FXUS65 KGGW 111641 AAA
AFDGGW

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE GLASGOW MT
941 AM MST FRI DEC 11 2009

.SHORT TERM...FOR NORTHEAST MONTANA...TODAY THROUGH SUNDAY...
STRONG NORTHWEST FLOW ALOFT WITH DUAL JET CORES IS PRESENT OVER
WESTERN CANADA THIS MORNING. THE NORTHERN JET HAS THE ARCTIC AIR
LOCKED INTO THE PRAIRIE PROVINCES OF CANADA...WITH MODIFIED ARCTIC
AIR NORTH OF THE SOUTHERN JET. THE SOUTHERN BRANCH IS RESPONSIBLE
FOR CHINOOK ARCHING OVER CENTRAL MONTANA AND RELATIVELY MILDER AIR
ALOFT. THE RELATIVELY WARMER AIR WILL CREEP INTO THE HIGHER
ELEVATIONS OF THE SOUTHWEST ZONES...SO MAXIMUM TEMPERATURES WERE
RAISED A FEW DEGREES. OTHERWISE...THE REMAINDER OF THE FORECAST IS
IN GOOD SHAPE. AJZ

PREVIOUS SHORT TERM DISCUSSION...
STRONG NW FLOW ALOFT CONTINUES OVER NE MT...ASSOCIATED WITH THE
LARGE...STRONG...AND PERSISTENT UPPER LOW THAT DOMINATES MUCH OF
CANADA AND THE U.S. THIS IS RESPONSIBLE FOR THE COLD WEATHER LATELY.
SHORTWAVE ACTIVITY IN THIS SLIGHTLY CYCLONIC FLOW WAS LESS ACTIVE
OVERNIGHT...WITH JUST PARTLY CLOUDY SKIES. EXPECT THIS TO CONTINUE
TODAY...SO NO POPS. MODELS INDICATE SOME MODIFYING OF THE AIRMASS
YET TODAY. THE WARMING WE HAD YESTERDAY OVER THE PREVIOUS DAY WAS
MORE A RESULT OF LOW LEVEL MIXING THOUGH...WHICH WILL BE LESS
FAVORABLE TODAY.

THE UPPER LOW IS VERY SLOWLY HEADING S THRU N SK...BUT MORE
IMPORTANTLY ITS ORIENTATION IS CHANGING TO ONE THAT IS W TO E.
THIS TURNS UPPER FLOW TO W ALOFT OVER MT...ALTHOUGH THIS FLOW IS
STILL IN THE NORTHERN BRANCH OF THE JET. A NEW VERY COLD UPPER
TROUGH DEVELOPS AND ROTATES SOUTHWARD FROM THE CANADIAN ARCTIC
HEADING S TOWARD MT. THIS GRABS A NEW AND STRENGTHENING ARCTIC HIGH AS
WELL...WITH TEMPS THAT HAVE BEEN -40 IN NW TERRITORIES. THIS
COMBINATION DEVELOPS AN INCREASINGLY STRONG FRONTAL BOUNDARY AS IT
HEADS S TOWARD MT.

MODELS HAVE TRENDED TOWARD HOLDING BACK THE MAIN COLD PUSH...BUT
PREFER THE QUICKER ECMWF/UKMET IN HAVING THE ARCTIC FRONT MOVE
ACROSS OUR AREA FROM THE N SAT. WHILE THE BOUNDARY IS SHARP...NOT
MOVING QUICK ENOUGH OR DEEPENING ENOUGH FOR REAL WINDY
WEATHER...BUT SURFACE PRESSURE GRADIENTS INDICATE WIND CHILLS WILL
BE A CONCERN SAT NIGHT AND SUN. 850 MB TEMPS DROP TO AS LOW AS
-26C IN OUR N SUN AFTERNOON. HIGHS SUN BELOW ZERO OVER MUCH OF NE
MT.

FOR PRECIP THE STRONG UPPER FLOW THAT IS BACKING WILL FAVOR SOME
SNOW AS THE COLD AIR DEEPENS BEHIND THE FRONT. MODELS INDICATE A
MODERATE AMOUNT OF LIFT/MOISTURE DEVELOPING SAT NIGHT AND
SUN...WITHOUT MUCH OF ANY SHORTWAVE THOUGH. THIS TYPICALLY WILL
BRING ACCUMS OF AN INCH OR SO TO OUR AREA STORM TOTAL. MODEL QPF
WOULD INDICATE SUCH. SIMONSEN

.LONG TERM...SUNDAY NIGHT THROUGH FRIDAY...
FINAL LOBE OF THE STRONG POLAR VORTEX EXPECTED TO ROTATE FROM
SOUTHERN ALBERTA SUNDAY NIGHT AND INTO NORTHEAST MONTANA ON
MONDAY. WHILE MODELS SUGGESTING GOOD MOISTURE WITH THE SYSTEM AND
COLD TEMPERATURES WILL MAKE FOR EFFICIENT SNOW PRODUCTION...THE
ARCTIC BOUNDARY IS EXPECTED TO HAVE SAGGED INTO CENTRAL AND
SOUTHERN MONTANA PRIOR TO THE SHORTWAVE ARRIVAL. THE POSITION OF
THE BOUNDARY ALONG WITH THE ADDED COMPONENT OF UPSLOPE WILL GIVE
AREAS TO THE SOUTHWEST OF THE CWA THE BEST CHANCE FOR SNOW WITH
THIS SYSTEM. WILL TREND POPS HIGHEST IN THE SOUTHWEST AND
DIMINISHING TOWARD THE NORTHEAST FOR SUNDAY NIGHT. THE SHORTWAVE
WILL MOVE ACROSS NORTHEAST MONTANA ON MONDAY...DRAWING A VERY COLD
AND DRY HIGH PRESSURE INTO THE REGION. EXPECT TEMPERATURES TO NOT
RISE MUCH ABOVE ZERO MOST AREAS ON MONDAY AND ONCE AGAIN BE VERY
COLD MONDAY NIGHT.

MODELS ARE SUGGESTING WARMING TEMPERATURES FOR THE REMAINDER OF
THE WEEK AS AN UPPER RIDGE BUILDS INTO THE NORTHERN ROCKIES. WHILE
STRONG WARM AIR ADVECTION ALOFT EXPECTED...NO STRONG KICKER SYSTEM
INDICATED BY ANY OF THE MODELS WHICH WOULD SUGGEST THAT COLD AIR
WILL LINGER IN THE NORTHERN RIVER VALLEYS EVEN AS THE HIGHER
TERRAIN WARMS. ADJUSTED TEMPERATURE GRIDS TO REFLECT THIS
POTENTIAL. EBERT

&&

.AVIATION...
VFR CONDITIONS ARE EXPECTED TO PREVAIL THROUGH TODAY WITH
SCATTERED TO BROKEN CLOUD COVER AT OR ABOVE 8K FT. A GENERALLY
LIGHT SOUTHEAST WIND WILL OCCASIONALLY BRING LOW CLOUDS OFF FORT
PECK LAKE TO PRODUCE IFR CONDITIONS AT KGGW. A COLD FRONT SAGGING
SOUTHWARD TONIGHT WILL BRING DETERIORATING CONDITIONS WITH THE
POSSIBILITY OF LIGHT SNOW. RAE

&&

.GLASGOW WATCHES/WARNINGS/ADVISORIES...NONE.

&&

$$

WEATHER.GOV/GLASGOW