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
Last Updated: 336 AM EDT TUE JUN 25 2013