000
FXUS65 KTFX 032139
AFDTFX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
239 PM MST WED DEC 3 2008
.DISCUSSION...
TONIGHT THROUGH FRIDAY...AN UPPER LEVEL TROF HAS MOVED OVER THE
MIDWEST WHILE HIGH PRESSURE REMAINS OVER THE EASTERN PACIFIC. THIS
LEAVES THE ZONES UNDERNEATH COOL...NORTHWEST FLOW ALOFT. FLOW SHOULD
DRY DURING THE EVENING AND SKIES WILL CLEAR FROM THE NORTH. HIGH
PRESSURE WILL BUILD THROUGH FRIDAY AND THE AIRMASS WARMS ALTHOUGH
TEMPS WILL RECOVER SLOWLY THURSDAY AFTER A COLD OVERNIGHT LOW.
THURSDAY NIGHT TEMPS WILL BE TRICKY...DRY AIRMASS AND CLEAR
SKIES...BUT WINDS WILL BE INCREASING DURING THE NIGHT. WINDS WILL
CONTINUE TO INCREASE INTO FRIDAY WITH SOME 40-50 KT WINDS AT 850MB
OVER THE NORTHERN ROCKIES. A WEAK DISTURBANCE WILL MOVE THROUGH THE
FLOW FRIDAY BUT MAIN EFFECT WILL BE TO INCREASE WINDS. WINDS
APPROACH WARNING CRITERIA ON THE NAM BUT THE GFS IS WEAKER. TEMPS
WILL BEGIN A SLOW TREND UPWARDS THURSDAY...THE AIRMASS WILL BEGIN TO
WARM THURSDAY BUT WAIT UNTIL FRIDAY TO SIGNIFICANTLY WARM. TEMPS
WILL BE COLD TONIGHT AND WELL BELOW NORMALS...BUT RISE TO ABOVE
NORMALS BY FRIDAY. ZELZER
FRIDAY NIGHT THROUGH MONDAY NIGHT...MEDIUM RANGE MODELS REMAIN IN
FAIR AGREEMENT ON THE LARGE SCALE FEATURES THROUGH EARLY NEXT
WEEK...FEATURING A SOMEWHAT MOIST AND UNSETTLED W TO NW FLOW ALOFT.
A POLAR VORTEX NORTH OF HUDSON BAY ANCHORS A LONGWAVE TROF OVER
EASTERN NORTH AMERICA WHILE AN UPPER LEVEL RIDGE ALONG THE WEST
COAST WILL BE THE MAIN FEATURE IMPACTING THE REGION EARLY IN THE
PERIOD...BEFORE PACIFIC ENERGY BREAKS DOWN THE RIDGE SUNDAY INTO
MONDAY. PLENTY OF MOISTURE RIDES OVER THE UPPER LEVEL RIDGE FRIDAY
NIGHT THROUGH SUNDAY FOR MOSTLY CLOUDY CONDITIONS THROUGH THE
PERIOD. WHILE LIFTING MECHANISMS IN THE FLOW ARE WEAK...STILL CANNOT
RULE OUT SOME LIGHT PRECIPITATION...MAINLY OVER THE HIGHER TERRAIN
AND ALSO ACROSS EASTERN ZONES AS A WEAK OVERRUNNING PATTERN SETS UP.
GENERAL SURFACE WINDS WILL REMAIN FROM THE W AS A LEE-SIDE TROUGH
REMAINS ALONG THE EAST SLOPES...WHERE PRECIPITATION WILL BE LIMITED
AT BEST THROUGH SUNDAY DUE TO THE DOWNSLOPE FLOW. A STRONGER
SHORTWAVE APPROACHES ON SUNDAY WITH THE SURFACE TROUGH AND UPPER
LEVEL TROUGH AXIS PASSING ACROSS THE REGION SUNDAY NIGHT AND MONDAY.
WHILE FAIRLY FAST MOVING...THIS SYSTEM WILL HAVE THE POTENTIAL TO
BRING A PERIOD OF SNOW TO MUCH OF THE AREA SUNDAY NIGHT INTO MONDAY
MORNING AS THE FLOW ALOFT AND AT THE SURFACE TURNS TO NW BEHIND THE
TROUGH AXIS WITH DRIER CONDITIONS MOVING BACK IN BEHIND THE TROUGH
MONDAY NIGHT. TEMPERATURES WILL GENERALLY BE ABOVE SEASONAL
AVERAGES THROUGH SUNDAY...THEN DROP BACK TO AROUND SEASONAL NORMS
ON MONDAY UNDER THE UPPER LEVEL TROUGH. HOENISCH
TUESDAY THROUGH WEDNESDAY...MODELS ARE IN BASIC AGREEMENT DURING
THIS PERIOD...WITH SOME DIFFERENCES IN TIMING AND AMPLITUDE OF
FEATURES AFFECTING OUR FORECAST AREA. A WEAK UPPER LEVEL RIDGE OVER
THE PACIFIC NORTHWEST IS FLATTENED SOMEWHAT BY A SERIES OF WEAK
DISTURBANCES. THIS RESULTS IN A FAIRLY MOIST NORTHWESTERLY FLOW
ALOFT OVER THE REGION. MOSTLY CLOUDY SKIES ARE EXPECTED WITH
SCATTERED SNOW SHOWERS OVER THE HIGHER MOUNTAINS WITH ISOLATED RAIN
OR SNOW SHOWERS OVER MOST OTHER AREAS. SNOW SHOWERS WILL BE MORE
WIDESPREAD ALONG THE NORTHERN CONTINENTAL DIVIDE. GUSTY DOWNSLOPE
WINDS WILL HELP LIMIT PRECIPITATION OVER THE PLAINS AND LARGER
VALLEYS. THESE WINDS WILL INCREASE TUESDAY NIGHT...ESPECIALLY OVER
NORTH CENTRAL MONTANA. TEMPERATURES WILL BE WELL ABOVE SEASONAL
AVERAGES. A CANADIAN COLD FRONT BACKS INTO OUR NORTHEAST ZONES LATE
WEDNESDAY AFTERNOON...WITH NORTHWEST WINDS AND COOLER TEMPERATURES
BEHIND THE FRONT. EK
&&
.AVIATION...
UPDATED 1835Z.
A MOIST NORTHWEST FLOW ALOFT WILL CONTINUE OVER NORTH
CENTRAL...CENTRAL...AND SOUTHWEST MONTANA THROUGH 18Z THURSDAY.
WIDESPREAD LOW VFR TO HIGH MVFR CEILINGS WITH AREAS OF LIGHT SNOW
WILL PERSIST THROUGH THE AFTERNOON...AS WELL AS PARTIAL MOUNTAIN
OBSCURATION IN CLOUDS AND SNOW. THE FLOW ALOFT WILL BECOME MORE
NORTHERLY OVERNIGHT AND SURFACE HIGH PRESSURE WILL KEEP WINDS LIGHT.
CLOUDS AND SNOW WILL DECREASE LATE THIS AFTERNOON AND OVERNIGHT FROM
THE NORTHEAST OVER THE PLAINS OF NORTH CENTRAL AND CENTRAL MONTANA.
REGARDING FOG DEVELOPMENT...THE AREAS WITH THE GREATEST POTENTIAL
ARE THE KGTF AND KLWT TERMINALS DUE TO MORE FRESH SNOW COVER TODAY.
CLOUDS WILL LINGER LONG ENOUGH OVERNIGHT AT THE KGTF TERMINAL THAT
FOG DEVELOPMENT WILL MOST LIKELY BE HINDERED...BUT CLOUDS WILL
DECREASE ENOUGH AFTER 04Z AT THE KLWT TERMINAL TO ALLOW GOOD
RADIATION AND THEREFORE FOG POTENTIAL. AS MENTIONED...THE MOISTURE
WILL SHIFT INTO SOUTHWEST MONTANA AND KEEP THE KHLN AND KBZN
TERMINALS CLOUDY WITH MAINLY VFR CONDITIONS AND MOUNTAIN SNOW.
COULSTON
&&
.PRELIMINARY POINT TEMPS/POPS...
GTF 4 23 19 42 / 10 10 0 10
CTB -1 22 20 40 / 10 0 0 10
HLN 15 26 16 39 / 20 0 0 10
BZN 14 25 10 38 / 20 10 0 10
WEY 10 21 5 26 / 20 20 0 10
DLN 14 25 13 39 / 20 10 0 10
HVR 0 20 12 38 / 10 0 0 10
LWT 4 19 11 38 / 10 0 0 10
&&
.TFX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
WEATHER.GOV/GREATFALLS
