FXUS65 KTFX 231209
AFDTFX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
508 AM MST WED DEC 23 2009
UPDATED AVIATION
.DISCUSSION...
TODAY THROUGH FRIDAY...A LOW PRESSURE TROF WILL QUICKLY MOVE FROM
CENTRAL MONTANA INTO EASTERN MONTANA TODAY WHILE A HIGH PRESSURE
RIDGE OVER THE EASTERN PACIFIC BUILDS OVER THE WEST COAST. THIS WILL
PUT THE ZONES UNDERNEATH NORTH FLOW ALOFT AND KEEP THE REGION UNDER
A COLD AIRMASS. SNOW WILL QUICKLY TAPER OFF AS THE TROF MOVES EAST
ALTHOUGH NORTHERLY FLOW WILL CONTINUE TO KEEP A THREAT OF SNOW
SHOWERS IN THE AREA. CURRENT ADVISORIES WILL BE CONTINUED. BUILDING
HIGH PRESSURE WILL DOMINATE THE REMAINING PERIOD...THE AIRMASS WILL
STAY DRY AND SLOWLY WARM. TEMPS WILL REMAIN BELOW NORMALS THROUGH
THE PERIOD ALTHOUGH TRENDING WARMER THROUGH FRIDAY. ZELZER
FRIDAY NIGHT THROUGH WEDNESDAY...LONG-RANGE MODELS IN FAIR AGREEMENT
REGARDING STRONG RIDGE OF HIGH PRESSURE BUILDING OVER THE WESTERN
U.S. DURING THE START OF THE FORECAST PERIOD. NORTHERLY FLOW AND
SNOWPACK WILL KEEP TEMPERATURES IN CHECK WITH HIGH TEMPERATURES
AROUND SEASONAL AVERAGES SATURDAY AND SUNDAY. DRY CONDITIONS ARE
ALSO EXPECTED. THERE ARE SOME MODEL DIFFERENCES REGARDING THE
PLACEMENT OF THE HIGH ALOFT AS THE ECMWF ATTEMPTS TO BRING IN A WEAK
UPPER-LEVEL LOW ONTO THE WEST COAST ON SUNDAY WHICH WILL KEEP THE
CENTER OF THE HIGH OVER SOUTHERN ALBERTA RATHER THAN MONTANA AS THE
GFS INDICATES. NEVERTHELESS...DRY CONDITIONS ARE EXPECTED THROUGH
THE WEEKEND AND INTO EARLY NEXT WEEK. MODELS CONTINUE TO SHOW
CONSIDERABLE DIFFERENCES WITH REGARDS TO OUR NEXT PRECIP
CHANCES...HOWEVER BOTH THE GFS AND EC HINT AT A TROUGH OF LOW
PRESSURE MOVING INTO THE PACIFIC NORTHWEST TUESDAY AND WEDNESDAY OF
NEXT WEEK. A COLDER CANADIAN AIRMASS MAY ALSO SLIDE INTO THE AREA
DURING THIS SAME TIME FRAME SO TRENDED TEMPERATURES ABOUT 5 TO 10
DEGREES BELOW AVERAGE. MLS
&&
.AVIATION...
UPDATED 1200Z.
WIDESPREAD AREAS OF LIGHT SNOW AND PATCHY DENSE FREEZING FOG WILL
CONTINUE THROUGH THIS MORNING ACROSS NORTH-CENTRAL...CENTRAL AND
PORTIONS OF CENTRAL MONTANA AS AN UPPER-LEVEL TROUGH MOVES THROUGH
THE REGION. SNOW HAS ENDED AT KCTB AND CIGS/VIS HAVE INCREASED TO
VFR CATEGORY. KGTF AND KHLN CAN EXPECT MVFR AND OCCL IFR
CONDITIONS...HOWEVER LIGHT SNOW WILL BE OFF AND ON THROUGH THIS
MORNING BEFORE TAPERING OFF TO FLURRIES BY THIS AFTERNOON. LIGHT
SNOW AND FOG WILL PERSIST AT KHVR AND KLWT WITH PREDOMINANT IFR
CONDITIONS AND OCCL LIFR CONDITIONS DURING TIMES OF HEAVIER
SNOWFALL...CONDITIONS ARE EXPECTED TO IMPROVE FOR THESE LOCATIONS BY
LATER THIS AFTERNOON. BREEZING NORTHWEST WINDS OVER THE REGION WILL
ALSO CAUSE AREAS OF BLOWING AND DRIFTING SNOW WHICH COULD REDUCE
VISIBILITIES TO LESS THAN ONE MILE AT TIMES AS WELL. BY TONIGHT...A
RIDGE OF HIGH PRESSURE WILL BUILD INTO THE REGION YIELDING QUIETER
CONDITIONS. MLS
&&
.PRELIMINARY POINT TEMPS/POPS...
GTF 8 -2 15 1 / 30 10 0 0
CTB 7 -8 15 0 / 20 0 0 0
HLN 16 -1 12 -3 / 40 10 0 0
BZN 25 -3 16 -10 / 60 10 0 0
WEY 21 -10 13 -10 / 70 20 10 0
DLN 24 -3 17 -7 / 40 10 0 0
HVR 7 -17 0 -12 / 80 10 0 0
LWT 11 -6 12 -4 / 90 10 0 0
&&
.TFX WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY UNTIL 11 AM MST THIS MORNING FOR
CASCADE...CHOUTEAU...EASTERN GLACIER...EASTERN PONDERA...EASTERN
TETON...HILL...JUDITH BASIN...LIBERTY...MEAGHER...NORTHERN ROCKY
MOUNTAIN FRONT...SOUTHERN ROCKY MOUNTAIN FRONT...TOOLE.
WINTER WEATHER ADVISORY UNTIL 5 PM MST THIS AFTERNOON FOR
BLAINE...FERGUS.
&&
$$
WEATHER.GOV/GREATFALLS
