000 FXUS65 KTFX 112124 AFDTFX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GREAT FALLS MT 324 PM MDT SAT APR 11 2009 .DISCUSSION... TONIGHT THROUGH MONDAY...SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS HAVE DEVELOPED OVER NORTH CENTRAL...CENTRAL...AND SOUTHWEST MONTANA THIS AFTERNOON AHEAD OF AN UPPER LEVEL SHORTWAVE TROUGH. WITH THE ASSOCIATED WEAK FRONTAL BOUNDARY ALREADY CENTERED OVER THE TFX CWA...AM EXPECTING THE BETTER CHANCE FOR THUNDERSTORM ACTIVITY ALONG AND EAST OF A DILLON-TO-HELENA-TO-GREAT FALLS-TO JUST WEST OF HAVRE LINE. IN FACT...A STRONG THUNDERSTORM HAD ALREADY DEVELOPED AS OF 3 PM MDT IN BLAINE COUNTY. THE MAIN THREAT FROM THESE STORMS WILL BE SMALL HAIL AND BRIEF HEAVY RAINFALL...DUE TO PRECIPITABLE WATER VALUES OF 0.50 INCHES AND GREATER EAST OF THE AFOREMENTIONED LINE. ACTIVITY WILL DECREASE AFTER SUNSET AND OVERNIGHT AS THE COLD FRONT ASSOCIATED WITH THE SHORTWAVE TROUGH MOVES THROUGH THE CWA AND BREEZY WESTERLY WINDS DEVELOP IN THE WAKE OF THE FRONT. HOWEVER...CLEARING SKIES WITH LOW LEVEL MOISTURE IN SOUTHWEST MONTANA MAY CAUSE PATCHY VALLEY FOG THERE. AN UPPER LEVEL RIDGE WILL THEN KEEP THE AREA DRY ON SUNDAY. THE NEXT PACIFIC SYSTEM WILL APPROACH MONTANA SUNDAY NIGHT FOR AN INCREASINGLY MOIST SOUTHWESTERLY FLOW ALOFT AND AN INCREASING CHANCE OF SHOWERS OVER THE WESTERN MONTANA MOUNTAINS. THE SYSTEM WILL THEN MOVE INTO MONTANA ON MONDAY...FURTHER INCREASING THE FLOW ALOFT AND SHIFTING IT MORE WESTERLY. A COLD FRONT WILL ALSO MOVE SOUTHEAST THROUGH THE TFX CWA ON MONDAY...LIKELY BRINGING PRECIPITATION TO THE MOUNTAINS WITH A GOOD CHANCE OF PRECIPITATION IN THE VALLEYS. WESTERLY SURFACE WILL ALSO INCREASE ALONG AND BEHIND THE COLD FRONT...WHILE THE CHANCE FOR PRECIPITATION WILL INCREASE ON MONDAY IN THE VICINITY OF THE FRONT (ALONG AND SOUTH OF A GREAT FALLS-TO- HAVRE LINE). TEMPERATURES WILL REMAIN AROUND 5 TO 10 DEGREES ABOVE NORMAL DURING THE PERIOD...BUT WILL FALL CLOSER TO NORMAL BEHIND THE COLD FRONT ON MONDAY. COULSTON MONDAY NIGHT THROUGH THURSDAY NIGHT...MODELS ARE NOW IN MUCH BETTER AGREEMENT WITH THE TRACK OF THE WEATHER SYSTEM FOR THE PERIOD..THOUGH THERE ARE STILL SOME DIFFERENCES. THE LATEST RUN OF THE ECMWF HAS TAKEN A MORE NORTHERN TRACK WITH THE WEATHER SYSTEM THAN IT DID YESTERDAY. CONSEQUENTLY MODELS ARE IN GENERAL AGREEMENT THAT THE UPPER LOW PRESSURE AREA WILL MOVE INTO THE PACIFIC NORTHWEST MONDAY NIGHT THEN INTO THE GREAT BASIN BY WED AND INTO WYOMING OR COLORADO WED NIGHT OR THURSDAY. IT NOW APPEARS THE FORECAST AREA WILL BE UNDER THE GUN FOR A PRECIPITATION EVENT FROM TUESDAY INTO THURSDAY. FEEL CONFIDENT ENOUGH ABOUT THIS WEATHER SYSTEM TO RAISE THE CHANCES OF PRECIPITATION INTO THE LIKELY CATEGORY FOR PORTIONS OF THE FORECAST AREA AT LEAST TUESDAY INTO WEDNESDAY. AT THIS TIME IT APPEARS THE ROCKY MOUNTAIN FRONT AND NEARBY PLAINS WILL HAVE LESS OF A THREAT OF PRECIPITATION. IT STILL LOOKS LIKE THE MOUNTAINS COULD RECEIVE UP TO A FOOT OF SNOW WITH THE SOUTHWEST VALLEYS AND PLAINS POSSIBLY SEEING SEVERAL INCHES OF SNOW THROUGH WEDNESDAY NIGHT. BLANK FRIDAY THROUGH SATURDAY...MODELS ARE STRUGGLING WITH RUN TO RUN CONSISTENCY...BUT ARE IN ROUGH AGREEMENT WITH AN UPPER LEVEL RIDGE INFLUENCING THE FORECAST AREA DURING THIS PERIOD. THE RIDGE BUILDS IN BEHIND AN UPPER LEVEL TROUGH THAT MOVES OFF TO THE EAST EARLY FRIDAY. THERE ARE DIFFERENCES IN TIMING AND AMPLITUDE OF FEATURES... BUT A DRY AND MILD PERIOD IS EXPECTED UNDER PARTLY TO MOSTLY CLOUDY SKIES. A FEW RAIN OR SNOW SHOWERS LARGELY MOVE OFF TO THE EAST FRIDAY...BUT A FEW MOUNTAIN SHOWERS ARE POSSIBLE THROUGH SATURDAY. TEMPERATURES WILL WARM TO NEAR SEASONAL AVERAGES FOR MOST AREAS BY SATURDAY. EK && .AVIATION... UPDATED 1755Z. A WEATHER SYSTEM ALOFT WILL BE MOVING THROUGH THE AREA OVERNIGHT. EXPECT SHOWERS AND A FEW THUNDERSTORMS AHEAD OF IT. ALTHOUGH CONDITIONS WILL BE PRIMARILY VFR CAN NOT RULE OUT LOCAL MVFR CONDITIONS WITH THE SHOWERS AND THUNDERSTORMS. ALTHOUGH NOT MENTIONED IN THE TAFS AFTER THE SYSTEM MOVES EAST LATE TONIGHT AND CLOUDS DECREASE COULD SEE PATCHY FOG IN THE SW VALLEYS. BLANK && .PRELIMINARY POINT TEMPS/POPS... GTF 36 60 39 56 / 30 0 10 30 CTB 34 57 36 51 / 20 0 10 20 HLN 33 61 38 55 / 30 0 20 40 BZN 31 61 33 59 / 40 0 20 50 WEY 26 52 26 48 / 50 10 0 50 DLN 29 54 32 53 / 20 0 20 50 HVR 37 62 35 60 / 50 10 10 20 LWT 34 57 34 56 / 50 0 10 40 && .TFX WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...COULSTON LONG TERM...BLANK/EK AVIATION...BLANK WEATHER.GOV/GREATFALLS