000 FXUS65 KTFX 022035 AFDTFX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GREAT FALLS MT 235 PM MDT THU APR 2 2009 .DISCUSSION... TODAY THROUGH SATURDAY...THE COOL AND UNSETTLED PATTERN OF LATE CONTINUES FOR THE NEXT COUPLE DAYS WITH THE NEXT UPPER LEVEL TROUGH TO IMPACT THE REGION MOVING INTO THE CENTRAL AND SOUTHERN ROCKIES TODAY. A SURFACE LOW DEVELOPS OVER WESTERN AND CENTRAL MT TODAY IN RESPONSE TO THE INCOMING TROUGH WITH LATEST MODELS TRENDING SLIGHTLY DRYER FOR THE REGION TODAY. A WINTER WEATHER EVENT IS STILL EXPECTED TO IMPACT PORTIONS OF THE FORECAST AREA LATER TONIGHT THROUGH TOMORROW. TEMPS WILL INITIALLY BE WARM ENOUGH FOR A RAIN SNOW MIX AT LOWER ELEVATIONS. STEADIER PRECIPITATION DEVELOPS TONIGHT WITH SNOW LEVELS FALLING TO MOST OF THE LOWER ELEVATIONS BY LATE EVENING. THE BEST CHANCE FOR SIGNIFICANT SNOW AMOUNTS APPEARS TO BE ALONG THE NORTH AND EAST SLOPES OF THE ROCKY MTN FRONT AND LITTLE BELT AND BIG SNOWY MTN RANGES. A SECONDARY MAXIMUM IN SNOW IS EXPECTED OVER THE SW MT MTNS NEAR THE ID AND WY BORDERS. THE VALLEYS OF SW MT AND NORTH CENTRAL PLAINS BELOW 4000 FEET IN ELEVATION WILL SEE SNOW ACCUMULATIONS GENERALLY LESS THAN 3 INCHES. HAVE ISSUED A WINER STORM ADVISORY FOR PORTIONS OF THE FORECAST AREA TO HIGHLIGHT SNOW POTENTIAL. THE SYSTEM EXITS THE REGION FRIDAY NIGHT THOUGH SATURDAY WITH COOL/MOIST AND SOMEWHAT UNSTABLE NORTHERLY FLOW ALOFT PERSISTING FOR LINGERING SNOW SHOWERS AND CONTINUED COOL TEMPERATURES. GUSTAFSON SATURDAY NIGHT THROUGH TUESDAY NIGHT...THERE CONTINUES TO BE DIFFERENCES BETWEEN THE GFS AND ECMWF WITH HOW FAST THE UPPER RIDGE MOVES OVER THE FORECAST AREA EARLY NEXT WEEK. THE GFS CONTINUES TO BE FASTER THAN THE ECMWF WITH THE GFS MOVING THE UPPER RIDGE OVER THE FORECAST AREA MONDAY WHILE THE ECMWF HOLDS OFF UNTIL MONDAY NIGHT. ALTHOUGH THERE ARE DIFFERENCES WITH THE TIMING OF THE UPPER RIDGE..MODELS DO TEND TO AGREE THERE WILL BE SOME LINGERING MOISTURE IN THE NORTHERLY FLOW ALOFT AHEAD OF THE UPPER RIDGE. HAVE REINTRODUCED A THREAT OF SNOW SHOWERS IN THE AREA FROM SOUTHERN FERGUS AND AND JUDITH BASIN COUNTIES TO MOST OF MEAGHER AND GALLATIN COUNTIES FOR SATURDAY NIGHT. MODELS ALSO TEND TO AGREE ON A THREAT OF PRECIPITATION FOR THE FAR EASTERN ZONES ON SUNDAY SO ADDED SLIGHT CHANCE POPS TO BLAINE AND FERGUS COUNTIES. RIDGING SHOULD KEEP THE AREA DRY SUNDAY NIGHT THROUGH MONDAY NIGHT. THE QUESTION THEN BECOMES HOW QUICKLY WILL MOISTURE MOVE INTO THE AREA AS THE UPPER RIDGE SLOWLY MOVES EAST. LIKE WITH THE UPPER RIDGE THE GFS IS FASTER THAN THE ECMWF. GFS DEVELOPS PRECIPITATION OVER MOST OF THE THE AREA BY TUESDAY WHILE THE ECMWF IS AT LEAST A DAY LATER. DUE TO UNCERTAINTY WITH SOLUTIONS THAT FAR OUT WILL CONTINUE WITH SLIGHT CHANCE TO CHANCE POPS FOR ABOUT THE SOUTHWEST HALF OF THE FORECAST AREA BY TUESDAY. WOULD NOT BE SURPRISED IF THE PRECIPITATION BECOMES DELAYED IN FUTURE RUNS. WITH THE AREA FEELING THE EFFECTS OF THE UPPER RIDGE RAISED HIGH TEMPERATURES FOR MONDAY. ALSO FEEL MOISTURE AND COOLING WILL BE SLOWER TO MOVE INTO THE AREA THAN WHAT THE GFS HAS FOR TUESDAY SO HAVE ALSO RAISED HIGH TEMPERATURES FOR THAT DAY AS WELL. BLANK WEDNESDAY AND THURSDAY...MOST MODELS INDICATE A WEAK UPPER LEVEL RIDGE OVER MONTANA WITH A DEEP UPPER LEVEL LOW OVER THE UPPER MIDWEST. MODELS ALSO INDICATES AN UPSLOPE FLOW PATTERN DURING THE PERIOD. THUS...WILL GO WITH A LITTLE COOLER THAN SEASONAL AVERAGE WITH A SLIGHT CHANCE OF RAIN AND SNOW SHOWERS. WILLIAMSON DC && .AVIATION... UPDATED 1750Z CLOUD COVER WILL STEADILY INCREASE ACROSS CENTRAL AND SOUTHWEST MT THIS AFTN AS LEADING EDGE OF MOISTURE FROM QUICK-MOVING UPPER LEVEL DISTURBANCE...CURRENTLY IN ERN WA...MOVES IN FROM THE WEST. MIX OF VALLEY RAIN/MTN SNOW SHOWERS WILL ALSO DEVELOP THIS AFTN/EVE WITH CEILINGS DROPPING INTO MVFR TO OCCASIONAL IFR CATEGORIES...WITH MTN OBSCURATIONS. BULK OF THIS SYSTEM ARRIVES TONIGHT WITH PRECIP CHANGING TO ALL SNOW. FORECAST MODELS INDICATE MAIN SNOW AREA FROM KHLN TO KLWT SOUTHWARD WITH LIFR CONDITIONS POSSIBLE FROM KBZN TO KLWT EARLY FRI MORNING. SYSTEM SHOULD MAKE STEADY PROGRESS TO THE EAST TOMORROW WITH GRADUAL IMPROVEMENT BACK TO VFR AT ALL TERMINALS FROM 15Z ONWARD. WARANAUSKAS && .PRELIMINARY POINT TEMPS/POPS... GTF 29 37 25 40 / 70 70 60 20 CTB 26 36 23 38 / 70 70 40 20 HLN 28 38 28 42 / 50 70 60 20 BZN 28 39 28 42 / 60 80 70 30 WEY 25 35 21 36 / 80 70 50 30 DLN 26 36 25 36 / 50 70 60 20 HVR 28 42 25 41 / 20 40 20 10 LWT 27 35 23 35 / 90 90 60 40 && .TFX WATCHES/WARNINGS/ADVISORIES... WINTER WEATHER ADVISORY FROM 6 PM THIS EVENING TO MIDNIGHT MDT FRIDAY NIGHT FOR MTZ008-012-015-050-051-054-055. && $$ SHORT TERM...GUSTAFSON LONG TERM...WARANAUSKAS AVIATION...WARANAUSKAS WEATHER.GOV/GREATFALLS