FXUS65 KTFX 251147
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
447 AM MST FRI DEC 25 2009

UPDATED AVIATION

.DISCUSSION...

FRIDAY THROUGH SUNDAY...NORTH FLOW ALOFT WILL WEAKEN TODAY AND BEGIN 
TO SWITCH TO THE NORTHEAST BY LATE AFTERNOON AS AN UPPER LEVEL HIGH 
PRESSURE RIDGE OVER THE PACIFIC NORTHWEST MOVES EAST. THIS RIDGE 
WILL BE OVER THE ZONES BY SUNDAY.  WEAK DISTURBANCES MOVING THROUGH 
THE FLOW ALOFT WILL CONTINUE TO CAUSE INCREASED SKY COVER...MAINLY 
OVER THE SOUTHWEST ZONES...AND A SLIGHT CHANCE OF SNOW SHOWERS. SNOW 
ACCUMULATION IS NOT EXPECTED. THE HIGH PRESSURE ALOFT WILL KEEP THE 
REGION DRY AND SLOWLY WARM THE AIRMASS BUT TEMPS IN MOST AREAS WILL 
REMAIN BELOW NORMALS THROUGH SUNDAY. ZELZER

SUNDAY NIGHT THROUGH FRIDAY NIGHT...HIGH PRESSURE WILL BEGIN TO PUSH 
EASTWARD EARLY IN THE PERIOD WITH WESTERLY FLOW ALOFT DEVELOPING. 
DRY CONDITIONS WILL PERSIST THROUGH TUESDAY BEFORE NEXT SHORTWAVE 
TROUGH MOVES INTO THE PACIFIC NORTHWEST. MODELS ARE CONSISTENT IN 
BRINGING THIS WEAK SHORTWAVE THROUGH WESTERN MONTANA AND THEN INTO 
SOUTHWEST MONTANA TUESDAY NIGHT...THUS INCREASED POPS ACROSS 
SOUTHWEST MT THROUGH WEDNESDAY. IN ADDITION...STRONG 
WEST-NORTHWESTERLY FLOW ALOFT MAY BRING STRONG AND GUSTY DOWNSLOPING 
WINDS ALONG THE ROCKY MOUNTAIN FRONT AND ADJACENT PLAINS. UNSETTLED 
NORTHWEST FLOW IS EXPECTED THROUGH THURSDAY...THEN MODELS DIVERGE IN 
TRENDS FOR THE NEW YEAR WEEKEND. LATEST EC INDICATES A BUILDING 
RIDGE OF HIGH PRESSURE AND ABOVE AVERAGE TEMPERATURES THROUGH THE 
END OF THE FORECAST PERIOD WHILE GFS AND GEM MODELS BRING A STRONG 
TROUGH OF LOW PRESSURE AND COLDER TEMPERATURES TO THE REGION. GIVEN 
THE UNCERTAINTY...KEPT TEMPERATURES ONLY SLIGHTLY ABOVE AVERAGE WITH 
POPS NEAR CLIMATOLOGY. MLS

&&

.AVIATION... 
UPDATED 1200Z.
BKN TO OVC MID-LEVEL CLOUDS WILL CONTINUE TO MOVE OVER THE REGION 
LOWERING CIGS THIS MORNING TOWARDS MVFR CATEGORY WITH SOME MOUNTAIN 
OBSCURATION ALSO POSSIBLE. AT KHVR AND KLWT...MVFR CEILINGS ARE 
ALREADY OCCURRING BUT AS HIGH PRESSURE BUILDS OVER THE REGION CIGS 
WILL INCREASE TO VFR CATEGORY. BY THIS AFTERNOON...VFR CONDITIONS 
ARE EXPECTED AT ALL TAF SITES THROUGH THE REMAINDER OF THE PERIOD. 
MLS

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  25   8  24  12 /   0   0   0   0 
CTB  25   4  26   8 /   0   0   0   0 
HLN  16   5  18   2 /  10   0   0   0 
BZN  21   6  22   1 /  10   0   0   0 
WEY  20   0  21  -2 /  20  10   0   0 
DLN  22   3  22   4 /  10   0   0   0 
HVR   5 -15  11  -8 /   0   0   0   0 
LWT  17   0  23   6 /   0   0   0   0 

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

WEATHER.GOV/GREATFALLS