MESOSCALE PRECIPITATION DISCUSSION 0233
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
824 PM EDT SAT SEP 07 2013
 
AREAS AFFECTED...EXTREME SOUTHEAST MT...SOUTHERN
ND...NORTHERWESTERN SD 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 080025Z - 080525Z
 
SUMMARY...SCATTERED TO NUMEROUS SHOWERS AND THUNDERSTORMS WITH
VERY HEAVY RAINFALL ARE EXPECTED TO INCREASE OVER THE NEXT SEVERAL
HOURS ACROSS EXTREME SOUTHEAST MONTANA AND MOVE EASTWARD ACROSS
PARTS OF SOUTHWESTERN ND AND NORTHWESTERN SD, BRINGING THE
POTENTIAL FOR LOCALIZED FLASH FLOODING.

DISCUSSION...LATEST SATL AND RADAR IMAGERY HAS SHOWN A RAPID
INCREASE IN TSTMS ACRS PARTS OF SE MT MOVING INTO SW ND/NW SD IN
RESPONSE TO STRONG AFTN HEATING TO THE NORTH OF WEAK STATIONARY
FRONT LOCATED TO THE SOUTH OF THE AREA.  THESE STORMS SHOULD
CONTINUE TO FIRE ALONG FAVORABLE SELY LOW LEVEL FLOW FEEDING OFF
OF MIXED LAYER CAPES OF 1500 J/KG NEAR AND JUST NORTH OF THE
BNDRY.   MODEL AND OBSERVED CAPES OF OVER 1.5 INCHES NOTED ACRS
THE AREA ARE WELL ABOVE 90TH PERCENTILE OF CLIMO NORMALS AND WILL
LIKELY SUPPORT OF VERY HEAVY RAINFALL RATES.  HAVE ALREADY SEEN AN
UPSTREAM REPORT OF 1.5 INCHES IN 20 MINUTES OVER SE MT INDICATING
HIGH POTNL FOR SOME SHORT TERM HEAVY RAINFALL RATES AS STORMS
CONTINUE TO BUILD EASTWARD OVER THE NEXT SEVERAL HOURS.   WHILE
CORFIDI VECTORS SUGGEST ANY MCS THAT DVLPS SHOULD BE RATHER
PROGRESSIVE...THE LATEST HRRR GUIDANCE SUGGESTS LOCAL 1 TO 1.5
INCH PLUS AMOUNTS WILL BE PSBL IN SOME SPOTS WHICH WOULD LIKELY
APPROACH OR PSBLY EXCEED SOME OF THE LOWER FF GUIDANCE VALUES OVER
THE AREA.  

SULLIVAN

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

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

LAT...LON   44710241 44910375 45330453 45960454 46440310 46190058
            45660015 44840046 44710241