Severe Thunderstorm Warning 39, NWS Great Falls, MT

SOUTHWEST AND NORTH CENTRAL MONTANA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
145 PM MDT WED JUN 18 2003

.DISCUSSION...

TONIGHT...UPPER LEVEL RIDGE OVER CENTRAL MONTANA BEGINS TO BREAK DOWN
AND SHIFT EAST. MOIST SOUTHWEST FLOW ON THE BACK SIDE OF THE RIDGE
ALONG WITH A FEW WEAK DISTURBANCES WILL CONTINUE TO TRIGGER SHOWERS
AND STORMS ALONG THE DIVIDE AND OVER THE MOUNTAINS. FAIRLY STIFF
SOUTHEAST WINDS WILL KEEP TEMPS TOASTY AS A SURFACE TROUGH (WEAK
COLD FRONT) SLOWLY CROSSES THE DIVIDE BY MORNING.

THURSDAY AND FRIDAY...WEAK SURFACE TROUGH MEANDERS ACROSS CENTRAL
MONTANA DURING THE DAY WITH NOT MUCH OF A SURFACE GRADIENT. THIS
BOUNDARY, COMBINED WITH UPPER LEVEL DISTURBANCES WILL TRIGGER
THUNDERSTORMS OVER THE SOUTHWEST MOUNTAINS BY EARLY AFTERNOON. THESE
STORMS WILL SPREAD EAST, POSSIBLY BECOMING THREATENING (STRONG
WINDS AND HAIL) OVER CENTRAL MONTANA BY LATE AFTERNOON AS SHEAR
PROFILES BECOME MORE FAVORABLE FOR SUSTAINED UPDRAFTS. SHOWERS AND
STORMS WILL CONTINUE THROUGH FRIDAY AS A SERIES OF DISTURBANCES
EJECT OUT AHEAD OF A STORM SYSTEM OFF THE PACIFIC NORTHWEST COAST.
JCA

SATURDAY THROUGH SUNDAY...PERIOD LOOKS COOL AND UNSETTLED SO DID NOT
CHANGE MUCH FROM INHERITED FORECAST OF CHANCE POPS AND HIGH
TEMPERATURES IN THE 60S. 12Z GFS HAS BACKED OFF CONSIDERABLY ON THE
STRENGTH OF A SHORTWAVE OVER WRN MT ON SUN BUT 12Z TUE ECMWF
CONTINUED TO HAVE A FAIRLY STRONG UPPER TROUGH.

MONDAY THROUGH WEDNESDAY...HIGH TEMPERATURES WILL CONTINUE TO
REMAIN BELOW NORMAL THROUGH THE PERIOD. COOL AIR REMAINS IN PLACE ON
MONDAY AND A CHANCE OF SHOWERS AND AFTERNOON THUNDERSTORMS WILL
CONTINUE. THE CURRENT RUN OF THE GFS IS QUITE CONSISTENT WITH THE
PREVIOUS RUN UNTIL TUESDAY. AT THIS TIME THE BUILDING RIDGE OF THE
PREVIOUS RUN IS REPLACED BY ZONAL FLOW/BROAD TROF OVER THE WEST
COAST. THIS DEVELOPS INTO AN UNSTABLE PATTERN BY WEDNESDAY. THIS IN
GENERAL AGREES WITH THE ECMWF PLACEMENT OF A LOW PRESSURE CENTER OVER
WA/BC TUESDAY. CONFIDENCE IS NOT HIGH BUT BELIEVE AN UNSETTLED
FORECAST WITH AT LEAST A MENTION OF THUNDERSTORMS IS APPROPRIATE DUE
TO THE APPROACH OF THE UPPER LEVEL LOW PRESSURE SYSTEM AND FLOW ALOFT
SWITCHING TO THE SOUTHWEST.  ZELZER

.CCF NUMBERS
GTF BE 059/085 054/076 046 05034
    BBBBB 065/042 064/044 068/045 067/045 069 43333333333
CTB BB 057/079 051/071 043 05334
    BBBEB 063/041 061/045 067/044 066/043 067 32333333334
HLN BB 059/086 055/077 048 05144
    BBBBB 066/046 064/045 070/047 066/049 071 44333333333
BZN BB 053/085 051/076 043 05034
    BBBBB 067/044 063/040 066/043 066/044 070 34333333333
WEY BE 046/080 047/070 041 05233
    BBBBB 063/035 058/038 061/039 060/037 060 45333333333
DLN BB 054/083 052/075 043 05244
    BBBBB 066/041 062/040 066/042 069/045 070 33333333333
HVR BE 061/088 057/079 049 05034
    BBBBB 069/046 067/048 073/049 068/048 073 44333333334
LWT BE 057/087 054/076 046 05024
    BBBBB 067/042 062/044 066/045 063/045 068 44333333333

.TFX...NONE.

MTZ008>015-044>055-190010-
HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE GREAT FALLS MT
610 AM MDT WED JUN 18 2003

THIS HAZARDOUS WEATHER OUTLOOK IS FOR NORTH CENTRAL AND SOUTHWEST
MONTANA

.DAY ONE...TODAY

THE PROBABILITY FOR WIDESPREAD HAZARDOUS WEATHER IS LOW.

NO WATCHES, WARNINGS, OR ADVISORIES CURRENTLY IN EFFECT

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY

A CHANCE OF AFTERNOON AND EVENING THUNDERSTORMS EXISTS THURSDAY
AFTERNOON AND EVENING. SOME OF THESE STORMS MAY BE SEVERE.

INCREASING MID-LEVEL FLOW COMBINED WITH DRY LOW LEVELS WILL PROVIDE
THE NECESSARY CONDITIONS FOR STRONG...GUSTY THUNDERSTORM OUTFLOWS.
GUSTS OF 50 TO 60 MPH ARE POSSIBLE. AN UNSTABLE AIRMASS ALONG WITH
SOME MID-LEVEL SHEAR WILL ALSO PROVIDE THE CONDITIONS FOR ISOLATED
LARGE HAIL OF THREE QUARTERS TO ONE INCH IN DIAMETER.

.SPOTTER INFORMATION STATEMENT...

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