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Excessive Rainfall Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1434Z Jul 29, 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
1034 AM EDT TUE JUL 29 2014

...VALID 15Z TUE JUL 29 2014 - 12Z WED JUL 30 2014...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
35 SSW DDC 30 NW JWG 25 SSE JWG HBR 40 NNE CDS 10 S BGD DHT
10 SSW CAO 40 ENE LVS 20 E SKX 20 N ALS 40 NE MYP 10 E CCU ASE
25 NNW GUC 15 WNW GUC 20 E MTJ 15 NE MTJ 30 N MTJ 15 E GJT
35 NNW GJT 30 SSE VEL 35 ENE PVU 25 ENE SLC 25 NE OGD 20 NE LGU
20 SE U78 JAC 35 SSW P60 P60 15 NNE P60 40 NW COD 15 ENE COD
20 ENE DGW TOR 15 SSW TOR 35 WNW ITR 45 WNW GCK 35 SSW DDC.

MODERATE RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
10 ENE PUB 25 WNW AFF BJC 10 NW FNL PUM CYS 20 E GXY 35 E DEN
10 SSE LIC 30 NNW LHX 10 ENE PUB.


THE VERY WET PATTERN WILL PERSIST THROUGH THE PERIOD ACROSS THE
INTERMOUNTAIN WEST. THE 12Z ANALYSIS SHOWED PRECIPITABLE WATER
VALUES BETWEEN TWO AND THREE STANDARD DEVIATIONS ABOVE NORMAL AT
BOTH SLC AND RIW...AN INDICATION OF THE AMOUNT OF MOISTURE
AVAILABLE IN THE PLUME. IN FACT...THE LOW LEVEL MOISTURE FLUX
BULLSEYE WAS LOCATED OVER WESTERN WY THIS MORNING. ACROSS THE
NORTHERN AND CENTRAL ROCKIES...CLOUDINESS THIS MORNING COULD PUSH
BACK THE TIMING OF CONVECTIVE INITIATION...BUT THE BULK OF
AVAILABLE MESOSCALE MODELS STILL SHOW CONVECTION DEVELOPING AFTER
THE 17Z-18Z TIME FRAME.

AFTER CONVECTIVE DEVELOPMENT...DIVERGENCE AHEAD OF A CLOSED LOW
OVER NORTHEAST AZ SHOULD AID IN SYNOPTIC SCALE ASCENT... PROMOTING
GREATER COVERAGE ACROSS NORTHEAST UT...WY INTO EASTERN CO.
PRECIPITABLE WATER VALUES BETWEEN TWO AND THREE STANDARD
DEVIATIONS WILL FUEL THE FLASH FLOOD THREAT. THE LATEST SSEO
PROBABILITY OF QPF EXCEEDING THREE HOUR FLASH FLOOD GUIDANCE
VALUES PEAKS NEAR 00Z OVER WESTERN WY...AN INDICATION OF THE HIGH
MOISTURE CONTENT OF THE AIR.

THE SLIGHT RISK ISSUED EARLIER FOR EASTERN CO AND SOUTHEAST WY
WILL EXTENDED BACK INTO WESTERN WY AND NORTHEAST UT TO ACCOUNT FOR
THE INCREASED THREAT DUE TO THE HIGH MOISTURE AIRMASS IN PLACE. A
MODERATE RISK AREA WAS MAINTAINED FOR PORTIONS OF SOUTHEAST WY AND
NORTHEAST CO...AS CONVECTION DEVELOPS AFTER 17Z OR 18Z AFTER THE
CIN IS REMOVED. THE HIGH MOISTURE CONTENT OF THE AIR AND UPSLOPE
FLOW SHOULD RESULT IN QPF VALUES GREATER THAN 2.00 INCHES IN THESE
LOCATIONS...AND THESE VALUES ARE SUPPORTED BY THE LATEST ECMWF AND
GEFS ENSEMBLE OUTPUT. GIVEN THAT THE THREE HOUR FLASH FLOOD
GUIDANCE VALUES ARE AS LOW AS 1.00 TO 1.50 INCHES...THE MODERATE
RISK WAS NOT MODIFIED.

AFTER 29/00Z...CONVECTION DEVELOPING IN SOUTHEAST CO IS EXPECTED
TO RIDE ALONG THE QUASI STATIONARY FRONT EXTENDING ACROSS
SOUTHWEST KS AND NORTH CENTRAL OK. MOST OF THE MODEL INSTABILITY
IS ELEVATED AS A 20 TO 30 KNOT SOUTHERLY FLOW OVERRUNS THE
BOUNDARY. THE INSTABILITY IS EXPECTED TO EXTEND ALONG THE FRONT
INTO NORTHWEST OK AND FAR NORTH TX THROUGH 29/12Z. THERE IS STILL
SOME SPREAD IN THE PLACEMENT OF THE QPF...AND THE LATEST ECMWF
ENSEMBLE AND GEFS OUTPUT SUGGEST THE POTENTIAL FOR 3 TO 4 INCHES
OF RAIN. THE SLIGHT RISK REMAINS IN PLACE HERE...AND DEPENDING ON
12Z OUTPUT...A SMALL MODERATE RISK COULD BE NEEDED FOR THIS
LOCATION.

CONVECTION ACROSS THE GREAT BASIN WILL BE PREDICATED MAINLY ON THE
COMBINATION OF MOISTURE IN THE INCREASED MONSOONAL FLOW AND
MARGINAL INSTABILITY DUE IN MOST PART TO STEEPENING MID LEVEL
LAPSE RATES. ORGANIZATION MAY BE MORE DIFFICULT AS THE MID LEVEL
RIDGE REMAINS MORE OR LESS IN PLACE. HOWEVER...GIVEN LOCAL
CIRCULATIONS AND RELATIVELY LOW ONE HOUR FLASH FLOOD GUIDANCE
VALUES...A SEE TEXT REMAINS IN PLACE.

HAYES