000
FXUS65 KTFX 272341
AFDTFX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
440 PM MST MON DEC 27 2010
UPDATED AVIATION
.DISCUSSION...
TONIGHT THROUGH TUESDAY...A TIGHT SURFACE GRADIENT IS CONTRIBUTING
TO STRONG WINDS ACROSS THE AREA. WIND SPEEDS SHOULD SLOWLY DECREASE
TONIGHT BUT WINDS WILL BECOME GUSTY AGAIN ON TUESDAY. THE DOWNSLOPE
WINDS WILL KEEP THE PLAINS GENERALLY DRY WITH SCATTERED SNOW
CONFINED TO THE WESTERN MOUNTAINS AND THE MOUNTAINS OF SOUTHWEST
MONTANA. TUESDAY WILL SEE INCREASING PRECIPITATION OVER THE WESTERN
MOUNTAINS AS THE FLOW ALOFT INCREASES AHEAD OF AN APPROACHING UPPER
TROF. TEMPERATURES WILL CONTINUE ABOVE SEASONAL AVERAGES TUESDAY.
TUESDAY NIGHT THROUGH THURSDAY...A SIGNIFICANT WINTER STORM IS
EXPECTED TO IMPACT THE REGION THIS PERIOD AS A DEEP UPPER LEVEL
TROUGH DIGS INTO THE WESTERN U.S. WITH SURFACE LOW PRESSURE
TRACKING EAST ACROSS FAR SW PORTIONS OF THE STATE. A MUCH COLDER
CANADIAN AIRMASS WILL PLUNGE SOUTH ACROSS THE CANADIAN BORDER BY
EARLY WEDNESDAY MORNING CONTINUING THROUGH CENTRAL AND SW MT BY
WEDNESDAY AFTERNOON. THIS WILL BRING FALLING TEMPERATURES TO MOST
OF THE FORECAST AREA ON WEDNESDAY WITH SINGLE DIGIT ABOVE AND
BELOW ZERO TEMPS BY WED NIGHT. MOISTURE AHEAD OF THE INCOMING UPPER
LEVEL TROUGH WILL SPREAD SNOW INTO THE FORECAST AREA FROM THE
WEST...REACHING NW ZONES BY DAYBREAK WEDNESDAY...SPREADING
SOUTHWARD BEHIND THE FRONT WEDNESDAY MORNING. GUSTY NORTH WINDS
WILL ALSO DEVELOP BEHIND THE FRONT ON ON WEDNESDAY...CREATING
SIGNIFICANT BLOWING AND DRIFTING OF THE SNOW. SNOW WILL CONTINUE
THROUGH WEDNESDAY NIGHT AS THE UPPER LEVEL SYSTEM CLOSES OFF TO OUR
SOUTH WITH MODELS CONTINUING TO INDICATE MOIST UPSLOPE FLOW
THROUGH EARLY THURSDAY BEFORE SNOW GRADUALLY DIMINISHES FROM WEST
TO EAST. HIGHEST PRECIP AMOUNTS APPEAR TO BE FOCUSED OVER NORTH
CENTRAL MT WITH SOMEWHAT LESSER AMOUNTS IN SOME OF THE SW MT
VALLEYS. SIGNIFICANT SNOW ACCUMULATIONS APPEAR LIKELY OVER MOST OF
THE FORECAST AREA WITH LOWEST CONFIDENCE IN AMOUNTS ON EXCESS OF 6
INCHES IN THE SW MT VALLEYS. WINDS WILL COMBINE WITH MUCH COLDER
TEMPERATURES TO PRODUCE VERY LOW WIND CHILLS BY WEDNESDAY EVENING
AND ADDITIONAL HIGHLIGHTS FOR WIND CHILL HEADLINES MAY BE NEEDED.
HOENISCH
ECMWF CONTINUES TO SUGGEST DECENT CHINOOK WINDS THAT WILL WARM
TEMPERATURES UP QUICKLY BEHIND THE WINTER WEATHER. GFS HOLDS THESE
WIND FURTHER WEST AND HAS A MORE NORTHWESTERLY FLOW SOLUTION FOR
THE WEEKEND. HAVE GONE CLOSER THE ECMWF SOLUTION AGAIN
HERE...HOWEVER EITHER SOLUTION WOULD BRING RELIEF FROM THE
BITTERLY COLD TEMPERATURES FORECASTED THROUGHOUT THE AREA THURSDAY
AND FRIDAY. HAVE CONTINUED TO KEEP TEMPERATURE BELOW MODEL
GUIDANCE ON THURSDAY NIGHT AND FRIDAY MORNING DUE TO THE EXTRA
COOLING EXPECTED WITH FRESH SNOW COVER OVERNIGHT. THE VALLEYS OF
SOUTHWEST MONTANA ARE STILL EXPECTED TO REMAIN COLDER LONGER DUE
TO THE TOPOGRAPHY LIMITING THE EFFECT OF THE CHINOOK WINDS THROUGH
THE SHELTERED VALLEYS. SUK
&&
.AVIATION...
UPDATED 0000Z.
MOUNTAIN OBSCURATION AND SHOWERS ARE STILL POSSIBLE ALONG THE
CONTINENTAL DIVIDE OVERNIGHT AS WEST TO NORTHWEST FLOW PERSISTS
ACROSS THE AREA. MID-HIGH LEVEL CLOUDS WILL ALSO INCREASE THROUGH
THE PERIOD AHEAD OF OUR NEXT PACIFIC STORM SYSTEM.
WEST-SOUTHWESTERLY WINDS WILL GRADUALLY DECREASE THIS EVENING OVER
THE NORTH-CENTRAL PLAINS AND DRIER CONDITIONS ARE EXPECTED TO
CONTINUE WITH DOWNSLOPING WINDS. ALSO NOTED A CHINOOK ARCH ALONG THE
ROCKY MOUNTAIN FRONT AND THAT MAY PERSIST THROUGH THE OVERNIGHT
PERIOD. SOME SHOWERS ARE POSSIBLE AT KBZN AND KHLN ON TUESDAY
AFTERNOON SO ADDED VCSH EVEN THOUGH MOST OF THE ACTIVITY SHOULD STAY
IN THE SURROUNDING MOUNTAINS. OVERALL...VFR CONDITIONS ARE EXPECTED
OVER THE NEXT 24 HOURS. LATE TUESDAY NIGHT...WIDESPREAD SNOW...COLD
AND STRONG WINDS ARE EXPECTED TO ARRIVE. FOR MORE DETAILS SEE LATEST
WINTER WEATHER STATEMENTS. MLS
&&
.HYDROLOGY...
FLOOD HIGHLIGHTS CONTINUE FOR THE MISSOURI RIVER IN THE GREAT FALLS
AREA. WITH WARMER TEMPERATURES EXPECTED THROUGH THIS
AFTERNOON...CONDITIONS IN THE JAM AREA SHOULD BEGIN TO CHANGE WITH
SEVERAL POSSIBLE RESULTS...FROM GRADUAL DISSIPATION...TO RELOCATION
OF THE JAMMING AND FLOODING AREAS...TO FLASH FLOODING DOWNSTREAM IF
THE JAM BREAKS QUICKLY. ALSO...THE MOUNTAINS WILL EXPERIENCE A
PERIOD OF ABOVE FREEZING TEMPERATURES THROUGH SUNDAY. THE SNOWMELT
COULD RESULT IN FURTHER ICE JAM PROBLEMS NOT ONLY IN GREAT FALLS AND
NEAR BEAVER CREEK BUT IN OTHER AREAS AND ON OTHER RIVERS AS WELL.
WEATHER SERVICE AND LOCAL OFFICIALS WILL CONTINUE TO CLOSELY MONITOR
THE SITUATION.
&&
.PRELIMINARY POINT TEMPS/POPS...
GTF 25 41 20 20 / 10 20 60 100
CTB 21 39 13 14 / 10 20 70 100
HLN 17 36 20 27 / 20 30 40 90
BZN 21 38 21 32 / 10 30 20 80
WEY 1 24 20 25 / 40 70 80 100
DLN 15 34 23 30 / 10 40 20 80
HVR 14 34 13 17 / 0 20 40 90
LWT 20 37 23 26 / 0 20 60 90
&&
.TFX WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WATCH FROM TUESDAY EVENING THROUGH THURSDAY MORNING
BLAINE...CASCADE...CENTRAL AND SOUTHERN LEWIS AND CLARK...
CHOUTEAU...EASTERN GLACIER...EASTERN PONDERA...EASTERN TETON...
FERGUS...HILL...JUDITH BASIN...LIBERTY...NORTHERN ROCKY MOUNTAIN
FRONT...SOUTHERN ROCKY MOUNTAIN FRONT...TOOLE.
WINTER STORM WATCH FROM LATE TUESDAY NIGHT THROUGH THURSDAY
MORNING BEAVERHEAD...BROADWATER...GALLATIN...JEFFERSON...
MADISON...MEAGHER.
FLASH FLOOD WATCH THROUGH TUESDAY AFTERNOON CASCADE.
&&
$$
WEATHER.GOV/GREATFALLS
