FXUS65 KMSO 271619
AFDMSO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
919 AM MST FRI NOV 27 2009

.UPDATE...

POPS INCREASED OVER SOUTHWEST MONTANA FOR REMAINDER OF THE MORNING.

&&

.DISCUSSION...

GIVEN THE CURRENTLY SPLITTING PACIFIC STORM SYSTEM INFILTRATING
NORTH CENTRAL IDAHO AND WESTERN MONTANA THIS MORNING...POPS HAVE
BEEN INCREASED FURTHER EAST THAN PREVIOUSLY FORECAST. THIS SYSTEM
APPEARS TO LACK MUCH COLD AIR...SO RAIN AND RAIN-SNOW MIX FOR
VALLEYS AND SNOW WITH LIGHT ACCUMULATIONS FOR THE MOUNTAINS AND
PASSES WILL REMAIN IN THE FORECAST FOR MUCH OF THE REGION TODAY.

&&

.AVIATION...CLOUDS WILL LOWER THROUGHOUT THE DAY AS PRECIPITATION
SPREADS ACROSS THE NORTHERN ROCKIES REGION. WIDESPREAD TERRAIN
OBSCURATION IS EXPECTED IN BOTH CLOUDS AND MOUNTAIN SNOWFALL. KGPI
WILL CONTINUE TO EXPERIENCE REDUCTIONS IN VISIBILITY AND LOWERED
CEILINGS THROUGH MUCH OF THE DAY AS RAINFALL DEVELOPS. KMSO MAY
ALSO EXPERIENCE VARIABLE VISIBILITY THROUGH LATE AFTERNOON.

&&

.PREV DISCUSSION... /ISSUED 357 AM MST FRI NOV 27 2009/ 

DISCUSSION...THE UPPER LEVEL HIGH PRESSURE RIDGE HAS FULLY
SHIFTED INTO THE CENTRAL PLAINS AS AN ELONGATED TROUGH WORKS ITS
WAY INTO THE WESTERN STATES THIS MORNING. AS EXPECTED...THE VAST
MAJORITY OF UPPER LEVEL ENERGY WILL DIG SOUTH ALONG THE PACIFIC
COAST INTO CALIFORNIA. HOWEVER A WEAKER... SHORTWAVE TROUGH WILL
MOVE THROUGH THE NORTHERN ROCKIES TODAY RESULTING IN WIDESPREAD
VALLEY RAIN AND MOUNTAIN SNOW. PRECIPITATION HAS ALREADY COMMENCED
ACROSS NORTHWEST MONTANA THIS MORNING AND WILL GRADUALLY SPREAD
SOUTH THROUGHOUT THE DAY. THE ATMOSPHERE ALOFT IS RELATIVELY WARM
WITH THIS SYSTEM WHICH WILL RESULT IN POOR SNOW PRODUCTION. HENCE
ONLY THE HIGHER MOUNTAINS AND PASS LEVELS CAN EXPECT TO RECEIVE UP
TO 3 INCHES OF SNOWFALL.

TONIGHT NORTHWESTERLY FLOW WILL DEVELOP OVER THE REGION WITH THE
POSSIBILITY OF CONVECTIVE SNOW SHOWERS CONTINUING THROUGH
SATURDAY. FORECAST MODELS CONTINUE TO SHOW AN ATMOSPHERE WHICH
COULD SUPPORT PERIODS OF ORGANIZED TERRAIN INDUCED CONVECTION
(SNOW BANDS). BUT GIVEN THE VARIABLE NATURE OF THE SNOW BANDING
PHENOMENON HAVE GONE WITH A MORE GENERALIZED FORECAST WHICH IS
ABOVE MODEL GUIDANCE CONSIDERING MODELS OFTEN TIMES UNDER FORECAST
NORTHWESTERLY FLOW. LATE SATURDAY INTO SUNDAY ANOTHER RIDGE OF
HIGH PRESSURE IS EXPECTED TO BUILD OVER THE WEST COAST. BUT
FORECAST MODELS SUGGEST SUFFICIENT MOISTURE WILL PASS OVER THE
BUILDING RIDGE TO KEEP LIGHT SHOWERS IN THE FORECAST...PRIMARILY
OVER NORTHWEST MONTANA.

MONDAY THROUGH THURSDAY...MONDAY A WEAK AND VERY SHORT LIVED RIDGE
BUILDS INTO THE REGION. BY TUESDAY A DISTURBANCE MOVING OUT OF
CANADA WILL BRING AN INCREASED CHANCE OF PRECIPITATION TO WESTERN
MONTANA. THIS WILL ALSO HELP BRING A SHOT OF COLDER ARCTIC AIR
ACROSS THE DIVIDE. THE COLDER AIR WILL GET WELL ENTRENCHED ACROSS
WESTERN MONTANA BY WEDNESDAY...WITH SOME LINGERING SNOW SHOWERS.
THE COLD NORTHERLY FLOW WILL CONTINUE THROUGH THURSDAY. 

&&

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

$$

UPDATE...ZUMPFE
SHORT TERM...DICKERSON
LONG TERM....KOLATA
AVIATION...DICKERSON