Severe Thunderstorm Warning 102, NWS Great Falls, MT

SOUTHWEST AND NORTH CENTRAL MONTANA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
315 PM MDT TUE AUG 6 2002

.SHORT TERM...ANOTHER ACTIVE EVENING LOOMING IN THE CONVECTION
DEPARTMENT. SCATTERED LOW CLOUDS OVER NORTH CENTRAL PLAINS HAVE
DELAYED SIGNIFICANT WARMING (AND THUS THE ONSET OF STORMS). BUT
VISIBLE IMAGES AT 2 PM INDICATE CUMULI IS FLOURISHING OVER HIGHER
TERRAIN. EVENTUALLY LOW-LEVEL CAP WILL BE BROKEN AND STORMS SHOULD
BEGIN TO FIRE UP ON THE PLAINS IN THE 4-5 PM TIME FRAME...WITH SEVERE
ACTION BEGINNING AROUND 6 PM. MODELS IN GOOD AGREEMENT...ENDING THE
EVENT IN OUR CWA AROUND 10-11 PM. UPPER TROUGH AXIS MOVES TO THE
WESTERN BORDER OF IDAHO BY TOMORROW EVENING...BRINGING A DEEP BATCH
OF MOISTURE. LOW LEVEL WARM AIR ADVECTION WITH STRONG VORTICITY
ADVECTION IN A 90 KT JET STREAK ARE A COMBINATION THAT CANNOT BE
IGNORED. SO WILL RAISE POPS TO LIKELY OVER MOST OF THE CWA FOR THE
WEDNESDAY NIGHT THROUGH THURSDAY NIGHT PERIOD. AS RAIN BEGINS LATE
WEDNESDAY AFTERNOON...IT WILL BE IN THE FORM OF THUNDERSTORMS...
GRADUALLY BECOMING MORE WIDESPREAD INTO THE EVENING. CHANCE OF
SEVERE STORMS WILL BE SLIM WITHOUT MUCH DAYTIME HEATING TAKING
PLACE. TOWARDS THURSDAY MORNING...PRECIPITATION WILL TRANSITION INTO
STRATIFORM. SO WILL NOT HAVE MENTION OF STORMS THURSDAY...ALTHOUGH
ISOLATED THUNDER IS NOT OUT OF THE QUESTION. UPPER TROUGH CUTS OFF
INTO A CLOSED LOW THURSDAY FOR A CHILLY SUMMER DAY...WITH SNOW LEVELS
AROUND 9000 FEET. FLOW BECOMES NORTHERLY BEHIND LOW ON FRIDAY...SO
EVEN THOUGH THERE WILL BE SOME CLEARING BY FRIDAY AFTERNOON...TEMPS
WILL NOT REBOUND SIGNIFICANTLY.

.EXTENDED...MODELS IN BETTER THAN NORMAL AGREEMENT ON GENERAL TRENDS
AT LEAST INTO MON. FOR SAT WLY FLOW ALOFT IS FORECAST TO BE OVER
THE AREA WITH A GENERALLY DRY AIRMASS. CHANGE IS IN STORE FOR SUN AS
AN UPPER TROUGH MOVES INTO THE AREA. MODELS DIFFER SOME ON TIMING.
12Z AVN RUN IS SLOWER WITH THE UPPER TROUGH THAN THE 00Z AVN RUN
AND IS NOW MORE IN LINE WITH THE EVEN SLOWER ECMWF/UKMET RUNS.
EXPECT COLD FRONT WITH A THREAT OF SHOWERS TO MOVE S OVER THE AREA
ON SUN. 00Z AVN HAS MON DRY BUT THEN BRINGS ANOTHER SHORTWAVE INTO
THE AREA ON TUE WITH ANOTHER CHANCE OF PRECIPITATION. NOT SURE
ABOUT TIMING OF SHORTWAVES AND ACCOMPANYING MOISTURE BEYOND SUN BUT
PATTERN APPEARS UNSETTLED SO WILL BROADBRUSH 20 PCT POPS.
TEMPERATURES SHOULD ALSO CONTINUE UNSEASONABLY COOL. BLANK

.CCF NUMBERS
GTF ER 050/070 048/065 047 19346
    BNEBB 071/050 083/052 072/044 070/045 072 76311132222
CTB EW 047/066 045/065 044 19225
    BNEBB 069/048 080/050 068/040 068/044 071 54311131222
HLN ER 050/072 050/069 050 19246
    BBEBB 072/052 085/054 076/047 074/049 076 76311122222
BZN ER 046/074 048/070 044 19246
    BBBBB 073/045 082/050 075/042 074/044 075 76311122222
WEY ER 038/070 040/061 038 19246
    BBEBB 068/036 075/038 070/033 068/035 068 76311122222
DLN EW 046/073 046/068 044 19245
    BBNBB 073/045 080/048 074/044 076/046 076 65311122222
HVR ER 053/074 050/071 050 19436
    BNEBB 073/052 085/054 074/045 072/048 074 66311132222
LWT ER 050/076 047/065 047 19546
    BBEBB 073/047 081/049 072/045 068/044 070 76311132222=

.TFX...SEVERE THUNDERSTORM WATCH MEAGHER/JUDITH BASIN/FERGUS/
       BLAINE COUNTIES THIS EVENING UNTIL 9 PM MDT