MESOSCALE PRECIPITATION DISCUSSION 0251
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1146 AM EDT FRI JUN 01 2018

AREAS AFFECTED...EAST CENTRAL MT

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

VALID 011545Z - 012000Z

SUMMARY...A REGION OF ENHANCED LOW-LEVEL CONVERGENCE AND FAVORABLE
MID/UPPER-LEVEL FLOW MAY SUPPORT HEAVY RAINFALL RATES AND
POTENTIAL AREAS OF LOCALIZED FLASH FLOODING THROUGH 20Z.

DISCUSSION...A SURFACE LOW CENTERED OVER SOUTHEAST MT THIS MORNING
WAS SUPPORTING A REGION OF ENHANCED LOW-LEVEL CONVERGENCE
NORTHWEST OF THE LOW CENTER, ACROSS EAST-CENTRAL MONTANA.
SOUTHERLY MID-LEVEL FLOW ACROSS THE NORTH CENTRAL U.S. WAS
TRANSPORTING MOIST AND UNSTABLE AIR NORTH ACROSS A SURFACE FRONT
INTO MONTANA, WITH PRECIPITABLE WATER VALUES NEAR 1 INCH, AND MOST
UNSTABLE CAPE AS HIGH AS 1000-1500 J/KG ACROSS THE OUTLINED AREA.
MID/UPPER-LEVEL FLOW WAS FAVORABLE AHEAD OF AN ADVANCING TROUGH
ACROSS THE NORTHERN INTERMOUNTAIN REGION, WITH MODEST UPPER
DIFFLUENCE, AND A ZONE OF ENHANCED 500 HPA SOUTH-SOUTHWESTERLY
FLOW (NEAR 50 KT PER LATEST SPC MESOANALYSIS). THE LOW-LEVEL
CONVERGENCE ZONE WAS SERVING TO FOCUS CONVECTION IN A NARROW BAND
NEAR BILLINGS, MT, WHICH WAS ORIENTED PARALLEL TO THE MID/UPPER
FLOW, RESULTING IN SOME CELL TRAINING. WHILE INDIVIDUAL CELL
MOVEMENT WAS NORTH-NORTHEAST AT ABOUT 20 KT, THE BROADER AREA OF
CONVECTION WAS PROPAGATING SLOWLY EASTWARD. RADAR ESTIMATES
SUGGEST RAINFALL RATES AROUND 1 IN/HR IN THE HEAVIER CONVECTIVE
CELLS. LATEST INFRARED SATELLITE SHOWS NEARLY STEADY CLOUD-TOP
TEMPERATURES, AND CONVECTION SEEMS TO BE MAINTAINING ITSELF IN THE
ENVIRONMENT WITH MODEST INSTABILITY BUT FAVORABLE DYNAMICS.

HI-RES GUIDANCE (INCLUDING THE HRRR, ARW, NMM AND NAM-CONEST)
GENERALLY SHOW A COUPLE BANDS OF FOCUSED RAINFALL ACROSS THE
OUTLINED AREA, ALTHOUGH AMOUNTS MAY BE UNDERDONE GIVEN RADAR
ESTIMATES AND A FEW GROUND TRUTH REPORTS WHICH ARE VERY CLOSE TO
THE ESTIMATES. GIVEN RELATIVELY LOW FFG VALUES ACROSS THIS AREA
(AROUND 1 IN/HR), LOCALIZED FLASH FLOODING IS POSSIBLE.

RYAN

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

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

LAT...LON   47790727 47700671 47230611 46460614 45880647
            45410693 45050798 45300864 45900873 46760845
            47390817 47700772