000 FXUS65 KTFX 220457 AFDTFX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GREAT FALLS MT 1054 PM MDT TUE APR 21 2009 UPDATED AVIATION .UPDATE... SATELLITE IMAGERY SHOWS CLOUDY SKIES OVER THE FAR NORTHWEST ZONES AT MID-EVENING AND EXPECT THIS CLOUD COVER TO SLOWLY SPREAD SOUTHEAST THE REMAINDER OF TONIGHT SO THE MAIN FORECAST CHANGE WAS TO INCREASE SKY COVER IN THE NW FOR THE REMAINDER OF TONIGHT. REMAINDER OF THE FORECAST LOOKS ON TRACK. AS FOR THE HIGH WIND SITUATION LOOKS VERY MARGINAL FOR HIGH WINDS BUT THERE STILL IS A SMALL THREAT FOR THEM SO DO NOT PLAN ON DROPPING THE HIGH WIND WATCH. BLANK && .AVIATION... UPDATED 0600Z. UPPER LEVEL RIDGE OF HIGH PRESSURE WILL SHIFT EASTWARD TONIGHT WITH FLOW BECOMING MORE ZONAL ON WEDNESDAY. DRY/VFR CONDITIONS WILL PERSIST OVER THE NEXT 24 HOURS WITH A FEW HIGH CLOUDS ARRIVING OVERNIGHT AND INCREASING MID TO HIGH CLOUDS ON WEDNESDAY AFTERNOON AHEAD OF OUR NEXT LOW PRESSURE TROUGH. VCSH AND ISOLATED THUNDERSTORMS ARE POSSIBLE AT KBZN WEDNESDAY AFTERNOON AND EVENING WITH VCSH POSSIBLE AT KCTB AND KHLN. GUSTY SURFACE WEST WINDS ARE ANTICIPATED ON WEDNESDAY ACROSS NORTH-CENTRAL AND CENTRAL MONTANA. STRONGEST WINDS ARE EXPECTED ALONG THE NORTHERN ROCKY MOUNTAIN FRONT AND ADJACENT PLAINS WHERE WIND GUSTS UP TO 50 MPH ARE POSSIBLE. MLS && .HYDROLOGY... TEMPERATURES ARE EXPECTED TO BE WELL ABOVE SEASONAL AVERAGES THROUGH WEDNESDAY. THERE IS A RISK THAT MOUNTAIN RUNOFF COULD CAUSE CREEKS AND SMALL STREAMS TO RISE TO NEAR OR ABOVE BANK FULL LEVELS IN PORTIONS OF SOUTHWEST AND NORTH CENTRAL MONTANA. && .PREV DISCUSSION... /ISSUED 555 PM MDT TUE APR 21 2009/ TONIGHT THROUGH THURSDAY...AN UPPER LEVEL HIGH PRESSURE RIDGE WILL BE OVER THE ZONES TONIGHT BUT MID LEVEL WINDS WILL REMAIN QUITE STRONG. HIGH WINDS ARE POSSIBLE OVER THE NORTHERN ROCKIES BUT THE AIRMASS LOOKS SLIGHTLY UNSTABLE OVER THE ROCKIES AND NOT REAL SUPPORTIVE OF HIGH WINDS. WILL PUSH GUSTS NEAR WARNING CRITERIA OVER THE ROCKIES BUT NOT ISSUE A STATEMENT. HOWEVER...WEDNESDAY AFTERNOON LOOKS VERY GOOD FOR A HIGH WIND EVENT...STRONG WINDS ALOFT AND VERY GOOD MIXING. WILL ISSUE A WATCH FOR MID MORNING THROUGH EARLY EVENING. THE NEXT WEATHER SYSTEM IS OVER THE EASTERN PACIFIC AND APPROACHING THE WEST COAST. OUR RIDGE MOVES OVER EASTERN MONTANA BY WEDNESDAY MORNING...HEIGHTS SLOWLY FALL...AND A CORE OF STRONGER FLOW ALOFT MOVES OVER THE AREA. AFTERNOON INSTABILITY BY WEDNESDAY AFTERNOON WILL STRETCH FROM SOUTHWEST MONTANA NORTH TO GTF-LWT LINE. MOISTURE AND SOME COOLING AT MID-LEVELS SHOULD BE ENOUGH FOR SLIGHT CHANCE OF THUNDERSTORMS. BY LATE WED NIGHT/THURSDAY MORNING COLDER AIR ALOFT WILL MOVE INTO NW MT AND PUSH SOUTH. A COLD FRONT SHOULD CROSS THE HILINE BEFORE MIDNIGHT...AND CTB AROUND 06Z THU. LOW LEVELS LOOK MOIST AND PRECIP SHOULD OCCUR WITH OR QUICKLY FOLLOWING FRONTAL PASSAGE. THE PUSH SOUTH SEEMS WEAK AND PRECIP DOES NOT APPEAR TO DEVELOP AS FAR SOUTH AS GTF UNTIL MID-MORNING THURSDAY. THURSDAY WILL BE SIGNIFICANTLY COOLER WITH TEMPS WELL BELOW NORMALS AND FALLING DURING THE DAY AS THE FRONT MOVES THROUGH THE ZONES. INSTABILITY LOOKS POSSIBLE AGAIN ACROSS THE EXTREME SOUTHWEST AND WILL CONTINUE A CHANCE OF THUNDERSTORMS IN THAT AREA...ELSEWHERE THE AIRMASS WILL BE QUITE STABLE. ZELZER THURSDAY NIGHT THROUGH SUNDAY NIGHT...MEDIUM RANGE MODELS CONTINUE IN GENERAL AGREEMENT TO START THE PERIOD. A POSITIVE TILT UPPER TROF WILL LIE ACROSS THE NORTHWEST UNITED STATES THURSDAY NIGHT PROVIDING A MOIST AND UNSTABLE SOUTHWEST FLOW ALOFT ACROSS THE AREA. ENOUGH COLD AIR WILL BE IN PLACE FOR PRECIPITATION TO FALL MAINLY AS SNOW. BY FRIDAY THE UPPER TROF BEGINS TO SPLIT WITH THE MAIN ENERGY DROPPING INTO NORTHERN CALIFORNIA. THE EUROPEAN MODEL IS MORE PRONOUNCED WITH THIS FEATURE BUT BOTH THE EUROPEAN AND GFS MODELS CONTINUE WITH WIDESPREAD PRECIPITATION OVER THE AREA FRIDAY. BY SATURDAY THE UPPER TROF AXIS MOVES THROUGH AND THE FLOW ALOFT BECOMES NORTHWEST. ENOUGH MOISTURE AND INSTABILITY REMAIN FOR SCATTERED SHOWERS. ANOTHER LOBE OF ENERGY ROTATES ACROSS THE AREA SUNDAY BRINGING ADDITIONAL PRECIPITATION. TEMPERATURES WILL REMAIN BELOW SEASONAL AVERAGES THROUGH THE PERIOD. MONDAY AND TUESDAY...LATEST MODELS INDICATE A DEEP LOW PRESSURE TROUGH MOVING THROUGH THE WEST. BELOW SEASONAL AVERAGE TEMPERATURES AND SCATTERED PRECIPITATION IS EXPECTED FOR MUCH OF THE REGION DURING THIS PERIOD. SAUCIER && .PRELIMINARY POINT TEMPS/POPS... GTF 48 75 38 42 / 0 10 40 60 CTB 46 67 32 32 / 0 10 60 60 HLN 48 76 40 46 / 0 20 20 60 BZN 37 79 41 53 / 0 20 20 60 WEY 26 62 31 51 / 0 20 20 70 DLN 39 71 39 50 / 10 20 20 60 HVR 45 75 38 43 / 0 10 50 50 LWT 42 74 39 40 / 0 20 20 60 && .TFX WATCHES/WARNINGS/ADVISORIES... HIGH WIND WATCH FROM 9 AM MDT WEDNESDAY THROUGH WEDNESDAY EVENING FOR MTZ009-010-044-046-048. && $$ WEATHER.GOV/GREATFALLS