000 FXUS65 KBYZ 102213 AFDBYZ AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BILLINGS MT 313 PM MST SAT DEC 10 2005 .SHORT TERM...VALID FOR SUN AND MON... DRY WEATHER AND ABOVE NORMAL TEMPERATURES WILL CONTINUE OVER THE FORECAST AREA UNTIL MON NIGHT. GFS HAD BETTER HANDLE ON TEMPERATURE PROFILES THAN NAM SO WENT WITH IT FOR THE PACKAGE. UPPER RIDGING WILL CONTINUE TO INFLUENCE AREA WEATHER THROUGH MONDAY. ON MON NIGHT...A PACIFIC SHORTWAVE WILL MOVE SE INTO THE REGION PUSHING A COLD FRONT THROUGH THE AREA. TEMPERATURES WILL BE MAIN FORECAST CHALLENGE TONIGHT THROUGH MONDAY. CLOUD COVER AND LOW-LEVEL INVERSION KEPT TEMPERATURES FROM REACHING THE 40S THIS AFTERNOON. PARTLY CLOUDY SKIES AND BREEZY CONDITIONS TONIGHT WILL LIMIT TEMPERATURE FALLS SIMILAR TO WHAT OCCURRED LAST NIGHT. HOWEVER...LOWERED TEMPERATURES ANYWAY DUE TO A COOLER START TO THE NIGHT THAN PREVIOUSLY WAS FORECAST. NUDGED TEMPS TOWARD THE MAV BUT DID NOT GO AS LOW AS MAV NUMBERS. ADJUSTED SUNDAY MAX TEMPS TO MAKE THEM A FEW DEGREES HIGHER THAN WHAT OCCURRED TODAY AS GFS SHOWED AIRMASS MODERATING A LITTLE AND UPPER LEVELS WILL BE A BIT DRIER THAN THEY WERE TODAY...SO EXPECT LESS CLOUD COVER. MONDAY WILL BE A PREFRONTAL DAY WITH INCREASING DOWNSLOPE FLOW OVER THE AREA...BUT STEEP LOW-LEVEL INVERSION WILL AGAIN BE PRESENT THROUGH THE DAY. OPTED TO GO SLIGHTLY WARMER THAN SUNDAY AND CLOSE TO MAV TEMPERATURES. GFS TRENDS SHOWED AIRMASS WILL BE RELATIVELY DRY AT LOW LEVELS MONDAY EVENING THEN WILL MOISTEN UP LATE AT NIGHT BEHIND THE FRONT AS SHORTWAVE MOVES INTO AREA. THUS REMOVED POPS FROM LOW ELEVATIONS IN THE WEST THROUGH 06Z. OTHERWISE POPS WERE IN LINE WITH LATEST GUIDANCE. LOWERED TEMPS A FEW DEGREES CLOSER TO MAV GUIDANCE MON NIGHT. ARTHUR .LONG TERM...VALID FOR TUE...WED...THU...FRI...SAT... RIDGE STILL EXPECTED TO BE BROKEN DOWN AS WHAT LOOKS LIKE A POTENT LITTLE SHORT WAVE DIVES SOUTHEAST FROM BRITISH COLUMBIA AND MOVES ACROSS THE STATE EARLY TUESDAY. THE ECMWF SEEMS TO BE IN AGREEMENT WITH THIS WAVE AS WELL. HOWEVER...PREVIOUS GFS RUNS DO NOT AGREE WITH TIMING OF THIS FEATURE. ALTHOUGH THE LAST COUPLE OF RUNS ARE BEGINNING TO AGREE WITH TIMING BETWEEN 12Z AND 18Z. FOR NOW...WILL NOT STRAY FROM CURRENT HIGH CHANCE POPS ACROSS THE ENTIRE FORECAST AREA. AFTER TUESDAY...ALL BETS ARE OFF AS MODELS IN TERRIBLE AGREEMENT. THE ECMWF PLACES A RIDGE OVER THE SAME AREA WITH RIDGE AXIS JUST TO OUR WEST ALLOWING FOR SLOWLY RISING HEIGHTS AND A DRY MILD NORTHWEST FLOW ALOFT. HOWEVER...THE GFS CARVES A TROUGH OVER THE NORTHERN ROCKIES WEDNESDAY AND THURSDAY WITH A MOIST ZONAL FLOW THURSDAY AND FRIDAY. IN ADDITION...THE GFS BRINGS A SURFACE LOW ACROSS YELLOWSTONE PARK AND NORTHERN WYOMING. THIS PATTERN WOULD BRING COLDER TEMPERATURES AND A MOIST UPSLOPE FLOW TO MOST OF THE FORECAST AREA. HOWEVER...THIS LOW IS NEW FOR THIS TIME AS PREVIOUS RUNS DID NOT SHOW THIS. AS THE PREVIOUS SHIFTS DISCUSSION MENTIONED...TROPICAL CONVECTION ACROSS THE DATELINE AND FAR WESTERN PACIFIC WILL BEGIN TO DECREASE. THIS WOULD ALLOW THE CURRENT RIDGE TO MOVE WEST A BIT KEEPING OUR AREA IN A COOLER UNSETTLED PATTERN. WILL THEREFORE SIDE MORE WITH THE GFS FOR NOW BUT NOT PUT ALL BETS ON IT. HAVE MADE ONLY A FEW MINOR TWEAKS TO FORECAST AND WILL LEAVE FORECAST AS IS UNTIL BETTER AND MORE CONSISTENT MODEL RUNS APPEAR. IF THE GFS CONTINUES TO TREND THE WAY IT IS...THE COMING WEEK COULD BE QUITE UNSETTLED WITH SEVERAL PERIODS OF SNOW POSSIBLE. HOOLEY && .AVIATION... MID TO HIGH LEVEL CLOUDS WILL CONTINUE TO STREAM ACROSS THE FORECAST AREA FOR THE REMAINDER OF THE AFTERNOON AND THROUGHOUT THE OVERNIGHT HOURS. IN ADDITION...WINDY CONDITIONS WILL OCCUR IN THE VICINITY OF KLVM...AS WELL AS...THE ENTIRE FRONT RANGE OF THE ROCKIES. OTHERWISE...NO AVIATION HAZARDS ARE EXPECTED. HOOLEY && .PRELIMINARY POINT TEMP/POPS... SUN MON TUE WED THU FRI SAT ----------------------------------------------------------- BIL 032/041 028/043 022/033 017/029 013/025 012/023 012/028 00/U 00/U 03/S 33/S 23/S 33/S 33/S LVM 030/044 027/046 021/033 017/026 013/024 010/022 010/030 00/U 00/N 23/S 33/S 33/S 33/S 33/S HDN 028/046 025/048 020/033 016/027 012/026 012/021 012/029 00/U 00/U 03/S 33/S 23/S 33/S 33/S MLS 029/042 022/044 017/031 014/025 010/023 006/018 006/021 00/B 00/U 03/S 33/S 23/S 32/S 22/S 4BQ 023/046 022/048 020/033 015/027 009/022 008/022 008/029 00/B 00/B 03/S 33/S 23/S 32/S 22/S BHK 026/039 021/041 017/028 011/024 005/021 006/019 005/020 00/B 00/B 03/S 33/S 23/S 32/S 22/S SHR 025/044 017/046 016/034 010/026 007/026 008/024 008/029 00/B 00/U 03/S 33/S 23/S 33/S 33/S && .BYZ WATCHES/WARNINGS/ADVISORIES... MT...NONE. WY...NONE. && $$ WEATHER.GOV/BILLINGS