Flash Flood Guidance
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000
AWUS01 KWNH 272249
FFGMPD
SDZ000-NDZ000-MTZ000-WYZ000-280447-

MESOSCALE PRECIPITATION DISCUSSION 0394
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
649 PM EDT MON JUL 27 2015

AREAS AFFECTED...EASTERN MT & WESTERN DAKOTAS

CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE

VALID 272247Z - 280447Z

SUMMARY...AN OCCLUDING CYCLONE IS EXPECTED TO BRING HEAVY RAINFALL
TO EASTERN MT AND PORTIONS OF THE WESTERN DAKOTAS AS CIN ERODES.
FLASH FLOODING IS POSSIBLE.

DISCUSSION...A STRENGTHENING CYCLONE AHEAD OF AN INCREASINGLY
NEGATIVELY TILTED UPPER TROUGH IS LOCATED NORTH OF MILES CITY MT,
WITH A VARIETY OF SURFACE FEATURES LINKING IN TOWARDS ITS CENTER.
RECENT SPC MESOANALYSES INDICATE THAT CIN IS ERODING ACROSS THE
REGION, WHICH SEEMS TO BE VERIFIED AS THUNDERSTORMS ACROSS THE
REGION ARE SHOWING COOLING CLOUD TOPS.  PRECIPITABLE WATER VALUES
ARE ~1.25", AND MIXED LAYER CIN IS 1500-2000 J/KG ACROSS THE
REGION, WITH HIGHER VALUES IN THE 3000-4000 J/KG RANGE ACROSS
CENTRAL ND AND EASTERN SD.  INFLOW AT 850/700 HPA IS IN THE 25 KTS
RANGE OUT OF THE SOUTHEAST DIRECTED TOWARDS EASTERN MT.

RECENT RAP RUNS SHOW PRECIPITABLE WATER VALUES INCREASING INTO THE
1.50-1.75" RANGE OVER THE NEXT SEVERAL HOURS -- 2.5-3 SIGMAS ABOVE
AVERAGE -- AS THUNDERSTORMS SATURATE THE ATMOSPHERE.  INFLOW
INCREASES TO THE 45 KT RANGE OVERNIGHT AS WELL.  THE EXPECTED
MOISTURE COULD ALLOW FOR HOURLY RAIN RATES AS HIGH AS 2" AN HOUR.
THE MESOSCALE GUIDANCE GENERALLY INDICATES LOCAL AMOUNTS IN 2-3"
RANGE WHICH COULD FALL QUICKLY AND EXCEED FLASH FLOOD GUIDANCE
VALUES.  CELL TRAINING IS POSSIBLE AS ORGANIZED CONVECTION STARTS
OUT MOVING NORTH AT 30 KTS BEFORE SHIFTING TO A MORE NORTHEAST TO
EAST-NORTHEAST TRACK AT 25 KTS WITH TIME -- CELL TRAINING AND
POSSIBLE CELL MERGERS ARE CONSIDERED THE MAIN FLASH FLOOD THREAT.
THE BIGGEST FLY IN THE OINTMENT PRECLUDING EXTENSIVE CELL TRAINING
AND/OR WIDESPREAD FLASH FLOOD ISSUES WOULD BE THE POTENTIAL FOR
FORWARD PROPAGATION AS A POSSIBLE CONVECTIVE LINE NEAR THE
TRAILING COLD FRONT ACCELERATES EASTWARD AS THE CYCLONE OCCLUDES
INTO THE REGION OF HIGHER INSTABILITY TO ITS EAST.  AN AVERAGE OF
THE 12Z AND 18Z SSEO NEIGHBORHOOD PROBABILITIES OF EXCEEDING THE
THREE HOUR FLASH FLOOD GUIDANCE SUGGEST THAT CHANCES EXCEED 50%
AROUND 02Z.

ROTH

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

ATTN...WFO...ABR...BIS...BYZ...GGW...UNR...

ATTN...RFC...MBRFC...NCRFC...

LAT...LON   49110479 49090466 49080253 49100092 49030092
            46400082 45000115 44590341 44950596 44980681
            45000772 45000772 45000772 45680794 46310786
            48610687 49040647


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