000 FXUS65 KTFX 251809 AFDTFX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GREAT FALLS MT 1108 AM MST MON FEB 25 2008 UPDATED AVIATION DISCUSSION .UPDATE... TODAY...THE LARGE SCALE PATTERN HAS AN UPPER LEVEL HIGH PRESSURE RIDGE BUILDING OVER THE WEST COAST WHILE A BROAD LOW PRESSURE TROF MOVES EAST INTO THE MIDWEST. THIS LEAVES THE ZONES BENEATH NORTHWEST FLOW ALOFT. THE MAIN INTEREST FOR TODAY IS A VORT MAX MOVING THROUGH THIS FLOW...ACROSS NORTHWEST MONTANA INTO THE SOUTHWEST ZONES. SOME GOOD LIFT AND MOISTURE WILL ALLOW FOR A GOOD BURST OF SNOW AS THIS FEATURE MOVES SOUTHWARD BUT IT WILL MOVE RAPIDLY AND THE HEAVIEST SNOW SHOULD BE SHORT LIVED. TO THE NORTH...UPSLOPE FLOW IS WEAK AND WILL CONTINUE TO WEAKEN. HAVE DROPPED POPS IN THE NORTH FOR THE REMAINDER OF THIS MORNING AND THIS AFTERNOON. WILL LEAVE THE ADVISORY IN PLACE BUT PLAN ON ALLOWING IT TO EXPIRE AT NOON. ZELZER && .PREV DISCUSSION... /ISSUED 606 AM MST MON FEB 25 2008/ UPDATE... FORECAST PACKAGE AND HAZARDOUS WEATHER OUTLOOK ARE BEING UPDATED TO ACCOUNT FOR HIGHER SNOW AMOUNTS THIS MORNING OVER SOUTHWEST MONTANA...AS SNOW BANDS WORK THEIR WAY SOUTHEASTWARD AHEAD OF A FAST-MOVING...MID-LEVEL SHORTWAVE TROUGH. OVER SOUTHWEST MONTANA FOR THIS MORNING...ADDITIONAL SNOW ACCUMULATIONS OF 1 TO 2 INCHES ARE EXPECTED OVER THE VALLEYS...WITH 2 TO 4 INCHES IN THE MOUNTAINS. COHEN/BRUSDA && .AVIATION... UPDATED 1800Z. AN UPPER LEVEL DISTURBANCE WILL CONTINUE TO TRACK SOUTHEASTWARD ACROSS SOUTHWEST MT THIS AFTERNOON WITH A RIDGE OF HIGH PRESSURE BUILDING IN BEHIND THE SYSTEM TONIGHT THOUGHT TOMORROW. SNOW WILL CONTINUE ACROSS MUCH OF CENTRAL AND SW MT THROUGH THIS AFTERNOON...MAINLY FROM KHLN TO KBZN AND SOUTH. NORTH OF THIS...EXPECT A FEW FLURRIES WITH MAIN IMPACT BEING CONTINUED LOW CEILINGS AND FOG. EXPECT SLOW IMPROVEMENT TO THESE AREAS THIS AFTERNOON WITH BETTER IMPROVEMENT THIS EVENING. CLEARING TONIGHT LOW ALLOW FOR THE DEVELOPMENT OF VALLEY FOG AT SOME LOCATIONS. HOENISCH && .PREV DISCUSSION... /ISSUED 500 AM MST MON FEB 25 2008/ BROAD UPPER LEVEL TROUGH OVER THE CENTRAL CONUS WILL CONTINUE TO PROGRESS EASTWARD TODAY...AS NORTHWESTERLY FLOW ALOFT SETS UP OVER THE REGION. CURRENT IR AND WATER VAPOR SATELLITE IMAGERY INDICATE A RATHER COMPACT MID LEVEL SHORTWAVE TROUGH QUICKLY MOVING SOUTHEASTWARD OVER MONTANA AND IDAHO. MODELS PICK UP ON THIS FEATURE WELL...AND TAKE IT THROUGH THE SOUTHWEST HALF OF MONTANA THIS MORNING. WITH MORE THAN ADEQUATE DEEP MOISTURE ALREADY IN PLACE...LIFT ASSOCIATED WITH THIS SYSTEM WILL PRODUCE AREAS OF SNOW SOUTH OF A CHOTEAU-GREAT FALLS-LEWISTOWN LINE. TO THE NORTH OF THIS LINE...RUC AND OTHER MODELS ARE SHOWING VERY LITTLE...IF ANY...ADDITIONAL SNOWFALL...AS THE BULK OF THE UPPER LEVEL ENERGY RIDES SOUTH OF THOSE AREAS. THUS...THE NORTHERN PORTIONS OF THE SNOW ADVISORY HAVE BEEN CANCELLED...WITH THE REST OF THE SNOW ADVISORY REMAINING IN EFFECT UNTIL NOON MST TODAY. SOUTH OF THE CHOTEAU-GREAT FALLS-LEWISTOWN LINE...UP TO AN INCH OF NEW SNOW WILL BE POSSIBLE OVER THE PLAINS AND VALLEYS...WITH UP TO 2 INCHES OVER THE MOUNTAINS...WITH WEAK UPSLOPE FLOW CONTINUING. FOR THIS AFTERNOON...THE DEEP MOISTURE WILL CONTINUE TO BE SHUNTED TO THE SOUTH OF THE REGION...WITH SOME LINGERING LOW LEVEL MOISTURE AROUND IN THE EVENING. BY LATE EVENING...SKIES SHOULD CLEAR ACROSS MUCH OF THE AREA. WHILE THIS COULD POTENTIALLY PROMOTE FOG DEVELOPMENT...SOUTHWESTERLY SURFACE WINDS DEVELOP BY MIDNIGHT...WHICH WOULD SCOUR OUT THE FOG POTENTIAL RATHER FAST. WILL LET LATER FORECASTS RE-EVALUATE THIS FOG POTENTIAL. ALSO...LOW TEMPS TONIGHT ARE TRICKY...AS ENOUGH CLEARING WITH LIGHT WINDS WOULD SUPPORT SINGLE DIGIT TEMPERATURES...BUT THE SOUTHWEST WINDS WOULD PROVIDE A SUBSTANTIAL MODERATING EFFECT. TEMPS COULD FALL FAST BY LATE EVENING...AND THEN STAY STEADY OR SLOWLY RISE LATER IN THE NIGHT. FOR LOW TEMPS TONIGHT...I WENT WITH A COMPROMISE...GOING UNDER GUIDANCE A BIT...WITH LOW TEMPS TONIGHT IN THE TEENS ACROSS MUCH OF THE AREA. AS FOR FOG THIS MORNING...THE SOUTHWEST TWO THIRDS OF THE CWA COULD EXPERIENCE PATCHY FOG THROUGH EARLY MORNING.. THEN ON TUESDAY...A POSITIVELY TILTED UPPER LEVEL RIDGE WILL BUILD INTO THE REGION...WITH LARGE SCALE SUBSIDENCE PROMOTING PARTLY TO MOSTLY SUNNY SKIES. THEN BY TUESDAY NIGHT AND WEDNESDAY...A FAST MOVING...WEAK SHORTWAVE TROUGH WILL TRAVERSE ACROSS THE REGION IN MOIST WEST-NORTHWESTERLY FLOW ALOFT...WHICH WILL COMBINE WITH INCREASING DEEP MOISTURE TO PRODUCE SNOW OVER THE WESTERN MOUNTAINS. SOME PRECIP IN THE FORM OF A RAIN/SNOW MIX COULD GET GOING OVER THE PLAINS ON WEDNESDAY. STRONG WINDS WILL BE POSSIBLE OVER THE ROCKY MOUNTAIN FRONT AND ADJACENT PLAINS ON WEDNESDAY. OTHERWISE...TEMPERATURES ON TUESDAY AND WEDNESDAY WILL BE ABOVE SEASONAL AVERAGES ACROSS THE FORECAST AREA WITH THE RIDGE BUILDING IN...ALONG WITH LEE TROUGHING IN CENTRAL/EASTERN MONTANA SUPPORTING DOWNSLOPE LOW LEVEL FLOW. COHEN WEDNESDAY NIGHT THROUGH THURSDAY...A WEAK UPPER LEVEL RIDGE OF HIGH PRESSURE WILL COLLAPSE OVER MONTANA DURING THIS PERIOD...AS AN UPPER LEVEL DISTURBANCE MOVES SOUTHWARD OUT OF ALBERTA TOWARDS CENTRAL MONTANA. EXPECT WINDY CONDITIONS OVER NORTH CENTRAL MONTANA WEDNESDAY NIGHT INTO THURSDAY MORNING...WHILE THE CHANCES FOR SNOW WILL INCREASE DURING THE NIGHT OVER THE NORTHERN SECTIONS OF NORTH CENTRAL MONTANA. BY THURSDAY...WITH THE UPPER LEVEL DISTURBANCE MOVING THROUGH...THERE WILL BE A GOOD CHANCE FOR SNOW ACROSS PORTIONS OF THE REGION...THUS POPS HAVE BEEN INCREASED A BIT FOR THURSDAY FROM CUT BANK...TO GREAT FALLS...TO LEWISTOWN. FOR THURSDAY NIGHT THROUGH FRIDAY NIGHT...EXPECT A QUICK TRANSITION FROM COOL AIR TO VERY MILD AIR...AS A WARM FRONT MOVES THROUGH THE REGION ON THURSDAY NIGHT. AFTER THE WARM FRONT MOVES THROUGH...EXPECT VERY WINDY CONDITIONS TO DEVELOP ON FRIDAY...HELPING TO USHER IN THE WARMER AIR. RIGHT NOW...WIND SPEEDS SHOULD REMAIN BELOW WARNING CRITERIA...BUT THIS WILL NEED TO BE WATCHED CLOSELY OVER THE NEXT FEW DAYS. AFTERNOON TEMPERATURES ON FRIDAY WILL AVERAGE BETWEEN 10 AND 15 DEGREES ABOVE NORMAL ACROSS THE REGION. FOR SATURDAY AND SATURDAY NIGHT...THE GFS/ECMWF BOTH SHOW ANOTHER CANADIAN COLD FRONT MOVING SOUTHWARD THROUGH THE REGION. EXPECT ANOTHER QUICK CHANGE IN TEMPERATURES...WITH TEMPERATURES TURNING COLDER AND FALLING BACK BELOW NORMAL. ADDITIONALLY...EXPECT ANOTHER ROUND OF RAIN/SNOW ACROSS CENTRAL AND SOUTHWEST MONTANA AS THE COLD FRONT MOVES THROUGH. BRUSDA SUNDAY AND MONDAY...MODELS CONTINUE TO BRING A PACIFIC DISTURBANCE THROUGH THE REGION. A CHANCE FOR SCATTERED SNOW SHOWERS IN THE MOUNTAINS AND A SLIGHT CHANCE ON THE PLAINS. TEMPERATURES ARE EXPECTED TO BE NEAR NORMAL THROUGH THIS PERIOD. SAUCIER && .PRELIMINARY POINT TEMPS/POPS... GTF 32 19 46 27 / 100 0 0 0 CTB 31 16 44 24 / 40 0 0 10 HLN 33 20 44 23 / 100 20 10 0 BZN 35 13 42 16 / 100 40 10 0 WEY 29 4 30 8 / 100 50 10 10 DLN 32 16 40 21 / 100 40 0 0 HVR 30 13 42 20 / 20 0 0 0 LWT 31 18 42 22 / 100 10 0 0 && .TFX WATCHES/WARNINGS/ADVISORIES... SNOW ADVISORY UNTIL NOON MST TODAY FOR MTZ012>014-048>051-054. && $$