000 FXUS65 KTFX 112334 AFDTFX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GREAT FALLS MT 534 PM MDT MON MAY 11 2009 ...UPDATE TO AVIATION... && .DISCUSSION... TONIGHT THROUGH WEDNESDAY...SURFACE CAPES ARE NEARLY NEUTRAL AND THE AIRMASS HAS DRIED SOMEWHAT DURING THE DAY...AND THE CHANCE FOR EVENING CONVECTION IS SLIGHT. THE NEXT WEATHER PRODUCING SYSTEM WILL MOVE OVER THE WEST COAST BY TUESDAY MORNING. THE UPPER LEVEL JET WILL DIG UNDERNEATH THE SOUTHWEST ZONES TUESDAY AND DIVERGENCE ALOFT WILL SPREAD ACROSS THE CENTRAL AND SOUTHWEST ZONES. THE UPPER LEVEL TROF WILL CROSS THE ROCKIES LATE TUESDAY AND WEDNESDAY NIGHT. UPPER LEVEL LOW WILL MOVE ACROSS NORTHWEST MT AND MOVE EAST OVER THE HILINE/NORTHERN ZONES DURING THE DAY. COLD AIR AT 500 MB WILL MOVE OVER THE ZONES...-30C AND COLDER OVER THE SW ZONES. A CANADIAN COLD FRONT ASSOCIATED WITH THE LOW PRESSURE SYSTEM WILL CROSS THE HILINE AROUND MIDNIGHT TUESDAY NIGHT. AMS WILL BE QUITE MOIST AT LOWER LEVELS ACROSS NORTH AND CENTRAL ZONES THROUGH MID MORNING WEDNESDAY. TEMPS WILL REMAIN AROUND FREEZING AND SOME SNOW ACCUMULATION IS POSSIBLE ACROSS THE NORTH AND CENTRAL ZONES. TEMPS WILL DROP BELOW NORMALS TUESDAY AND REMAIN BELOW THROUGH WEDNESDAY. ZELZER WEDNESDAY NIGHT THROUGH SATURDAY NIGHT...OVERALL PATTERN REMAINS FAIRLY PROGRESSIVE THROUGH THE REMAINDER OF THIS WEEK WITH A TREND TOWARD STRONGER UPPER LEVEL RIDGING ALONG THE WEST COAST BY THE WEEKEND. PERIOD BEGINS WITH A WEAK SHORTWAVE RIDGE OVER THE REGION WEDNESDAY NIGHT FOR MAINLY DRY CONDITIONS BEFORE ANOTHER BROAD TROUGH DROPS INTO THE NORTHERN ROCKIES THURSDAY AND THURSDAY NIGHT. MODELS ARE HAVING SOME DIFFICULTY WITH THE TIMING OF THE MAIN SHORTWAVE FEATURE WITHIN THE UPPER LEVEL TROUGH. THEREFORE CONFIDENCE IS NOT HIGH ENOUGH FOR MUCH MORE THAN CHANCE POPS IN ANY ONE PERIOD THURSDAY THROUGH FRIDAY. A NORTHWEST FLOW ALOFT DEVELOPS LATE FRIDAY THROUGH SATURDAY NIGHT OVER THE REGION BEHIND THE DEPARTING TROUGH AND IN RESPONSE TO A BUILDING LONGWAVE RIDGE ALONG THE WEST COAST. MODELS DISAGREE WITH RESPECT TO MOISTURE AND WEAK ENERGY EMBEDDED WITHIN THE NW FLOW WITH GFS MODEL QUICKER TO DRY OUT THE AREA WHILE THE ECMWF MAINTAINS ENOUGH ENERGY ACROSS NORTHERN ZONES TO MAINTAIN A SLIGHT CHANCE FOR SHOWERS THROUGH AT LEAST SATURDAY MORNING. TEMPERATURES WILL BE SLIGHTLY BELOW SEASONAL AVERAGES THURSDAY AND FRIDAY BEFORE REBOUNDING TO NEAR OR EVEN SLIGHTLY ABOVE AVERAGE FOR THE WEEKEND. HOENISCH SUNDAY AND MONDAY...MODELS CONTINUE TO DEPICT A HIGH PRESSURE BUILDING IN FROM THE WEST WHICH WILL INCREASE TEMPERATURES TO SLIGHTLY ABOVE SEASONAL AVERAGES FOR THE NORTH CENTRAL PLAINS. WESTERLY WINDS WILL LIKELY BE BREEZY ALONG THE NORTHERN ROCKY MOUNTAIN FRONT AND THE CENTRAL PLAINS. SAUCIER && .AVIATION... UPDATED 2345Z. VFR CONDITIONS WILL PREVAIL AT ALL TAF SITES FOR THE NEXT 24 HOURS. DIURNAL HEATING HAS PEAKED AND THE ISOLATED STORMS IN THE AREA ARE ALREADY STARTING TO WEAKEN. THESE STORMS SHOULD CONTINUE TO DECREASE IN INTENSITY AND COVERAGE OVER THE NEXT FEW HOURS. SOME ISOLATED STORMS MAY CONTINUE AFTER DUSK DUE TO THE WEAK UPPER LEVEL DISTURBANCE MOVE ACROSS THE AREA. WINDS WILL INCREASE TOMORROW MORNING WITH PEAK HEATING AND A SLIGHTLY TIGHTER PRESSURE GRADIENT AHEAD OF THE SYSTEM SET TO MOVE OVER THE AREA WEDNESDAY. SOME AFTERNOON SHOWERS ARE POSSIBLE AGAIN TOMORROW. SUK && .PREV DISCUSSION... /ISSUED 239 PM MDT MON MAY 11 2009/ TONIGHT THROUGH WEDNESDAY...SURFACE CAPES ARE NEARLY NEUTRAL AND THE AIRMASS HAS DRIED SOMEWHAT DURING THE DAY...AND THE CHANCE FOR EVENING CONVECTION IS SLIGHT. THE NEXT WEATHER PRODUCING SYSTEM WILL MOVE OVER THE WEST COAST BY TUESDAY MORNING. THE UPPER LEVEL JET WILL DIG UNDERNEATH THE SOUTHWEST ZONES TUESDAY AND DIVERGENCE ALOFT WILL SPREAD ACROSS THE CENTRAL AND SOUTHWEST ZONES. THE UPPER LEVEL TROF WILL CROSS THE ROCKIES LATE TUESDAY AND WEDNESDAY NIGHT. UPPER LEVEL LOW WILL MOVE ACROSS NORTHWEST MT AND MOVE EAST OVER THE HILINE/NORTHERN ZONES DURING THE DAY. COLD AIR AT 500 MB WILL MOVE OVER THE ZONES...-30C AND COLDER OVER THE SW ZONES. A CANADIAN COLD FRONT ASSOCIATED WITH THE LOW PRESSURE SYSTEM WILL CROSS THE HILINE AROUND MIDNIGHT TUESDAY NIGHT. AMS WILL BE QUITE MOIST AT LOWER LEVELS ACROSS NORTH AND CENTRAL ZONES THROUGH MID MORNING WEDNESDAY. TEMPS WILL REMAIN AROUND FREEZING AND SOME SNOW ACCUMULATION IS POSSIBLE ACROSS THE NORTH AND CENTRAL ZONES. TEMPS WILL DROP BELOW NORMALS TUESDAY AND REMAIN BELOW THROUGH WEDNESDAY. ZELZER WEDNESDAY NIGHT THROUGH SATURDAY NIGHT...OVERALL PATTERN REMAINS FAIRLY PROGRESSIVE THROUGH THE REMAINDER OF THIS WEEK WITH A TREND TOWARD STRONGER UPPER LEVEL RIDGING ALONG THE WEST COAST BY THE WEEKEND. PERIOD BEGINS WITH A WEAK SHORTWAVE RIDGE OVER THE REGION WEDNESDAY NIGHT FOR MAINLY DRY CONDITIONS BEFORE ANOTHER BROAD TROUGH DROPS INTO THE NORTHERN ROCKIES THURSDAY AND THURSDAY NIGHT. MODELS ARE HAVING SOME DIFFICULTY WITH THE TIMING OF THE MAIN SHORTWAVE FEATURE WITHIN THE UPPER LEVEL TROUGH. THEREFORE CONFIDENCE IS NOT HIGH ENOUGH FOR MUCH MORE THAN CHANCE POPS IN ANY ONE PERIOD THURSDAY THROUGH FRIDAY. A NORTHWEST FLOW ALOFT DEVELOPS LATE FRIDAY THROUGH SATURDAY NIGHT OVER THE REGION BEHIND THE DEPARTING TROUGH AND IN RESPONSE TO A BUILDING LONGWAVE RIDGE ALONG THE WEST COAST. MODELS DISAGREE WITH RESPECT TO MOISTURE AND WEAK ENERGY EMBEDDED WITHIN THE NW FLOW WITH GFS MODEL QUICKER TO DRY OUT THE AREA WHILE THE ECMWF MAINTAINS ENOUGH ENERGY ACROSS NORTHERN ZONES TO MAINTAIN A SLIGHT CHANCE FOR SHOWERS THROUGH AT LEAST SATURDAY MORNING. TEMPERATURES WILL BE SLIGHTLY BELOW SEASONAL AVERAGES THURSDAY AND FRIDAY BEFORE REBOUNDING TO NEAR OR EVEN SLIGHTLY ABOVE AVERAGE FOR THE WEEKEND. HOENISCH SUNDAY AND MONDAY...MODELS CONTINUE TO DEPICT A HIGH PRESSURE BUILDING IN FROM THE WEST WHICH WILL INCREASE TEMPERATURES TO SLIGHTLY ABOVE SEASONAL AVERAGES FOR THE NORTH CENTRAL PLAINS. WESTERLY WINDS WILL LIKELY BE BREEZY ALONG THE NORTHERN ROCKY MOUNTAIN FRONT AND THE CENTRAL PLAINS. SAUCIER && .PRELIMINARY POINT TEMPS/POPS... GTF 38 54 31 55 / 20 40 50 10 CTB 37 50 30 52 / 20 30 60 10 HLN 40 52 34 59 / 10 40 30 10 BZN 40 57 32 59 / 20 60 40 10 WEY 32 46 19 48 / 20 50 50 10 DLN 37 51 27 54 / 20 40 30 10 HVR 38 61 33 58 / 30 30 60 10 LWT 36 53 29 53 / 30 50 50 20 && .TFX WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...ZELZER LONG TERM...BRUSDA AVIATION...SUK WEATHER.GOV/GREATFALLS