000 FXUS65 KTFX 261052 AFDTFX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GREAT FALLS MT 352 AM MST THU FEB 26 2009 .DISCUSSION... TODAY THROUGH SATURDAY...WILL CANCEL THE ADVISORY FOR WIND CHILL AND CHANGE MOST OF THE WINTER WEATHER WATCH TO A SNOW ADVISORY. AN UPPER LEVEL LOW PRESSURE TROF IS MOVING THROUGH THE PACIFIC NORTHWEST. MOIST...SOUTHWEST FLOW AHEAD OF THIS SYSTEM CONTINUES TO OVER THE CWA. TIMING AND POSITIONING OF HEAVIEST SNOW REMAINS AN ISSUE. MODELS HAVE SHIFTED BACK TO A SOUTHERN SOLUTION FOR THE UPPER LEVEL LOW...AND MOVEMENT IS SLIGHTLY FASTER. IN ADDITION...NAM AND GFS DIFFER IN QPF AMOUNTS AND TIMING...WITH THE GFS BEING ABOUT 6 HOURS FASTER. THE TROF MOVES OVER IDAHO LATE THURSDAY AFTERNOON AND SHOULD BE MOVING EAST OF THE ZONES BY FRIDAY. NORTHWEST FLOW ALOFT WILL MOVE INTO PLACE AS A HIGH PRESSURE RIDGE BUILDS TO THE WEST. AT LOWER LEVELS...UPSLOPE FLOW IS QUITE WEAK. IN ADDITION...THE LATEST RUN OF THE NAM DOES NOT INDICATE AS MUCH MOISTURE AT LOW LEVELS. GENERATION OF LARGE AMOUNTS OF SNOW WILL NOT COME FROM THIS SOURCE. THE BUILDING HIGH PRESSURE RIDGE MOVES THE ROCKIES FRIDAY BUT A WEAK DISTURBANCE FLATTENS THE RIDGE DURING THE NIGHT. THIS WILL KEEP SOME INCREASED SKY COVER IN THE FORECAST. COLD AIR REMAINS IN THE AREA THROUGH THE PERIOD. THE COLD AIR HAS REACHED SOUTHWEST MONTANA AND MUCH COLDER TEMPS WILL BE SEEN THROUGH THE PERIOD. TEMPS RECOVER SOMEWHAT FRIDAY ACROSS THE NORTH AND CENTRAL ZONES AND RISE TO NEAR NORMALS AGAIN ON SATURDAY. ZELZER SATURDAY NIGHT THROUGH TUESDAY...A RIDGE WILL BUILD IN ON SATURDAY AND INTO SUNDAY AS WITH MOIST FLOW OUT OF THE SOUTHWEST AHEAD OF THE NEXT APPROACHING SYSTEM. VARIOUS RIPPLES WILL KEEP INSTABILITY ALOFT POSSIBLE THROUGH THE LATE WEEKEND AND FIRST PART OF THE WEEK AND ALLOW FOR SCATTERED SHOWERS ACROSS THE REGION. THE NEXT SYSTEM MAJOR SHOULD MOVE OVER OUR AREA MONDAY NIGHT...ALTHOUGH WEEKEND FROM CROSSING OVER THE ROCKIES. A WEEK RIDGE WILL QUICKLY BUILD OVER US IN ITS WAKE BUT SHOULD BE SHORT LASTING AS THE NEXT SYSTEM APPROACHES. NO SIGNIFICANT DISAGREEMENT BETWEEN THE MODELS AGAIN TODAY...SYSTEM SEEMS TO BE MOVING SLIGHTLY FASTER THAN THE MODELS ANTICIPATE...AND HAVE TAKEN THAT INTO ACCOUNT IN THE FORECAST. TEMPERATURES HAVE WARMED UP COMPARED TO THE PREVIOUS FORECAST THANKS TO THE STRONGER LONGER LASTING RIDGE DEVELOPING. SUK WEDNESDAY AND THURSDAY...MODELS SHOW A LONG WAVE TROUGH OVER THE EASTERN PACIFIC ON THURSDAY AND OVER THE WEST COAST FRIDAY WITH AN UPPER LEVEL RIDGE OVER THE UPPER MIDWEST. SO...WILL LEAN TOWARD SLIGHTLY WARMER THAN SEASONAL AVERAGE TEMPERATURES ALONG WITH AT LEAST A SLIGHT CHANCE OF SHOWERS THROUGH THE PERIOD. WILLIAMSON DC && .AVIATION... UPDATED 0500Z ARCTIC AIRMASS WILL CONTINUE TO RESIDE OVER MUCH OF THE AREA THROUGH THE NEXT 24 HRS WITH SOUTHERN BOUNDARY OF THIS AIRMASS ALONG THE I-90 CORRIDOR. WIDESPREAD LOW CLOUDS AND FOG WILL CONTINUE IN THE COLD/MOIST AIRMASS NORTH OF THE BOUNDARY AS WELL AS OCCASIONAL LIGHT SNOW DUE TO WEAK DISTURBANCES MOVING OVERHEAD. MVFR TO IFR CONDITIONS WILL PREVAIL WITH LOCAL LIFR CONDITIONS IN FOG AND SNOW. FURTHER SOUTH...SCATTERED SNOW SHOW SHOWERS WITH LOCAL IFR CONDITIONS AT TIMES CAN BE EXPECTED THROUGH THE REMAINDER OF TONIGHT. AN UPPER LEVEL LOW APPROACHING FORM THE WEST WILL SPREAD SNOW ACROSS MUCH OF CENTRAL AND SW MT THURSDAY AFTERNOON AND EVENING. LOWEST CIGS/VSBYS IN SNOW IS EXPECTED ACROSS CENTRAL MT INCLUDING THE KHLN/KGTF/KLWT TERMINALS. HOENISCH && .PRELIMINARY POINT TEMPS/POPS... GTF 11 3 32 14 / 80 70 20 10 CTB 5 -2 30 9 / 70 60 20 10 HLN 24 14 35 17 / 70 80 30 20 BZN 36 16 33 12 / 70 80 40 10 WEY 33 6 22 -8 / 80 80 40 10 DLN 30 13 31 13 / 60 70 40 10 HVR 4 -7 18 3 / 50 50 20 10 LWT 15 4 27 12 / 60 70 30 20 && .TFX WATCHES/WARNINGS/ADVISORIES... WINTER WEATHER ADVISORY FROM 11 AM THIS MORNING TO 11 PM MST THIS EVENING FOR MTZ009-012-014-046-048-049-052-053. WINTER WEATHER ADVISORY FROM 11 AM THIS MORNING TO 5 AM MST FRIDAY FOR MTZ050-051-054. && $$ WEATHER.GOV/GREATFALLS