000 FXUS65 KTFX 171533 AFDTFX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GREAT FALLS MT 925 AM MDT SUN MAY 17 2009 UPDATE...BROAD AREA OF HIGH LEVEL MOISTURE MOVING THROUGH THE NORTHERN BOUNDARY OF THE UPPER RIDGE IS GENERATING WIDESPREAD HIGH CLOUD COVER OVER MOST OF CWA THIS MORNING. WITH ADDITIONAL MOISTURE UPSTREAM...EXPECT CLOUD COVER TO PERSIST WELL INTO THE AFTERNOON... WHICH WILL ACT TO LIMIT MAX TEMPS TODAY. THUS HAVE TWEAKED AFTN/EARLY EVE SKY GRIDS TO INCREASE CLOUD COVER AND DECREASE FORECAST HIGH TEMPS BY 2 TO 3 DEG OVER THE CENTRAL AND NORTHERN ZONES. REST OF FORECAST LOOKS GOOD AT THIS TIME. WARANAUSKAS .DISCUSSION... TODAY THROUGH TUESDAY...UPPER RIDGE PERSISTS OVER THE AREA AND WILL BRING WARM AND STABLE CONDITIONS TODAY. SOME HIGH CLOUDS DEPICTED AS A CHINOOK ARCH ON SATELLITE IMAGERY SHOULD BREAK DOWN DURING THE AFTERNOON HOURS. SURFACE WINDS WILL AGAIN BECOME BREEZY THIS AFTERNOON. ON MONDAY...A WEAK SURFACE COLD FRONT MAKES ITS WAY ACROSS THE AREA FROM NORTHEAST TO SOUTHWEST. PASSAGE OF THIS FRONT WILL BE MOSTLY DRY BUT ISOLATED CONVECTIVE ACTIVITY IS A POSSIBILITY OVER THE HIGHER TERRAIN OF SOUTHWEST MONTANA. HAVE LOWERED HIGH TEMPERATURES MONDAY BY A FEW DEGREES. A DEEPENING UPPER TROF OVER THE WEST COAST ON TUESDAY WILL RESULT IN AN INCREASING SOUTHWEST FLOW ALOFT OVER THE COUNTY WARNING AREA. ENOUGH MOISTURE AND INSTABILITY MOVING OVER THE AREA TUESDAY AFTERNOON FOR ISOLATED THUNDERSTORMS TO DEVELOP. PREFRONTAL SURFACE HEATING IN ADVANCE OF ANOTHER SURFACE COLD FRONT TUESDAY NIGHT WILL ALLOW TEMPERATURES REMAIN IN THE 80S TUESDAY AFTERNOON. TEMPERATURES WILL REMAIN ABOVE SEASONAL AVERAGES. EMANUEL TUESDAY NIGHT THROUGH FRIDAY NIGHT...THE UPPER LOW CONTINUES TO MOVE INLAND AND CONTINUE THE CHANCE FOR SHOWERS AND THUNDERSTORMS OVER THE AREA INTO TUESDAY NIGHT. ALSO A COLD FRONTAL PASSAGE WILL ALLOW COOLER AIR TO OVERSPREAD THE REGION TUESDAY NIGHT. AS THE UPPER LEVEL SYSTEM CONTINUES TO MOVE THROUGH SOUTHERN CANADA ON WEDNESDAY...EXPECT MORE SCATTERED SHOWERS AND WINDY CONDITIONS ON WEDNESDAY. BY THURSDAY...MORE WESTERLY FLOW RETURNS WITH TEMPERATURES NEAR SEASONAL NORMALS AND A SLIGHT CHANCE FOR AFTERNOON SHOWERS AS SURFACE HIGH PRESSURE DOMINATES. THE MODELS CONTINUE IN REASONABLE AGREEMENT WITH A RIDGE REBUILDING ACROSS WESTERN NORTH AMERICA INTO FRIDAY NIGHT. THIS SHOULD KEEP SHOWERS CONFINED TO THE MOUNTAINS AND MOSTLY DRY CONDITIONS AND NEAR NORMAL TEMPERATURES. DB SATURDAY THROUGH SUNDAY...LONG TERM MODELS IN GENERAL AGREEMENT HAVING A ZONAL FLOW SITUATION WITH SOME RIDGING OCCURRING LATER IN THE PERIOD. HAVE LEANED MORE TOWARDS THE GFS SOLUTION ON DUE TO ITS CONSISTENCY IN KEEPING A LOW RIGHT OFF OF THE COAST OF CANADA SIMILAR TO PREVIOUS MODEL RUNS. INCREASED WINDS SLIGHTLY AND TWEAKED POPS NEAR CLIMATOLOGY DUE TO THE UNCERTAINTY BETWEEN THE MODELS TIMING OF VARIOUS SHORTWAVE PERTURBATIONS THAT WILL MOVE OVER OUR AREA DURING THIS TIME FRAME. SUK && .AVIATION... AN UPPER LEVEL RIDGE ALONG THE WEST COAST WILL CONTINUE TO DOMINATE THE AREA WEATHER AS IT SLOWLY MOVES EASTWARD. WINDS WILL KICK UP A BIT AND GUST ALONG THE EAST SLOPES OF THE ROCKIES AFTER 18Z SUNDAY...CONTINUING INTO EARLY EVENING. A COLD FRONT SHOULD PUSH INTO THE NORTHERN TERMINALS AFTER 06Z MONDAY...SWITCHING WINDS TO A MORE NORTHERLY DIRECTION. AT PRESENT IT APPEARS THAT THIS FRONT WILL BE DRY. DB && .HYDROLOGY... AN UPPER LEVEL RIDGE OF HIGH PRESSURE WILL BRING WARM TEMPERATURES TO THE REGION TODAY AND CONTINUE INTO THE FIRST PART OF THE WEEK. OVERNIGHT LOW TEMPERATURES WILL ALSO LIKELY REMAIN ABOVE FREEZING ...EVEN OVER THE HIGHER MOUNTAINS. THESE CONDITIONS WILL AID IN THE MELTING OF WHAT IS STILL A SIGNIFICANT SNOWPACK ACROSS THE HIGHER ELEVATIONS OF CENTRAL AND SOUTHWEST MONTANA. THIS WILL LIKELY CAUSE SMALLER CREEKS AND STREAMS TO RISE ACROSS THE REGION. && .PRELIMINARY POINT TEMPS/POPS... GTF 84 51 80 48 / 0 0 0 10 CTB 79 41 73 39 / 0 0 10 10 HLN 86 44 86 43 / 0 0 10 10 BZN 90 42 88 39 / 0 0 10 20 WEY 70 30 70 32 / 10 0 10 10 DLN 82 42 83 42 / 0 0 10 0 HVR 86 40 73 38 / 0 0 0 10 LWT 80 42 75 40 / 0 0 0 10 && .TFX WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...EMANUEL LONG TERM...DB/SUK AVIATION...DB WEATHER.GOV/GREATFALLS