Severe Thunderstorm Warning 38, NWS Great Falls, MT

SOUTHWEST AND NORTH CENTRAL MONTANA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
300 PM MDT MON JUL 3 2000

BIG STORY THIS EVENING IS SEVERE WEATHER THAT HAS DEVELOPED OVER
SOUTHWESTERN AND EASTERN ZONES. UPPER LEVEL LOW PRESSURE AREA OVER
PACIFIC NORTHWEST WITH UPPER LEVEL RIDGE OVER CENTRAL CONUS PUTTING TFX
CWA UNDER STRONG AREA OF DIVERGENCE ALOFT. THIS IS BRINGING
PRECIPITATION TO MOST OF CWA...WITH STRONG TO SEVERE THUNDERSTORMS
DEVELOPING OVER SOUTHWESTERN ZONES AND PROGRESSING NORTHEASTWARD AND
STRENGTHENING OVER EASTERN ZONES. STORMS STRENGTHENING IN AREA OF WARMER
SURFACE TEMPERATURES...50+ DEGREE DEWPOINTS...AND GOOD DIRECTIONAL SHEAR
(EAST TO SOUTHEASTERLY WINDS AT SURFACE WITH MORE SOUTHWESTERLY WINDS
ALOFT). STRONGEST CONVECTION EXPECTED TO CONTINUE THROUGH EARLY
EVENING...WITH SEVERE THUNDERSTORM WATCH ISSUED THROUGH 02Z. MOST
CONVECTION SHOULD DIMINISH LATER THIS EVENING AS DIVERGENCE ALOFT AND
700 MB OMEGA MOVE NORTHEASTWARD OUT OF CWA. ALSO AIDING IN KILLING OF
CONVECTION IS COOLER AIR BEING DRAWN OVER CWA FROM NORTHWEST BY SURFACE
LOW PRESSURE DEVELOPING OVER NORTHERN WYOMING AT 20Z AND MOVING
NORTHWARD INTO EASTERN MONTANA OVERNIGHT. 700 MB WINDS OF 25 TO 35 KT
AND HIGHER SURFACE PRESSURE BUILDING FROM THE WEST OVERNIGHT WILL ALLOW
WESTERLY DOWNSLOPE WINDS TO DEVELOP ALONG THE EAST SLOPES OF THE ROCKIES
FOR DIMINISHING SHOWERS AS WELL. AIR MASS TO DRY DURING THE DAY ON
TUESDAY AS DOWNSLOPE WINDS TO CONTINUE. HOWEVER...SCATTERED SHOWERS AND
AFTERNOON AND EVENING THUNDERSTORMS TO REDEVELOP OVER SOUTHWESTERN AND
EAST CENTRAL ZONES AS WEAK VORT MAXES ROTATE OVER THE AREA. SLIGHTLY
STRONGER DYNAMICS ACROSS THE SOUTHERN CWA WITH SLIGHTLY STRONGER
INSTABILITY OVER NORTHERN ZONES FOR WEDNESDAY. UPPER LEVEL TROUGH MOVES
EASTWARD TOWARDS CWA...BRINGING COOLER AIR ALOFT TO THE NORTH AS WELL AS
SLIGHTLY STRONGER VORT MAXES TO SOUTHERN ZONES. OVERNIGHT TEMPERATURES
SHOULD REMAIN ON THE WARM SIDE WITH CONTINUED CLOUDINESS AND
PRECIPITATION. TUESDAY SHOULD BE A LITTLE COOLER THAN TODAY WITH THE
COOLER AIR FILTERING IN BEHIND THE SURFACE LOW. TUESDAY NIGHT THROUGH
WEDNESDAY WILL SEE COOLER NIGHTTIME TEMPERATURES AND SLIGHTLY WARMER
DAYTIME TEMPERATURES WITH MUCH LESS CLOUDINESS. IN GENERAL...WILL STAY
NEAR MOS TEMPERATURES.  COULSTON

EXTENDED DISCUSSION...ABBREVIATED DISCUSSION DUE TO SEVERE WEATHER.
STATE REMAINS UNDER SWLY FLOW ALOFT THRU THURSDAY NIGHT FOR A CHANCE OF
SHOWERS AND THUNDERSTORMS. BY FRIDAY FLOW BECOMES MORE WLY BEFORE HIGH
AMPLITUDE UPPER RIDGE OVER PAC NW. WITH NWLY FLOW EXPECT ISOLATED
SHOWERS AND THUNDERSTORMS INTO WEEKEND. TEMPS WILL SLOWLY WARM THROUGH
PERIOD. BRITTON

CCF NUMBERS
GTF BE 050/071 046/076 052 108322
CTB BE 046/068 042/071 050 107323
HLN EE 050/070 048/075 053 10+322
BZN WW 050/070 048/074 053 108434
WEY WW 043/064 039/069 045 108434
DLN WW 047/068 044/072 050 108223
HVR WE 053/073 047/077 055 108422
LWT WE 051/071 046/077 053 108433