258
FXUS65 KMSO 210309
AFDMSO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
809 PM MST FRI NOV 20 2009
UPDATE
UPDATED EARLIER TONIGHT TO LOWER THE POPS ACROSS
NORTHWEST MONTANA FROM 00Z TO 03Z. ALSO LOWERED SOME MIN
TEMPERATURES TONIGHT.
DISCUSSION
MODELS ARE SLOWER AT BRINGING THE SYSTEM INTO
WESTERN MONTANA AND NORTH CENTRAL IDAHO TONIGHT. IN
ADDITION...SATELLITE IMAGERY AND RADARS TO OUR WEST HAS SHOWN THAT
THE SYSTEM IS MOVING SLOWER THEN EARLIER EXPECTED. SO UPDATED THE
POPS AND WEATHER FOR TONIGHT TO SHOW THE SLOWER TREND. SOME
LOCATIONS WERE AT THE FORECASTED LOW TEMPERATURE FOR TONIGHT AND
OTHERS WERE WITHIN A COUPLE OF DEGREES. MOST LOCATIONS FROM
MISSOULA NORTH NEVER WARMER UP TODAY...WITH OBSERVED HIGHS ABOUT
6 DEGREES BELOW NUMERIC GUIDANCE. SO LOWERED A NUMBER OF LOCATIONS
MAINLY ACROSS NORTHWEST MONTANA. REST OF THE FORECAST LOOKS TO BE
ON TRACK. WILL CONTINUE THE WINTER WEATHER ADVISORY FOR IDZ005-006
AVIATION
AN APPROACHING PACIFIC SYSTEM WILL CONTINUE TO
LOWER CLOUDS DECKS AND INCREASE PRECIPITATION CHANCES ACROSS THE
NORTHERN ROCKIES OVERNIGHT. AHEAD OF THE ADVANCING SURFACE COLD
FRONT...SHOWERS WILL BE A MIX OF RAIN AND SNOW BEFORE TURNING TO
ALL SNOW AFTER 21/0600Z. EXPECT THE MOST INTENSE PERIODS OF
PRECIPITATION ALONG AND JUST BEHIND THE FRONTAL PASSAGE BETWEEN
21/0600Z-21/1200Z. CEILINGS ARE EXPECTED TO LOWER OVERNIGHT
CAUSING MOUNTAINS AND PASSES TO BE OBSCURED.
PREV DISCUSSION
/ISSUED 301 PM MST FRI NOV 20 2009/
DISCUSSION...COMPLEX WEATHER PATTERN SETTING UP OVER THE
INTERMOUNTAIN REGION FOR THIS WEEKEND. BEEN AN INTERESTING DAY AS
CLOUDS AHEAD OF APPROACHING SYSTEM WERE QUITE MORE INTENSE THAN
THE MODELS HAD ADVERTISED. AS A RESULT...THE WARMING EXPECTED
TODAY WAS LIMITED TO THE SOUTHERN MOST VALLEYS (HIGHER VALLEYS)
THAT MIXED OUT EARLIER THIS MORNING AND ACHIEVED FULL MIXING
DESPITE THE CLOUDS. CENTRAL AND NORTHERN MONTANA VALLEYS WERE
INHIBITED BY THESE CLOUDS AND KEPT THE MUCH COOLER TEMPERATURES
TRAPPED IN THEIR VALLEYS. EXAMPLE...MISSOULA 37 DEGREES...HAMILTON
54 AT 230 PM MST.
THE AFOREMENTIONED WEATHER SYSTEM WILL MOVE OVER THE PACIFIC
NORTHWEST THIS EVENING SPREADING PRECIPITATION FROM WEST TO EAST
THIS EVENING AND OVERNIGHT. WARM AIR AHEAD OF THE COLD FRONT WILL
KEEP SNOW LEVELS RATHER HIGH...THEN DROPPING TO MOST VALLEY FLOORS
AFTER THE COLD FRONTAL PASSAGE AFTER MIDNIGHT. THE HIGHER VALLEYS
OF THE NORTHERN CLEARWATER MOUNTAINS LOOK TO BE THE MOST IMPACTED
BY ENOUGH ACCUMULATING SNOW TO WARRANT A WINTER HEADLINE.
THEREFORE THE WINTER WEATHER ADVISORY FOR SNOW AND BLOWING SNOW
ABOVE 3000 FEET WILL REMAIN IN PLACE. OTHER VALLEYS OF NORTH
CENTRAL IDAHO AND WESTERN MONTANA CAN ALSO EXPECT TO SEE SOME
LIGHT SNOW ACCUMULATIONS COME SATURDAY MORNING. AT THIS
TIME...LOOKS LIKE THE BEST TIME FRAME FOR CENTRAL AND SOUTHERN
VALLEYS OF WESTERN MONTANA TO SEE SNOW ACCUMULATIONS WILL BE 2 AM
THROUGH 9 AM...BUT NOT ENOUGH ACCUMULATIONS TO WARRANT HEADLINES.
HOWEVER...THIS SNOW WILL IMPACT ANY TRAVELERS HEADED OVER THE
CONTINENTAL DIVIDE PASSES. IN ADDITION...WINDS BEHIND THE FRONT
WILL BLOW THE SNOW AROUND AND REDUCE VISIBILITIES AT
TIMES...ESPECIALLY OVER THE PASSES.
A SECOND WEATHER SYSTEM AND ASSOCIATED SURFACE LOW WILL IMPACT THE
INTERMOUNTAIN REGION SUNDAY. THIS SYSTEM IS LOOKING MORE IMPRESSIVE
WITH EACH RUN...AND MAY BRING ANOTHER ROUND OF ACCUMULATING SNOW
TO THE CLEARWATER MOUNTAINS AND PORTIONS OF THE CAMAS
PRAIRIE...MAINLY GRANGEVILLE...GREER AND WHITEBIRD GRADES. WITH
CURRENT WINTER HEADLINES OUT...HAVE OPTED TO HOLD OFF ON A WATCH
BUT IF THE MODELS CONTINUE TO ADVERTISE THE STRENGTH AND POSITION
OF THIS SECOND SYSTEM THE WAY THEY ARE NOW...WINTER WEATHER
WATCHES MAY BE NECESSARY ONCE AGAIN. IN ADDITION...THE PLACEMENT
OF THIS SECOND WAVE LOOKS GOOD FOR PORTIONS OF WESTERN AND
SOUTHWEST MONTANA VALLEYS TO SEE ACCUMULATING SNOW TO THE VALLEY
FLOORS. AGAIN...AMOUNTS DO NOT APPEAR TO BE HEADLINE WORTHY...BUT
MAY IMPACT TRAVELERS. ANOTHER ROUND OF WIND IS EXPECTED WITH THIS
SECOND SYSTEM...SO MORE VISIBILITY ISSUES FROM BLOWING AND
DRIFTING SNOW ARE POSSIBLE.
A RIDGE OF HIGH PRESSURE WILL BEGIN TO BUILD OVER THE REGION
MONDAY WITH THE RIDGE AXIS SETTLING OVER THE REGION BY WEDNESDAY.
INITIALLY...THE RIDGE WILL BE WEAK ENOUGH TO ALLOW A FEW WEAK
DISTURBANCES TO MOVE THROUGH THE REGION BOTH MONDAY AND TUESDAY.
THE MAIN FOCUS OF PRECIPITATION IS EXPECTED TO BE ACROSS NORTHWEST
MONTANA BUT SHOULD REMAIN FAIRLY LIGHT WITH LITTLE IN THE WAY OF
ACCUMULATING SNOW. AS THE RIDGE AXIS MOVES OVERHEAD TUESDAY
NIGHT...SHOWER ACTIVITY WILL DWINDLE. WITH STRENGTHENING
INVERSIONS UNDER THIS STRONG UPPER LEVEL RIDGE...VALLEY FOG COULD
BECOME AN ISSUE WEDNESDAY AND THURSDAY. HAVE GONE AHEAD AND ADDED PATCHY
FOG TO THE FORECAST FOR THE TIME BEING BUT THE POTENTIAL FOR DENSE
FOG...POTENTIALLY IMPACTING HOLIDAY TRAVEL IS NOT OUT OF THE
QUESTION.
FORECAST MODELS INDICATE ANOTHER LOW PRESSURE TROUGH IMPACTING THE
NORTHERN ROCKIES FRIDAY IN TO NEXT WEEKEND. THE DETAILS AND TIMING OF
THIS SYSTEM REMAIN LOW FOR THE TIME BEING.
AVIATION...AN APPROACHING PACIFIC SYSTEM WILL CONTINUE TO
LOWER CLOUDS DECKS AND INCREASE PRECIPITATION CHANCES ACROSS THE
NORTHERN ROCKIES THIS EVENING AND OVERNIGHT. AHEAD OF THE ADVANCING
SURFACE COLD FRONT...SHOWERS WILL BE A MIX OF RAIN AND SNOW BEFORE
TURNING TO ALL SNOW AFTER 21/0600Z. PARTS OF NORTHWEST MONTANA AND
NORTH CENTRAL IDAHO WILL SEE SHOWER ACTIVITY START EARLIER FRIDAY
EVENING BEFORE CHANCES SPREAD ACROSS THE REMAINDER OF WESTERN
MONTANA BY 21/0600Z. EXPECT THE MOST INTENSE PERIODS OF
PRECIPITATION ALONG AND JUST BEHIND THE FRONTAL PASSAGE BETWEEN
21/0600Z-21/1200Z. CEILINGS ARE EXPECTED TO LOWER OVERNIGHT
CAUSING MOUNTAINS AND PASSES TO BE OBSCURED.
MSO WATCHES/WARNINGS/ADVISORIES
MT...ID...WINTER WEATHER ADVISORY UNTIL 10 AM PST SATURDAY FOR NORTHERN
CLEARWATER MOUNTAINS-SOUTHERN CLEARWATER MOUNTAINS.
SHORT TERM...KOLATA
LONG TERM....MEAD/PALLISTER
AVIATION...KOLATA
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page