Special Weather Statement, NWS Missoula, MT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
522 PM MDT WED JUN 22 2011

.UPDATE...INCREASED PRECIP/THUNDER COVERAGE ACROSS WEST CENTRAL
AND SW MONTANA INTO CENTRAL IDAHO

&&

.DISCUSSION...RADAR SHOWING AN INCREASE IN SHOWER/THUNDER ACTIVITY
IN CNTRL ID AND WRN MT. MAJORITY OF THUNDERSTORMS THAT HAVE
DEVELOPED WILL IMPACT THE REGION WITH HEAVY RAIN. THERE IS  A FEW
STRONG CELLS IN EASTERN OREGON PRODUCING SOME SMALL HAIL WHICH MAY
IMPACT CENTRAL IDAHO OVER THE NEXT FEW HOURS.

&&

.AVIATION...MID AND HIGH LEVEL CLOUD COVER WILL INCREASE OVER THE
NORTHERN ROCKIES TODAY AHEAD OF AN APPROACHING UPPER LEVEL TROUGH.
A FEW ISOLATED THUNDERSTORMS WILL BE POSSIBLE THIS AFTERNOON AS
THE ATMOSPHERE DESTABILIZES...MAINLY ACROSS SOUTHWEST MONTANA AND
NORTH CENTRAL IDAHO POSSIBLY IMPACTING AIRFIELDS KBTM AND KSMN.
ADDITIONAL CONVECTIVE DEVELOPMENT IS FORECAST FOR THIS EVENING AND
OVERNIGHT...POTENTIALLY IMPACTING KMSO AND KGPI. A COLD FRONT IS
FORECAST TO MOVE THROUGH THE NORTHERN ROCKIES TOMORROW WITH FROPA
AT KGPI AND KMSO BETWEEN 17Z-20Z AND KSMN AND KBTM BETWEEN 19Z AND
00Z.

&&

.PREV DISCUSSION... /ISSUED 311 PM MDT WED JUN 22 2011/

DISCUSSION...SOME WEAK CONVECTION HAS BEGUN TO DEVELOP THIS
AFTERNOON OVER EASTERN OREGON AND CENTRAL IDAHO. AT PRESENT TIME
NO UPPER LEVEL SUPPORT EXISTS SO LITTLE DEVELOPMENT BEYOND FAIR
WEATHER CUMULUS CLOUDS AND AN ISOLATED THUNDERSTORM ARE EXPECTED
THROUGH THE REMAINDER OF THIS AFTERNOON. HOWEVER THIS SHOULD CHANGE
LATER THIS EVENING AS AN APPROACHING UPPER LEVEL TROUGH MOVES
INLAND. ALL FORECAST MODELS CONTINUE TO SUGGEST THAT AN AREA OF
SHOWERS AND THUNDERSTORMS WILL FORM OVER EASTERN OREGON AFTER 9PM
MDT AND SLOWLY PROPAGATE EASTWARD THROUGHOUT THE NIGHT IN A
CONTINUED UNSTABLE AIR MASS AHEAD OF AN APPROACHING COLD FRONT.

THE MODELS ARE FINALLY IN AGREEMENT THAT THE COLD FRONT
WILL PASS THROUGH CENTRAL IDAHO TOMORROW MORNING AND ACROSS
WESTERN MONTANA DURING THE AFTERNOON. THIS LATTER FRONTAL PASSAGE
WILL ALLOW TEMPERATURES ACROSS MUCH OF WESTERN AND SOUTHWESTERN
MONTANA TO WARM CONSIDERABLY TOMORROW...APPROACHING 80 DEGREES IN
SOME VALLEY LOCATIONS. THERE IS A SMALL CHANCE THAT SOME STRONG TO
SEVERE THUNDERSTORMS MAY FORM ACROSS LEMHI COUNTY AND IN THE BUTTE
AREA. HOWEVER THESE STORMS FORMING DURING THE AFTERNOON HOURS WILL
QUICKLY MOVE EAST OF THE DIVIDE. THE BIGGEST THREAT FROM THESE
STORMS WILL BE HEAVY RAIN AND THE POTENTIAL FOR HAIL. ELSEWHERE
LOCATIONS ALONG THE CONTINENTAL DIVIDE WILL LIKELY SEE SHOWERS
AND THUNDERSTORMS DEVELOPING DURING THE AFTERNOON BUT ONLY PRODUCE
PERIODS OF HEAVY RAINFALL. BREEZY CONDITIONS ARE ALSO FORECAST
AHEAD OF THE COLD FRONT WITH THE STRONGEST WINDS EXPECTED ACROSS
LEMHI COUNTY AND SOUTHWEST MONTANA. IT APPEARS AS THOUGH THE
DIRECTION OF THE WIND WILL NOT BE FAVORABLE FOR EXCEPTIONAL WINDS
ACROSS FLATHEAD LAKE. HOWEVER BREEZY CONDITIONS THROUGHOUT THE DAY
WILL LIKELY PRODUCE A BIT MORE CHOP ON THE LAKE THAN NORMAL.

FRIDAY WILL BE A BREEZY...POST FRONTAL DAY WITH THE CHANCE FOR
SOME SHOWERS AND THUNDERSTORMS OVER SOUTHWEST MONTANA WHERE A
WEAK...STALLED FRONTAL BOUNDARY PERSISTS. ANOTHER AREA OF
POTENTIAL CONVECTIVE DEVELOPMENT WILL BE ACROSS FAR NORTHWEST
MONTANA AS A LARGE...COLD UPPER LEVEL LOW PRESSURE SYSTEM OVER
WESTERN CANADA SLOWLY DIPS OVER THE PACIFIC AND INLAND
NORTHWESTERN STATES.

SATURDAY THROUGH WEDNESDAY...UNTIL RECENTLY...MODEL GUIDANCE HAD
BEEN PRODUCING WILDLY DIVERGENT SOLUTIONS FOR THE EXTENDED FORECAST
PERIODS. ECMWF AND GFS HAVE SINCE COME INTO BETTER AGREEMENT WITH
RESPECT TO THIS WEEKEND...BOTH DEPICTING A FAIRLY COOL PACIFIC STORM
SYSTEM MOVING ACROSS THE SOUTHERN CANADIAN ROCKIES. THIS SYSTEM WILL
COOL THE NORTHERN U.S. ROCKIES AND INTRODUCE SOME SCATTERED
PRECIPITATION. DESPITE THIS COOL WEATHER...RIVER AND STREAM LEVELS
WILL REMAIN HIGH...WITH SOME OVER FLOOD STAGE...THROUGH THE END OF
THIS WEEKEND. EARLY NEXT WEEK...MODEL GUIDANCE AGREES ON A
STRENGTHENING RIDGE OF HIGH PRESSURE BEING PRESENT OVER THE NORTHERN
ROCKIES. THIS RIDGE APPEARS TO BRING SIGNIFICANT WARMTH ACROSS NORTH
CENTRAL IDAHO AND WESTERN MONTANA...WITH VALLEY TEMPERATURES PUSHING
90 DEGREES. WIDELY SCATTERED TERRAIN BASED THUNDERSTORMS ARE
POSSIBLE EACH AFTERNOON AND EVENING DURING EARLY NEXT WEEK. THIS
HEAT MAY SIGNAL ANOTHER ROUND OF RISING RIVER AND STREAMS DUE TO
HIGH ELEVATION SNOW MELT.

AVIATION...MID AND HIGH LEVEL CLOUD COVER WILL INCREASE OVER THE
NORTHERN ROCKIES TODAY AHEAD OF AN APPROACHING UPPER LEVEL TROUGH.
A FEW ISOLATED THUNDERSTORMS WILL BE POSSIBLE THIS AFTERNOON AS
THE ATMOSPHERE DESTABILIZES...MAINLY ACROSS SOUTHWEST MONTANA AND
NORTH CENTRAL IDAHO POSSIBLY IMPACTING AIRFIELDS KBTM AND KSMN.
ADDITIONAL CONVECTIVE DEVELOPMENT IS FORECAST FOR THIS EVENING AND
OVERNIGHT...POTENTIALLY IMPACTING KMSO AND KGPI. A COLD FRONT IS
FORECAST TO MOVE THROUGH THE NORTHERN ROCKIES TOMORROW WITH FROPA
AT KGPI AND KMSO BETWEEN 17Z-20Z AND KSMN AND KBTM BETWEEN 19Z AND
00Z.

NOTE: FLOOD WATCHES...WARNINGS AND ADVISORIES WILL NOT BE LISTED BELOW.

&&

NOTE: FLOOD WATCHES...WARNINGS AND ADVISORIES WILL NOT BE LISTED BELOW.

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...NONE.
ID...NONE.
&&

SHORT TERM...RPN
LONG TERM....ZUMPFE
AVIATION...NOLTE

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