FXUS65 KTFX 160431
AFDTFX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
931 PM MST TUE DEC 15 2009
.UPDATE...
MADE SOME CHANGES TO THE FORECAST THIS EVENING...MAINLY WITH
WINDS. WINDS HAVE SHIFTED TO A SOUTH-SOUTHEASTERLY DIRECTION OVER
PARTS OF THE NORTH-CENTRAL PLAINS IN RESPONSE TO PRESSURE FALLS
OVER CENTRAL CANADA. THESE WINDS WILL ALSO BE LIGHTER THAN
PREVIOUSLY THOUGHT...HOWEVER WITH OVERALL WESTERLY PATTERN ALOFT AM
EXPECTING OCCL BREEZY CONDITIONS. ALSO TWEAKED A FEW TEMPERATURES
AS A MILDER AIRMASS CONTINUES TO PROGRESS INTO THE DEEPER VALLEYS
INCLUDING THE MISSOURI RIVER VALLEYS AND HELENA VALLEY. IN
ADDITION...MOIST WESTERLY FLOW WILL SPREAD INTO WESTERN MONTANA
WITH SOME PACIFIC MOISTURE REACHING THE CONTINENTAL DIVIDE SO HAVE
KEPT HIGHER POPS IN THIS AREA AS WELL AS OVER THE MOUNTAINS OF FAR
SOUTHWEST MONTANA. THE REMAINDER OF THE FORECAST AREA SHOULD
REMAIN DRY OVERNIGHT. AS FOR TEMPERATURES...DID INCREASE LOW TEMPS
OVER SOME AREAS BASED ON CURRENT OBSERVATIONS AS WELL AS PERSISTENT
CLOUD COVER AND WINDS. MLS
&&
.AVIATION...
UPDATED 0010Z.
UPPER LEVEL RIDGE AXIS MOVES TO EASTERN MONTANA WITH A MOIST
SOUTHWEST TO WESTERLY FLOW ALOFT CONTINUING OVER THE FORECAST AREA
TONIGHT AND WEDNESDAY. SURFACE LOW PRESSURE TROUGH THROUGH ALBERTA
AND NORTH CENTRAL MONTANA WILL FUEL GUSTY WESTERLY DOWNSLOPE WINDS
WITH GENERALLY DRY CONDITIONS PREVAILING AT LOWER ELEVATIONS.
SCATTERED TO NUMEROUS SNOW SHOWERS WILL AFFECT THE WESTERN AND
SOUTHWEST MOUNTAINS WITH MOUNTAIN OBSCURATIONS AND IFR/LIFR
CONDITIONS OVER THE PEAKS THROUGH THE PERIOD. MPJ
&&
.PREV DISCUSSION...
/ISSUED 510 PM MST TUE DEC 15 2009/
TONIGHT THROUGH THURSDAY...WESTERLY FLOW ALOFT AND DEEPENING LOW
PRESSURE TO THE LEE OF THE ROCKIES CONTINUES TO EVICT THE COLD
AIRMASS THAT HAS BEEN IN PLACE OVER MUCH OF THE REGION. STILL SOME
POCKETS OF COLDER AIR ARE PERSISTING ALONG THE HI-LINE AND DOWN
THE MILK AND LOWER MISSOURI RIVER VALLEYS BELOW 3000FT ELEVATION
AS WELL IS IN THE HELENA VALLEY. EXPECT THESE ARES TO WARM ONLY
GRADUALLY THROUGH THIS EVENING WITH MORE SIGNIFICANT WARMING
ARRIVING LATER TONIGHT AND TOMORROW. MOIST WESTERLY FLOW ALOFT
WILL MAINTAIN CLOUDY CONDITIONS OVER MOST OF THE AREA THROUGH THE
NEXT SEVERAL DAYS WITH LIGHT PRECIPITATION INCREASING SOME TONIGHT
OVER THE MOUNTAINS AND ESPECIALLY ALONG THE CONTINENTAL DIVIDE.
CONTINUED WARMING IS EXPECTED TOMORROW WITH TEMPS REACHING ABOVE
AVERAGE LEVELS ACROSS MOST OF THE FORECAST AREA. SLIGHT COOLING
IS EXPECTED ON THURSDAY AS A WEAK UPPER LEVEL TROUGH MOVES THROUGH
THE REGION...HOWEVER TEMPS WILL REMAIN NEAR TO ABOVE SEASONAL
AVERAGES IN MILD WESTERLY FLOW FROM THE PACIFIC. PRECIPITATION
WILL MAINLY BE CONFINED TO THE MOUNTAINS THROUGH THE PERIOD AS
WESTERLY DOWN-SLOPE WINDS PROMOTE DRYING OVER THE PLAINS. PERIODS
OF SNOWFALL WILL LIKELY BRING SEVERAL INCHES OF NEW ACCUMULATION
TO THE WESTERN AND FAR SW MOUNTAINS ABOVE 6000 FT...HOWEVER THIS
WILL BE SPREAD OVER A 48 HR PERIOD AND NO WINTER WEATHER
HIGHLIGHTS ARE ANTICIPATED AT THIS TIME. WINDY CONDITIONS WILL
CONTINUE OVER MUCH OF THE PLAINS THROUGH THURSDAY. HOENISCH
THURSDAY NIGHT THROUGH SUNDAY NIGHT...THE 12Z RUN OF THE EUROPEAN
MODEL NOW SHOWS BETTER AGREEMENT WITH THE GFS ON CONDITIONS FOR THE
MIDTERM FORECAST PERIOD. BOTH MODELS INDICATE THAT A TRANSIENT
UPPER RIDGE WILL MOVE ACROSS MT ON FRI...BRINGING PARTLY CLOUDY
SKIES AND ABOVE NORMAL TEMPERATURES. A SHORTWAVE TROF FROM THE
PACIFIC FOLLOWS CLOSE BEHIND ON SAT AFTN...SPREADING CLOUDS...COOLER
TEMPERATURES AND LIGHT SNOW ACROSS THE REGION. THERE ARE STILL SOME
SLIGHT TIMING AND QPF DIFFERENCES IN THE MODEL SOLUTIONS FOR THIS
SYSTEM...BUT NOT THE STARK DIFFERENCES SEEN IN THE RUNS OF THE PAST
2-3 DAYS AND MENTIONED IN EARLIER DISCUSSIONS. THE TROF WILL MAKE
STEADY EASTWARD PROGRESS OVERNIGHT SAT AND ONLY A FEW LINGERING
SNOW-SHOWERS ARE EXPECTED ON SUN MORNING. SKIES SHOULD GRADUALLY
CLEAR SUN AFTN AS THE TROF MOVES DOWNSTREAM. HIGH TEMPS WILL BE A
FEW DEGREES ABOVE NORMAL ON SAT BUT DROP BACK TO TYPICAL SEASONAL
VALUES ON SUNDAY. WARANAUSKAS
MONDAY THROUGH TUESDAY...MODEL DIFFERENCES AND RUN TO RUN
INCONSISTENCIES DETRACT FROM FORECAST CONFIDENCE DURING THIS PERIOD.
A COMPROMISE FORECAST WOULD INDICATE A WEAK UPPER LEVEL RIDGE OVER
MONTANA BEING FLATTENED AS AN UPPER LEVEL TROUGH DROPS SOUTH OVER
THE REGION. AN ASSOCIATED COLD FRONT WILL DROP SOUTH OUT OF CANADA
STALLING BEFORE REACHING OUR SOUTHWEST ZONES. DUE TO UNCERTAINTY
PRECIPITATION CHANCES WERE KEPT NEAR CLIMATOLOGICAL VALUES...WITH
ONLY MODERATE DROPS IN TEMPERATURE INDICATED. THIS PERIOD WILL BE
MONITORED FOR THE POTENTIAL OF MORE SNOW AND EVEN COLDER
TEMPERATURES. EK
&&
.PRELIMINARY POINT TEMPS/POPS...
GTF 29 45 29 43 / 10 10 10 10
CTB 23 43 28 42 / 0 10 10 10
HLN 10 29 21 40 / 10 20 20 10
BZN 20 36 18 35 / 10 20 20 20
WEY 21 31 16 30 / 80 80 80 80
DLN 23 38 20 37 / 10 20 10 10
HVR -5 30 19 38 / 10 20 10 10
LWT 26 45 25 41 / 10 20 10 20
&&
.TFX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
WEATHER.GOV/GREATFALLS
