Flash Flood Warning 1, NWS Great Falls, MT

SOUTHWEST AND NORTH CENTRAL MONTANA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
300 PM MDT WED JUN 2 1999

MOIST PERIOD IN STORE FOR THE FORECAST AREA. VORTICITY LOBES ARE
FORECAST TO MOVE INTO MT TONIGHT THROUGH THU NIGHT. LIKE TUE MODELS ARE
QUITE DIFFERENT ON SHORTWAVE DETAILS. ALSO MODELS ACTUALLY DO OR HINT AT
UPPER LOW DEVELOPMENT OVER MT THU. BY LATE THU AFTERNOON ETA HAS UPPER
LOW OVER NE MT WHILE NGM HAS UPPER LOW OVER SW MT. AVN NEVER DEVELOPS
UPPER LOW AND WAS PRETTY MUCH IGNORED FOR THIS FORECAST PACKAGE. MODELS
IN BETTER AGREEMENT IN TREATMENT OF SURFACE LOW WHICH MOVES SLOWLY N
THROUGH ERN MT TONIGHT THROUGH THU NIGHT. ETA/NGM IN GENERAL AGREEMENT
IN BAND OF HEAVY QPF FROM SW MT TO CENTRAL MT LATER TONIGHT THROUGH THU
NIGHT. RESPONSIBLE FACTORS ARE A GOOD AMOUNT OF DYNAMICS INCLUDING AT
TIMES...WARM AIR ADVECTION...JET DYNAMICS...LOW LEVEL CONVERGENCE...AND
LOW LEVEL UPSLOPE. QPF VALUES FROM SW TO CENTRAL MT ABOVE .75 INCH
ALMOST CERTAIN AND COULD LOCALLY APPROACH 2 INCHES. SNOW LEVELS WILL BE
HIGH...I.E. 8500 TO 9500 FEET. DUE TO RECENT RAINFALL THESE FORECAST QPF
VALUES HAVE POTENTIAL TO PRODUCE MORE FLOODING OVER PORTIONS OF SW MT.
FOR THIS REASON A FLOOD WATCH WAS ISSUED EARLIER TODAY. AS FAR AS
THUNDERSTORM SITUATION GOES...BETTER INSTABILITIES ARE OVER ERN PORTION
OF FORECAST AREA THIS AFTERNOON SO WILL INDICATE POSSIBILITY OF
THUNDERSTORMS THERE. CAPES ARE NOT THAT IMPRESSIVE SO LITTLE THREAT OF
SEVERE THUNDERSTORMS. FOR THU...AS MSO MENTIONS IN COORD CALL...SHOULD
BE A STRATIFORM RAIN EVENT OVER MUCH OF AREA. LONE EXCEPTION COULD BE SE
PORTION OF AREA WHERE POSSIBILITY OF THUNDERSTORMS WILL BE MENTIONED.
LOOKING AHEAD TO FRI...UPPER LOW SHOULD MOVE INTO CANADA SO LOOK FOR
IMPROVING CONDITIONS. WAS NOT SURE OF TIMING OF THE END OF PRECIP EVENT
SO HAVE STUCK CLOSE TO NGMS HIGH SCATTERED POPS. LATER SHIFTS CAN TAKE A
CLOSER LOOK AT THIS.
EXTENDED...LATEST MRF HAS CHANGED TUNE AND NOW INDICATES BETTER THREAT
OF PRECIPITATION OVER THE WEEKEND. ANOTHER PIECE OF ENERGY THAT WAS
EARLIER FORECAST TO STAY S OF MT NOW ROTATES INTO MT FROM SW U.S.
MEANWHILE PACIFIC UPPER TROUGH IS FASTER MOVING INTO AREA. BLANK
GTF 7984 HLN 7984 HVR 6874