FXUS65 KGGW 231007
AFDGGW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GLASGOW MT
307 AM MST WED DEC 23 2009

.SHORT TERM...FOR NORTHEAST MONTANA...TODAY THROUGH FRIDAY...
WILL ISSUE A WINTER WEATHER ADVISORY TODAY FOR SNOW ALONG WITH
BLOWING SNOW. WILL END ADVISORY AT 5 PM THIS AFTERNOON IN MOST
AREAS AND 11 PM THIS EVENING IN THE EAST. 

COLD FRONT CURRENTLY MOVING THROUGH THE FORECAST AREA WILL EXIT
THE STATE THIS MORNING. MOISTURE MOVING NORTH ON SOUTHERLY FLOW
ALOFT IS OVERRUNNING THE FRONT AND IS BRINGING SNOW TO MUCH OF
NORTHEAST MONTANA AT 09Z WITH THE HEAVIEST SNOW NORTH AND WEST OF
GLASGOW. THE SNOW WILL OVERSPREAD ALL OF NORTHEAST MONTANA THIS
MORNING AND GRADUALLY DIMINISH FROM WEST TO EAST ACROSS THE AREA
THIS AFTERNOON AND EVENING AS THE OVERRUNNING SHIFTS TO THE EAST.
ARCTIC AIRMASS WILL DROP SOUTH INTO MONTANA TODAY BEHIND THE FRONT
FOLLOWED BY AN UPPER LOW TONIGHT. LOOK FOR BELOW ZERO TEMPERATURES
FOR LOWS IN MOST LOCATIONS THE REMAINDER OF THE WEEK.

AT THIS POINT...IT APPEARS TO BE A HIGH END ADVISORY EVENT WITH UP
TO 5 INCHES OF SNOW POSSIBLE AND 15 TO 25 MPH WHICH WILL CREATE
DECENT BLOWING AND DRIFTING SNOW BUT WINDS SPEEDS SHOULD STAY
BELOW BLIZZARD WARNING CRITERIA OF 35 MPH. 

SURFACE HIGH PRESSURE DROPS SOUTH INTO AREA TONIGHT AS THE UPPER
LOW MOVES SOUTH THROUGH EASTERN MONTANA. THE UPPER LOW SHOULD
MAINTAIN CLOUD COVER IN THE EAST WHILE THE WEST SHOULD SEE SOME
CLEARING. THIS WILL ALLOW FOR COLDER TEMPERATURES IN THE WEST
TONIGHT THAN IN THE EAST. WHILE THE WIND WILL GRADUALLY
DIMINISH...WIND CHILLS SHOULD REACH ADVISORY CRITERIA OF -20 THIS
EVENING IN SOME AREAS BEFORE THE WIND DIMINISHES. WILL NOT ISSUE A
SEPARATE WIND CHILL ADVISORY AT THIS TIME FOR TONIGHT. WILL
MENTION WIND CHILLS IN HAZARDOUS WEATHER OUTLOOK FOR NOW. 

UPPER LOW MOVES TO THE SOUTH ON THURSDAY AND COLD HIGH PRESSURE
PREVAILS OVER EASTERN MONTANA THROUGH CHRISTMAS DAY. THE AREA WILL
BE IN NORTHERLY FLOW ALOFT BETWEEN AN UPPER RIDGE TO THE EAST AND
A SLOW MOVING UPPER LOW TO THE EAST. THAT UPPER LOW WILL BECOME A
MAJOR WINTER STORM WHICH WILL BE BRINGING SNOW AS FAR WEST AS THE
DAKOTAS THURSDAY AND FRIDAY OF WHICH THE WESTERN EDGE MAY CLIP FAR
EASTERN MONTANA AT THIS. WILL MENTION A SLIGHT CHANCE OF SNOW FOR
NOW. FORRESTER

.LONG TERM...FRIDAY NIGHT THROUGH WEDNESDAY...
THE EXTENDED PERIOD BEGINS WITH LARGE CYCLONIC WINTER STORM
CHURNING OVER THE EASTERN HALF OF CONUS WHILE AN UPPER LEVEL RIDGE
RAMPS UP OVER WESTERN CONUS AND CANADA. NORTHEAST MONTANA WILL
REMAIN UNDER A NORTHERLY FLOW ALOFT WITH WRAP-AROUND LOW CLOUDS
POSSIBLE AS THE EASTERN STACKED LOW STALLS OVER THE SOUTHERN GREAT
LAKES REGION DURING THE WEEKEND. THE UPPER RIDGE WILL LEAN OVER TO
THE EAST INTO ALBERTA AND SASKATCHEWAN...SLOWLY PUSHING THE
STATIONARY FRONT TO THE EAST. THIS WILL BEGIN TO RETURN
TEMPERATURES TOWARDS NORMAL...ALTHOUGH WITH SNOW ON THE GROUND
THIS WILL BE A SLOW PROCESS. THE UPPER HIGH CLOSES OFF WHEN IT
CENTERS OVER THE NORTHERN ROCKIES SUNDAY. AN UPPER DISTURBANCE
BEGINS TO DEVELOP MONDAY OVER SOUTHERN BC AND WASHINGTON STATE
THAT MODELS HAVE DIFFICULTY WITH AS IT TREKS EAST. THE GFS SENDS A
CLIPPER OVER THE ZONES AROUND TUESDAY NIGHT OR WEDNESDAY WHILE THE
ECMWF KEEPS THE DISTURBANCE TO OUR NORTH. THE ECMWF HAS BEEN THE
MORE STABLE MODEL IN THE LATE PERIODS SO WILL STAY MOSTLY DRY FOR
NOW. THEN THE UPPER RIDGE REBUILDS IN OVER THE WEST IN THE LAST
PERIODS OF THE EXTENDED FORECAST. SCT

&&

.AVIATION...
A WINTER STORM CONTINUING TO MOVE INTO THE AREA WILL PRODUCE MVFR
TO IFR CEILINGS AND VISIBILITIES TODAY. WIDESPREAD SNOW COULD
GENERATE SEVERAL INCHES OF ACCUMULATION. AS STRONG NORTHWEST WINDS
DEVELOP LATER TODAY SNOWFALL WILL DIMINISH BUT DRIFTING AND
BLOWING SNOW COULD DEVELOP...ESPECIALLY AT KGDV AND KSDY. SCT

&&

.GLASGOW WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY UNTIL 5 PM MST THIS AFTERNOON FOR 
CENTRAL AND SOUTHEAST PHILLIPS-CENTRAL AND SOUTHERN VALLEY-
DANIELS-WESTERN ROOSEVELT-PETROLEUM-GARFIELD-MCCONE-NORTHERN 
PHILLIPS-SOUTHWEST PHILLIPS-NORTHERN VALLEY.

WINTER WEATHER ADVISORY UNTIL 11 PM MST THIS EVENING FOR 
SHERIDAN-RICHLAND-DAWSON-PRAIRIE-WIBAUX-EASTERN ROOSEVELT.

&&

$$

WEATHER.GOV/GLASGOW