MESOSCALE PRECIPITATION DISCUSSION 0072
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1207 AM EDT MON MAY 27 2013
 
AREAS AFFECTED...EASTERN MT...NORTHEAST WY...NORTHWEST SD AND
WESTERN ND 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY 
 
VALID 270405Z - 270800Z
 
SUMMARY...COLD-TOPPED CONVECTION ADVANCING GRADUALLY EAST THROUGH
EASTERN MT AND NORTHEAST WY WITH INTENSE RAINFALL RATES OF LOCALLY
OVER 1 INCH/HR...PROMOTING ELEVATED SHORT-TERM FLASH FLOOD
CONCERNS.

DISCUSSION...A MID LEVEL TROUGH ADVANCING OUT INTO THE FAR
NORTHERN HIGH PLAINS ATTM IS INTERACTING WITH A NOSE OF HIGHER LOW
LEVEL THETA-E AND A MODERATELY UNSTABLE BOUNDARY AS PER LATEST RAP
ANALYSIS. SBCAPE VALUES OF 1000 TO 2000 J/KG ARE SEEN POOLED OVER
NERN WY JUST EAST OF THE BIG HORN MTNS AND EXTENDING NWD INTO SERN
MT. PWATS ARE MAXIMIZED CURRENTLY OVER SERN MT WHERE THEY ARE AS
HIGH AS 1.2 INCHES...WHICH WOULD BE OVER 2 STD DEV ABOVE NORMAL.
LATEST IR SAT IMAGERY ALREADY SHOWS CLUSTERS OF COLD-TOPPED
CONVECTION WITH INTENSE RAINFALL RATES OVER ERN MT AND DOWN INTO
NERN WY. CLOUD TOP TEMPS ARE AS COLD AS -65C ATTM INVOF THE BIG
HORN MTNS...INDICATIVE OF INTENSE UPDRAFTS AND LIKELY ENHANCED
RAINFALL RATES WITH THE AID LOCALLY OF OROGRAPHICS. EXPECTING
THERE TO BE AT LEAST A BKN CLUSTER OF COLD-TOP CONVECTION THAT
WILL ADVANCE EAST OVER THE NEXT FEW HOURS...GRADUALLY REACHING
NWRN SD AND WRN ND AS THE AFOREMENTIONED MID LEVEL TROUGH ADVANCES
FARTHER EAST. THE CONVECTION WILL LIKELY BE SUSTAINABLE AS IT
INTERACTS WITH A SRLY LOW LEVEL JET OF 30 TO 40 KTS WHICH HELP
PROVIDE FAVORABLE THERMODYNAMICS. FFG VALUES ARE LOCALLY QUITE LOW
DUE TO WET ANTECEDENT CONDITIONS AND SO THERE SHOULD AT LEAST BE A
SHORT-TERM THREAT OF FLASH FLOODING.

ORRISON


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

LAT...LON   46240112 45480139 44500216 43790316 43390412 43220521
            43300641 43650727 44310742 45250810 46050768 46460737
            47180678 47910668 48500697 48990657 49200556 49210393
            48680176 47410108 46240112