FXUS65 KMSO 212255 CCA
AFDMSO

AREA FORECAST DISCUSSION...CORRECTED
NATIONAL WEATHER SERVICE MISSOULA MT
354 PM MST MON DEC 21 2009

.DISCUSSION...

TONIGHT...A SHORT-WAVE DISTURBANCE WITH A FRONTAL BOUNDARY WILL BE
MOVING INTO NORTH-CENTRAL IDAHO AND WESTERN MONTANA TONIGHT.
THIS SYSTEM WILL PROVIDE CONSIDERABLE MOISTURE TO THE NORTHERN
ROCKIES IN THE FORM OF SHOWERS. SNOW LEVELS WILL BEGIN RELATIVELY
HIGH WITH MOST VALLEY LOCATIONS SEEING RAIN THROUGH THE EVENING
HOURS. AS THE ATMOSPHERE COOLS OVERNIGHT...SNOW LEVELS WILL BE
LOWERING TO THE VALLEY FLOOR BY EARLY TOMORROW MORNING. MOUNTAINS
WILL LIKELY BE PICKING UP MODERATE AMOUNTS OF SNOW DURING THE
OVERNIGHT PERIOD.

TUESDAY THROUGH WEDNESDAY...THE PRIMARY LOW PRESSURE SYSTEM WILL
BE DIGGING ACROSS THE PACIFIC NORTHWEST INTO THE GREAT BASIN. THE
BULK OF THE ENERGY/MOISTURE ASSOCIATED WITH THIS SYSTEM WILL BE
DIRECTED INTO CALIFORNIA/NEVADA/UTAH BY A STRONG JET STREAK. A
SECONDARY TROUGH OF LOW PRESSURE WILL BE MOVING INTO NORTHERN
IDAHO AND WESTERN MONTANA OUT OF SOUTHWEST CANADA. THIS NEXT
SYSTEM WILL BRING A REINFORCING SHOT OF MOISTURE AND COLDER AIR.
MANY AREAS WILL SEE LIGHT SNOWFALL...BUT IT DOES LOOK LIKE THE
WEST GLACIER/BOB MARSHALL/SEELEY-SWAN REGIONS ALONG THE DIVIDE
STAND THE GREATEST CHANCE OF GETTING APPRECIABLE SNOWFALL.
TEMPERATURES WILL BE COLDER WEDNESDAY AS COLD AIR SURGES SOUTH OUT
OF CANADA.

A SIGNIFICANT CHANGE TO COLDER CONDITIONS IS EXPECTED THURSDAY
THROUGH NEXT WEEKEND. A COLD AND DRY NORTHERLY FLOW WILL INFLUENCE
THE REGION THURSDAY INTO FRIDAY. WITH LONG NIGHTS AND LIGHT
WINDS...THERE SHOULD BE A NET LOSS OF HEAT FROM THE VALLEYS WITH
TEMPERATURES COOLING A BIT EACH DAY...DESPITE SOME WARMING ALOFT.
BY LATE IN THE WEEK...SOME VALLEY FOG AND LOW CLOUDS WILL BEGIN TO
DEVELOP. ALL THE MODELS SHOW A RIDGE OF HIGH PRESSURE OVER THE
REGION NEXT WEEKEND. THE BIGGEST IMPACTS SHOULD BE PERSISTING COLD
CONDITIONS IN THE VALLEYS AND AREAS OF FREEZING FOG.

&&

.AVIATION...A DISTURBANCE CAUGHT UP IN A SOUTHWESTERLY FLOW ALOFT 
WILL PROVIDE MOISTURE AND INSTABILITY FOR INCREASED CLOUDS AND
SHOWERS. AREAS OF VALLEY FOG CONTINUE TO PLAGUE WEST-CENTRAL
MONTANA VALLEYS INCLUDING THE MISSOULA VALLEY INTO THE EVENING
HOURS. DECREASING ATMOSPHERIC STABILITY AND INCREASED SHOWER
ACTIVITY SHOULD AID IN MIXING FOG/STRATUS OVERNIGHT. CLOUDS AND
SHOWERS WILL BE OBSCURING HIGHER TERRAIN/MOUNTAINS/PASSES DURING
THE NEXT 24 HOURS.

&&

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

$$

SHORT TERM...MSJ
LONG TERM....BAUCK
AVIATION...MSJ