FXUS65 KTFX 071138
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
435 AM MST MON DEC 7 2009

AVIATION DISCUSSION UPDATED

.DISCUSSION...

TODAY THROUGH WEDNESDAY...CROSS POLAR UPPER LEVEL FLOW AND A DEEP 
UPPER LEVEL TROUGH EXTENDING FROM A POLAR VORTEX IN THE CANADIAN 
ARCTIC INTO THE WESTERN U.S. WILL REINFORCE/MAINTAIN THE COLD ARCTIC 
AIRMASS CURRENTLY IN PLACE OVER THE REGION THROUGH AT LEAST TUESDAY 
EVENING. SNOW COVER...LIGHT WINDS...A VERY COLD AIRMASS AND 
SEASONALLY LOW SUN ANGLES WILL LIMIT THE EFFECTS OF DAYTIME WARMING 
THROUGH TUESDAY WITH MOST LOCATIONS REMAINING BELOW ZERO THROUGH 
TUESDAY NIGHT. EXPECT WIDESPREAD TEMPS IN THE TEENS BELOW TO 
TWENTIES BELOW ZERO AGAIN TONIGHT WITH CLOUD-COVER AGAIN PLAYING A 
LARGE ROLE WITH WESTERN AND NW ZONES MOST LIKELY TO SEE CLEARING AND 
COLDER TEMPS. SHALLOW MOISTURE IN THE ARCTIC AIRMASS WILL 
OCCASIONALLY BE WRUNG OUT IN THE FORM OF ICE CRYSTALS OR FLURRIES 
WITH NO MEASURABLE PRECIPITATION EXPECTED. WINDS HAVE GENERALLY 
SUBSIDED TO 10 MPH OR LESS AND WILL REMAIN LIGHT THROUGH TUESDAY SO 
WILL ALLOW THE WIND CHILL ADVISORY TO EXPIRE...HOWEVER AMBIENT TEMPS 
WILL STILL FEEL VERY COLD. THE SURFACE HIGH CENTERED OVER THE REGION 
THROUGH TUESDAY WILL BEGIN TO SHIFT EAST TUESDAY NIGHT AND 
WEDNESDAY...ALLOWING FOR WESTERLY FLOW TO DEVELOP AND BEGIN A SLOW 
MODERATING TREND TO TEMPERATURES...INITIALLY ALONG THE EAST SLOPES 
OF THE ROCKIES TUESDAY NIGHT THEN SPREADING ACROSS THE REMAINDER OF 
THE AREA ON WEDNESDAY. TEMPERATURES HOWEVER WILL REMAIN WELL BELOW 
NORMAL UNDER A VERY COLD UPPER LEVEL TROUGH AND THE ADDITION OF 
WINDS IN EXCESS OF 10 MPH WEDNESDAY AFTERNOON WILL LIKELY MAKE THIS 
INITIAL WARMING HARD TO NOTICE. COLD AND UNSTABLE NW FLOW ALOFT 
COULD BRING A FEW FLURRIES AND SNOW SHOWERS MUCH OF THE AREA 
WEDNESDAY AFTERNOON AS WELL. HOENISCH 

WEDNESDAY NIGHT THROUGH MONDAY...MODELS MAINTAINED GOOD CONSISTENCY 
AND AGREEMENT FOR FIRST HALF OF THIS PERIOD BUT NOW SHOWING MARKED 
DIFFERENCES FOR THE WEEKEND AND MONDAY.  DEEP LONGWAVE TROF THAT 
BROUGHT THE BITTERLY COLD TEMPS WILL CONTINUE TO WEAKEN AND 
GRADUALLY MOVE EASTWARD DURING MIDWEEK.  RESIDUAL MOISTURE MOVING 
ALONG WESTERN BOUNDARY OF THE TROF WILL BRING WIDESPREAD CLOUD COVER 
AND SPOTTY LIGHT SNOW SHOWERS TO THE CWA ON THURS AND FRI.  GIVEN 
THE CLOUD COVER AND NORTHWEST FLOW ALOFT...STILL REMAINING 
PESSIMISTIC ABOUT QUICK WARM-UP INDICATED IN SOME MODEL SOLUTIONS AS 
THE LONGWAVE DEPARTS.  SO HAVE KEPT MAX TEMPERATURES WELL BELOW 
NORMAL ON THURS AND FRI.  GFS AND EUROPEAN MODELS BEGIN TO DIVERGE 
ON SAT...WITH GFS KEEPING CONDITIONS DRY AS WEAK UPPER LEVEL RIDGE 
MOVES IN FROM THE GREAT BASIN WITH NEXT WEATHER SYSTEM APPROACHING 
THE PACIFIC COAST.  MEANWHILE EUROPEAN PUSHES A VERY MOIST SHORTWAVE 
TROF ALONG THE US/CAN BORDER AND SPREADS LIGHT SNOW OVER NORTH 
CENTRAL MT.  DIFFERENCES CONTINUE INTO SUN/MON AS GFS SLOWLY BRINGS 
THE PACIFIC SYSTEM EASTWARD WITH LIGHT SNOW MAINLY CONFINED TO 
SOUTHWEST ZONES AND ALONG THE ROCKY MTN FRONT.  EURO SOLUTION SHOWS 
A SPLIT FLOW SCENARIO...DIGGING THE PACIFIC SYSTEM WELL SOUTH WHILE 
BRINGING HUGE SWATH OF LIGHT PRECIPITATION OVER THE ENTIRE NORTHERN 
ROCKIES AREA.  SIDED WITH NEIGHBORING FORECAST OFFICES AND WENT WITH 
THE GFS SOLUTION FOR THE TIME BEING FOR THE WEEKEND AND MON GRIDS.  
THIS INCLUDES CONTINUING THE GRADUAL WARM-UP IN TEMPS...WITH MAX 
TEMPS GETTING BACK TO UPPER 20S TO LOW 30S IN CENTRAL PLAINS BY SUN 
AND 3 TO 5 DEGREES ABOVE FREEZING ON MONDAY.
WARANAUSKAS 

&&

.AVIATION...
UPDATED 1135Z.
BROAD AND WEAKENING UPPER LEVEL TROUGH WILL KEEP AREAS OF 
LOW/MID-LEVEL CLOUDS OVER CENTRAL AND SOUTHWEST MT TODAY.  CEILINGS 
SHOULD GENERALLY REMAIN VFR BUT SOME TERMINALS COULD SEE BRIEF 
PERIODS OF MVFR CONDITIONS WITH LIGHT SNOW TODAY AND TONIGHT.  ALSO 
EXPECT INTERMITTENT OBSCURATIONS OF MOUNTAIN TERRAIN.  WINDS WILL BE 
LIGHT ACROSS THE REGION TODAY.   WARANAUSKAS

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  -9 -27  -5 -11 /  20  10   0   0 
CTB  -9 -34  -5  -8 /  10   0   0  10 
HLN  -4 -23  -2 -15 /  10   0   0   0 
BZN  -2 -29  -2 -22 /  10  10  10   0 
WEY   1 -27   2 -27 /  30  20  20  20 
DLN  -3 -25   0 -18 /  10   0   0   0 
HVR  -5 -24  -2 -15 /  10  10   0  10 
LWT  -4 -20  -3 -14 /  20  20  10   0 

&&

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

$$

SHORT TERM...HOENISCH
LONG TERM...WARANAUSKAS
AVIATION...SUK

WEATHER.GOV/GREATFALLS