FXUS65 KGGW 050314
AFDGGW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GLASGOW MT
814 PM MST FRI DEC 4 2009
.SHORT TERM...FOR NORTHEAST MONTANA...TONIGHT THROUGH SUNDAY...
UPDATED THE SHORT TERM FORECAST TO LOWER THE OVERNIGHT TEMPERATURES
A FEW DEGREE IN THE NORTHEAST ZONES. TEMPERATURES WERE ONLY A
DEGREE OR TWO FROM REACHING THE FORECAST LOWS. CLOUD COVER IS MOVING IN
FROM THE WEST BUT THERE IS STILL ENOUGH CLEARING WEST OF THE CLOUD
COVER...WHICH WILL MOVE ACROSS THE NORTHEAST ZONES LATE TONIGHT AND ALLOW
THE TEMPERATURES TO DROP BETWEEN 3 TO 5 DEGREES BELOW ZERO. REST OF
THE SHORT TERM FORECAST LOOKS TO BE ON TRACK...WITH THE UP COMING
WINTER STORM LOOKING LIKE IT WILL IMPACT THE MOUNTAINS OF WESTERN AND
CENTRAL MONTANA THE HARDEST. WESTERN ZONE OF THE CWA IN NORTHEAST
MONTANA STILL LOOKS LIKE THEY COULD PICK UP 3 TO 5 INCHES OF
SNOWFALL. RSMITH
A WINTER WEATHER ADVISORY IS IN EFFECT FOR PETROLEUM AND PHILLIPS
COUNTY FROM 09Z SATURDAY THROUGH 12Z SUNDAY AND GARFIELD COUNTY
FROM 18Z SATURDAY THROUGH 12Z SUNDAY. CONTINUE READING FOR
FURTHER DETAILS.
TONIGHT THROUGH EARLY SATURDAY NIGHT... A LOW TO MID LEVEL LEE SIDE
TROUGH IS EXPECTED TO EJECT OFF THE FRONT RANGE AND PASS OVER THE
REGION TONIGHT THIS WILL PROVIDE A FOCAL POINT FOR EARLY LIMITED
SNOWFALL ACROSS THE CWA OF LESS THAN A HALF INCH. BY SATURDAY
MORNING SYNOPTIC SCALE LOW PRESSURE FORMING OFF OF THE FRONT RANGE
ACROSS NORTHERN CENTRAL MONTANA AND SOUTHERN ALBERTA WILL BEGIN
SLIDING SOUTHEAST INTO SOUTHERN MONTANA AND NORTHERN WYOMING WHERE
IT SHOULD ELONGATE AND STALL BY SATURDAY EVENING. THIS FEATURE
WILL PROVIDE LIFT TO LIMITED MOISTURE AT THE MID LEVELS STREAMING
IN FROM SOUTHERN IDAHO AND GENERATE A SWATH OF PRECIPITATION
ACROSS CENTRAL AND WESTERN MONTANA. WHILE THE BULK OF THIS SYSTEMS
SNOW WILL CONCENTRATE ACROSS WESTERN AND CENTRAL MONTANA ENOUGH
PRECIPITATION OVER THE COARSE OF THE SYSTEM LIFETIME SHOULD CLIP
WESTERN PORTIONS OF THE CWA TO GENERATE 2 TO 5 INCHES OF SNOWFALL.
AREAS OF FOCUS WITH THIS SYSTEM WILL BE ENHANCED BY SLIGHT UP SLOPE
FLOW POINT TOWARDS THE HIGHER SNOWFALL TOTALS IN WESTERN
PETROLEUM... THE LITTLE ROCKIES... AND THE SNOWBELTS OF WESTERN
GARFIELD COUNTY. AREAS LONG THE EASTERN AND ESPECIALLY
NORTHEASTERN PORTIONS OF THE CWA WILL SEE SIGNIFICANTLY LESS
SNOWFALL WITH THIS SYSTEM WITH POSSIBLY ONLY A TRACE OF FLURRIES.
EARLY SUNDAY MORNING ONWARD... COLD ARCTIC AIR AND HIGH PRESSURE IS
ANTICIPATED TO FILTER INTO THE BULK OF THE REGION WITH CALMING
WINDS AND 850 MB TEMPERATURES IN THE UPPER NEGATIVE TEENS.
REMNANTS OF THE EXITING SYSTEM MAY STILL BE ABLE TO PRODUCE A
TRACE OF SNOWFALL AND FLURRIES ACROSS THE SOUTH. GAH
.LONG TERM...SUNDAY NIGHT THROUGH FRIDAY...
SOME TWEAKING OF THE FORECAST...MAINLY TO LOWER TEMPERATURES
SLIGHTLY AS UPCOMING WEEK LOOKS TO BE VERY COLD. STORM SYSTEM TO
AFFECT THE REGION OVER THE WEEKEND WILL BE MOVING OUT BY SUNDAY
NIGHT BUT COULD SEE SOME LINGERING LIGHT SNOW. REMAINDER OF THE
PERIOD LOOKS MOSTLY DRY BUT A SECOND SURGE OF ARCTIC WILL PUSH
INTO THE REGION TUESDAY NIGHT/WEDNESDAY. TEMPERATURES ALOFT
MODERATE TOWARD THE END OF THE WEEK AS UPPER FLOW TURNS WESTERLY
BUT NO STRONG KICKER TO MIX OUT THE ARCTIC AIRMASS SO EXPECT A
POTENTIALLY SLOW TEMPERATURE RECOVERY. EBERT
PREVIOUS LONG TERM DISCUSSION...THE EXTENDED FORECAST STARTS WITH
A OMEGA BLOCK PATTERN AS A RIDGE OF HIGH PRESSURE EXTENDS
NORTHWARD INTO CENTRAL ALASKA. A POLAR VORTEX ALONG WITH SIBERIAN
AIR IS SITTING ON TOP OF THE POLE IS PROGGED TO MOVE SOUTH INTO
NORTHERN CANADA AND HANG OUT FOR FEW DAYS OVER THE NUNAVUT
REGION...WHICH COULD MAKE THINGS VERY INTERESTING AND REALLY COLD
NEXT WEEKEND.
BOTH THE GFS AND THE ECMWF ARE IN AGREEMENT WITH THE OMEGA BLOCK PATTERN
TO START OUT THE EXTENDED PERIOD. WITH THE UPPER TROF LOCATED OVER
THE SIERRA MOUNTAINS IN CALIFORNIA...THE COLD CONDITIONS WILL CONTINUE
OVER EASTERN MONTANA AS 850 MB TEMPERATURES REMAIN BETWEEN -18 AND
-22 DEGREES CELSIUS THROUGH TUESDAY...WITH THICKNESS VALUES BELOW 510
DM.
BY WEDNESDAY THE POLAR VORTEX THAT SETTLED OVER NUNAVUT WILL
TRIGGER THE UPPER TROF OVER THE SIERRA MOUNTAINS TO MOVE EASTWARD
RAPIDLY. THIS WILL FORCE THE UPPER RIDGE WHICH HAD THE OMEGA SHAPE
TO BECOME A MORE CLASSIC LOOKING LONGWAVE RIDGE. THIS WILL TRIGGER
THE POLAR VORTEX AND SIBERIAN AIR TO ROTATE WESTWARD AND BEGIN A
SOUTHWARD JOURNEY ON THURSDAY WHICH ACCORDING TO THE MODELS BRINGS
IT VERY CLOSE TO EASTERN MONTANA BY THE WEEKEND. THE ECMWF SEEMS
TO BE MORE AGGRESSIVE WITH THE LATE WEEK ARCTIC AIR ALTHOUGH THE
GFS IS STARTING TO COME AROUND A LITTLE. THE GFS STILL DOES NOT
BRING THE BRUNT OF THE ARCTIC AIR AS CLOSE TO THE REGION AS THE
ECMWF DOES HOWEVER. KEPT THINGS DRY PRECIPITATION WISE PAST WEDNESDAY AND
SINCE THIS ARCTIC AIR MASS WILL BE APPROACHING THE REGION BY LATE WEEK
CONTINUED THE TREND OF LOWERING THE OVERNIGHT LOWS AND DAYTIME HIGHS
IN THE EXTENDED. IF THE ECMWF DOES PAN OUT -30 CELSIUS 850 MB
TEMPERATURES WILL GET VERY CLOSE TO NEMONT. RSMITH
&&
.AVIATION...
VFR CONDITIONS WILL DETERIORATE A BIT OVERNIGHT WITH A WINTER
STORM SYSTEM DROPPING INTO CENTRAL MONTANA. MVFR CONDITIONS WITH
LOW CLOUDS AND REDUCED VISIBILITIES FROM LIGHT SNOW MAY AFFECT
KGGW AFTER 6Z TONIGHT. THESE CONDITIONS WILL PERSIST INTO
SATURDAY. RAE/TFJ
&&
.GLASGOW WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY FROM 2 AM SATURDAY TO 5 AM MST SUNDAY
FOR CENTRAL AND SOUTHEAST PHILLIPS-PETROLEUM-NORTHERN PHILLIPS-
SOUTHWEST PHILLIPS.
WINTER WEATHER ADVISORY FROM 11 AM SATURDAY TO 5 AM MST SUNDAY
FOR GARFIELD.
&&
$$
WEATHER.GOV/GLASGOW
