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Excessive Rainfall Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1858Z Aug 19, 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
258 PM EDT TUE AUG 19 2014

...VALID 18Z TUE AUG 19 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 SE IGM 45 NNW IGM 30 E LSV 55 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 35 NNW 4HV 35 SW 4HV 25 SE PGA
60 E GCN 30 S SJN 40 E DUG 135 SSE DUG 125 E MMHO 70 E MMHO
85 SSE OLS 35 S OLS 30 NW DMA CGZ 15 SSE GYR 35 W LUF 60 WNW LUF
45 SE IGM.

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.

MODERATE RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
30 ENE FFZ 25 NE FFZ 15 ENE SDL SDL LUF 20 WNW LUF 30 NW LUF
35 NNW LUF 20 SSW PRC 15 WNW PRC 35 N PRC 25 S 40G 10 NW FLG
20 SE FLG 35 S INW 50 WSW SOW 50 ENE FFZ 30 ENE FFZ.


SOUTHWEST INTO THE GREAT BASIN

A FAIRLY LARGE SLIGHT RISK AREA MAINTAINED IN THE LATEST EXCESSIVE
RAINFALL POTENTIAL OUTLOOK FROM AZ INTO UT---WITH ONLY SOME SLIGHT
NARROWING OF THE AXIS FROM THE PREVIOUS ISSUANCE.  ABOVE AVERAGE
PW VALUES IN A FAIRLY DIFFLUENT REGION DOWNSTREAM OF THE
CALIFORNIA CLOSED LOW WILL CONTINUE TO SUPPORT ORGANIZED
CONVECTION INTO THE REMAINING PART OF THE AFTERNOON ACROSS LARGE
PORTIONS OF AZ INTO SOUTHERN TO CENTRAL UT.  A MODERATE RISK AREA
WAS DEPICTED OVER CENTRAL AZ IN THE MOGOLLON RIM AREA WHERE
PREVIOUS HEAVY RAINS  IN THE 1-3" RANGE HAVE OCCURRED AND
ADDITIONAL HEAVY AMOUNTS LIKELY OVER THE NEXT SEVERAL HOURS. 
MODELS CONTINUE TO SHOW THE MID TO UPPER LEVEL HEIGHT FALLS THAT
HAVE BEEN MOVING NORTHEASTWARD INTO THE SOUTHWEST/GREAT BASIN OVER
THE PAST FEW DAYS PUSHING NORTHEASTWARD THROUGH THE GREAT
BASIN---PORTIONS OF THE NORTHERN TO CENTRAL ROCKIES AND INTO THE
NORTHERN PLAINS THIS EVENING INTO WEDNESDAY MORNING.  THE AXIS OF
ABOVE AVERAGE PW VALUES THAT THESE HEIGHT FALLS HAVE BEEN EMBEDDED
IN WILL ALSO PRESS NORTHEASTWARD.  SUBSEQUENTLY---PRECIPITATION
SHOULD BE ON A DECREASE FROM THE SOUTHWESTERN U.S. THIS EVENING AS
THE BEST MOISTURE AND HEIGHT FALLS LIFT NORTHEASTWARD.  THIS WILL
LIKELY BRING A SIGNIFICANT DECREASE IN THE POTENTIAL FOR RUNOFF
ISSUES---WITH THE GREATEST RISK DURING THE AFTERNOON TODAY.

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.

ORAVEC