FXUS65 KGGW 120415
AFDGGW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GLASGOW MT
915 PM MST FRI DEC 11 2009
.SHORT TERM...FOR NORTHEAST MONTANA...TONIGHT THROUGH SUNDAY...
UPDATE...MADE MINOR TWEAKS TO TEMPERATURES IN UPDATE. ARCTIC FRONT
IS CURRENTLY JUST NORTH OF REGINA. THE FRONT IS FORECASTED TO DROP
SOUTH ACROSS THE AREA DURING THE DAY ON SATURDAY. SOME VERY LIGHT
SNOW IS SHOWING UP ON RADAR NORTH OF US 2 AT THE MOMENT. GOING
CHANCE OF SNOW OVERNIGHT LOOKS REASONABLE. FORRESTER
PREVIOUS SHORT TERM...
CURRENT GOES WATER VAPOR IMAGERY SHOWS A LARGE POLAR VORTEX OVER
NORTH-CENTRAL CANADA WITH DUAL CYCLONIC JETS ROUNDING THE
SOUTHWESTERN LOBE OF THE UPPER CYCLONE. THIS UPPER LOW WILL
CONTINUE TO SINK SOUTHWARD AND EVENTUALLY PUSH EAST OVER SOUTHERN
CANADA SUNDAY. HOWEVER...A SECONDARY COLD POOL SETTLES OVER THE
CANADIAN ROCKIES. THE SOUTHWARD MOVEMENT OF THE UPPER LOW WILL
TRIGGERS AN ARCTIC FRONT TO CROSS THE LOCAL AREA SATURDAY NIGHT
AND THE SECONDARY UPPER LOW WILL BRING THE POTENTIAL FOR
ACCUMULATING SNOW. THIS WILL CREATE A WINTRY WEEKEND FOR
NORTHEAST MONTANA WITH DANGEROUSLY COLD WIND CHILL VALUES ALONG
WITH ACCUMULATING SNOW AND AREAS OF BLOWING SNOW.
A WEAK FRONTAL BOUNDARY WILL SAG SOUTH AND SETTLE OVER THE
NORTHERN ZONES THIS EVENING AND SATURDAY. CLOUDS WILL
INCREASE ALONG WITH AREAS OF LIGHT SNOW OR FLURRIES. THIS WILL
INHIBIT TEMPERATURE FROM PLUMMETING TONIGHT. MAXIMUM TEMPERATURES
WILL ONLY RISE SLIGHTLY ACROSS THE NORTH SUNDAY...AND BE
SEASONALLY COOL ACROSS THE SOUTH. THE WARMER MET VALUES WERE
PREFERRED AS THEY VERIFIED BETTER TODAY THAN THE COOLER MAV.
SNOW SHOULD BEGIN TO INCREASE IN INTENSITY LATE SATURDAY AFTERNOON
AN PERSIST THROUGH SUNDAY WITH THE INFLUENCE OF THE SECONDARY
UPPER LOW...INCREASED VERTICAL ASCENT WITH LATENT HEAT RELEASE
RESULTING FROM A DEEP SATURATED LAYER AS UPPER LEVEL PACIFIC
MOISTURE OVERRUNS FRIGID ARCTIC AIR AT THE SURFACE...AND VERTICAL
ASCENT FROM THE RIGHT REAR QUADRANT OF AN UPPER JET. TEMPERATURES
SHOULD PLUMMET WELL BELOW ZERO SATURDAY NIGHT AND REMAIN STEADY TO
SLOWLY RISING SUNDAY. THIS COMBINED WITH A NORTH TO NORTHEASTERLY
SURFACE WIND OF 12 TO 20KT WILL CREATE A PROLONGED PERIOD OF
DANGEROUSLY COLD WIND CHILLS SATURDAY NIGHT AND SUNDAY.
GIVEN THIS A WINTER STORM WATCH HAS BEEN ISSUED FROM 03Z SUNDAY
THROUGH 16Z MONDAY. THE GREATEST THREAT APPEARS TO BE LOW WIND
CHILL VALUES. HOWEVER...ACCUMULATING SNOW AND BLOWING SNOW IS
POSSIBLE ACROSS THE WEST AND SOUTH...WITH THE NORTHEAST HAVING THE
LEAST THREAT OF SNOW. AMOUNTS OF 2 TO 5 INCHES ARE POSSIBLE WITH
HIGH SNOW TO LIQUID RATIOS. CURRENT QPF AMOUNTS WERE GENERATED
USING A 50/50 BLEND OF 15Z SREF AND 18Z HPC QPF. AJZ
.LONG TERM...SUNDAY NIGHT THROUGH FRIDAY...
A RATHER STRONG UPPER LEVEL SHORT-WAVE DEVELOPING OVER THE
CANADIAN ROCKIES SUNDAY EVENING SWINGS SOUTHEAST OVER SOUTHERN
SASKATCHEWAN AND NORTHEAST MONTANA MONDAY BRINGING ANOTHER WAVE OF
VERY COLD AIR WITH IT. A STRONG SURFACE HIGH ALSO NUDGING SOUTH
FROM CANADA WILL LIMIT ANY PRECIPITATION OVER THE NORTHERN ZONES
MONDAY. THE FAST MOVING SHORT-WAVE DEPARTS THE REGION MONDAY NIGHT
WHILE THE SURFACE HIGH SETTLES OVER THE AREA FOR ANOTHER VERY COLD
BUT DRY NIGHT. WITH 00Z TUESDAY 850MB TEMPERATURES OF
-28*C...TMINS LOWER THAN -20*F ARE POSSIBLE. BASED ON LATEST
GUIDANCE...TRENDED TEMPERATURES LOWER.
TUESDAY AND WEDNESDAY...HEIGHTS BEGIN TO INCREASE AS MODERATE
RIDGING MOVES OVER THE WEST. 850MB TEMPERATURES RISE ABOVE 0*C
TUESDAY NIGHT. WEAK MIXING WILL ALSO BEGIN TUESDAY NIGHT IN THE
SOUTHWEST INITIALLY BUT WITH NOT ENOUGH ENERGY TO QUICKLY SCOUR
THE COLD AIR OUT OF THE VALLEYS.
THURSDAY...THE ECMWF...MORE THAN THE GFS...BRINGS A SHORT-WAVE
DISTURBANCE OVER THE TOP OF THE RIDGE FLATTENING IT AROUND
WEDNESDAY NIGHT OR THURSDAY. NO MOISTURE IS ASSOCIATED WITH THIS
DISTURBANCE SO ITS MAIN EFFECT WILL BE TO SHIFT SURFACE WINDS
AROUND THE NORTH TEMPORARILY.
FRIDAY...MODELS ARE IN AGREEMENT WITH THE UPPER RIDGE AMPLIFYING
OVER WESTERN CONUS BRINGING IN MUCH WARMER...BUT NEAR NORMAL
TEMPERATURES INTO THE WEEKEND. SCT
PREVIOUS DISCUSSION...
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 WITH SCATTERED TO BROKEN CLOUD COVER AT OR ABOVE
8K FEET THIS EVENING WILL BE INTERRUPTED LATER TONIGHT AND
SATURDAY BY A COLD FRONT SAGGING SOUTHWARD...BRINGING
DETERIORATING CONDITIONS WITH MVFR CEILINGS AND THE POSSIBILITY
OF LIGHT SNOW. SCT
&&
.GLASGOW WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WATCH FROM SATURDAY EVENING THROUGH MONDAY MORNING
FOR CENTRAL AND SOUTHEAST PHILLIPS-CENTRAL AND SOUTHERN VALLEY-
DANIELS-SHERIDAN-WESTERN ROOSEVELT-PETROLEUM-GARFIELD-MCCONE-
RICHLAND-DAWSON-PRAIRIE-WIBAUX-NORTHERN PHILLIPS-SOUTHWEST
PHILLIPS-NORTHERN VALLEY-EASTERN ROOSEVELT.
&&
$$
WEATHER.GOV/GLASGOW
