MESOSCALE PRECIPITATION DISCUSSION 0312
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1116 PM EDT FRI AUG 22 2014
 
AREAS AFFECTED...NORTHEAST WY...EXTREME SOUTHEAST MT...EXTREME
WESTERN SD 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY 
 
VALID 230300Z - 230630Z
 
SUMMARY...A CLUSTER OF INTENSE CONVECTION WILL FOSTER SERIOUS
FLASH FLOOD CONCERNS OVER THE NEXT FEW HOURS AS THE ACTIVITY BACK
BUILDS AND TRAINS OVER THE SAME AREA.

DISCUSSION...A RELATIVELY SMALL CLUSTER OF STRONG THUNDERSTORMS IS
NOTED IN SAT AND RADAR IMAGERY OVER NERN WY ATTM. THE CONVECTION
IS FORMING GENERALLY WEST OF THE BLACK HILLS BUT IS FORMING IN AN
AREA WHERE THERE IS MODEST INSTABILITY AS PER THE LATEST RAP
ANALYSIS. THE STRONGER FORCING MECHANISM IS THE APPROACH OF THE
DEEP LYR TROUGH OVER THE NWRN U.S. WHICH IS AIDING SFC LOW
PRESSURE DEVELOPMENT ALONG A FRONTAL ZONE OVER ERN WY.

VERY STRONG DYNAMICS ARE ARRIVING IN ASSOC WITH THIS UPR
TROUGH...AND IT IS LIKELY THAT THE ONGOING CONVECTION WILL PERSIST
AND MAY EVEN EXPAND SOME OVER THE NEXT COUPLE OF HOURS GIVEN THE
EXPECTATION FOR STRONGER LOW LVL MOISTURE TRANSPORT ARRIVING FROM
THE N CNTRL PLAINS AND INTERACTING WITH THE FRONT.

THERE IS POTENTIAL FOR LOCALLY VERY SERIOUS FLASH FLOODING THROUGH
06Z AS THE 18Z NAM-CONEST AND 00Z HRRR INDICATE A CONCENTRATED
AREA OF EXTREMELY HVY RAINFALL AMTS OVER NERN WY AND NEAR THE MT
BORDER THROUGH 06Z.

RAINFALL RATES OF 1 TO 2 INCHES/HR ARE EXPECTED TO CONTINUE AND
WITH AN ENVIRONMENT CONDUCIVE FOR BACK-BUILDING AND
TRAINING...THERE WILL LIKELY BE SOME VERY HVY TOTALS. STORM TOTALS
THROUGH 06Z EXCEEDING 5 INCHES ARE POSSIBLE BASED ON THE
AFOREMENTIONED HI-RES MODELS. WILL CONTINUE TO MONITOR.

ORRISON

ATTN...WFO...UNR...CYS...BYZ...

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

LAT...LON   45520349 44390365 43430457 43330519 43440572 43810590
            44700548 45780484 45920395 45520349