FXUS65 KTFX 141953
AFDTFX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
1253 PM MST MON DEC 14 2009
.UPDATE...
UPDATED MAX TEMPS TODAY FOR PORTIONS OF NORTH CENTRAL MT WHERE
SNOW-COVER AND LOW SUN ANGLE IS HELPING KEEP TEMPS VERY COLD
DESPITE WARMING ALOFT. EXPECT TEMPS TO REMAIN WELL BELOW ZERO ON
THE PLAINS WITH A GRADUAL INCREASE IN TEMPS THROUGH THIS
AFTERNOON. WILL LIKELY SEE A MORE SIGNIFICANT JUMP IN TEMPS LATE
THIS EVENING AND OVERNIGHT AS SOUTH TO SOUTHWEST WINDS DEVELOP.
HOENISCH
&&
.AVIATION...
UPDATED 1725Z.
EXPECT MIX OF VFR TO IFR CONDITIONS ACROSS NORTH CENTRAL AND CENTRAL
MT TODAY AS RESIDUAL MOISTURE ASSOCIATED WITH THE DEPARTING UPPER
LEVEL TROUGH WILL CONTINUE TO PRODUCE AREAS OF LOW CLOUD COVER AND
LIGHT SNOW. LOCATIONS IN SOUTHWEST MT SHOULD BE PREDOMINANTLY
VFR...THOUGH SOME BRIEF PERIODS OF MVFR TO IFR ARE POSSIBLE IN SNOW
SHOWERS OVER HIGHER TERRAIN ALONG/EAST OF LINE FROM KHLN TO KBZN.
AREAS OF SNOW SHOULD DISSIPATE BY THIS EVE WITH GRADUAL RETURN TO
VFR CONDITIONS AT ALL TERMINALS. WINDS WILL BE LIGHT TODAY AND
GRADUALLY TURN TO WEST-SOUTHWEST TONIGHT.
WARANAUSKAS
&&
.PREV DISCUSSION...
/ISSUED 1025 AM MST MON DEC 14 2009/
FXUS65 KTFX 141730
AFDTFX
UPDATE... ARCTIC HIGH PRESSURE REMAINS IN PLACE ACROSS THE
NORTHERN TWO THIRDS OF THE FORECAST AREA THIS MORNING. DEPTH OF
THE COLD AIR IS DECREASING AND CURRENTLY EXTENDS UP TO AROUND
6000FT MSL PER MORNING SOUNDING AND OBSERVATIONS WITH LOCATIONS
ABOVE 6000 FT ALREADY SEEING TEMPS RISE ABOVE ZERO. HAVE MADE SOME
ADJUSTMENTS TO MAX TEMPS TODAY TO BRING SOME WARMING TO HIGHER
ELEVATIONS AND ALSO TO PORTIONS OF SW MT ALREADY OUT OF THE ARCTIC
AIR. THE BULK OF NORTH CENTRAL MT HOWEVER SHOULD GENERALLY REMAIN
BELOW ZERO TODAY WITH WARMING ARRIVING LATER TONIGHT. LIGHT BANDED
SNOW SHOWERS/FLURRIES CONTINUE TO MOVE ACROSS CENTRAL/NORTH
CENTRAL MT ZONES THIS MORNING IN ASSOCIATION WITH A WEAK SHORTWAVE
AND SOMEWHAT UNSTABLE/MOIST CONDITIONS ABOVE THE ARCTIC AIRMASS.
SHORTWAVE EXITS AND MOIST/UNSTABLE LAYER IS REDUCED THIS AFTERNOON
OVER NORTHERN ZONES WHICH SHOULD PROVIDE SOME DRYING AND PARTIAL
CLEARING FOR AREAS FROM GREAT FALLS AND NORTHWARD LATER THIS
AFTERNOON AND EVENING. HOENISCH
MONDAY THROUGH WEDNESDAY...A DRAMATIC WARM UP IS EXPECTED THROUGH
THE FIRST PART OF THE WORK WEEK AS TEMPERATURES WILL BEGIN TO RISE
TO HIGHS IN THE SINGLE DIGIT BELOW ZERO RANGE IN NORTH CENTRAL AND
CENTRAL MONTANA. HIGHS TUESDAY WILL BEGIN TO APPROACH THE MELTING
POINT FOR MUCH OF THE AREA ACROSS MUCH OF NORTH CENTRAL AND
CENTRAL MONTANA. BY WEDNESDAY TEMPERATURES SHOULD GENERALLY BE
ABOVE FREEZING FOR MUCH OF NORTH CENTRAL AND CENTRAL MONTANA.
SOUTHWEST MONTANA WILL NOT SEE AS STRONG OF A TEMPERATURE
INCREASE...HOWEVER THIS IS MOSTLY DUE TO THE FACT THAT THE
TEMPERATURES NEVER PLUNGED AS FAR BELOW FREEZING. SOME INSTABILITY
ALOFT WILL MOVE ACROSS THE AREA TODAY AND TUESDAY...THIS WILL
LIKELY YIELD SCATTERED SNOW SHOWERS ESPECIALLY ACROSS THE HIGHER
TERRAIN. NO SIGNIFICANT ACCUMULATIONS ARE EXPECTED WITH THESE
SHORT LIVED SHOWERS. SUK
WEDNESDAY NIGHT THROUGH SATURDAY NIGHT...THE ECMWF AND GFS MODEL
RUNS ARE NOT IN VERY GOOD AGREEMENT WITH UPPER AIR TRENDS AND
FORECAST PRECIPITATION DURING THE PERIOD. ECMWF MODEL RUN BRINGS A
STRONGER WEATHER DISTURBANCE THROUGH THE AREA ON THURSDAY THAN THE
GFS MODEL RUN. DESPITE THIS DIFFERENCE BOTH MODELS ARE MOSTLY DRY
OVER THE PLAINS. CONTINUED THE INHERITED IDEA OF HOLDING ON TO A
SLIGHT CHANCE OF PRECIPITATION FOR THE EAST SLOPES OF THE ROCKY
MOUNTAINS WITH OF COURSE HIGHER CHANCES OF PRECIPITATION OVER THE
MOUNTAINS. FOR THURSDAY NIGHT THROUGH SATURDAY NIGHT EXPECT THE AREA
TO BE UNDER THE INFLUENCE OF AN UPPER RIDGE OVER THE PACIFIC
NORTHWEST. THERE IS THE POSSIBILITY THAT THIS UPPER RIDGE COULD MOVE
OVER THE FORECAST AREA SATURDAY NIGHT. MODELS DIFFER ON MOISTURE
FORECAST IN THE NORTHWEST FLOW ALOFT OVER THE AREA. THE ECMWF TENDS
TO HAVE A STRONGER UPPER RIDGE AND HENCE IS DRIER THAN THE GFS. THE
INHERITED FORECAST SEEMS TO BE A NICE COMPROMISE BETWEEN THE TWO
SOLUTIONS IN THAT IT KEEPS A CHANCE OF SNOW OVER THE MOUNTAINS WHILE
THE PLAINS AND VALLEYS ARE MOSTLY DRY. BLANK
SUNDAY THROUGH MONDAY...MODEL DIFFERENCES ONCE AGAIN COMPLICATE
THE FORECAST DURING THIS PERIOD. A BLENDED SOLUTION WAS USED
LEANING TOWARD THE ECMWF WHICH STILL SHOWS BETTER CONSISTENCY. A
WEAK UPPER LEVEL RIDGE OVER MONTANA SUNDAY IS FLATTENED BY A
SERIES OF DISTURBANCES RIDING OVER THE RIDGE. A WEAK DRY BACKDOOR
COLD FRONT LIES OVER OUR NORTHEAST ZONES. MOSTLY CLOUDY SKIES ARE
EXPECTED WITH SCATTERED SNOW SHOWERS OVER THE MOUNTAINS AND A FEW
RAIN OR SNOW SHOWERS SPREADING TO SOME THE THE PLAINS AND VALLEYS
SUNDAY. DOWNSLOPE WIND WILL HELP LIMIT THE CHANCE OF PRECIPITATION
OVER THE PLAINS AND LARGER VALLEYS SATURDAY. TEMPERATURES WILL
COOL TO NEAR SEASONAL AVERAGES. EK
&&
.PRELIMINARY POINT TEMPS/POPS...
GTF -6 -7 33 26 / 70 10 10 10
CTB -7 -10 31 21 / 80 10 10 0
HLN 2 0 34 18 / 70 20 10 10
BZN 10 5 33 17 / 70 20 20 10
WEY 20 11 24 15 / 100 40 50 60
DLN 29 14 33 21 / 50 10 10 10
HVR -9 -24 15 10 / 60 10 10 10
LWT -5 -13 32 20 / 70 20 10 10
&&
.TFX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SHORT TERM...SUK
LONG TERM...BLANK
AVIATION...WARANAUSKAS
WEATHER.GOV/GREATFALLS
