FXUS65 KGGW 262155
AFDGGW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GLASGOW MT
255 PM MST SAT DEC 26 2009

.SHORT TERM...FOR NORTHEAST MONTANA...TONIGHT THROUGH MONDAY...
NORTHERN PLAINS STORM SYSTEM PULLING TO THE EAST WITH JUST EDGE OF
THE CLOUDS AND STRONG WINDS LINGERING IN FAR EASTERN MONTANA. WITH
THE GUSTY WINDS AND FRESH SNOW...BLOWING AND DRIFTING SNOW STILL A
BIT OF AN ISSUE FROM THE YELLOWSTONE VALLEY EASTWARD...ALTHOUGH
TRAVEL RESTRICTIONS HAVE BEEN LIFTED IN MONTANA. WILL CONTINUE TO
ADVISORY/WARNING TO ALLOW A FEW MORE HOURS FOR THE WIND TO DIMINISH.

HIGH PRESSURE CONTINUES TO SLIDE INTO EASTERN MONTANA BEHIND THE
DEPARTING STORM...WITH CLEAR SKIES AND GENERALLY LIGHT WINDS. COLD
AIR REMAINS TRAPPED IN THE MILK/MISSOURI VALLEY UNDER SHALLOW
INVERSION WHILE THE RIDGE TOPS HAVE WARMED...AND EXPECT THIS
PATTERN TO CONTINUE OVER THE NEXT FEW DAYS EVEN AS A WARM UPPER
HIGH FOLDS OVER FROM ALBERTA INTO MONTANA. EBERT

.LONG TERM...MONDAY NIGHT THROUGH SATURDAY...
A WEAK CLIPPER SYSTEM PASSES TO THE NORTHEAST OF THE LOCAL AREA
TUESDAY NIGHT WITH LITTLE IMPACT OTHER THAN A RE-ENFORCING SHOT OF
SHALLOW MODIFIED ARCTIC AIR. A MORE SUBSTANTIAL COLD FRONT DROPS
SOUTH THROUGH NORTHEAST MONTANA WEDNESDAY NIGHT AND THURSDAY
BRINGING A PUSH OF ARCTIC AIR...ALTHOUGH THE VERY FRIGID DEEP
ARCTIC AIR REMAINS LOCKED OVER HUDSON BAY AND THE ARCTIC OCEAN.
MOISTURE IS VERY LIMITED...BUT IT APPEARS THERE IS ENOUGH VERTICAL
ASCENT TO GENERATE SOME LIGHT SNOW. UNCERTAINTY INCREASES AFTER
THIS POINT AS OPERATIONAL GFS AND ECMWF DIVERGE. THE 12Z GFS
PUSHES THE COLD AIR EAST ALLOWING COOL PACIFIC AIR TO SPILL OVER
THE CONTINENTAL DIVIDE...WHILE THE 12Z ECMWF BANKS THE COLD AIR
AGAINST THE ROCKIES AND GENERATES WIDESPREAD UPSLOPE SNOW LATE IN
THE WEEK AND NEXT WEEKEND AS A VIGOROUS SHORTWAVE MOVES SOUTHEAST
ALONG THE CONTINENTAL DIVIDE. ENSEMBLE MEAN DATA FROM GEFS AND
NAEFS SUGGESTS THESE TWO OPERATIONAL SOLUTIONS ARE AT THE OPPOSITE
ENDS OF THE SPECTRUM OF POSSIBILITIES...SO AN ENSEMBLE MEAN
SOLUTION IS FAVORED. THE OVERALL EXTENDED FORECAST IS IN GOOD
SHAPE WITH ONLY A FEW TWEAKS. AJZ

PREVIOUS LONG TERM DISCUSSION...
WEAK UPPER RIDGING OVER THE REGION WILL BE INTERRUPTED BY A
CLIPPER/SHORT WAVE EJECTING OUT OF THE SOUTHERN CANADIAN ROCKIES
TUESDAY. THE MODELS DISAGREE WITH ITS TRACK BUT THE MAIN EFFECTS
APPEAR TO BE SENDING A WEAK COLD FRONT ACROSS THE ZONES AND
CHANGING SOUTHWESTERLY WINDS TO THE NORTHWEST. NOT ENOUGH
MOISTURE TO CAUSE ANY PRECIPITATION BUT TEMPERATURES WILL BE
KNOCKED DOWN A BIT AND DO NOT RECOVER MUCH FOR MOST OF THE
EXTENDED PERIOD.

THE UPPER TROUGH FURTHER DEVELOPS BEHIND THE SHORTWAVE WEDNESDAY.
A SHARPER COLD FRONT/BOUNDARY WILL DRAPE ACROSS THE CWA WITH MUCH
COLDER AIR TO THE NORTH. LITTLE QPF IS AVAILABLE BUT LIMITED
OVERRUNNING MOISTURE COULD GENERATE LIGHT SNOW ALONG THE COLD
BOUNDARY WEDNESDAY THROUGH THURSDAY. IF ANY SNOW DEVELOPS...IT
WILL LIKELY BE OVER OUR SW ZONES WHILE A STRONG SURFACE HIGH KEEPS
OUR NE DRY. BEEFED POPS UP A BIT WEDNESDAY NIGHT AND THURSDAY.

THURSDAY NIGHT MODELS DEVELOP ANOTHER UPPER RIDGE OVER THE
WEST WHICH WILL MAINTAIN A NORTHERLY FLOW ALOFT AND CONTINUED
COLD...BUT DRY...CONDITIONS. HOWEVER THE RIDGE IS FLATTENED BY THE
NEXT SHORTWAVE TREKKING EAST ACROSS THE PACNW...REACHING NE MT
FRIDAY NIGHT WITH A LITTLE MORE QPF IN TOW FOR THE POSSIBILITY OF
SNOW. SCT

&&

.AVIATION...
THE SURFACE PRESSURE GRADIENT WILL CONTINUE TO CARRY A NORTHWEST
WIND OF 15-20KT THROUGH THE EVENING AT KSDY AND KGDV. THIS WIND
WILL CONTINUE TO PRODUCE DRIFTING SNOW AND OCCASIONAL REDUCED
VISIBILITY IN STRONGER GUSTS. AN AREA OF LOW CLOUDS AND FOG
FORMED OVER NORTH CENTRAL MONTANA LAST NIGHT ON THE BACK SIDE OF A
SURFACE HIGH CENTERED ROUGHLY OVER KGGW. THIS AREA HAS NOT
COMPLETELY DISSIPATED THROUGH THE DAY AND IT SHOULD EXPAND
OVERNIGHT AND COULD CREEP NEAR KGGW AS THE SURFACE HIGH DRIFTS
EAST. OTHERWISE...VFR CONDITIONS SHOULD PREVAIL UNDER A CLEAR SKY
WITH A LIGHT WIND. AJZ

&&

.CLIMATE...
THROUGH CHRISTMAS DAY...THE TEMPERATURE AT GLASGOW FOR DECEMBER
2009 HAS AVERAGED 4.5 DEGREES. THIS IS 12 DEGREES BELOW NORMAL AND
RANKS AS THE SEVENTH COLDEST FIRST 25 DAYS OF DECEMBER ON RECORD.
AJZ

&&

.GLASGOW WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY UNTIL 5 PM MST THIS AFTERNOON FOR 
RICHLAND-DAWSON-PRAIRIE-EASTERN ROOSEVELT.

WINTER STORM WARNING UNTIL 5 PM MST THIS AFTERNOON FOR WIBAUX.

&&

$$

WEATHER.GOV/GLASGOW