MESO: Nws Weather Prediction Center College Park Md

AWUS01 KWNH 122053
FFGMPD
COZ000-WYZ000-130252-

MESOSCALE PRECIPITATION DISCUSSION 0241
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
452 PM EDT THU SEP 12 2013

AREAS AFFECTED...CENTRAL CO...SOUTHEAST WY

CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY

VALID 122052Z - 130252Z

SUMMARY...HEAVY RAINFALL IS BEGINNING TO INCREASE IN COVERAGE
ACROSS PORTIONS OF CENTRAL CO IN A LINE JUST TO THE EAST OF
DENVER. DUE TO THE HEAVY RAINS IN THIS REGION SINCE LAST NIGHT,
REGIONAL FLASH FLOODING IS CONSIDERED LIKELY.

DISCUSSION...A NORTH-SOUTH ORIENTED BAND OF HEAVY RAINS WITH
HOURLY RATES OF 0.5-1 INCH PER HOUR IS ALIGNED JUST TO THE EAST OF
A STATIONARY FRONT DRAPED AGAINST THE FRONT RANGE OF THE ROCKIES.
PRECIPITABLE WATER VALUES OF 1.25-1.50 INCHES IN THE 99TH
PERCENTILE FOR THE REGION FOR MID-SEPTEMBER AND NEAR RECORD HIGH
VALUES FOR SEPTEMBER, WHICH IS INCREASING PRECIPITATION EFFICIENCY
TO WELL ABOVE NORMAL VALUES. THE SATELLITE-DERIVED LIGHTNING
DENSITY PRODUCT INDICATES MINIMAL LIGHTNING IN THIS REGION,
INDICATIVE OF WARM RAIN PROCESSES AT PLAY.

NO REDUCTION OF 850-700 HPA UPSLOPE FLOW IS ANTICIPATED OVER THE
NEXT SEVERAL HOURS PER THE 19Z RAP GUIDANCE, WITH DIVERGENCE ALOFT
EXPECTED TO REMAIN EXCELLENT OVER CO BETWEEN A DEEP-LAYERED LOW IN
THE GREAT BASIN AND AN UPPER LEVEL TROUGH IN THE GREAT LAKES
DURING THIS TIME FRAME. CAPES OF 500-1000 J/KG ARE BEING IMPORTED
INTO THE REGION, WHICH HAS BEEN ENOUGH TO DRIVE THIS HEAVY
RAINFALL EVENT SO FAR. INDIVIDUAL CELLS ARE EXPECTED TO MOVE
NORTHWARD AT 10 KNOTS, IN LINE WITH THE 12Z NAM 850-400 HPA MEAN
LAYERED WIND AND THE 12Z GFS CORFIDI VECTORS. MOST OF THE
MESOSCALE MODELS INDICATE HEAVY RAINFALL BEING IN THE CARDS OVER
THE NEXT SEVERAL HOURS. CONSIDERING THE LONG DURATION OF HEAVY
RAINFALL IN THIS REGION, WHICH HAS LOWERED FLASH FLOOD GUIDANCE
VALUES TO NEAR ZERO ACROSS NORTH-CENTRAL CO, FLASH FLOODING IS
CONSIDERED LIKELY INTO TONIGHT.

ROTH

...PLEASE SEE WWW.WPC.NCEP.NOAA.GOV FOR GRAPHIC PRODUCT...

ATTN...WFO...PUB...BOU...CYS...GJT...

ATTN...RFC...ABRFC...CBRFC...MBRFC...WGRFC...

LAT...LON 41860556 40850448 39380352 38190385 37640428 37400514
37770593 38700645 39510652 41330693 41860556

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