Hail in Montana, May 21, 2002

SOUTHWEST AND NORTH CENTRAL MONTANA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
240 PM MDT TUE MAY 21 2002

.SHORT TERM...A LOW PRESSURE TROF OVER THE PACIFIC NORTHWEST IS
MOVING SLOWLY EAST WITH A LARGE AREA OF DIFLUENCE DEVELOPING
OVER THE CWA. TEMPS ARE RELATIVELY COOL BUT CAA ALOFT...MAINLY
SOUTH...CONTINUES TO KEEP THE AIRMASS UNSTABLE. THE 7H LOW MOVES OVER
SE MT BY 18Z WED WITH A TROF EXTENDING NE TOWARDS FCA. RH IS HIGH AND
PRECIP SHOULD EXTEND ACROSS MOST OF THE CWA...WITH SNOW LEVELS
DROPPING BELOW 6000 FEET AFTER MIDNIGHT OVER THE NORTHERN ROCKIES. A
COLDER AIRMASS MOVES SOUTH OUT OF CANADA EARLY WEDNESDAY AND SNOW
SHOULD DEVELOP OVER THE NORTHERN CWA DURING THE MORNING...SPREADING
TO THE SOUTHERN CWA BY LATE AFTERNOON. SNOW AMOUNTS WILL BE TRICKY
WITH RAIN/SNOW MIX AS WELL AS WARM GROUND A FACTOR ON WEDNESDAY...
BUT WILL ASSUME ALL SNOW OVERNIGHT. WINTER STORM WARNING WILL BE
NECESSARY REGARDLESS DUE TO HIGH QPF AND STRONG WINDS ON WEDNESDAY.
AIRMASS DRIES QUICKLY FROM THE NORTH THURSDAY MORNING. HIGH
PRESSURE ALOFT ALSO BEGINS TO REBUILD THURSDAY...HOWEVER NORTHWEST
FLOW CONTINUES ALOFT AND AIRMASS MAY ALLOW FOR SOME ADDTIONAL
SCATTERED SHOWERS. ANOTHER SHORT WAVE MOVES ONSHORE OVER THE PACIFIC
NORTHWEST ON SATURDAY BUT THE LOCAL AREA WILL REMAIN UNDER THE
INFLUENCE OF THE HIGH. ZELZER

.EXTENDED....SW FLOW ALOFT IS EXPECTED OVER THE FORECAST AREA LATE
IN THE WEEKEND THROUGH EARLY NEXT WEEK. MODELS DIFFER ON SAT WITH
12Z TUE RUN OF THE UKMET AND 12Z MON RUN OF THE ECMWF SHOWING NW
FLOW ALOFT FOR SAT. DO NOT FORESEE ANY MODERATE OR STRONG SHORTWAVES
DURING THE PERIOD. ALTHOUGH THERE COULD BE ISOLATED SHOWERS OVER THE
PLAINS DURING THE PERIOD DUE TO THE PASSAGE OF WEAK SHORTWAVES...FOR
CONTINUITIES SAKE WILL CONTINUE DRY FORECAST OVER THE PLAINS. LATEST
AVN AND AVN EXTENSION DOES HAVE SOME QPF OVER SW MT FOR SUN THROUGH
TUE SO WILL GO WITH A SLIGHT CHANCE OF SHOWERS. BLANK

.CCF NUMBERS
GTF SW 044/047 030/045 030 13++7
    BBBBB 062/040 068/042 070/042 070/042 070 31111111111
CTB SW 040/043 026/044 030 13++6
    BEBBB 058/040 064/040 065/040 065/040 065 31111111111
HLN SW 045/049 034/052 034 13++7
    BBEEE 065/043 070/045 071/045 071/045 071 31111222222
BZN SW 042/048 030/050 030 13+97
    BBEEE 060/038 065/040 066/040 066/040 066 31111222222
WEY SW 033/043 025/038 022 13+97
    BBEEE 050/028 060/033 060/033 060/033 060 31111222222
DLN SW 038/045 032/047 030 13886
    BBEEE 060/038 065/040 066/040 066/040 066 31111222222
HVR SW 047/051 030/046 033 13++7
    BBBBB 060/040 070/042 071/042 071/042 071 31111111111
LWT SW 044/050 030/043 030 13++7
    BBBBB 059/038 068/040 068/040 068/040 068 31111111111=

.TFX...WINTER STORM WARNING FOR ROCKY MOUNTAIN FRONT TUESDAY
       NIGHT THROUGH WEDNESDAY NIGHT
    ...WINTER STORM WARNING FOR AREAS OF SOUTHWEST MONTANA TUESDAY
       NIGHT THROUGH WEDNESDAY NIGHT
    ...WINTER STORM WARNING NORTH CENTRAL MONTANA WEDNESDAY AND
       WEDNESDAY NIGHT.
    ...FLOOD WATCH FOR THE DEARBORN RIVER THROUGH WEDNESDAY