FXUS65 KTFX 240433
AFDTFX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
933 PM MST WED DEC 23 2009
.UPDATE...
ALREADY UPDATED ZONE FORECASTS...WILL UPDATE STATE FORECAST
SHORTLY. MAIN UPDATES WERE TO LOWER TEMPERATURES MOST PLACES A FEW
DEGREES...DECREASE WINDS...AND SPREAD PATCHY FREEZING FOG INTO
SOUTHWEST MONTANA (KEEPING IT IN NORTH CENTRAL AND CENTRAL
MONTANA). SURFACE HIGH PRESSURE CONTINUES TO BUILD DOWN OUT OF
CANADA THIS EVENING...CAUSING SKIES TO GRADUALLY CLEAR FROM THE
NORTHWEST. DEWPOINTS HAVE BEEN FALLING WITH THE
TEMPERATURES...WHICH LEADS ME TO BELIEVE THAT WIDESPREAD FOG IS
UNLIKELY. HOWEVER...SOME OF THE LOWER LYING AREAS SHOULD SEE SOME
FOG DEVELOPMENT. DENSE FOG IS POSSIBLE IN SOME AREAS...BUT AGAIN
IS UNLIKELY. TEMPERATURES WILL FALL INTO THE TEENS AND 20S BELOW
ZERO MOST AREAS ACROSS NORTH CENTRAL AND CENTRAL MONTANA...CAUSING
WIND CHILL TEMPERATURES TO FALL INTO THE 25 TO 35 DEGREE BELOW
ZERO RANGE AT TIMES. HOWEVER...AM EXPECTING WINDS TO GENERALLY
REMAIN BELOW 10 MPH. THEREFORE...WILL NOT ISSUE A WIND CHILL
ADVISORY AT THIS TIME. COULSTON
&&
.AVIATION...
UPDATED 2354Z.
VFR CONDITIONS WILL DOMINATE OVER THE NEXT 24 HOUR
PERIOD...HOWEVER ALL TAF SITES DO HAVE A SMALL CHANCE OF FOG
FORMING DURING THE OVERNIGHT HOURS. WILL CONTINUE TO MONITOR
TEMPERATURES AS THE SUNSETS UNDER CLEARING SKIES. TEMPERATURES
ARE ALREADY DROPPING SIGNIFICANTLY AND WITH FRESH SNOWFALL SOME
RADIATIONAL FOG COULD FORM. MODELS ARE CURRENTLY SHOWING ENOUGH
OF A DRAINAGE WIND AT SITES ACROSS THE AREA THAT FOG OR EVEN LOW
STRATUS WOULD BE INHIBITED. CURRENTLY THE LIKELIHOOD OF FOG
FORMATION IS LOW ENOUGH TO AVOID MENTIONING IN THE CURRENT SET OF
TAFS. IF CONDITIONS CHANGE AMENDMENTS WILL BE ISSUED. SUK
&&
.PREV DISCUSSION...
/ISSUED 454 PM MST WED DEC 23 2009/
TONIGHT THROUGH CHRISTMAS DAY...FAIRLY QUIET BUT COLD WEATHER
EXPECTED OVER THE REGION THROUGH CHRISTMAS. PRECIPITATION THIS
AFTERNOON IS COMING TO AN END OVER THE REGION...WITH ANY NEW SNOW
FALL MAINLY CONFINED TO THE MOUNTAINS...WITH SNOW ACCUMULATIONS
LESS THAN A QUARTER OF AN INCH. WITH CLEARING SKIES
TONIGHT...FORECASTED LOWS ARE A BIT COLDER THAN GUIDANCE...AS GOOD
RADIATIONAL COOLING SHOULD OCCUR AFTER MIDNIGHT.
ADDITIONALLY...PATCHY FREEZING FOG COULD ALSO
DEVELOP...ESPECIALLY OVER NORTH CENTRAL MONTANA. FOR
THURSDAY...GENERALLY SEASONABLY COLD CONDITIONS EXPECTED OVER THE
REGION...BUT NO PRECIP IS EXPECTED. EXPECT THE QUIET TREND TO
CONTINUE INTO CHRISTMAS DAY...WITH NO PRECIPITATION EXPECTED
ACROSS THE REGION AT THIS TIME. TEMPERATURES SHOULD MODERATE A
BIT...BUT STILL REMAIN ABOUT 10 DEGREES BELOW NORMAL. BRUSDA
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
&&
.PRELIMINARY POINT TEMPS/POPS...
GTF -18 12 -8 23 / 0 0 0 0
CTB -20 11 -9 28 / 0 0 0 0
HLN -11 9 -5 17 / 0 0 0 0
BZN -11 8 -12 16 / 10 0 0 0
WEY -15 13 -12 17 / 30 10 10 10
DLN -8 14 1 21 / 10 0 0 0
HVR -23 -3 -17 13 / 0 0 0 0
LWT -16 7 -10 22 / 10 0 0 0
&&
.TFX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SHORT TERM...COULSTON/BRUSDA
LONG TERM...MLS
AVIATION...SUK
WEATHER.GOV/GREATFALLS
