000 FXUS65 KTFX 291628 AFDTFX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GREAT FALLS MT 928 AM MST SAT DEC 29 2007 .UPDATE... ACTIVE WEATHER PATTERN ALREADY IN PLACE OVER THE REGION THIS MORNING. A WEAK SHORT WAVE MOVING THROUGH THE MOIST WESTERLY FLOW WILL PRODUCE MOUNTAIN SNOW SHOWERS THROUGH THE DAY...BEFORE THE STRONGER SYSTEM MOVES IN TONIGHT. INHERITED FORECAST FOR TODAY LOOKS PRETTY GOOD...ONLY SIGNIFICANT CHANGE WAS TO LOWER CLOUD COVER OVER THE PLAINS FOR THIS MORNING. WILL WORK OUT WHAT NEEDS TO BE DONE WITH THE WINTER WEATHER HIGHLIGHTS FOR THE AFTERNOON PACKAGE. THOMSON && .AVIATION... UPDATED 1143Z. A WEAK STORM SYSTEM OVER WESTERN MONTANA WILL TRANSITION TO A MORE SIGNIFICANT PERIOD OF STORMINESS DURING THE NEXT 24 HOURS. VFR FLIGHT CONDITIONS ARE EXPECTED TO PREVAIL DURING THIS TIME...WITH AREAS OF MVFR CEILINGS AND VISIBILITIES DUE TO SNOW NEAR KBZN AND KHLN AFTER 00Z. VICINITY SNOW SHOWERS FOR KBZN AND KHLN AFTER 21Z...AND ELSEWHERE AFTER 04Z. SNOW WILL LIKELY BE HIGHEST IMPACT AFTER 06Z. SURFACE WINDS WILL RANGE FROM LIGHT AND VARIABLE...TO UNDER 15KTS FROM THE WEST AND SOUTHWEST THROUGHOUT THE FORECAST AREA DURING THE FORECAST PERIOD AS WELL. ZUMPFE && .PREV DISCUSSION... (ISSUED 443 AM MST SAT DEC 29 2007) DISCUSSION... TODAY THROUGH MONDAY...MY FORECAST AREA IS IN FOR A VERY ACTIVE WEEKEND AS A MOIST WEST TO NORTHWEST FLOW ALOFT COMBINES WITH A STRONG UPPER LEVEL JET. PERIODIC IMPULSES MOVING THROUGH THE UPPER FLOW WILL BRING PERIODS OF MODERATE TO HEAVY SNOW TO THE MOUNTAINS OF SOUTHWEST MONTANA AND THE CONTINENTAL DIVIDE NORTH TO GLACIER PARK. THESE AREAS ARE EXPECTED TO RECEIVE ANYWHERE FROM 8 TO 20 INCHES OF SNOW WITH STRONG WINDS THROUGH MOUNTAIN PASSES CAUSING REDUCED VISIBILITIES IN BLOWING SNOW. HAVE UPGRADED THE WATCH TO A WINTER STORM WARNING FOR THIS AREA TONIGHT AND SUNDAY. THE STRONGEST WINDS ARE EXPECTED EARLY SUNDAY MORNING. AS THE STRONGEST IMPULSE MOVES THROUGH THE AREA ON SUNDAY...UPPER LEVEL FLOW WILL SWITCH TO THE NORTHWEST ACROSS MY ENTIRE FORECAST AREA. MODELS ARE NOW INDICATING THAT THE MOUNTAINS OF CENTRAL MONTANA COULD RECEIVE WARNING CRITERIA SNOW AMOUNTS ALONG WITH BLOWING SNOW SUNDAY AFTERNOON AND NIGHT. WILL ISSUE A WINTER STORM WATCH FOR THE LITTLE BELT...CASTLE AND NORTHERN CRAZY MOUNTAINS. ACTIVE WEATHER ACROSS MY CWA TAPERS OFF QUICKLY ON MONDAY AS A SIGNIFICANT UPPER LEVEL RIDGE BUILDS OVER THE PACIFIC NORTHWEST AND BEGINS TO EDGE TOWARD THE NORTHERN ROCKY MOUNTAINS. MPJ MONDAY NIGHT THROUGH THURSDAY NIGHT...THE EXTENDED PERIOD WILL BE CHARACTERIZED BY A RAPID WARMUP...FOLLOWED BY A PERSISTENTLY WARM PATTERN. THE LAST BIT OF SNOW POTENTIAL FROM A WEEKEND STORM SYSTEM WILL LINGER OVER THE HIGH ELEVATIONS OF CENTRAL AND SOUTHWEST MONTANA DURING MONDAY EVENING...WITH COLD AIR STILL IN PLACE OVER MUCH OF THE FORECAST AREA. HOWEVER...THE PATTERN WILL QUICKLY TRANSITION TO DRY AND VERY WARM BY TUESDAY AS A BROAD UPPER LEVEL RIDGE OF HIGH PRESSURE APPROACHES THE FORECAST AREA FROM THE WEST. THIS RIDGE WILL UNDOUBTEDLY PRODUCE RAPID WARMING DURING TUESDAY DURING THE DAY...WITH WARMING INITIALLY MOST PRONOUNCED ACROSS THE NORTH CENTRAL PLAINS. TEMPERATURES WILL REMAIN WELL ABOVE THE SEASONAL AVERAGE THROUGH THE REMAINDER OF THE FORECAST PERIOD. THE RIDGING PATTERN WILL TRANSITION TO A DISTURBED SOUTHWESTERLY FLOW ALOFT BY LATE WEDNESDAY...WITH SUFFICIENT MOISTURE AND FORCING FOR SNOW TO DEVELOP ALONG THE CONTINENTAL DIVIDE REGION DURING THURSDAY. ZUMPFE FRIDAY AND SATURDAY...ENSEMBLES AS WELL AS THE GFS HAS LONG WAVE TROUGH OVER THE EASTERN PACIFIC FOR A MOIST WEST TO SOUTHWEST FLOW ALOFT. MEANWHILE...A SERIES OF SURFACE LOWS ARE PROGGED TO MOVE ACROSS SOUTHERN CANADA FOR DOWNSLOPE WINDS OVER THE PLAINS. THUS...WILL GO FOR MOSTLY DRY OVER THE PLAINS WITH SCATTERED SNOW SHOWERS OVER THE MOUNTAINS. TEMPERATURES WILL RUN A LITTLE ABOVE SEASONAL AVERAGE...ESPECIALLY OVER NORTH CENTRAL MONTANA. WILLIAMSON DC && .PRELIMINARY POINT TEMPS/POPS... GTF 34 19 29 11 / 20 20 20 20 CTB 33 10 30 8 / 10 20 30 20 HLN 33 20 32 18 / 30 40 30 30 BZN 31 18 32 15 / 30 50 40 40 WEY 21 11 22 6 / 80 70 80 50 DLN 28 17 29 12 / 30 50 50 30 HVR 30 11 27 9 / 10 20 30 20 LWT 32 16 28 11 / 10 20 20 30 && .TFX WATCHES/WARNINGS/ADVISORIES... WINTER STORM WARNING FROM 6 PM THIS EVENING TO 5 PM MST SUNDAY FOR ELEVATIONS ABOVE 5500 FEET MTZ009-014-048. WINTER STORM WARNING FROM 6 PM THIS EVENING TO 5 PM MST SUNDAY FOR ELEVATIONS ABOVE 6500 FEET MTZ008-015-055. WINTER STORM WATCH FROM LATE SUNDAY MORNING THROUGH LATE SUNDAY NIGHT FOR THE LITTLE BELT AND CASTLE MOUNTAINS...AND FOR NORTHERN PORTIONS OF THE CRAZY MOUNTAINS (MTZ012-050-054). && $$ SHORT TERM...THOMSON/MPJ LONG TERM...ZUMPFE/DC WILLIAMSON AVIATION...ZUMPFE WEATHER.GOV/GREATFALLS