MESOSCALE PRECIPITATION DISCUSSION 0298
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
805 PM EDT SUN JUN 04 2017

AREAS AFFECTED...WESTERN MT...NORTH CENTRAL ID

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

VALID 050005Z - 050530Z

SUMMARY...EXPANDING CONVECTION MOVING INTO BETTER ENVIRONMENT FOR
RAINFALL PRODUCTION CURRENTLY...WITH SOME ISOLATED TRAINING
ONGOING.  MAIN HEIGHT FALLS WILL ARRIVE TO THE AREA NEAR 03Z AND
PROVIDE AN ADDITIONAL ROUND OF MODERATE TO HVY RAINFALL. 

DISCUSSION...GOES-16 EXPERIMENTAL MESO VISIBLE IMAGERY INDICATES A
RECENT UPTICK IN CONVECTIVE VIGOR ACROSS SW MISSOULA TO N LEWIS
AND CLARK COUNTY MT CONVERGENCE LINE LIFTS NORTHWARD INTO SLIGHTLY
BETTER ENVIRONMENTAL CONDITIONS FOR CONVECTIVE GROWTH - MLCAPES TO
1000 J/KG AND RAINFALL EFFICIENCY -SFC TDS IN UPPER 40S TO MID 50S
WITH TPWS NEARING 1" SUPPORTING RAIN RATES AS HIGH AS 1"/HR. 
BROAD ANTICYCLONIC CURVATURE NOTED IN WV OVER THE AREA IS
INDICATIVE OF SOME UPPER LEVEL DIVERGENCE AS WELL TO HELP MAINTAIN
THE CONVECTION. RECENT MSX RADAR AND GOES-16 VISIBLE IMAGERY ALSO
DEPICTS SOME ALIGNMENT OF CONVECTIVE CORES FOR SOME SHORT-TERM
TRAINING.  LIMITING FACTORS DO REMAIN MAINLY IN FORWARD
PROPAGATION OF THE CELLS TO THE NNE...AT 30KTS PLUS CELL MOTIONS
OF 30KTS AS WELL...SHOULD LIMIT DURATION OF RAINFALL AND TOTALS
LIKELY AT OR JUST BELOW 1" MAX. ANOTHER LIMITING FACTOR IS
SUB-CLOUD EVAPORATION AS TDD ARE MODEST PER 18Z TFX SOUNDING WITH
LIMITED MST FLUX TO MOISTEN IT...THOUGH LOWER LEVEL MOISTURE
PROFILES ARE A BIT BETTER WITH 850-700 LAYERED CIRA TPW SHOWING A
MAXIMUM CORRIDOR OVER N ID INTO NW MT.

A SECOND ROUND OF UPSTREAM FORCING (DENOTED BY EXPANDING
CONVECTION OVER SW ID LIFTING NE IS EXPECTED AROUND 03Z AS THE
SHORTWAVE APPROACHES. GOES-WV LOOP SHOWS THE WAVE IS NARROWING IN
WAVELENGTH AS WELL AS THE BASE IS SWINGING MORE NEGATIVE TILT WITH
TIME SUPPORTING INCREASED CAA ALOFT AND STRONG DPVA FOR STRONG
LARGE SCALE ASCENT.  THIS COMBINED WITH LIFTING JET AXIS LEAVING W
MT IN THE RIGHT ENTRANCE OF 3H JET AS WELL FURTHER. RAP ALSO
SUGGESTS SOME INSTABILITY WILL REMAIN MAINLY ON THE EASTER SIDE OF
THE HIGHLIGHTED MPD AREA FOR THIS SECONDARY ROUND.  GIVEN FIRST
BATCH/CLUSTERS WILL MOISTEN THE LOWER LEVELS THROUGH THE
EVAPORATIVE PROCESS...RAINFALL RATES UP TO .5"-.75"/HR POSE SOME
LOCAL RUNOFF ISSUES (PARTICULARLY IN COMPLEX TERRAIN).

THIS SCENARIO IS SUPPORTED BY RECENT HRRR AND ESRL HRRR V.3 RUNS
WITH SOME SUGGESTION OF NEIGHBORHOOD PROBABILITY OF EXCEEDING FFG
VALUES IN THE 50% RANGE...WHICH IS A GOOD PROXY FOR MODERATE
CONFIDENCE IN LOCALIZED FLASH FLOODING CONDITIONS OCCURRING.

GALLINA

ATTN...WFO...MSO...TFX...

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

LAT...LON   48991194 48851074 47811150 46521334 45761452
            45701544 46431542 47041475 48751358