FXUS65 KGGW 212135
AFDGGW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GLASGOW MT
235 PM MST MON DEC 21 2009

.SHORT TERM...FOR NORTHEAST MONTANA...TONIGHT THROUGH WEDNESDAY...
SNOW TAPERING OFF THIS AFTERNOON FROM NW TO SE AS UPPER DISTURBANCE 
MOVES DOWN THE FRONT OF A BROAD UPPER TROUGH. SNOW AMOUNTS HAVE  
REACHED 4 TO 5 INCHES IN THE SOUTHERN ZONES WITH THE LATEST SYSTEM 
WITH AN LSR TO BE ISSUED AFTER ALL REPORTS ARE COMPILED (BY EARLY 
THIS EVENING).

A SURFACE LOW OVER THE PACIFIC NW HAS A LEADING STATIONARY FRONT 
EXTENDING THROUGH SE MONTANA. THE ATTENTION WILL THEN BE ON AN 
ARCTIC FRONT THAT DROPS INTO CENTRAL AND EASTERN MONTANA TUESDAY 
NIGHT AND WEDNESDAY. THIS FRONT WILL BE PROVIDE AN IMPETUS FOR 
SNOWFALL AS IT WORKS WITH AN INVERTED TROUGH. SEVERAL INCHES OF 
SNOWFALL LOOK LIKELY OVER THE WESTERN AND CENTRAL ZONES. SOME WIND 
BEHIND THE ARCTIC FRONT COULD BRING BLOWING SNOW WEDNESDAY AFTERNOON 
TO THE WESTERN ZONES...BUT DRIFTING LOOKS MORE LIKELY. SOMETIMES 
THOUGH MODELS ARE A BIT WEAK WITH WINDS IN A CASE LIKE THIS...SO 
WENT ON THE HIGH SIDE. JAMBA

.LONG TERM...WEDNESDAY NIGHT THROUGH MONDAY...
MODELS DURING THE EXTENDED PERIOD BEGINNING ON WEDNESDAY NIGHT
SHOW QUITE A BIT AF VARIANCE BETWEEN THE GFS AND THE EC. ACCORDING
TO SUGGESTIONS FROM THE ENSEMBLES...THE EC APPEARS TO BE THE BETTER
CHOICE. THE EC CONTINUES TO SHOW THE DEVELOPING STORM IN MIDDLE
PLAINS MAINTAINING ITS INTENSITY AND CONTINUING TO SHOW A STRONG
INVERTED TROUGH NORTH INTO THE EASTERN ZONES SO RAISED POPS TO
LIKELY IN THE EXTREME SOUTHEAST ZONES.

HIGH PRESSURE SLIDES INTO THE AREA BY FRIDAY. SAW NO REASON TO
INTRODUCE ANY POPS DURING THE REST OF THE EXTENDED AS THE UPPER
RIDGE REMAINS QUITE STRONG. THE ONLY CONCERN REMAINS IN A
NORTHWEST FLOW AS MOST OF THE TROUGHS DIVE SOUTHEAST IN NORTH DAKOTA.
ONLY SOME CLOUD COVER WAS LEFT IN TO RESEMBLE THOSE. WILL HAVE TO
WATCH ON SUNDAY AND TUESDAY TO SEE IF THOSE SHORTWAVES TRACK CLOSE
ENOUGH TO INTRODUCE SOME POPS INTO THE NORTHEAST ZONES. BUT
OTHERWISE A DRY FORECAST IN FOR THIS WEEKEND AND INTO MON AND
TUES. SHALLENBERGER

PREVIOUS LONG TERM DISCUSSION...REASONABLE MODEL CONSISTENCY
DEVELOPING FOR THE LATTER PART OF THE WEEK...WITH POOR MODEL
CONTINUITY CONTINUING FOR THE BEGINNING OF NEXT WEEK. SPLIT TROF
MOVING OUT OF THE MOUNTAINS ON WEDNESDAY WITH A SIGNIFICANT WINTER
STORM EXPECTED FOR THE CENTRAL PLAINS. INVERTED TROF AND MOISTURE
WILL EXTEND NORTHWARD FROM THIS STORM WILL BE MOVING EAST INTO THE
DAKOTAS BY WEDNESDAY NIGHT...WITH DRIER AND COLDER HIGH PRESSURE
PUSHING INTO NORTH CENTRAL MONTANA. THIS HIGH WILL SLIDE ACROSS
EASTERN MONTANA ON THURSDAY.

PATTERN FOR THE HOLIDAY WEEKEND CONSIST OF UPPER RIDGE ALONG THE
WEST COAST AND TROF MOVING THROUGH THE GREAT LAKES. THIS WILL PUT
THE NORTHERN PLAINS IN NORTHWEST FLOW AND COULD RESULT IN EITHER
DOWNSLOPE WARMING WITH A DOMINATE RIDGE PER THE ECMWF/6Z GFS...OR
A STRONG ARCTIC FRONT PER THE 0Z GFS. SIDED WITH THE SLIGHTLY MORE
CONSISTENT ECMWF ALTHOUGH WITH FRESH SNOW A COLDER SOLUTION CAN BE
EXPECTED PARTICULARLY IN THE NORTHEAST. EBERT

&&

.AVIATION...
SNOW IS EXPECTED TO TAPER OFF THIS EVENING AS THE SNOW MOVE OUT OF
THE AREA AND VISIBILITIES WILL IMPROVE ALONG WITH THE LOW CEILINGS. LOW
CEILINGS ARE EXPECTED TO REDEVELOP OVERNIGHT AS THE STATIONARY FRONT
SLOWLY MOVES EAST. MORNING CEILINGS AND LOW VISIBILITIES IN FOG
ACROSS THE TAF SITES WILL VARY BETWEEN IFR AND LIFR CONDITIONS. DJS

&&

.CLIMATE...
THE FIRST 20 DAYS OF DECEMBER IN GLASGOW AVERAGED ONLY 4.8
DEGREES...WHICH IS 12.4 DEGREES BELOW NORMAL. DESPITE BEING
SLIGHTLY WARMER THAN NORMAL THE PAST 4 DAYS...THIS IS STILL THE
COLDEST FIRST 20 DAYS IN DECEMBER SINCE 1983...7TH COLDEST START
EVER. THE -30 DEGREE LOW ON THE 14TH WAS ALSO THE COLDEST IT HAS
BEEN SO EARLY IN THE SEASON SINCE 1977. SIMONSEN

&&

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

&&

$$

WEATHER.GOV/GLASGOW