000 FXUS65 KTFX 082333 AFDTFX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GREAT FALLS MT 533 PM MDT THU MAY 8 2008 ...UPDATE TO AVIATION... .DISCUSSION... TONIGHT...A SLIGHTLY UNSTABLE AIRMASS WILL CONTINUE TO RESIDE OVER NORTH CENTRAL MONTANA...AS THE MAIN UPPER LEVEL TROF REMAINS TO OUR WEST. THUS ISOLATED TO SCATTERED SHOWERS CAN BE EXPECTED ACROSS THE REGION...WITH THE BEST CHANCE FOR PRECIP AND ISOLATED THUNDERSTORMS CONTINUING IN THE HAVRE AREA. OVERNIGHT LOWS WILL BE NEAR NORMAL. FOR FRIDAY...THE MAIN UPPER LEVEL LOW WILL SLOWLY DRIFT OVER THE REGION...CREATING AN UNSTABLE AIRMASS. THUS SCATTERED SHOWERS WILL BE LIKELY OVER THE REGION...SIMILAR TO THE PRECIP ACTIVITY THAT IS HAPPENING OVER NORTHERN WASHINGTON THIS AFTERNOON...WITH THE BEST CHANCE FOR PRECIP OCCURRING OVER NORTH CENTRAL MONTANA. AN ALL DAY RAIN IS NOT EXPECTED ON FRIDAY...BUT SEVERAL SHORT LIVED SHOWERS COULD PASS OVER THE SAME AREA THROUGHOUT THE DAY. WITH THE UPPER LEVEL LOW OVER THE REGION...TEMPERATURES WILL BE BELOW NORMAL. FOR FRIDAY NIGHT THROUGH SATURDAY...A WEAK UPPER LEVEL RIDGE WILL START TO BUILD OVER THE REGION. THUS EXPECT A DRYING TREND WITH MOST OF THE SHOWER ACTIVITY ENDING BY LATE FRIDAY NIGHT OR EARLY ON SATURDAY MORNING. TEMPERATURES WILL SLOWLY WARM BACK UP TO NEAR SEASONAL NORMALS BY SATURDAY AFTERNOON. BRUSDA SATURDAY NIGHT THROUGH TUESDAY NIGHT...THE PERIOD BEGINS WITH A WEAK UPPER RIDGE OVER THE AREA. BY SUNDAY THE RIDGE BECOMES FLATTENED AS AN UPPER TROF RACES ALONG THE INTERNATIONAL BOUNDARY. DOWNSLOPE WESTERLY FLOW ALOFT WILL LIMIT PRECIPITATION TO THE WESTERN MOUNTAINS WHILE KEEPING THE PLAINS DRY. MOISTURE BEGINS TO INCREASE OVER THE AREA SUNDAY AS AN UPPER TROF DIGS OVER THE PACIFIC NORTHWEST. A BROAD UPPER TROF OVER THE AREA MONDAY WILL BRING SCATTERED SHOWERS AND COOLER TEMPERATURES. A POSITIVE TILT UPPER RIDGE BEGINS BUILDING OVER WESTERN MONTANA LATE TUESDAY PORTENDING A WARMER AND DRIER PERIOD BY MIDWEEK. TEMPERATURES WILL BE NEAR OR SLIGHTLY BELOW SEASONAL AVERAGES. WEDNESDAY AND THURSDAY...MODELS CONTINUE TO SHOW A RATHER STRONG UPPER LEVEL HIGH OVER THE PACIFIC NORTHWEST WITH A NORTHWEST TO NORTH FLOW ALOFT ACROSS MONTANA. THUS...WILL GO WITH TEMPERATURES NEAR SEASONAL AVERAGE WITH ISOLATED...MAINLY AFTERNOON AND EVENING SHOWERS OVER THE MOUNTAINS. THE PLAINS AND VALLEYS WILL BE MOSTLY DRY. WILLIAMSON DC && .AVIATION... AN UPPER LEVEL LOW OVER THE SOUTHERN BRITISH COLUMBIA AND ALBERTA BORDER REGION WILL MOVE SOUTHEAST TONIGHT AND FRIDAY. A SOMEWHAT UNSTABLE SOUTHWEST FLOW ALOFT WILL BRING ISOLATED TO SCATTERED SHOWERS TO THE FORECAST AREA WITH LOCAL MVFR CONDITIONS POSSIBLE IN PRECIPITATION THROUGH 04Z THIS EVENING. AS THE UPPER LOW MOVES OVER NORTH CENTRAL MONTANA SCATTERED SHOWERS WILL REDEVELOP ACROSS THE FORECAST AREA AFTER 09Z. A SURFACE COLD FRONT WILL ALSO MOVE SOUTH OF THE CANADIAN BORDER WITH AREAS OF LIGHT RAIN AND SNOW INCREASING IN COVERAGE FROM KCTB-KHVR AND MOVING SOUTH. AREAS MVFR AND LOCAL IFR CONDITIONS ARE EXPECTED ACROSS NORTH CENTRAL MONTANA THROUGH THE DAY ON FRIDAY. MPJ && .PRELIMINARY POINT TEMPS/POPS... GTF 33 50 28 61 / 20 40 20 10 CTB 29 48 26 61 / 20 50 20 10 HLN 38 54 34 63 / 30 30 30 10 BZN 35 53 31 60 / 40 30 40 10 WEY 29 46 24 48 / 60 60 40 20 DLN 32 49 27 58 / 20 30 20 10 HVR 33 52 28 61 / 30 50 20 10 LWT 31 48 26 56 / 30 40 30 10 && .TFX WATCHES/WARNINGS/ADVISORIES... NONE. && $$ WEATHER.GOV/GREATFALLS