Severe Thunderstorm Warning 42, NWS Great Falls, MT

SOUTHWEST AND NORTH CENTRAL MONTANA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
300 PM MDT SAT JUL 14 2001

SYNOPSIS...SCATTERED SHOWERS AND THUNDERSTORMS ARE EXPECTED ACROSSTHE
CWA FOR THE NEXT SEVERAL DAYS. THUNDERSTORMS THIS EVENING WILL BE
MORE NUMEROUS OVER SOUTHWEST MT WITH SOME THUNDERSTORMS POSSIBLY
SEVERE. TEMPERATURES WILL BE SLIGHTLY COOLER SUNDAY AS A PACIFIC
DISTURBANCE PUSHES THROUGH.

DISCUSSION...A DRIER AIR MASS OVER THE CWA EARLY IN THE DAY ALLOWED
FOR PLENTY OF SURFACE HEATING. AND NOW...SATELLITE IMAGES INDICATE
ANOTHER PUSH OF MOISTURE WOKING INTO THE SOUTHERN CWA. FOR MOST OF
THE CWA...HEATING WILL BE THE PRIMARY TRIGGER FOR CONVECTIVE
DEVELOPMENT. THE CONVECTIVE TEMPERATURE FROM THE TFX MORNING SOUNDING
WAS 82 AND MOST OF THE CWA NEAR OR PAST THIS POINT ALREADY. AS
MOISTURE WORKS IN SHOULD SEE SOME SCATTERED THUNDERSTORMS DEVELOP.
SOUTHWEST MT HAS SOME ADDITIONAL DYNAMICS WORKING INTO THE MIX AS A
DISTURBANCE PUSHES UP FROM THE SOUTHWEST. GOES SOUNDER IMAGES
INDICATING LI/S BETWEEN -2 AND -5 OVER THE SOUTHERN CWA WITH SOME -5
TO -8 NEAR IDAHO FALLS. ADDITIONALLY...MODELS SHOW SOME COUPLING OF
LOW LEVEL CONVERGENCE AND UPPER DIVERGENCE AS WELL AS SOME VERTICAL
SHEAR IN THAT AREA. THUNDERSTORMS STARTED KICKING OFF ABOUT 19Z OVER
SOUTHWEST MT AND ARE RAPIDLY INCREASING IN COVERAGE. AT LEAST A
POSSIBILITY OF SEVERE THUNDERSTORMS IN THIS AREA AND WILL WORD
SOUTHERN ZONES FOR HAIL AND STRONG WIND. MEANTIME...A LOW PRESSURE
TROUGH IS BEGINNING TO DIG INTO THE PACIFIC NORTHWEST AND WILL BE
SPINNING DISTURBANCES ACROSS THE PACIFIC NORTHWEST AND INTO MONTANA
SUNDAY AND MONDAY. IN ADDITION TO BRINGING IN SOME SLIGHTLY COOLER
AIR...THESE DISTURBANCES WILL AGAIN PROVIDE SOME DYNAMICS TO MIX WITH
THE PERSISTENT INFLUX OF MONSOONAL MOISTURE CONTINUING THE
POSSIBILITY OF SHOWERS AND THUNDERSTORMS INTO EARLY NEXT WEEK.

EXTENDED...NO APPRECIABLE CHANGES NOTED TO EXTENDED PERIOD. MODELS ON
SAME PAGE...SLOWLY MOVING H5 PACIFIC TROUGH EAST INTO AREA THROUGH
PERIOD. THIS WILL SUSTAIN A MOIST AND UNSTABLE SOUTHWEST FLOW OVER
CWA. COOLING ALOFT WILL INCREASE INSTABILITY. MRF SHOWING GOOD H2
DIFFLUENCE ON TUESDAY...AND THEN A GOOD JET MAX ENTERING SOUTHERN MT
ON WEDNESDAY. MODERATE DOWNSLOPE ON THURSDAY FOR DECREASING CHANCES
OF CONVECTION. SECOND DIGGING TROUGH OVER PACIFIC NW ON FRIDAY
PROPAGATES EAST THROUGH SATURDAY FOR A REINFORCING MOIST/UNSTABLE
SOUTHWEST FLOW ALOFT. UPSHOT IS SLIGHTLY COOLER AND UNSETTLED WEATHER
THROUGH THE PERIOD./SCHMIDT

CCF NUMBERS
GTF TE 054 083 053 083 051 033532
CTB TE 049 080 049 079 048 032422
HLN TE 055 084 054 084 054 034523
BZsN TE 050 082 049 080 050 036513
WEY TE 047 080 046 078 046 036513
DLN TE 048 084 047 084 048 036513
HVR TE 058 090 057 088 057 033532
LWT TE 054 084 052 082 051 035522