945 FXUS65 KMSO 152202 AFDMSO AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MISSOULA MT 302 PM MST FRI JAN 15 2010 .DISCUSSION...CLOUD COVER AND PRECIPITATION IS INCREASING IN NORTHWEST MONTANA AT THIS HOUR AS SOUTHWEST FLOW ALOFT CONTINUES TO STREAM MOISTURE INTO THE NORTHERN ROCKIES TONIGHT THROUGH SATURDAY. SEVERAL WEATHER-RELATED IMPACTS ARE ANTICIPATED. STRONG SOUTH WINDS IN PORTIONS NORTH CENTRAL IDAHO AND SOUTHWEST MONTANA ARE EXPECTED TO REMAIN STRONG THROUGH EARLY EVENING. THE TIGHTENED SURFACE PRESSURE GRADIENT IS OCCURRING AS A RESPONSE TO THE SYSTEM CURRENTLY TRACKING INTO NORTHWEST MONTANA IN ADDITION TO UNSTABLE SURFACE CONDITIONS. WINDS ARE EXPECTED TO DISSIPATE LATE THIS EVENING. WIND ADVISORIES FOR THE AFFECTED AREAS MENTIONED ABOVE REMAIN IN EFFECT THROUGH THIS EVENING...WITH WINDS EXPECTED TO DISSIPATE LATE THIS EVENING. PRECIPITATION ACROSS NORTHWEST MONTANA TONIGHT IS EXPECTED TO BE IN THE FORM OF SNOW OR A RAIN SNOW MIX AS AIR ALOFT REMAINS COOL WITH THE PASSAGE OF A SURFACE FRONT. IN NORTH CENTRAL IDAHO...RAIN OR A RAIN SNOW MIX SHOULD BE THE PRIMARY FORM OF PRECIPITATION. INCREASED CLOUD COVER WILL KEEP TEMPERATURES RELATIVELY MILD OVERNIGHT...THUS KEEPING A SLIGHT CHANCE OF FREEZING RAIN IN THE FORECAST FOR THE VALLEYS OF NORTHWEST MONTANA AND NORTHERN CLEARWATERS IN IDAHO DURING THE OVERNIGHT AND SATURDAY MORNING TIMEFRAME. ADDITIONAL OROGRAPHIC LIFT ALONG WITH A 90 KNOT JET STREAK WILL ENHANCE SNOWFALL IN THE HIGHER TERRAIN OF NORTHWEST MONTANA... PARTICULARLY ALONG THE CONTINENTAL DIVIDE NEAR GLACIER PARK TONIGHT. SOUTHWEST WINDS WILL BECOME VERY STRONG LATE THIS EVENING IN RESPONSE TO THE JET STREAK OVERHEAD AND THE SURFACE FRONT PASSAGE TOWARD SATURDAY MORNING. THE COMBINATION OF SNOW AND STRONG WINDS WILL CREATE WHITEOUT CONDITIONS AND HAZARDOUS DRIVING LATE THIS EVENING THROUGH LATE SATURDAY MORNING. A WINTER WEATHER ADVISORY HAS BEEN ISSUED FOR MARIAS PASS FOR SNOW AND BLOWING SNOW. FOR THE LATEST INFORMATION ON CURRENT ADVISORIES FOR THE MISSOULA WARNING AREA...PLEASE REFER TO WWW.WEATHER.GOV/MISSOULA. SATURDAY NIGHT THROUGH MONDAY NIGHT...A CLASSIC EL NINO WEATHER PATTERN CONTINUES TO BE DEPICTED FOR THE MID TERM FORECAST PERIODS...WITH EMBEDDED WEAK DISTURBANCES MOVING WITHIN A PERSISTENT SOUTHWESTERLY FLOW OVER THE NORTHERN ROCKIES. PRECIPITATION IS POSSIBLE FOR MUCH OF THIS PERIOD...WITH EXCEPTION OF EARLY SUNDAY...WHEN SATURATED AIR WITHIN VALLEYS WILL ALLOW FOG AND FREEZING FOG TO DEVELOP. IN THE ABSENCE OF ROBUST STORM SYSTEM FEATURES...PRECIPITATION AMOUNTS ARE NOT EXPECTED TO BE IMPRESSIVE. THE RELATIVELY WARM NATURE OF THE SOUTHWESTERLY FLOW WILL KEEP VALLEYS WITH A MIXTURE OF RAIN...SNOW...AND OCCASIONAL FREEZING RAIN. NORTHWEST MONTANA APPEARS MOST FAVORED FOR FREEZING RAIN...WITH MODEL GUIDANCE DEPICTING RIDGE TOP TEMPERATURES HOVERING NEAR FREEZING FOR MUCH OF THE MID TERM. ALSO...WITH LITTLE LOW LEVEL DRYING AND WATER REMAINING ON THE GROUND AND ROAD SURFACES OF AREA VALLEYS... OVERNIGHT REFREEZING MAY RESULT IN SUDDEN HAZARDOUS ROAD CONDITIONS DEVELOPING. TEMPERATURES WILL BE ABOVE NORMAL FOR THE MID TERM AS WELL. TUESDAY THROUGH FRIDAY...MODELS HAVE REMAINED CONSISTENT THROUGH THIS PERIOD. THE LOW WILL REMAIN OFF OF THE NORTHERN PACIFIC COAST. THIS WILL CONTINUE TO PUSH WAVES OF PRECIPITATION ACROSS THE REGION. && .AVIATION...A MOIST SOUTHWEST FLOW ALOFT WILL USHER PRECIPITATION ACROSS NORTHWEST MONTANA AND THE IDAHO PANHANDLE TONIGHT. THIS WILL CREATE LOWERED CEILINGS AND VISIBILITY...CAUSING THE HIGHER TERRAIN TO BE OBSCURED THROUGH SATURDAY. AIRFIELD KGPI CAN EXPECT REDUCED CEILINGS AND VISIBILITY IMPACTS DUE TO PRECIPITATION TO BEGIN AROUND 16/0500Z. THE MAIN PRECIPITATION TYPE EXPECTED WILL BE A RAIN SNOW MIX IN THE VALLEY LOCATIONS...HOWEVER PATCHY FREEZING RAIN IS NOT OUT OF THE QUESTION AFTER 16/0600Z. ACROSS SOUTHWEST MONTANA AND CENTRAL IDAHO...STRONG SOUTH TO SOUTHWEST WINDS WILL CONTINUE INTO THE EVENING HOURS. WINDS ARE EXPECTED TO DECREASE AFTER 16/0300Z. && .MSO WATCHES/WARNINGS/ADVISORIES... MT...WINTER WEATHER ADVISORY FROM 8 PM THIS EVENING TO 11 AM MST SATURDAY FOR WEST GLACIER REGION. WIND ADVISORY UNTIL 8 PM MST THIS EVENING FOR BUTTE/BLACKFOOT REGION. ID...WIND ADVISORY UNTIL 7 PM PST THIS EVENING FOR OROFINO/GRANGEVILLE REGION. WIND ADVISORY UNTIL 7 PM PST THIS EVENING FOR LOWER HELLS CANYON/SALMON RIVER REGION. && $$ SHORT TERM...DEROSA/PALLISTER LONG TERM....ZUMPFE/KOLATA AVIATION...PALLISTER