MESOSCALE PRECIPITATION DISCUSSION 0329
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
429 PM EDT TUE JUN 19 2018

AREAS AFFECTED...CENTRAL MONTANA

CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE

VALID 192030Z - 200130Z

SUMMARY...HIGHLY ISOLATED FLASH FLOOD RISK FOR SLOW MOVING CELLS
OVER VERY SATURATED SOILS. 

DISCUSSION...GOES-16 VISIBLE IMAGERY SHOWS COMPACT CENTER TO THE
UPPER LOW OVER NORTH CENTRAL MT RETROGRADING EASTWARD WITH A BROAD
SHIELD OF MID-LEVEL ALTO-STRATUS IN THE SOUTHERN QUADRANT.  EAST
OF THE CLOUD DECK...DAYTIME HEATING HAS INCREASED TEMPS INTO THE
MID TO UPPER 60S WITH TDS IN THE 50S SUPPORTING SBCAPES TO 2000
J/KG PER RAP ANALYSIS.  WEAKER INSOLATION NEAR THE CENTER AND
NORTHEAST SIDE AS INCREASED TO 500-1000 J/KG.   FLOW IS GENERALLY
WEAK IN THE LOW LEVEL BETWEEN THE UPPER LOW AND THE S/W
UNDERCUTTING THE UPPER LOW IN WY...HOWEVER WEAK EASTERLY FLOW HAS
ALLOWED FOR MODERATE MOISTURE TO POOL IN THE EASTERN HEMISPHERE OF
THE UPPER LOW IN MT WITH TPWS AS HIGH AS 1.0".  THE COMBINATION
HAS BEEN SUFFICIENT FOR DEEPER CONVECTION TO DEVELOP WITH SOME
LIGHTNING IN STILLWATER/SWEET GRASS COUNTIES AS WELL AS IN THE
DEEPER MST/INSTABILITY CORE ALONG THE YELLOWSTONE/TREASURE NORTH
INTO GARFIELD COUNTIES.  WEAK CLOUD BEARING FLOW WILL LIMIT
FORWARD PROGRESS AND ENHANCE LOCALIZED RAIN TOTALS UP TO 1-1.5" IN
THE NEXT 3HR.  GIVEN FFG VALUES IN THE AREA ARE LESS THAN 1"/HR
WITH AREAS ON THE WESTERN SIDE OF MPD AREA AS LOW AS
.25"/HR...NEIGHBORHOOD FFG EXCEEDANCE PROBABILITIES ARE 70-95%.

HI-RES CAMS ALSO SUPPORT CELLS TO EVENTUALLY SLIDE WNW AS A SPOKE
OF THE UPPER LOW SHIFTS EAST UNDER IT AND THE UPPER LOW
RETROGRADES...NARROWING A SW TO NE FLOW CONFLUENCE FROM CHOUTEAU
TO YELLOWSTONE COUNTY AFTER 00Z.  THIS MAY AID SOME REPEAT TRACKS
AND KEEP THE ISOLATED FLASH FLOODING RISK PSBL THROUGH THE LATE
EVENING.

GALLINA

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

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

LAT...LON   48411068 48400972 48040871 47700750 47130660
            46390649 45620685 45140745 45060862 45080883
            45110983 45710989 46410975 46810997 47071020
            47181045 47541094