High Wind in Idaho, December 15, 2006

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
857 PM MST THU DEC 14 2006

.DISCUSSION...COMPLEX WEATHER CONTINUES ACROSS THE NORTHERN
ROCKIES TONIGHT. WARM ADVECTION PRECIPITATION IS FAIRLY
WIDESPREAD...BUT PRECIPITATION TYPES HAVE BEEN MIXED. COLD AIR
REMAINS OVER FAR NORTHWEST MONTANA AND PORTIONS OF THE IDAHO
PANHANDLE...AND THEY HAVE HAD ACCUMULATING SNOW DOWN TO THE LOWER
VALLEYS. HOWEVER...THE WARMER AIR IS STARTING TO MOVE
NORTHWARD...AND SNOW LEVELS ARE CLIMBING RAPIDLY OVER NORTH
CENTRAL IDAHO AND WEST CENTRAL MONTANA. THEREFORE...DO NOT EXPECT
THE LOWER ELEVATION SNOW TO LAST MUCH LONGER IN THE NORTHWEST. THE
SOUTHERLY WINDS HAVE BEEN A BIT DELAYED...BUT ARE BEGINNING TO
SHOW THEMSELVES IN IDAHO. GRANGEVILLE HAS BEEN GUSTING IN THE MID
30S...WITH SOME 50 MPH PLUS GUSTS UPSTREAM IN NORTHEAST OREGON.
THE COLD FRONT EXTENDS FROM THE WASHINGTON CASCADES BACK TO
SOUTHWEST OREGON THIS EVENING. THIS WILL MOVE INTO IDAHO AND
NORTHWEST MONTANA IN THE WEE HOURS OF THE MORNING...AND INTO WEST
CENTRAL MONTANA JUST AHEAD OF DAYBREAK. SNOW LEVELS WILL RAPIDLY
DROP BEHIND THE FRONT BRINGING THE WHITE BACK TO THE VALLEYS BY
AFTERNOON. ACCUMULATIONS WILL STILL BE BEST IN THE
MOUNTAINS...PARTICULARLY FROM BOB MARSHALL THROUGH GLACIER
PARK...AS WELL AS IN THE CLEARWATERS/BITTERROOTS. HOWEVER...THERE
COULD BE SOME LOCAL BLOWING SNOW IN THE VALLEYS FRIDAY AFTERNOON.

&&

.AVIATION...A SIGNIFICANT PACIFIC STORM SYSTEM WILL MOVE THROUGH
THE NORTHERN ROCKIES TONIGHT AND TOMORROW. EXPECT WIDESPREAD
PRECIPITATION AND LOWERED CEILINGS/VISIBILITIES ALONG WITH STRONG
WESTERLY WINDS...PLEASE SEE APPROPRIATE TAFS AND TWEBS.

&&

.PREV DISCUSSION... /ISSUED 255 PM MST THU DEC 14 2006/

DISCUSSION...TONIGHT AND FRIDAY. A VIGOROUS STORM SYSTEM WILL
MOVE INTO THE NORTHERN ROCKIES THIS EVENING. INCREASING PRESSURE
GRADIENTS AND STRONG WINDS ALOFT WILL COMBINE TO BRING NORTHWEST
MONTANA AND NORTH CENTRAL IDAHO SIGNIFICANT MOUNTAIN SNOWS. VERY
STRONG WINDS WILL PRODUCE LOCAL BLIZZARD/WHITE OUT
CONDITIONS...ESPECIALLY IN MOUNTAIN PASSES AND RIDGES FRIDAY
MORNING WHEN THE COLD FRONT IS EXPECTED TO PASS THROUGH THE
REGION. HIGH WIND WARNINGS WILL CONTINUE IN THE CAMAS PRAIRIE AND
HELLS CANYON REGION AS STRONG WINDS WITH GUSTS OVER 60 MPH ARE
LIKELY TO DEVELOP LATER THIS EVENING. WINDS AT MOUNTAIN TOPS ARE
EXPECTED TO BE IN THE 60-70 KNOT RANGE. WIND ADVISORIES HAVE BEEN
POSTED FOR THE REMAINDER OF WEST CENTRAL AND SOUTHWEST MONTANA AS
WELL AS LEMHI COUNTY IN IDAHO. THESE WINDS ARE EXPECTED TO DEVELOP
LATE THIS EVENING. GUSTS TO 50 MPH ARE POSSIBLE...ESPECIALLY ON
THE LEE SIDES OF MOUNTAINS. PRECIPITATION WILL START OFF AS RAIN
AS A WARM FRONT PUSHES THROUGH TONIGHT AND TRANSITION TO SNOW AS
THE COLD FRONT MOVES THROUGH FRIDAY MORNING. UNSTABLE AIR BEHIND
THE FRONT WILL PRODUCE SNOW SHOWERS THROUGHOUT THE DAY. THE STRONG
WINDS IN PLACE COMBINED WITH THIS SNOW COULD PRODUCE BLOWING SNOW
DURING THE DAY FRIDAY. WILL PRODUCE BLOWING SNOW. SNOW AMOUNTS ARE
EXPECTED TO BE LIGHT WITH THESE SHOWERS.

FRIDAY NIGHT THROUGH SUNDAY NIGHT...AFTER COLD FRONT PASSAGE
FRIDAY...THE ATMOSPHERE WILL REMAIN QUITE UNSTABLE THROUGH OUT THE
LOW AND MID LEVELS. THIS INSTABILITY WILL COMBINE WITH REMNANT
MOISTURE TO CONTINUE SHOWERS ACROSS THE NORTHERN ROCKIES THROUGH
SATURDAY MORNING. VALLEY LOCATIONS WILL SEE LESS IN THE WAY OF
PRECIPITATION HOWEVER...AS DOWNSLOPING DUE TO STRONG WESTERLY
WINDS ALOFT COMES INTO PLAY. A SHORT LIVED HIGH PRESSURE RIDGE
WILL TRANSITION THROUGH THE REGION SATURDAY...DECREASING SHOWER
COVERAGE THROUGH SUNDAY MORNING. BY SUNDAY AFTERNOON...ANOTHER LOW
PRESSURE TROUGH WILL INCREASE SHOWER ACTIVITY ACROSS WESTERN
MONTANA AND NORTH CENTRAL IDAHO. DYNAMICS LOOK FAIRLY WEAK WITH
THIS SYSTEM HOWEVER...SO MOSTLY LIGHT MOUNTAIN SNOW SHOWERS ARE
EXPECTED.

MONDAY THROUGH TUESDAY A HIGH AMPLITUDE...POSITIVELY TILTED UPPER
LEVEL RIDGE WILL MOVE THROUGH THE PACIFIC NORTHWEST. ALTHOUGH
UPPER LEVEL RIDGING WILL BE OVER THE NORTHERN ROCKIES...FORECAST
MODELS ARE INDICATING DECENT ISENTROPIC LIFT OVER NORTHWESTERN
MONTANA AND NORTH CENTRAL IDAHO MONDAY EVENING THROUGH TUESDAY
AFTERNOON. THUS I HAVE INCREASED CHANCES FOR PRECIPITATION MONDAY
AND TUESDAY OVER THE AFOREMENTIONED AREAS. FORECAST MODELS
DIFFER IN THE STRENGTH AND PASSAGE OF A WEATHER SYSTEM ON TUESDAY
NIGHT. I CHOSE TO GO WITH A BLEND OF THE ECMWF...GFS AND CANADIAN
MODEL SOLUTIONS WHICH WOULD CALL FOR A FASTER MOVING WEATHER SYSTEM
PASSING ALONG THE CANADIAN BORDER OVERNIGHT TUESDAY INTO WEDNESDAY.
AT THIS TIME IT APPEARS AS THOUGH MAINLY NORTHWESTERN MONTANA STANDS
THE BEST CHANCE FOR PRECIPITATION WITH THIS SYSTEM.

BEYOND WEDNESDAY FORECAST MODELS BECOME QUITE VARIABLE AND
INCONSISTENT. THUS I HAVE CHOSEN TO KEEP THE OVERALL FORECAST NEAR
CLIMATOLOGICAL VALUES SUPPORTING THE ZONAL FLOW ADVERTISED BY THE
GFS FORECAST MODEL. HOWEVER...TELECONNECTIONS IN THE PACIFIC AND THE
LATEST ECMWF HINT AT THE POSSIBILITY OF RIDGING BUILDING OVER THE
PACIFIC COAST/INTERMOUNTAIN WESTERN UNITED STATES LATE NEXT WEEK.
THIS WILL HAVE TO BE MONITORED IN FUTURE FORECASTS.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...WIND ADVISORY UNTIL 5 PM MST FRIDAY FOR BUTTE/BLACKFOOT REGION-
     POTOMAC/SEELEY LAKE REGION.

     SNOW AND BLOWING SNOW ADVISORY FROM 5 AM TO 5 PM MST FRIDAY FOR
     BITTERROOT/SAPPHIRE MOUNTAINS.

     WIND ADVISORY UNTIL 5 AM MST FRIDAY FOR BITTERROOT/SAPPHIRE
     MOUNTAINS.

     WIND ADVISORY UNTIL 5 PM MST FRIDAY FOR MISSOULA/BITTERROOT
     VALLEYS.

     WINTER STORM WARNING UNTIL 5 PM MST FRIDAY ABOVE 4000 FEET FOR
     KOOTENAI/CABINET REGION-LOWER CLARK FORK REGION.

     WIND ADVISORY UNTIL 5 PM MST FRIDAY FOR FLATHEAD/MISSION VALLEYS.

     WINTER STORM WARNING UNTIL 5 PM MST FRIDAY ABOVE 4000 FEET FOR
     WEST GLACIER REGION.

ID...WIND ADVISORY UNTIL 5 PM MST FRIDAY FOR EASTERN LEMHI COUNTY-
     WESTERN LEMHI COUNTY.

     SNOW AND BLOWING SNOW ADVISORY FROM 4 AM TO 4 PM PST FRIDAY FOR
     SOUTHERN CLEARWATER MOUNTAINS.

     WIND ADVISORY UNTIL 4 AM PST FRIDAY FOR SOUTHERN CLEARWATER
     MOUNTAINS.

     WINTER STORM WARNING UNTIL 4 PM PST FRIDAY ABOVE 4000 FEET FOR
     NORTHERN CLEARWATER MOUNTAINS.

     HIGH WIND WARNING UNTIL 4 AM PST FRIDAY FOR LOWER HELLS
     CANYON/SALMON RIVER REGION-OROFINO/GRANGEVILLE REGION.

&&

UPDATE...WHITMORE
PREVIOUS DISCUSSION...RPN/DICKERSON/VIA
AVIATION...SMITH