Severe Thunderstorm Warning 1, NWS Great Falls, MT

SOUTHWEST AND NORTH CENTRAL MONTANA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
230 PM MDT FRI MAY 25 2001

AIRMASS STILL UNSTABLE OVER THE TFX CWA THIS AFTERNOON...WITH LIFTED
INDICES OF -2 TO -4...AND SCATTERED THUNDERSTORMS DEVELOPING OVER
SOUTHWESTERN MONTANA. EXPECT THESE TO CONTINUE INTO THE EVENING...
BUT THEY SHOULD DISSIPATE WITH LOSS OF DAYTIME HEATING AS THEY ARE
AIRMASS THUNDERSTORMS AND HAVE LITTLE DYNAMICS TO SUPPORT AN EXTENDED
EVENT. OTHERWISE...THE COLD FRONT FROM THIS MORNING HAS MOVED OUT
OF THE CWA AND SKIES CLEARED QUICKLY BEHIND IT ACROSS THE PLAINS...
BUT NOW CONVECTIVE CUMULUS HAS NOW STARTED TO DEVELOP THERE. WILL GO
WITH A SLIGHT CHANCE OF SHOWERS OR THUNDERSTORMS THERE...AS A WEAK
AREA OF VORTICITY MOVES ACROSS THE HI-LINE THIS EVENING. SKIES
SHOULD BECOME MOSTLY CLEAR/PARTLY CLOUDY ALL ZONES BY MIDNIGHT. THE
UPPER RIDGE THEN REBUILDS DURING THE DAY ON SATURDAY...WITH THE
AXIS OVER THE CENTRAL AND NORTHERN ROCKIES. ANOTHER AREA OF WEAK
VORTICITY MOVES INTO SOUTHWESTERN MONTANA DURING THE AFTERNOON...
BUT WITH THE AIRMASS DRYING THROUGHOUT THE DAY...WILL ONLY KEEP POPS
OF 20% THERE. WILL ALSO GO WITH A SLIGHT CHANCE OVER THE MOUNTAINS
OF THE ROCKY MOUNTAIN FRONT. TEMPERATURES WILL WARM ABOUT 5 TO 10
DEGREES OVER TODAY AS THICKNESSES RISE AND SKIES WILL BE LESS
CLOUDY. SATURDAY NIGHT...AN UPPER TROUGH DIGS OFF THE PACIFIC
NORTHWEST COAST...FORCING THE UPPER RIDGE AXIS INTO CENTRAL MONTANA
AND CREATING A MORE MOIST SOUTHWEST FLOW ALOFT OVER THE CWA. UPPER
DYNAMICS TO SUPPORT ANY PRECIPITATION WILL MOVE INTO SOUTHWESTERN
MONTANA THROUGHOUT THE NIGHT...AND THEN SPREAD NORTHEAST ACROSS THE
CWA DURING THE DAY ON SUNDAY. WILL GO WITH CHANCE POPS IN THE
SOUTHWEST AND SLIGHT CHANCE POPS IN THE CENTRAL ZONES...INCREASING
TO ALL SCATTERED POPS ON SUNDAY...AND SPREADING CHANCE POPS
NORTHEAST INTO NORTHERN ZONES ON SUNDAY. WILL ALSO GO WITH MENTION
OF THUNDERSTORMS ON SUNDAY. SATURDAY NIGHT TEMPERATURES WILL REMAIN
A BIT MILDER OVER SOUTHWEST AND CENTRAL ZONES WITH INCREASED
CLOUDINESS...WHILE THOSE IN NORTHERN ZONES SHOULD STAY CONSISTENT.
SUNDAY TEMPERATURES SHOULD THEN GENERALLY BE COOLER THAN SATURDAY
WITH THE INCREASED CLOUD COVER AND PRECIPITATION. THE ONLY THREAT
OF WINDS WILL BE ON SUNDAY ACROSS THE EASTERN ZONES AS SOUTHEAST 850
MB WINDS INCREASE TO 15 TO 25 KT. THIS IS DUE TO THE INVERTED
SURFACE TROUGH (PARKED OVER WESTERN MONTANA THROUGH SATURDAY NIGHT)
SHIFTING SLOWLY EAST ON SUNDAY WITH THE ADVANCE OF THE UPPER
TROUGH.  COULSTON

EXTENDED...LATEST RUN OF MRF IS MORE IN LINE WITH ECWMF/UKMET AND
JAPANESE GLOBAL MODEL. UPPER LEVEL TROUGH MOVES THROUGH PAC NW ON
MONDAY...WITH SFC COLDFRONT MOVING THROUGH CENTRAL MONTANA FOR A
FEW SHOWERS AND BREEZY CONDITIONS. BY TUESDAY...A BROAD RIDGE OVER
THE WESTERN HALF OF THE CONUS WILL PUSH THE MAIN BAND OF WESTERLIES
INTO SRN-CNTRL CANADA. A WEAK CUTOFF LOW OVER THE SWRN CONUS MAY
CHANNEL SOME MOISTURE OVER SW MT. WILL STICK WITH A MAINLY DRY
FORECAST BY MIDWEEK. MPJ

GTF BW 047/084 050/081 047 10212
CTB BE 044/081 047/078 047 10201
HLN BW 049/086 052/078 047 10423
BZN BW 042/086 048/078 045 10423
WEY BW 036/079 040/070 040 10423
DLN BW 045/085 050/076 046 10323
HVR BE 047/087 047/085 050 10201
LWT BW 046/084 049/079 047 10212