MESOSCALE PRECIPITATION DISCUSSION 0129
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
336 AM EDT TUE JUN 25 2013
 
AREAS AFFECTED...EASTERN MT 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 250735Z - 251135Z
 
SUMMARY...SHOWERS AND THUNDERSTORMS WITH HEAVY RAIN HAVE BEEN
TRAINING ACROSS NORTHEAST MT.  FLASH FLOODING IS POSSIBLE OVER THE
NEXT SEVERAL HOURS, CAUSED BY A QUICK 1-2" OF RAINFALL.

DISCUSSION...A COUPLE BANDS OF SHOWERS AND THUNDERSTORMS HAVE BEEN
TRAINING ACROSS EASTERN MT OVERNIGHT.  THIS CONVECTIVE AREA
CONTINUES TO BE FOCUSED NEAR A TROWAL IN THE COLD SECTOR OF A
SYNOPTIC-SCALE LOW AND NEAR AN AREA OF 750-650 HPA FRONTOGENESIS. 
THE AREA REMAINS STRONGLY DIVERGENT ALOFT AHEAD OF A
NEGATIVELY-TILTED TROUGH.  CELL PROPAGATION IS EXPECTED TO BECOME
MORE NORTHERLY, AND POSSIBLY NORTH-NORTHWESTERLY, WITH TIME AS THE
TROWAL PIVOTS ACROSS THE REGION PER 00Z GFS CORFIDI VECTORS. 
PRECIPITABLE WATER VALUES CONTINUE TO BE QUITE HIGH FOR THE
REGION, BETWEEN 1.25-1.50 INCHES, NEAR THE 99TH PERCENTILE FOR
LATE JUNE.  

A COUPLE FACTORS SHOULD LEAD TO DISSIPATION OF THE RAIN AREA
AROUND 11Z, INCLUDING A WEAKENING LOW-LEVEL JET AND INCREASING CIN
NEAR THE EASTERN PORTION OF THE PIVOTING SURFACE BOUNDARY, PER 00Z
ARW GUIDANCE.  SINCE FLASH FLOOD GUIDANCE VALUES ARE SO LOW -- 1
INCH IN THREE HOURS -- AND THERE IS CELL TRAINING, FLASH FLOODING
IS CONSIDERED POSSIBLE IN THIS REGION, DESPITE THE RECENT LOSS OF
SOME OF THE CONVECTIVE ORGANIZATION.  A QUICK 1-2" OF RAIN IN A
SHORT TIME PERIOD COULD CAUSE FLASH FLOODING.

ROTH

ATTN...WFO...BYZ...GGW...TFX...

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

LAT...LON   48920920 49110819 49100630 48890556 48080543 47570560
            46590622 46250759 46590817 47590857 48920920