FXUS65 KGGW 221716
AFDGGW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GLASGOW MT
1016 AM MST TUE DEC 22 2009
.SHORT TERM...FOR NORTHEAST MONTANA...TODAY THROUGH THURSDAY...
MAIN CHALLENGES TODAY ARE POPS AND FOG.
CAMERAS ARE SHOWING DENSE FOG OVER THE SW ZONES. A DENSE FOG
ADVISORY HAS BEEN ISSUED UNTIL THIS AFTERNOON AS A TIGHT INVERSION
IS IN PLACE. MANY OF THESE PLACES HAVE HAD A SUDDEN DROP IN
VISIBILITIES. IT/S UNCERTAIN AT THIS TIME ON WHERE AND WHEN THIS
WILL BE DISSIPATING BUT WILL HOPEFULLY HAVE A BETTER IDEA WITH
STATEMENT ISSUANCE.
SNOW SHOWERS ARE POSSIBLE TODAY AS AN UPPER DISTURANCE RIPPLES NE
INTO THE CWA. GFS SHOWING 0.50 TOTAL QPF...A BIT OF CONVECTIVE
FEEDBACK MAYBE. THIS WAS MOSTLY DISREGARDED. TRIMMED POPS INTO THE
EVE HOURS FOR THE SE ZONES AS SNOW DOESN/T LOOK TO ARRIVE TILL LATE
TONIGHT OR WEDNESDAY. REST OF FORECAST LOOKED GOOD. JAMBA
PREVIOUS DISCUSSION...
GOES WATER VAPOR CHANNEL REVEALS A POTENT UPPER TROUGH DIGGING
SOUTH AND SLOWLY EAST OVER THE WEST COAST EARLY THIS MORNING AS A
NARROW HIGH AMPLITUDE RIDGE BUILD OVER THE EAST PACIFIC.
MEANWHILE...THE BUILDING UPPER RIDGE IS TRIGGERING A VIGOROUS COLD
UPPER LOW TO MOVE SOUTH-SOUTHEAST OVER NORTHERN BRITISH COLUMBIA.
THE SURFACE AIRMASS ASSOCIATED WITH THIS TROUGH IS ARCTIC. AS OF
09Z THE OBSERVATION AT WATSON LAKE YUKON TERRITORY...IMMEDIATELY
ACROSS THE BORDER FROM BRITISH COLUMBIA...IS REPORTING A
TEMPERATURE OF -33F AND A MEAN SEA LEVEL PRESSURE OF 1035MB.
OVERALL SEVERAL LOCATIONS ARE IN THE -20S AND -30S IN THIS
AIRMASS.
THE UPPER TROUGH WILL CONTINUE TO SLOWLY MOVE EAST TODAY WITH THE
COLD UPPER LOW CONTINUING ITS SOUTHERLY TRACK ALONG THE SPINE OF
THE CANADIAN ROCKIES. THE OLD STATIONARY FRONTAL BOUNDARY WILL
REMAIN OVER NORTHEAST MONTANA...BUT GRADUALLY BECOME MORE DIFFUSE
THROUGH THE DAY. LIGHT SNOW WILL BE POSSIBLE...ESPECIALLY ACROSS
THE NORTH. DENSE FOG HAS STAYED OUT OF THE LOCAL AREA OVERNIGHT AND
WILL LIKELY NOT BE AN ISSUE FOR THE FAR SOUTHERN ZONES.
A ROBUST AREA OF VERTICAL ASCENT ARRIVES LATE TONIGHT WITH STRONG
VORTICITY ADVECTION AHEAD OF THE NORTHERN WAVE. AN UPPER JET
STREAK ALSO STRENGTHENS AHEAD OF THIS APPROACHING WAVE FURTHER
ENHANCING VERTICAL MOTION. MEANWHILE...THE SOUTHERN WAVE WILL
CONTINUE TO ADVECT UPPER LEVEL PACIFIC MOISTURE NORTHWARD. THESE
INGREDIENTS SHOULD COMBINE TO PRODUCE EFFICIENT SNOW GROWTH ACROSS
NORTHEAST MONTANA FROM LATE TONIGHT THROUGH WEDNESDAY
EVENING...ESPECIALLY WITH THE AID OF SURFACE CONVERGENCE WITH AN
INVERTED TROUGH ACROSS THE AREA. SNOW AMOUNTS HAVE THE POTENTIAL
TO REACH SIX INCHES SO A WINTER STORM WATCH WILL BE ISSUED FOR THE
ENTIRE CWA. COLD ADVECTION BEGINS WEDNESDAY AFTERNOON AS THE
AFOREMENTIONED COLD AIRMASS PLOWS INTO THE REGION. THIS SHOULD
CREATE ENOUGH WIND TO CREATE DRIFTING...WITH REDUCED VISIBILITY IN
BLOWING SNOW ALSO POSSIBLE.
TEMPERATURES ARE LIKELY TO FALL WELL BELOW ZERO WEDNESDAY NIGHT
AND STRUGGLE TO RISE ABOVE ZERO IN THE NORTH THURSDAY AS THE
SURFACE HIGH SETTLES OVER THE AREA. WIND CHILL VALUES ARE LIKELY
TO REACH ADVISORY CRITERIA WEDNESDAY NIGHT AND THURSDAY MORNING. A
FEW AREAS ACROSS THE NORTH COULD APPROACH WARNING VALUES DEPENDING
ON HOW MUCH THE AIRMASS MODIFIES AS IT MOVES SOUTH...WHICH MAY BE
VERY LITTLE GIVEN EXTENSIVE SNOW COVER. WIND CHILL HIGHLIGHTS WILL
NOT BE ISSUED AT THIS TIME AS SUBSEQUENT SHIFTS WILL BE ABLE TO
REFINE HOW COLD THEY WILL ACTUALLY BECOME. AJZ
.LONG TERM...THURSDAY NIGHT THROUGH TUESDAY...
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 THIS EVENING THROUGH WEDNESDAY AFTERNOON
FOR CENTRAL AND SOUTHEAST PHILLIPS-CENTRAL AND SOUTHERN VALLEY-
PETROLEUM-GARFIELD-NORTHERN PHILLIPS-SOUTHWEST PHILLIPS-NORTHERN
VALLEY.
DENSE FOG ADVISORY UNTIL 3 PM MST THIS AFTERNOON FOR CENTRAL AND
SOUTHEAST PHILLIPS-PETROLEUM-GARFIELD-SOUTHWEST PHILLIPS.
WINTER STORM WATCH FROM LATE TONIGHT THROUGH WEDNESDAY EVENING
FOR DANIELS-SHERIDAN-WESTERN ROOSEVELT-MCCONE-RICHLAND-DAWSON-
PRAIRIE-WIBAUX-EASTERN ROOSEVELT.
&&
$$
WEATHER.GOV/GLASGOW
