000
FXUS65 KMSO 272135
AFDMSO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
235 PM MST MON DEC 27 2010
...SIGNIFICANT WINTER STORM TO IMPACT THE NORTHERN ROCKIES LATE TUESDAY
NIGHT THROUGH WEDNESDAY NIGHT...
.DISCUSSION...
TONIGHT THROUGH TUESDAY...WEST TO EAST ORIENTED LINES OF LIGHT
SNOW...EMBEDDED WITH LOCALLY MODERATE SNOWFALL...WILL PLAGUE
IDAHO/MONTANA BORDER PASSES AND WEST CENTRAL MONTANA THIS EVENING
BEFORE GIVING WAY TO ENHANCED UPSLOPE PRECIPITATION OVERNIGHT. A
STEADY INFLUX OF PACIFIC MOISTURE AND INCREASING WESTERLY FLOW
ALOFT WILL FAVOR SNOW OVER THE HIGHER ELEVATION WEST-FACING SLOPES
OF THE CLEARWATER MOUNTAINS...THE BITTERROOT RANGE...THE MISSION
MOUNTAINS AND THE WEST GLACIER/BOB MARSHALL AREAS THROUGH TUESDAY.
THE PRIMARY CONCERN DURING THIS TIME IS ACCUMULATING SNOW...SLICK
ROADWAYS AND OCCASIONAL MOUNTAIN PASS WHITEOUT CONDITIONS THAT
WILL CREATE HAZARDOUS DRIVING CONDITIONS. WINTER WEATHER
ADVISORIES REMAIN IN EFFECT THROUGH EARLY TUESDAY EVENING TO
HIGHLIGHT THESE IMPACTS. IN ADDITION...NORTHWEST MONTANA VALLEYS
STILL HAVE A GOOD CHANCE OF SEEING ACCUMULATING SNOW TUESDAY
MORNING AS AN ENHANCED SHOT OF MOISTURE MOVES OVER THIS AREA.
DAYTIME TEMPERATURES SHOULD WARM INTO THE LOW TO MID 30S DUE TO A
TIGHTENING PRESSURE GRADIENT...WHICH WILL RESULT IN BREEZY
SOUTHWEST WINDS SPREADING ACROSS THE REGION FROM SOUTH TO NORTH
THROUGH THE DAY. THE GRANGEVILLE/LOWER HELLS CANYON REGIONS WILL
LIKELY EXPERIENCE BREEZY SOUTH WINDS TONIGHT THROUGH TUESDAY.
HOWEVER...LITTLE CHANGES HAVE BEEN OBSERVED IN MODEL GUIDANCE AND
THEREFORE WIND SPEEDS REMAIN JUST BELOW ADVISORY CRITERIA AT THIS
TIME. THIS REGION WILL NEED TO BE MONITORED CLOSELY FOR POTENTIAL
WIND HIGHLIGHTS ON TUESDAY.
FORECAST MODELS ARE INDICATING A STRONG LOW PRESSURE SYSTEM
SWINGING THROUGH THE NORTHERN ROCKIES LATE TUESDAY NIGHT THROUGH
WEDNESDAY DAY EVENING. THIS FEATURE WILL CAUSE SUBSTANTIAL
SNOWFALL ACROSS THE REGION, ESPECIALLY IN THE HIGHER TERRAIN. THE
MOUNTAINS COULD POSSIBLY SEE A FOOT OR TWO OF SNOW, WHILE THE
VALLEYS RECEIVE 4 TO 9 INCHES. THE BIGGEST CONCERN WILL BE THE
PATH OF THE LOW PRESSURE SYSTEM, BECAUSE THIS WILL DETERMINE WHERE
THE HEAVIEST SNOWFALL WILL BE. AT THIS TIME, THE HEAVIEST SNOW IS
EXPECTED ACROSS THE NORTHERN CLEARWATER MOUNTAINS UP INTO
NORTHWEST MONTANA.
ALSO AS THIS SYSTEM MOVES THROUGH, THE SOUTHERN PORTION OF THE LOW
COULD SEE ENOUGH WARMING THAT PRECIPITATION WILL START OFF AS RAIN
IN THE LOWER VALLEYS OF NORTH CENTRAL IDAHO.
AN INCREASE IN THE PRESSURE GRADIENT DUE TO THIS SYSTEM COULD
CAUSE GUSTY EASTERLY WINDS ACROSS NORTHWEST MONTANA. LOCATIONS
LIKE BAD ROCK CANYON, EUREKA, ESSEX, AND WEST GLACIER COULD SEE
SIGNIFICANT WIND GUSTS BY WEDNESDAY AFTERNOON. THE COMBINATION OF
WIND AND SNOW SHOULD CAUSING BLOWING AND DRIFTING SNOW ACROSS
NORTHWEST MONTANA.
AS THE SURFACE LOW MOVES INTO EASTERN MONTANA WEDNESDAY EVENING, AN
UPPER LEVEL TROUGH WILL SETTLE OVER THE NORTHERN ROCKIES. THIS
TROUGH WILL USHER IN A COLDER AIR MASS. WITH CLEARING SKIES AND
THE COLDER AIR MASS, MAXIMUM TEMPERATURES FOR THURSDAY AND FRIDAY
SHOULD BE IN THE SINGLE DIGITS TO LOWER TEENS. WHILE OVERNIGHT
TEMPERATURES FOR THURSDAY NIGHT SHOULD BE BELOW ZERO.
NEW YEARS EVE THROUGH MONDAY...COLD HIGH PRESSURE CONTINUES FOR
THE NEW YEARS WEEKEND WITH JUST A SLIGHT CHANCE OF LIGHT SNOW.
NIGHTTIME TEMPERATURES WILL DEPEND ON CLOUD COVER...WITH CLEAR
SKIES RESULTING IN NEAR ZERO AND BELOW ZERO LOWS. COLD AIR IN THE
VALLEYS IS EXPECTED GET WASHED OUT WITH THE NEXT PACIFIC WEATHER
SYSTEM MOVING IN EARLY NEXT WEEK.
&&
.AVIATION...UNSETTLED UPPER LEVEL FLOW WILL LINGER BEHIND THE
FIRST IN A SERIES OF STORMS THAT WILL IMPACT AVIATION OPERATIONS
FOR THE REST OF THIS WEEK. ISOLATED SHOWERS TO WEAK BANDS OF SNOW
WILL CONTINUE TO PASS ACROSS WEST CENTRAL MONTANA THIS AFTERNOON
WHICH WILL PRIMARILY IMPACT KMSO...CREATING PERIODS OF RAPIDLY
DETERIORATING CONDITIONS DUE TO POOR VISIBILITIES AND LOWERED
CEILINGS. THE NEXT STORM SYSTEM BEGINS TO ENTER THE REGION
TONIGHT...FIRST IMPACTING NORTHWEST MONTANA BEFORE SPREADING AREA-
WIDE. KGPI APPEARS TO BE IMPACTED BY THIS SYSTEM AFTER 28/0600Z
TONIGHT WHILE KMSO SHOULD EXPERIENCE THE SNOW AROUND 28/1200Z
TUESDAY MORNING. KSMN AND KBTM SHOULD BE IMPACTED LATER ON IN
THE DAY.
&&
.MSO WATCHES/WARNINGS/ADVISORIES...
MT...WINTER WEATHER ADVISORY UNTIL 5 PM MST TUESDAY
BITTERROOT/SAPPHIRE MOUNTAINS.
WINTER STORM WATCH FROM LATE TUESDAY NIGHT THROUGH LATE
WEDNESDAY NIGHT BITTERROOT/SAPPHIRE MOUNTAINS...
BUTTE/BLACKFOOT REGION...FLATHEAD/MISSION VALLEYS...
KOOTENAI/CABINET REGION...MISSOULA/BITTERROOT VALLEYS...
POTOMAC/SEELEY LAKE REGION...WEST GLACIER REGION.
WINTER STORM WATCH FROM TUESDAY AFTERNOON THROUGH LATE WEDNESDAY
NIGHT LOWER CLARK FORK REGION.
WINTER WEATHER ADVISORY UNTIL 5 PM MST TUESDAY LOWER CLARK FORK
REGION.
WINTER WEATHER ADVISORY UNTIL 5 PM MST TUESDAY WEST GLACIER
REGION.
WINTER WEATHER ADVISORY FROM MIDNIGHT TONIGHT TO 5 PM MST
TUESDAY KOOTENAI/CABINET REGION.
ID...WINTER WEATHER ADVISORY UNTIL 5 PM MST TUESDAY EASTERN LEMHI
COUNTY.
WINTER STORM WATCH FROM LATE TUESDAY NIGHT THROUGH LATE
WEDNESDAY NIGHT EASTERN LEMHI COUNTY...WESTERN LEMHI COUNTY.
WINTER WEATHER ADVISORY UNTIL 4 PM PST TUESDAY NORTHERN
CLEARWATER MOUNTAINS.
WINTER STORM WATCH FROM TUESDAY AFTERNOON THROUGH LATE WEDNESDAY
NIGHT NORTHERN CLEARWATER MOUNTAINS...SOUTHERN CLEARWATER
MOUNTAINS.
WINTER WEATHER ADVISORY UNTIL 4 PM PST TUESDAY SOUTHERN
CLEARWATER MOUNTAINS.
&&
$$
SHORT TERM...DEROSA
LONG TERM....SMITH/SIGLER
AVIATION...SMITH
