FXUS65 KGGW 220355
AFDGGW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GLASGOW MT
855 PM MST MON DEC 21 2009
.SHORT TERM...FOR NORTHEAST MONTANA...TONIGHT THROUGH WEDNESDAY...
A FEW WIDELY SCATTERED VERY LIGHT SNOW SHOWERS PERSIST AROUND THE
AREA WITH POSSIBLY A LITTLE FREEZING DRIZZLE IN SOUTHERN GARFIELD
COUNTY.
ARE WATCHING CLOSELY FOR POTENTIAL FOG FORMATION. THE COOL AND
MOIST BOUNDARY LAYER GIVES SOME POTENTIAL FOR
FOG...HOWEVER...SURFACE WIND AND CLOUD COVER ARE SO FAR PREVENTING
ITS FORMATION. WITH LOW AND MID LEVEL CLOUDY CONDITIONS EXPECTED
TO PREVAIL OVERNIGHT...FOG MAY NOT DEVELOP.
TUESDAY LOOKS LIKE MOSTLY A PAUSE IN THE WINTER
WEATHER AHEAD OF THE NEXT UPPER LEVEL STORM SYSTEM PROGGED TO MOVE
DOWN FROM ALBERTA ON WEDNESDAY...HOWEVER...A FEW SHOWERS ARE STILL
POSSIBLE AND 850 MB TEMPERATURES ARE FORECAST BY THE NAM TO BE
AROUND FREEZING IN THE SOUTHERN HALF OF THE CWA FOR MOST OF
TUESDAY...LEADING TO THE POSSIBILITY OF FREEZING PRECIPITATION
SHOULD ANY SHOWERS DEVELOP IN THAT AREA.
NEXT SIGNIFICANT ROUND OF SNOW STILL LOOKS TO BEGIN
WEDNESDAY MORNING AND LAST THROUGH EARLY THURSDAY MORNING. WITH
MUCH COOLER TEMPERATURES...THIS EVENT SHOULD BE ALL SNOW. 0Z NAM
HAS AROUND .26 INCHES LIQUID EQUIVALENT WITH THIS STORM...THE 18Z
GFS HAS AROUND .20 INCHES...AND THE TYPICALLY PPT HEAVY 12Z EC HAS
AROUND .42. THE EC ALSO HAS THE FRONT ASSOCIATED WITH THE SYSTEM
MOVING THROUGH EARLY THAN THE US MODELS...SUGGESTING SOME
UNCERTAINTY IN THE TIMING.
COLD PUSH BEHIND WEDNESDAYS FRONT AND SNOW GIVES RAPIDLY DECLINING
TEMPERATURES WEDNESDAY NIGHT. MARTIN
PREVIOUS DISCUSSION...
SNOW TAPERING OFF THIS AFTERNOON FROM NW TO SE AS UPPER
DISTURBANCE MOVES DOWN THE FRONT OF A BROAD UPPER TROUGH. SNOW
AMOUNTS HAVE REACHED 4 TO 5 INCHES IN THE SOUTHERN ZONES WITH THE
LATEST SYSTEM WITH AN LSR TO BE ISSUED AFTER ALL REPORTS ARE
COMPILED (BY EARLY THIS EVENING).
A SURFACE LOW OVER THE PACIFIC NW HAS A LEADING STATIONARY FRONT
EXTENDING THROUGH SE MONTANA. THE ATTENTION WILL THEN BE ON AN
ARCTIC FRONT THAT DROPS INTO CENTRAL AND EASTERN MONTANA TUESDAY
NIGHT AND WEDNESDAY. THIS FRONT WILL PROVIDE AN IMPETUS FOR
SNOWFALL AS IT WORKS WITH AN INVERTED TROUGH. SEVERAL INCHES OF
SNOWFALL LOOK LIKELY OVER THE WESTERN AND CENTRAL ZONES. SOME WIND
BEHIND THE ARCTIC FRONT COULD BRING BLOWING SNOW WEDNESDAY
AFTERNOON TO THE WESTERN ZONES...BUT DRIFTING LOOKS MORE LIKELY.
SOMETIMES THOUGH MODELS ARE A BIT WEAK WITH WINDS IN A CASE LIKE
THIS...SO WENT ON THE HIGH SIDE. JAMBA
.LONG TERM...WEDNESDAY NIGHT THROUGH MONDAY...
MODELS DURING THE EXTENDED PERIOD BEGINNING ON WEDNESDAY NIGHT
SHOW QUITE A BIT AF VARIANCE BETWEEN THE GFS AND THE EC. ACCORDING
TO SUGGESTIONS FROM THE ENSEMBLES...THE EC APPEARS TO BE THE
BETTER CHOICE. THE EC CONTINUES TO SHOW THE DEVELOPING STORM IN
MIDDLE PLAINS MAINTAINING ITS INTENSITY AND CONTINUING TO SHOW A
STRONG INVERTED TROUGH NORTH INTO THE EASTERN ZONES SO RAISED POPS
TO LIKELY IN THE EXTREME SOUTHEAST ZONES.
HIGH PRESSURE SLIDES INTO THE AREA BY FRIDAY. SAW NO REASON TO
INTRODUCE ANY POPS DURING THE REST OF THE EXTENDED AS THE UPPER
RIDGE REMAINS QUITE STRONG. THE ONLY CONCERN REMAINS IN A
NORTHWEST FLOW AS MOST OF THE TROUGHS DIVE SOUTHEAST IN NORTH DAKOTA.
ONLY SOME CLOUD COVER WAS LEFT IN TO RESEMBLE THOSE. WILL HAVE TO
WATCH ON SUNDAY AND TUESDAY TO SEE IF THOSE SHORTWAVES TRACK CLOSE
ENOUGH TO INTRODUCE SOME POPS INTO THE NORTHEAST ZONES. BUT
OTHERWISE A DRY FORECAST IN FOR THIS WEEKEND AND INTO MON AND
TUES. SHALLENBERGER
PREVIOUS LONG TERM DISCUSSION...REASONABLE MODEL CONSISTENCY
DEVELOPING FOR THE LATTER PART OF THE WEEK...WITH POOR MODEL
CONTINUITY CONTINUING FOR THE BEGINNING OF NEXT WEEK. SPLIT TROF
MOVING OUT OF THE MOUNTAINS ON WEDNESDAY WITH A SIGNIFICANT WINTER
STORM EXPECTED FOR THE CENTRAL PLAINS. INVERTED TROF AND MOISTURE
WILL EXTEND NORTHWARD FROM THIS STORM WILL BE MOVING EAST INTO THE
DAKOTAS BY WEDNESDAY NIGHT...WITH DRIER AND COLDER HIGH PRESSURE
PUSHING INTO NORTH CENTRAL MONTANA. THIS HIGH WILL SLIDE ACROSS
EASTERN MONTANA ON THURSDAY.
PATTERN FOR THE HOLIDAY WEEKEND CONSIST OF UPPER RIDGE ALONG THE
WEST COAST AND TROF MOVING THROUGH THE GREAT LAKES. THIS WILL PUT
THE NORTHERN PLAINS IN NORTHWEST FLOW AND COULD RESULT IN EITHER
DOWNSLOPE WARMING WITH A DOMINATE RIDGE PER THE ECMWF/6Z GFS...OR
A STRONG ARCTIC FRONT PER THE 0Z GFS. SIDED WITH THE SLIGHTLY MORE
CONSISTENT ECMWF ALTHOUGH WITH FRESH SNOW A COLDER SOLUTION CAN BE
EXPECTED PARTICULARLY IN THE NORTHEAST. EBERT
&&
.AVIATION...
A PROLONGED PERIOD OF REDUCED FLIGHT CONDITIONS WILL CONTINUE AT
THE TAF SITES. MVFR CEILING...WITH A FEW BREAKS TO VFR WILL
PREVAIL AT THE TERMINALS THROUGH 06Z BEFORE THE CEILING DROPS TO
IFR AND LIFR BY MORNING. VISIBILITY WILL FALL TO IFR IN FOG TOWARD
MORNING WITH LIGHT SNOW OR LIGHT FREEZING DRIZZLE POSSIBLE.
STEADY SNOW WILL RETURN BY TUESDAY NIGHT. THE WIND WILL BE
EASTERLY AT 5-10KT. AJZ
&&
.GLASGOW WATCHES/WARNINGS/ADVISORIES...NONE.
&&
$$
WEATHER.GOV/GLASGOW
