FXUS65 KTFX 150538
AFDTFX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
1040 PM MST MON DEC 14 2009
.UPDATE...
SOUTHERLY GAP WINDS HAVE INCREASED THIS EVENING ALONG U.S. 191
BETWEEN JUDITH GAP AND EDDIES CORNER AS PRESSURE GRADIENT TIGHTENS
THROUGH THIS AREA. BREEZY SOUTHERLY WINDS AND VERY COLD
TEMPERATURES WILL CREATE WIND CHILL VALUES OF 35 BELOW ZERO TO 55
BELOW ZERO THROUGH EARLY TUESDAY MORNING SO HAVE ISSUED A WIND
CHILL WARNING FOR PORTIONS OF JUDITH BASIN AND FERGUS COUNTIES.
AREAS OF BLOWING AND DRIFTING SNOW ARE ALSO EXPECTED WHICH MAY
REDUCE VISIBILITIES TO LESS THAN ONE MILE AT TIMES. ALSO LOWERED
MIN TEMPS THIS EVENING...HOWEVER TEMPERATURES WILL GRADUALLY RISE
OVERNIGHT AS SOUTH-SOUTHWEST WINDS INCREASE FROM WEST TO EAST.
REMAINDER OF THE FORECAST IS ON TRACK AND WILL CONTINUE TO MONITOR
TEMPERATURES AND WIND CHILLS FOR ANY ADDITIONAL HIGHLIGHTS. MLS
&&
.AVIATION...
UPDATED 0540Z.
UPPER LEVEL RIDGE WILL BUILD OVER WESTERN AND CENTRAL MONTANA
TONIGHT BUT IS FLATTENED ON TUESDAY AS SHORTWAVE ENERGY MOVES
THROUGH THE REGION. COLD ARCTIC AIRMASS OVER CENTRAL MONTANA WILL
MOVE EAST BY MIDDAY TUESDAY WITH SOUTHWEST WINDS INCREASING ACROSS
THE FORECAST AREA. VFR CONDITIONS ARE EXPECTED AT ALL TERMINALS
THROUGH THE FORECAST PERIOD. MPJ
&&
.PREV DISCUSSION...
/ISSUED 510 PM MST MON DEC 14 2009/
TONIGHT THROUGH WEDNESDAY...COLD ARCTIC AIRMASS REMAINS IN PLACE
OVER THE PLAINS OF NORTH CENTRAL MT THIS AFTERNOON HOWEVER EXITING
UPPER LEVEL TROUGH AND INCREASING WESTERLY FLOW ALOFT WILL BEGIN
THE PROCESS OF SWEEPING OUT THE ARCTIC AIR LATER THIS EVENING.
MINIMUM TEMPS TONIGHT WILL LIKELY OCCUR EARLY THIS EVENING BEFORE
WINDS ARRIVE LATE THIS EVENING BEGINNING THE GRADUAL WARMUP. WINDS
CONTINUE TO INCREASE ON TUESDAY FOR MORE SIGNIFICANT WARMING WITH
MOST AREAS SEEING TEMPS RISE TO NEAR OR ABOVE FREEZING AS WINDS
VEER MORE AROUND TO THE SW. COMBINATION OF INCREASING WINDS AND
THE STILL RELATIVELY FRESH SNOWPACK COULD CREATE SOME AREAS OF
REDUCED VISIBILITY IN BLOWING AND DRIFTING SNOW TUESDAY MORNING.
PACIFIC SYSTEM CURRENTLY MOVING ONSHORE WILL MOVE INTO THE
NORTHERN ROCKIES TUESDAY AND TUESDAY NIGHT WITH ANOTHER SYSTEM
MOVING ACROSS THE REGION ON WEDNESDAY. THE MOIST WESTERLY FLOW
WILL ALLOW FOR CONTINUED WARMING ON WEDNESDAY. PRECIPITATION WILL
MAINLY BE CONFINED TO THE WESTERN AND SW MTNS TUESDAY AND
WEDNESDAY WITH DOWNSLOPE WINDS LIMITING PRECIPITATION CHANCES IN
THE PLAINS. HOENISCH
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 -15 33 26 / 70 10 10 10
CTB -7 -20 31 21 / 80 10 10 0
HLN 2 -7 34 18 / 70 20 10 10
BZN 10 1 33 17 / 70 20 20 10
WEY 20 11 24 15 / 100 40 50 60
DLN 29 16 33 21 / 50 10 10 10
HVR -9 -28 15 10 / 60 10 10 10
LWT -5 -15 32 20 / 70 20 10 10
&&
.TFX WATCHES/WARNINGS/ADVISORIES...
WIND CHILL WARNING UNTIL 5 AM MST TUESDAY FOR FERGUS...JUDITH
BASIN.
&&
$$
WEATHER.GOV/GREATFALLS
