Severe Thunderstorm Warning 53, NWS Great Falls, MT

SOUTHWEST AND NORTH CENTRAL MONTANA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
940 AM MDT FRI JUN 20 2003

.DISCUSSION...

UPDATES PLANNED FOR THE ZONES AND STATE

TODAY...RADAR IMAGERY NOT INDICATING MUCH IN THE WAY OF ECHOES OVER
THE FORECAST AREA AS OF 15Z. ETA INITIALIZATION LOOKED BETTER THAN
THE 6HR GFS FORECAST WITH A SHORTWAVE OVER ERN WA/ERN OR AT 12Z. GFS
WAS TOO POSITIVELY TILTED AND MAYBE TOO FAR E IN THE NRN. SHORTWAVE
IS ASSOCIATED WITH A JET STREAK. SHORTWAVE MOVES VERY SLOWLY E TODAY
AND IF ETA IS RIGHT SPLITS WITH ONE PORTION MOVING INTO WRN ALTA AND
ANOTHER INTO SW MT LATE THIS AFTERNOON/EARLY EVENING. SRN PORTION OF
A COLD FRONT APPEARS TO HANG BACK OVER SW MT THROUGH THE DAY WHILE
HARD TO PICK OUT NRN PORTION MOVES TO A LINE E OF LWT/HVR BY 00Z. AS
FOR CHANGES WILL BE DROPPING MENTION OF PRECIPITATION FOR THIS
MORNING OVER THE ERN ZONES. ONE AREA OF SHOWERS/TSTMS IS MOVING INTO
BEAVERHEAD COUNTY WHILE ANOTHER AREA  W OF THE DIVIDE COULD AFFECT
THE WRN ZONES BY 18Z. MAIN LIFT WILL BE OVER THE SRN AND CNTRL ZONES
THIS AFTERNOON SO WILL TONE BACK POPS OVER THE NW ZONES TO SCATTERED
FOR TODAY. AS FOR SEVERE WEATHER STILL APPEARS MAIN THREAT WILL BE E
OF A N/S LINE THROUGH GTF. SHEAR IS IN PLACE BUT CAPES INCREASE THE
FARTHER E ONE GOES OVER THE PLAINS OF MT. CAPES OVER THE WRN ZONES
WILL LIKELY NOT BE HIGH ENOUGH FOR STRONG CONVECTION. LOCAL
OFFICE WILL ISSUE 18Z SOUNDING IN SUPPORT OF SEVERE WEATHER.
FORECAST HIGHS LOOK PRETTY GOOD BUT WILL BUMP UP GTF BASED ON
SOUNDING AND COMPARSION TO MAV MOS. WILL ALSO RAISE WEY BASED ON
LATEST 15Z OB. BLANK

TONIGHT...THE SEVERE THREAT SHOULD DIMINISH BY MIDNIGHT...WITH
SHOWERS BECOMING LESS NUMEROUS AS THE ATMOSPHERE STABILIZES.

SATURDAY THROUGH SUNDAY...COOL AND BREEZY CONDITIONS WILL RULE THE
WEEKEND AS THE UPPER LEVEL TROUGH OVER THE NORTHWEST U.S. BROADENS
AND MOVES INTO MONTANA. DOWNSLOPE WINDS WILL ALSO INCREASE EAST OF
THE ROCKIES MAKING IT FEEL EVEN COOLER. WITH MULTIPLE DISTURBANCES
ROTATING AROUND THE MAIN UPPER LOW IN CANADA...WILL KEEP MAINLY
CHANCE POPS OVER HIGHER TERRAIN AND SLIGHT CHANCE POPS FOR PLAINS
LOCATIONS DUE TO DOWNSLOPE WINDS. THE BEST CHANCE FOR PRECIP WILL BE
DURING THE AFTERNOON HOURS WHEN IT WILL BE MOST UNSTABLE. VILLANI

MONDAY THROUGH FRIDAY...CURRENT AND PREVIOUS RUNS OF GFS
GENERALLY QUITE SIMILAR. SOME DIFFERENCES IN AMPLITUDE BUT TIMING IS
VERY CLOSE.  ECMWF ALSO AGREES THRU TUESDAY BUT THEN IS QUITE A BIT
SLOWER TO MOVE SYSTEM EAST. A BROAD UPPER LEVEL LOW PRESSURE TROF
WILL BE OVER THE ZONES ON MONDAY ALTHOUGH MOST OF THE DYNAMICS WILL
BE SOUTH OF THE CWA. THE AIRMASS WILL REMAIN QUITE MOIST AND
UNSETTLED. THE TROF MOVES EAST OF ZONES BY TUESDAY BUT MOIST
NORTHWEST FLOW ALOFT KEEPS SOME SHOWERS IN THE FORECAST. THE AIRMASS
THEN CONTINUES TO DRY WEDNESDAY THROUGH FRIDAY. TEMPS REMAIN BELOW
NORMALS MONDAY THROUGH WEDNESDAY...MOVING BACK NEAR NORMAL THURSDAY
AND FRIDAY. ZELZER

.CCF NUMBERS
GTF TB 074/046 066/044 064 16652
    BBBBB 040/065 042/063 044/070 046/071 049 21334444333
CTB TB 064/044 060/041 059 16421
    EBBBB 040/061 042/062 042/069 045/069 047 11333333223
HLN TB 071/047 066/045 065 16663
    BBEBB 042/066 045/065 047/071 049/073 050 32334444332
BZN TB 072/044 065/039 064 16663
    BBEBB 039/063 042/065 043/071 045/070 046 32344444442
WEY TB 072/038 058/031 058 16652
    BBEBB 035/059 038/057 036/060 037/063 040 22344444311
DLN TB 067/043 064/039 064 16653
    BBTBB 039/063 042/065 044/069 042/072 045 32345544311
HVR TB 080/049 070/045 067 16662
    BBBBB 044/066 046/067 047/076 049/075 051 22334433332
LWT TB 078/046 065/042 061 16663
    BBEBB 039/061 043/062 044/066 045/069 047 32334444442

.TFX...NONE

MTZ008>015-044>055-210010-
HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE GREAT FALLS MT
1200 PM MDT FRI JUN 20 2003

THIS HAZARDOUS WEATHER OUTLOOK IS FOR NORTH CENTRAL AND SOUTHWEST MONTANA

.DAY ONE...TODAY

NO WATCHES, WARNINGS, OR ADVISORIES CURRENTLY IN EFFECT

A SEVERE THUNDERSTORM WATCH IS IN EFFECT UNTIL 8 PM MDT FOR MUCH OF
THE AREA. THUNDERSTORMS WILL BE CAPABLE OF PRODUCING WINDS TO 70 MPH
AND HAIL UP TO ONE INCH IN DIAMETER.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY

THE PROBABILITY FOR WIDESPREAD HAZARDOUS WEATHER IS LOW.

.SPOTTER INFORMATION STATEMENT...

WEATHER SPOTTERS ARE ENCOURAGED TO REPORT SIGNIFICANT WEATHER
CONDITIONS ACCORDING TO STANDARD OPERATING PROCEDURES.