FXUS65 KMSO 101035
AFDMSO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
335 AM MST THU DEC 10 2009

.DISCUSSION...AN EXTREMELY STRONG POLAR VORTEX ROTATING OVER
CENTRAL CANADA WILL KEEP NORTHWESTERLY FLOW ALOFT OVER THE
NORTHERN ROCKIES REGION TODAY. A WEAK WEATHER DISTURBANCE CAN BE
SEEN ON INFRARED SATELLITE IMAGERY EARLY THIS MORNING WHICH IS
SPREADING CLOUD COVER AND VERY LIGHT SNOW ACROSS WESTERN MONTANA.
THIS WILL GENERALLY BE THE CASE THROUGH THE MORNING HOURS WITH
SNOW AND CLOUDS DECREASING IN COVERAGE THIS AFTERNOON AND BECOMING
ISOLATED ALONG MAINLY THE CANADIAN BORDER...GLACIER NATIONAL
PARK AND THE SEELEY LAKE REGIONS THIS AFTERNOON. CLOUDS WILL
DECREASE EVEN FURTHER OVERNIGHT IN THE WAKE OF THIS SYSTEM
LEAVING MOSTLY CLEAR TO PARTLY CLOUDY SKIES ACROSS THE AREA.
THIS WILL ALLOW ANOTHER NIGHT OF VERY GOOD RADIATIONAL COOLING
WHICH WILL RESULT IN THE TYPICALLY COLD LOCATIONS SEEING YET
ANOTHER ROUND OF BELOW ZERO TEMPERATURES BY FRIDAY MORNING. ON
FRIDAY NORTHWESTERLY FLOW WILL GRADUALLY FLATTEN BECOMING
WESTERLY...OR ZONAL FLOW BY SATURDAY MORNING. SINCE MUCH OF THE
AREA WILL FALL IN BETWEEN APPROACHING WEATHER SYSTEMS...PARTLY
CLOUDY SKIES WITH SOME TEMPERATURE MODERATION...ESPECIALLY IN THE
MOUNTAINS...CAN BE EXPECTED.

SATURDAY THROUGH TUESDAY... THE MAIN UPPER LEVEL PATTERN IS SIMILAR
BETWEEN GUIDANCE WITH A TRANSITION TO A SPLIT WESTERLY FLOW OVER THE
UNITED STATES. THE MAIN FEATURES OF CONCERN CONTINUE TO BE THE
CANADIAN LOW TRACKING SOUTHWARD TOWARDS THE REGION AND THE PACIFIC
LOW PRESSURE SYSTEM PASSING TO THE SOUTH SATURDAY THROUGH SUNDAY.
A CLASH OF AIR MASSES WILL TAKE PLACE AS IDAHO AND MONTANA WILL LIE
DIRECTLY BETWEEN THESE TWO SYSTEMS. WARMER AND MORE MOIST AIR MOVING
IN FROM THE SOUTH WILL ENCOUNTER THE MUCH COLDER AIR MASS TO THE
NORTH SETTING THE STAGE FOR WIDESPREAD STRATIFORM SNOW STARTING
SATURDAY AND THROUGH SUNDAY. THE PROGRESSION OF THE COLD AIR FROM THE
NORTH REMAINS ONE OF THE BIGGEST CHALLENGES BETWEEN THE NUMERICAL
MODELS WITH THE GFS CONSISTENTLY STALLING AN ARCTIC BOUNDARY OVER
WESTERN MONTANA WHILE THE ECMWF HOLDS THE COLD AIR TO THE EAST.
WITH THESE UNCERTAINTIES MADE LITTLE CHANGES TO THE PREVIOUSLY
FORECAST TEMPERATURES THROUGH TUESDAY.

LONGER RANGE MODELS AND GLOBAL TELECONNECTIONS SUGGEST THAT A
RIDGE OF HIGH PRESSURE SHOULD DEVELOP DURING THE MIDDLE OF NEXT
WEEK. GIVEN THIS POTENTIAL AND THE LIKELIHOOD FOR WIDESPREAD
SNOWFALL THIS WEEKEND...HAVE KEPT VALLEY TEMPERATURES RATHER COOL
DEPICTING THE POSSIBILITY OF STEEP TEMPERATURE INVERSIONS
DEVELOPING. ALSO...GIVEN THE VAST ARRAY OF POTENTIAL SOLUTIONS
OVER THE WEEKEND BELIEVE LITTLE CONFIDENCE CAN BE GARNERED IN HOW
DOMINANT THE RIDGING MAY BE NEXT WEEK. THUS HAVE KEPT
CLIMATOLOGICAL POPS WITH SLOWLY MODERATING TEMPERATURES IN THE
MOUNTAINS.

&&

.AVIATION...INCREASING CLOUDS WITH AREAS OF VERY LIGHT SNOW CAN BE
EXPECTED THROUGH THE MORNING AT KMSO AND KGPI. LOWER CLOUDS WILL
LIKELY OBSCURE TERRAIN FEATURES BUT DECREASING CLOUDS CAN BE
EXPECTED EARLY THIS EVENING.

&&

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

$$

SHORT TERM...DICKERSON
LONG TERM....KITSMILLER/DICKERSON
AVIATION...DICKERSON