000 FXUS65 KTFX 222353 AFDTFX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GREAT FALLS MT 555 PM MDT WED APR 22 2009 UPDATED AVIATION .DISCUSSION... TONIGHT THROUGH FRIDAY...AN UPPER LEVEL LOW PRESSURE TROF OVER THE EASTERN PACIFIC WILL MOVE OVER THE WEST COAST DURING THE NIGHT. A CORE OF STRONG SOUTHWEST WINDS ALOFT WILL DROP ACROSS THE NORTHWEST ZONES AND OVER THE CENTRAL CWA BY THURSDAY AFTERNOON. A COLD FRONT WILL CROSS THE CANADIAN BORDER BY 06Z THURSDAY...THE FRONT SHOULD BE APPROACHING GTF BY EARLY MORNING. UPSLOPE PRECIP SHOULD SPREAD ACROSS THE NORTH AND CENTRAL ZONES THROUGH THE MORNING ALONG WITH FALLING TEMPS. THE FRONT WILL MOVE INTO SW MT DURING THE AFTERNOON. A SLIGHT CHANCE OF THUNDERSTORMS WILL EXIST AS THE FRONT PUSHES INTO SLIGHTLY UNSTABLE AIR IN THE SOUTH. THE AIRMASS REMAINS VERY MOIST AND CONTINUES TO COOL THROUGH FRIDAY. THE UPPER LEVEL TROF CROSSES THE ROCKIES EARLY FRIDAY AND THE ZONES BEGIN TO DRY OUT FROM THE NORTH. TEMPS BEGIN TO DROP QUICKLY TONIGHT AND THURSDAY...TEMPS WILL BE WELL BELOW NORMALS THROUGH THE PERIOD. ZELZER FRIDAY NIGHT THROUGH MONDAY NIGHT...MEDIUM RANGE MODELS CONTINUE TO EXHIBIT SIMILAR SOLUTIONS EARLY IN THE PERIOD BUT TEND TO DIVERGE BY MONDAY. AN UPPER TROF WILL PERSIST OVER THE NORTHERN ROCKIES AND WILL BRING SHOWERS AND COOLER CONDITIONS TO THE AREA. SNOW IS LIKELY AT THE HIGHER ELEVATIONS WITH RAIN OR A MIXTURE OF RAIN AND SNOW IN THE VALLEYS AND OVER THE PLAINS. PRECIPITATION AMOUNTS ARE HARD TO DETERMINE GIVEN GROUND WARMTH AND DIFFERENCES IN THE MODEL SOLUTIONS. WITH THE UPPER RIDGE REMAINING OVER THE PACIFIC DURING THIS PERIOD...UNSETTLED CONDITIONS WILL RULE. TEMPERATURES WILL REMAIN BELOW SEASONAL AVERAGES. TUESDAY AND WEDNESDAY...LATEST EXTENDED MODELS CONTINUE TO DEPICT A DEEP LOW PRESSURE TROUGH MOVING THROUGH THE REGION. SCATTERED SHOWERS ARE EXPECTED FOR MUCH OF THE SOUTHWEST MOUNTAINS AND THE CENTRAL PLAINS. PRECIPITATION CHANCES DIMINISH FOR THE NORTH CENTRAL PLAINS BY LATE WEDNESDAY BUT WILL CONTINUE FOR THE SOUTH WEST AND SOUTH CENTRAL MOUNTAINS. TEMPERATURES WILL BE BELOW SEASONAL AVERAGES FOR MUCH OF THE REGION. SAUCIER && .AVIATION... UPDATED 0000Z. A STRONG PACIFIC COLD FRONT WILL GRADUALLY APPROACH THE GLACIER PARK-KCTB-KHVR AREAS BY 0600Z THURSDAY...KGTF-KLWT BY 0900Z...AND SOUTHWEST MONTANA BY 1500Z THURSDAY. CLOUDS WILL CONTINUE TO INCREASE THIS EVENING NORTH TO SOUTH WITH VCSH EXPECTED ALONG THE FRONT AND MORE WIDESPREAD PRECIPITATION POST-FRONTAL PASSAGE. PRECIPITATION WILL START MAINLY AS RAIN SHOWERS IN THE VALLEYS BUT AS THE AIRMASS COOLS...RAIN WILL CHANGEOVER TO SNOW FOR THE MAJORITY OF THE AREA ON THURSDAY MORNING WITH A MIX OF RAIN AND SNOW POSSIBLE FOR SOME OF THE LOWER VALLEYS IN THE AFTERNOON. VFR CONDITIONS WILL PREVAIL THROUGH 1200Z THURSDAY BUT AS PRECIP BECOMES MORE WIDESPREAD AND RAIN MIXES WITH AND CHANGES OVER TO SNOW...MVFR AND OCCL IFR CIGS/VIS WITH MOUNTAIN OBSCURATION ARE EXPECTED. MLS && .HYDROLOGY... TEMPERATURES WERE WELL ABOVE SEASONAL NORMS TODAY AND INCREASED RUNOFF FROM WARM TEMPERATURES WILL CONTINUE INTO THIS EVENING. 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. TEMPERATURES ON THURSDAY WILL BE MUCH COLDER THE RISK FROM MOUNTAIN RUNOFF WILL DECREASE. && .PRELIMINARY POINT TEMPS/POPS... GTF 38 41 22 40 / 50 70 60 40 CTB 30 33 17 37 / 70 80 60 40 HLN 39 48 26 47 / 20 70 60 50 BZN 41 55 31 46 / 20 80 70 60 WEY 29 50 28 40 / 20 80 80 70 DLN 40 54 29 43 / 20 70 60 50 HVR 38 42 23 43 / 40 70 60 40 LWT 40 43 23 36 / 20 80 70 60 && .TFX WATCHES/WARNINGS/ADVISORIES... NONE. && $$ WEATHER.GOV/GREATFALLS