Severe Thunderstorm Warning 98, NWS Great Falls, MT

SOUTHWEST AND NORTH CENTRAL MONTANA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
300 PM MDT THU AUG 10 2000

HAVING TROUBLE SORTING THINGS OUT FOR TONIGHT AND FRIDAYS FORECAST.
VORTICITY CENTER WAS OVER NW WY AT 18Z. ETA AND NGM WERE A LITTLE TOO
FAR N WHILE AVN DID NOT HANDLE FEATURE WELL AT ALL. THERE WAS SOME
LIGHTNING OVER SW MT ASSOCIATED WITH FEATURE. THOUGHT THERE WOULD BE NO
MORE THUNDERSTORMS IN DRIER AIR UPSTREAM BUT A FEW HAVE DEVELOPED NEAR
MT/ID BORDER WELL S OF MSO. A SECOND STREAM OF MOISTURE IS EVEN FARTHER
UPSTREAM AND WAS MOVING INTO SRN ID EARLY THU AFTN. THIS SECOND STREAM
OF MOISTURE WILL AFFECT SW MT LATER THIS AFTERNOON AND THEN CENTRAL MT
AS WELL. ETA/MESOETA KEEP QPF ALL NIGHT IN THE N BUT NOT SURE WHY THEY
DO THIS. HAVE DECIDED TO GO WITH DIURNAL CONVECTION. MODELS LOOK SLOW
WITH VORTICITY CENTER OVER NRN CA BUT LOOK PRETTY GOOD WITH ASSOCIATED
SHORTWAVE INTO OREGON. THIS SHORTWAVE IS FORECAST TO BECOME POSITIVELY
TILTED AND MOVE THROUGH THE FORECAST AREA FRI. MODELS KEEP SOME RH AND
DYNAMICS IN THE N SO WILL GO WITH 30 PCT POP AT CTB AND 20 PCT POPS
FARTHER S. MODELS TEND TO HAVE A LITTLE INSTABILITY OVER THE FAR S AT
LEAST EARLY IN THE DAY. AFTER COORD WITH MSO AND BIL WILL GO WITH THIS
MORNINGS FORECAST WHICH HAD A SLIGHT CHANCE OF CONVECTION EARLY IN THE
DAY. BEHIND SHORTWAVE WITH INCREASED FLOW ALOFT AND AT SURFACE SHOULD
SEE SOME GUSTY WINDS PARTICULARLY OVER THE PLAINS. LOOKING AHEAD TO SAT
MODELS FORECAST ANTICYCLONIC SW FLOW ALOFT OVER THE AREA. ETA/MESOETA
HAVE GENERALLY DRY AND STABLE AIRMASS. AVN DOES HAVE SOME WEAK
INSTABILITY OVER THE FAR SW. AT THIS TIME PLAN TO GO DRY. AS FOR THE
CRITICAL FIRE WEATHER SITUATION FIRE WEATHER FORECASTER WILL CONTINUE
RED FLAG WARNING FOR TONIGHT FOR DRY THUNDERSTORMS. HE IS FEELING
CONFIDENT ENOUGH ABOUT WINDS FOR SAT TO GO WITH RED FLAG WARNING RATHER
THAN FIRE WEATHER WATCH AND THIS LOOKS GOOD. FIRE WEATHER SITUATION
SHOULD IMPROVE A LITTLE ON SAT WITH LESS WIND. COULD BE SOME HOOKUP
WINDS OVER FAR NRN E SLOPES BASED ON MID LEVEL FLOW. STILL THEY WILL NOT
BE AS STRONG AS ON FRI. BLANK

EXTENDED DISCUSSION...FCST AREA REMAINS UNDER SW-W FLOW ALOFT AS UPPER
LVL RDG BROADENS OVER SRN AND CENTRAL US AND PAC TROF REMAINS IN PLACE
OVER ERN PAC. MAIN DIFFERENCES IN MODELS APPEARS TO BE TIMING OF
EMBEDDED S/WV TROFS. NEW MRF SHOWS STRONGER S/WV TROF APPROACHING MT TUE
WITH ASSOC SFC TROF OVER CENTRAL MT BY TUE EVE. ECMWF HAS SIMILAR SOLTN.
EXPECT DOWNSLOPE FLOW WILL HAVE ITS AFFECT ON E SLOPES WITH ANY
CONVECTION BEING OROGRAPHICALLY INDUCED. EYSSAUTIER

CCF NUMBERS
GTF NU 060/085 050/083 050 042200
CTB NU 052/082 046/080 046 042300
HLN NU 060/088 050/085 052 042200
BZN BU 055/088 044/086 041 042100
WEY BU 045/082 035/082 032 042100
DLN BU 052/085 042/085 040 042100
HVR NU 055/089 052/085 053 042200
LWT NU 058/086 049/083 048 042200