FXUS65 KGGW 222132
AFDGGW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GLASGOW MT
232 PM MST TUE DEC 22 2009
.SHORT TERM...FOR NORTHEAST MONTANA...TONIGHT THROUGH THURSDAY...
NEAR BLIZZARD OR BLIZZARD CONDITIONS CAN BE EXPECTED
WEDNESDAY...ESPECIALLY ACROSS THE SE ZONES.
A DEEP WESTERN UPPER TROUGH HAS A COUPLE OF SYSTEMS THAT LOOK TO
CLASH OVER THE CWA WEDNESDAY. THE SOUTHERN SYSTEM IS HELPING TO
STREAM MOISTURE NORTH INTO THE AREA WHILE A WESTERN CANADIAN SYSTEM
IS DIVING SOUTHEAST AND WILL DRIVE NORTHWEST WINDS ACROSS THE AREA.
IN THE MEANTIME TONIGHT...SOME WEAK ENERGY SHOULD HELP TO PROVIDE
LIFT FOR SOME SNOWFALL LATE TONIGHT. AN INVERTED SFC TROUGH SHOULD
HELP TO PROVIDE SOME CONVERGENCE ALONG AND TO THE EAST. THE SNOW
HOWEVER DOES NOT LOOK TO BE ENOUGH TO WARRANT THE WATCH FOR LATE
TONIGHT...SO DROPPED IT FOR THE WESTERN ZONES.
WEDNESDAY...THE ARCTIC PUSH MOVES INTO THE AREA PUSHING THE INVERTED
TROUGH INTO THE DAKOTAS. THIS WILL ALLOW NW WINDS TO INCREASE DURING
THE DAY TO 18 TO 25 MPH SUSTAINED MOST PLACES. THIS WOULD ALLOW FOR
DECENT DRIFTING SNOW. BLIZZARD CONDITIONS LOOK POSSIBLE FOR THE SE
ZONES...SO CONVERTED WINTER STORM WATCH TO BLIZZARD WATCH. LOOKS
LIKE BEST CHANCE OF WARNING AMOUNTS OF SNOWFALL (6 INCHES OR
GREATER) LOOK TO OCCUR NEAR THE CANADIAN BORDER. BUT IT STILL LOOKS
UNCERTAIN AS TO WHAT WILL HAPPEN ELSEWHERE SO WILL LEAVE WATCH GOING
AND LET THE OVERNIGHT SHIFT MAKE THE DETERMINATION ON WHETHER TO GO
WITH WARNINGS/ADVISORIES.
WEDNESDAY NIGHT...THE BLOWING SNOW IS EXPECTED TO CONTINUE OVER THE
SE ZONES (POSSIBLY AS BLIZZARD CONDITIONS). ANY SNOWFALL SHOULD BE
LIGHT AND INSIGNIFICANT. TEMPERATURES WILL BEGIN TO PLUNGE WITH WIND
CHILLS BECOMING A FACTOR. WIND CHILLS DO NOT LOOK TO REACH WARNING
CRITERIA AT THIS TIME THOUGH.
ON THURSDAY...CONDITIONS OVER THE AREA ARE EXPECTED TO DIMINISH AS
AN ARCTIC HIGH PRESSURE CENTERS OVER THE AREA. DESPITE A RETURN TO
SUNSHINE...IT WILL FEEL BITTER WITH TEMPS CLOSE TO ZERO. JAMBA
.LONG TERM...THURSDAY NIGHT THROUGH TUESDAY...
NOT TOO MANY CHANGES IN THE LONG TERM FORECAST BOTH MODELS START
WITH THE UPPER LEVEL LOW MOVING INTO THE CENTRAL PLAINS. AT THE
SAME TIME AN UPPER LEVEL RIDGE BUILDS INTO THE WEST COAST FROM THE
PACIFIC. BOTH MODELS HAVE THE UPPER LOW MOVING FROM THE CENTRAL
PLAINS TO THE MINNESOTA ILLINOIS BORDER WHERE IT STALLS AND
BECOMES STACKED FOR THE WEEKEND DUE TO A BLOCKING RIDGE OVER NOVA
SCOTIA. THERE IS A SLIGHT DIFFERENCE IN HOW THE STACKED LOW
CONTINUES TO EFFECT NEMONT THROUGH THE WEEKEND. IF WE WERE TO
BELIEVE THE GFS THE UPPER LOW WILL BE TO FAR TO THE EAST TO HAVE
ANY IMPACT ON NEMONT OVER THE WEEKEND. THE ECMWF CONTINUES TO SHOW
A SLIGHT CHANCE OF SNOW ON THE BACK SIDE OF THE UPPER LOW THROUGH
SATURDAY.
ALSO BOTH MODELS ARE VERY SLOW TO MOVE OUT THE ARCTIC AIR MASS AND
WITH ALL OF THE NEW SNOW THAT WILL FALL WITH THE NEXT STORM SYSTEM
TEMPERATURES SHOULD REMAIN IN THE SINGLE DIGITS AND TEENS THROUGH
THE WEEKEND. BOTH MODELS ARE KEEPING THE UPPER RIDGE OVER THE
WESTERN US THROUGH MONDAY. THE GFS THEN TRIES TO BRING A SHORTWAVE
THROUGH NORTHERN MONTANA ON TUESDAY. THE ECMWF ON THE OTHER HAND
MAINTAINS THE RIDGE OVER EASTERN MONTANA. SINCE THE ECMWF HAS BEEN
THE BETTER PERFORMING MODEL WILL DISREGARD THE GFS AND LEAVE
FORECAST FOR MONDAY NIGHT THROUGH TUESDAY NIGHT DRY. RSMITH
PREVIOUS DISCUSSION...CONTINUED PREFERENCE FOR THE MORE STABLE
ECMWF MODEL THROUGH THE EXTENDED PERIOD...AS THE GFS CONTINUES TO
OSCILLATE BETWEEN ARCTIC OUTBREAK OR CHINOOK FOR EARLY NEXT WEEK.
DEEP LOW MOVING THROUGH THE CENTRAL PLAINS EARLY IN THE PERIOD
PULLING ARCTIC HIGH INTO MONTANA. CLEARING POSSIBLE THURSDAY NIGHT
WITH TEMPERATURES DROPPING WELL BELOW ZERO ALTHOUGH LOW MAY BE
NEAR ENOUGH TO KEEP CLOUDS OVER AT LEAST THE EASTERN ZONES. RIDGE
BUILDING ALONG THE WEST COAST WILL START TO SEND WARMER AIR ACROSS
THE DIVIDE BUT WITH NORTHERLY FLOW AND ARCTIC HIGH AS WELL AS
FRESH SNOW... WARMING WILL BE SLOW ON FRIDAY.
BLOCKING PATTERN DEVELOPS WITH CENTRAL PLAINS STORM BEING SLOW TO
MOVE THROUGH THE GREAT LAKES. THIS WILL KEEP THE WESTERN RIDGE
OVER THE ROCKIES...WITH NORTHEAST MONTANA IN A GENERALLY COLDER
NORTHERN FLOW. SOME MODERATION OF TEMPERATURES IS EXPECTED WITH A
CHINOOK DEVELOPING OVER SOUTHERN ALBERTA EARLY NEXT WEEK. EBERT
&&
.AVIATION...
LOW CLOUDS WILL PERSIST ACROSS THE REGION THROUGH TODAY WITH MVFR
TO OCCASIONAL IFR CONDITIONS. INTERMITTENT LIGHT SNOW MAY BRIEFLY
REDUCE VISIBILITIES AS WELL. WIDESPREAD SNOW WILL RETURN TO THE
REGION TONIGHT AND WEDNESDAY...WITH SEVERAL INCHES ACCUMULATION.
DRIFTING AND BLOWING SNOW WILL BE A PROBLEM AT ALL TERMINALS. RAE/RSMITH
&&
.GLASGOW WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WATCH FROM WEDNESDAY MORNING THROUGH WEDNESDAY
AFTERNOON FOR CENTRAL AND SOUTHEAST PHILLIPS-CENTRAL AND
SOUTHERN VALLEY-PETROLEUM-GARFIELD-NORTHERN PHILLIPS-SOUTHWEST
PHILLIPS-NORTHERN VALLEY.
BLIZZARD WATCH FROM WEDNESDAY MORNING THROUGH LATE WEDNESDAY
NIGHT FOR MCCONE-DAWSON-PRAIRIE-WIBAUX.
WINTER STORM WATCH FROM WEDNESDAY MORNING THROUGH LATE WEDNESDAY
NIGHT FOR DANIELS-SHERIDAN-WESTERN ROOSEVELT-RICHLAND-EASTERN
ROOSEVELT.
&&
$$
WEATHER.GOV/GLASGOW
