WITH SOME POTNL FOR CELL REGENERATION AND TRAINING
FROM EXTREME ERN NEB INTO SW IA/NRN MO OVERNIGHT.  SOME OF THE
LATEST HRRR RUNS SUPPORT POTNL FROM SOME LOCAL 2 TO 3 INCH RAINS
ACRS THIS AREA.  FFG VALUES ARE GENL HIGH ACRS THIS AREA SO
BELIEVE ANY EXCESSIVE RAINFALL ISSUES THAT MIGHT DEVELOPE HERE
WOULD BE RATHER ISOLD.

SULLIVAN