FXUS65 KGGW 261026
AFDGGW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GLASGOW MT
326 AM MST THU NOV 26 2009
.SHORT TERM...FOR NORTHEAST MONTANA...TODAY THROUGH SATURDAY...
TODAY THROUGH FRIDAY MORNING... A HIGH PRESSURE RIDGE WILL BE IN PLACE
ACROSS MONTANA GENERATING RELATIVELY WARM AND DRY CONDITIONS WITH
LIGHT WINDS. MEANWHILE... A LONG WAVE TROUGH SPANNING FROM THE
COAST OF BRITISH COLUMBIA TO OFF THE COAST OF CENTRAL CALIFORNIA
WILL MOVE ONSHORE IN TRACK OF THE INTERMOUNTAIN WEST AND MONTANA.
FRIDAY AFTERNOON THROUGH SATURDAY... THE LONG WAVE TROUGH IS
ANTICIPATED TO MAKE IT INTO GGW TERRITORY WITH MOISTURE IN THE MID
LEVELS AND A COLD FRONT IMPACTING THE AREA EARLY FRIDAY NIGHT.
1000-500 MB THICKNESS LEVELS ARE ANTICIPATED TO RAPIDLY DROP BELOW
THE 540 DM THRESHOLD AS ARE 850 MB TEMPERATURES ANTICIPATED TO
DROP INTO THE NEGATIVE SINGLE DIGITS. BY SATURDAY MORNING A
SHORTWAVE IS ANTICIPATED TO RIDE IN DIRECTLY BEHIND THE FRONT. IN
AN INGREDIENTS BASED FORECAST THIS WOULD USUALLY GENERATE SOME
STRONG PRECIPITATION FOR THE SNOW TOTALS. HOWEVER... THE DEVIL IS
IN THE DETAILS. FIRST... NEAR THE SURFACE DEWPOINT DEPRESSIONS ARE
ANTICIPATED TO BE RATHER HIGH WITH THE PASSAGE OF THIS EVENT. THIS
WOULD TEND TO UNDERCUT THE OVER ALL QPF GENERATED BY MODELS
SIGNIFICANTLY. THE BEST METHOD FOR GETTING AROUND THIS USUALLY IS
THROUGH WETBULB EFFECTS WITH AIR SLOWLY MOISTENING FROM THE UPPER
LEVELS DOWN IN EVAPORATE COOLING. THE SECOND PROBLEM HERE IS A
TIMING ISSUE... WITH THE LEVEL THAT WOULD BRING UPPER
MOISTURE... 600 TO 750 MB... ENTERING AND EXITING 6 TO 12 HOURS
AHEAD OF THE SHORTWAVE THAT GENERATES THE LIFT FOR THE
PRECIPITATION PROCESS TO BEGIN. THIRD... OTHER SIGNS SUCH AS
DECREASES IN WINDS SPEEDS IN MODEL WIND FIELDS BEHIND THE
SHORTWAVE ALSO POINT TO A RATHER LETHARGIC SHORTWAVE AS WELL WHICH
ALSO DECREASES LIFT CHANCES. THE BEST GUESS IS NO PRECIPITATION
WITH THIS EVENT FOR A LARGE PORTION OF THE CWA. ANY SNOW
ACCUMULATION SHOULD BE LESS THAN A HALF INCH. BY SATURDAY
AFTERNOON A DRY SLOT WITH CLEARING SKIES SHOULD BEGIN POKING ITS
HEAD INTO NORTHWESTERN PORTIONS OF THE CWA ENDING ALL CHANCES OF
PRECIPITATION. GAH
.LONG TERM...SATURDAY NIGHT THROUGH THURSDAY...
EXTENDED PERIOD OPENS WITH UPPER TROF EXITING THE REGION AND UPPER
RIDGE FOLDING OVER THE PACIFIC NORTHWEST INTO THE NORTHERN
ROCKIES. ANY PRECIP THAT OCCURS WITH THE UPPER TROF SHOULD EXITED
THE REGION SATURDAY NIGHT WITH THEN DRY CONDITIONS EXPECTED INTO
MONDAY. TEMPERATURES WILL ALSO BE WARMING AGAIN WITH HIGH PUSHING
INTO THE 40S FOR MONDAY.
NEXT SHORTWAVE TROF DIVES THROUGH SOUTHERN BC MONDAY NIGHT AND
MODELS IN RELATIVELY GOOD AGREEMENT WITH ARRIVAL OF WAVE INTO
MONTANA. STRONG COLD FRONT DROPS THROUGH MONTANA ON TUESDAY WITH
SOME CHANCE OF SNOW. POTENTIAL FOR STRONG WINDS HIGHER THAN FOR
PRECIP WITH TIGHT PRESSURE GRADIENT AND COLD AIR ADVECTION WITH
STACKED LOW PRESSURE CENTER TRACKING THROUGH SOUTHERN
SASKATCHEWAN.
FAIRLY MAJOR MODEL DIFFERENCES DEVELOP FOLLOWING THIS WAVE
ALTHOUGH GOOD AGREEMENT WITH SETTLING ARCTIC AIRMASS OVER THE
NORTHERN PLAINS. MAIN QUESTION IS HOW FAR WEST WILL THIS AIRMASS
PUSH...GFS PULLS THE TROF INTO THE UPPER MIDWEST WITH RIDGE ALONG
THE WEST COAST...WHILE THE ECMWF IS MUCH FURTHER WEST. FOR NOW
STICKING WITH TEMPERATURES NEAR CLIMATOLOGICAL NORMS WITH THE IDEA
OF A MORE EASTWARD LONGWAVE POSITION. EBERT
&&
.AVIATION...
VFR CONDITIONS WILL PREVAIL THROUGH TODAY WITH HIGH CLOUDS
STREAMING ACROSS THE REGION. WINDS WILL REMAIN MAINLY FROM THE
SOUTH TO SOUTHEAST AT 5 TO 10 KTS. RAE
&&
.GLASGOW WATCHES/WARNINGS/ADVISORIES...NONE.
&&
$$
WEATHER.GOV/GLASGOW
