Heavy Snow Warning 6, NWS Missoula, MT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
828 PM MST SUN FEB 18 2007

.DISCUSSION...SHOWERS HAVE STEADILY DECREASED THROUGH THE EARLY
EVENING AS MID LEVEL MOISTURE DIMINISHES. INSTABILITY AND LOW
LEVEL MOIST WEST FLOW WILL KEEP A THREAT OF PASSING SHOWERS
TONIGHT...BUT HAVE REDUCED SHOWER COVERAGE SOMEWHAT LATER TONIGHT
INTO MONDAY MORNING. EARLIER IT LOOKED LIKE SHALLOWING INSTABILITY
WOULD CREATE FAVORABLE CONDITIONS FOR SNOW BANDING...BUT NOW IT
LOOKS LIKE THE UNSTABLE LAYER WILL REMAIN TOO DEEP UNTIL MIDDAY
TOMORROW. THEREFORE...EXPECT CONTINUED CELLULAR SNOW SHOWERS
RATHER THAN BANDING. THE PREVIOUS FORECAST AND DISCUSSION
REGARDING THE NEXT SYSTEM LATE MONDAY IS STILL ON TRACK.

&&

.AVIATION...INSTABILITY WILL KEEP SOME SNOW SHOWER ACTIVITY OVER
THE NORTHERN ROCKIES...BUT THE MOISTURE WILL BECOME MORE LIMITED
AS THE NIGHT PROGRESSES. MOUNTAINS WILL LIKELY REMAIN OBSCURED
THROUGH MONDAY. SEE APPROPRIATE TAFS AND TWEBS.

&&

.PREV DISCUSSION... /ISSUED 208 PM MST SUN FEB 18 2007/

DISCUSSION...COLD FRONT AND UPPER LEVEL TROUGH CONTINUE TO PUSH
SOUTHEAST THROUGH THE SOUTHERN CLEARWATER MOUNTAINS AND LEMHI
COUNTY OF IDAHO AND WESTERN AND SOUTHWEST MONTANA THIS AFTERNOON.
WILL CONTINUE THE ADVISORIES IN THESE LOCATIONS UNTIL 5 PM. BEHIND
THE FRONT...THINGS ARE DRYING RAPIDLY AND MANY CAMERAS IN
NORTHWEST MONTANA AND THE IDAHO PANHANDLE ARE SHOWING SUNSHINE.
WITH THE TROUGH MOVING OVER THE REGION THIS EVENING...SCATTERED TO
NUMEROUS SNOW SHOWERS WILL CONTINUE OVER THE NORTHERN ROCKIES.
AFTER MIDNIGHT...A SHORT WAVE RIDGE WILL BUILD IN BEHIND THE
EXITING TROUGH AND AHEAD OF NEXT PACIFIC SYSTEM. WITH UNSTABLE
CONDITIONS IN THE LOWER ATMOSPHERE AND STABILIZING CONDITIONS
BUILDING IN ABOVE...LOOKS AS THOUGH A GOOD BANDING EVENT IS
SHAPING UP FROM THE EASTERN IDAHO PANHANDLE THROUGH THE MISSOULA
AND RAVALLI COUNTIES OVERNIGHT THROUGH EARLY MONDAY. THESE SHOWERS
COULD PRODUCE UP TO 3 INCHES UNDER PERSISTENT BANDS BY EARLY
MONDAY MORNING. MONDAY MORNING COMMUTE COULD BE A SLICK ONE WITH
FRESH SNOW COVER.

LATE MONDAY AFTERNOON THROUGH MONDAY NIGHT...THE NORTHERN ROCKIES
WILL BE INFLUENCED BY YET ANOTHER STRONG PACIFIC SYSTEM. A MID
LEVEL WARM FRONT WILL MOVE INTO THE NORTHERN CLEARWATER MOUNTAINS
AND NORTHWEST MONTANA MONDAY NIGHT. ANOTHER ROUND OF HEAVY
MOUNTAIN SNOW IS POSSIBLE MONDAY NIGHT INTO TUESDAY. AN UPPER
LEVEL JET AND STRONG MID LEVEL WINDS LOOK TO PRODUCE HAZARDOUS
WINTER WEATHER CONDITIONS FOR THE MOUNTAINS AND MOUNTAIN PASSES
OF NORTH CLEARWATER MOUNTAINS OF IDAHO AND NORTHWEST MONTANA
MONDAY NIGHT THROUGH TUESDAY. HAVE THEREFORE ISSUED A WINTER STORM
WATCH.

TUESDAY NIGHT THE ASSOCIATED COLD FRONT WILL COME SWEEPING
THROUGH. A HIGHLIGHT MAY BE NEEDED FOR THE FRONTAL PASSAGE...MOST
LIKELY A WINTER WEATHER ADVISORY AS WINDS WILL CONTINUE TO BE
STRONG. FORECAST MODELS ARE CONSISTENT WITH STALLING OUT THE
FRONT...THEY JUST DIFFER ON THE EXACT PLACEMENT. RIGHT NOW IT
LOOKS LIKE IT WILL STALL OUT ACROSS SOUTHERN IDAHO AND LEMHI
COUNTIES.

WEDNESDAY INTO FRIDAY AN APPROACHING UPPER TROUGH WILL DIG OFF THE
WEST COAST SPLITTING INTO TWO SYSTEMS. THIS WILL DRIVE A SOUTHWEST
FLOW ALOFT THAT WILL CONTINUE THE POTENTIAL FOR PRECIPITATION.

FRIDAY NIGHT INTO SUNDAY AN UPPER TROUGH DROPPING OUT OF THE GULF
OF ALASKA WILL BEGIN TO IMPACT THE NORTHERN ROCKIES CONTINUING
THE ACTIVE PATTERN. THERE WILL LIKELY BE A DRY PERIOD OR TWO
BETWEEN SYSTEMS...HOWEVER CONFIDENCE IS NOT HIGH ENOUGH TO TIME
THEM AT THIS POINT.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...WINTER STORM WATCH FROM MONDAY AFTERNOON THROUGH TUESDAY
     AFTERNOON FOR KOOTENAI/CABINET REGION-LOWER CLARK FORK
     REGION-WEST GLACIER REGION.

ID...WINTER STORM WATCH FROM MONDAY AFTERNOON THROUGH TUESDAY
     AFTERNOON FOR NORTHERN CLEARWATER MOUNTAINS.

&&

UPDATE...WHITMORE
PREVIOUS DISCUSSION...MEAD
AVIATION...WHITMORE