Issued by NWS Missoula, MT
000 FXUS65 KMSO 131018 CCA AFDMSO AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MISSOULA MT 410 AM MDT FRI MAR 13 2009 .DISCUSSION...PATCHY FREEZING FOG IS POSSIBLE THIS MORNING IN THE VALLEYS OF NORTHWEST MONTANA AND NORTH CENTRAL IDAHO. HIGH CLOUD COVER ASSOCIATED WITH A WEATHER DISTURBANCE IN CANADA HAS SLOWED THE RISE OF RELATIVE HUMIDITY VALUES EARLY THIS MORNING...BUT FULL SATURATION IS EXPECTED BY DAYBREAK. AN UPPER LEVEL RIDGE OF HIGH PRESSURE WILL CONTINUE A WARMING AND DRYING TREND TODAY WITH TEMPERATURES FORECASTED SLIGHTLY BELOW SEASONAL NORMALS. A MOIST PACIFIC LOW PRESSURE SYSTEM CAPABLE OF PRODUCING LIGHT TO MODERATE SNOW ACCUMULATIONS WILL IMPACT THE NORTHERN ROCKIES SATURDAY THROUGH SUNDAY. A WEAK DISTURBANCE AHEAD OF THE MAIN LOW WILL BRING SHOWERS TO NORTHWEST MONTANA SATURDAY MORNING. THE FULL ONSLAUGHT OF PRECIPITATION WILL OCCUR LATER SATURDAY AS THE UPPER LEVEL LOW MOVES INTO THE PACIFIC NORTHWEST. SNOW LEVELS WILL BE ABOVE MOST VALLEY FLOORS AT THE ONSET OF PRECIPITATION. AS SNOW LEVELS LOWER SATURDAY EVENING...PRECIPITATION WILL TRANSITION TO ALL SNOW WITH LITTLE TO NO ACCUMULATION IN MOST VALLEY LOCATIONS AND LIGHT TO MODERATE ACCUMULATIONS IN THE HIGHER TERRAIN. THE HEAVIEST ACCUMULATIONS ARE STILL ON TRACK TO OCCUR ACROSS THE CLEARWATER MOUNTAINS AND BITTERROOT RANGE SATURDAY NIGHT AS PRECIPITATION BECOMES ENHANCED BY GOOD OROGRAPHIC LIFT AND A STRONG JET STREAK NOSING IN FROM THE WEST. TRAVEL OVER LOOKOUT AND LOLO PASSES IS LIKELY TO BE IMPACTED BY ACCUMULATING SNOWS AND DETERIORATING DRIVING CONDITIONS...PARTICULARLY SATURDAY NIGHT. A NEW DEVELOPMENT WITH THIS SYSTEM IS THE POSSIBILITY OF STRONG AND GUSTY SOUTHERLY WINDS WITH THE PASSAGE OF THE SURFACE COLD FRONT SATURDAY NIGHT...PARTICULARLY IN THE HELLS CANYON/GRANGEVILLE AREAS. THIS SYSTEM WILL BE CLOSELY MONITORED FOR POTENTIAL WINTER HIGHLIGHTS FOR MOUNTAIN PASSES AND WINDS IN THE HELLS CANYON/GRANGEVILLE AREA. SUNDAY THROUGH TUESDAY...MODELS HAVE COME INTO ALIGNMENT PROMOTING MORE PROGRESSIVE AND MOIST WESTERLY FLOW. THIS PATTERN WILL EFFECT THE MOUNTAINS WITH OCCASIONAL SNOW SHOWERS AND SOME MODERATE ACCUMULATING SNOWS IMPACTING LOOKOUT AND LOLO PASSES PRODUCING DIFFICULT DRIVING CONDITIONS AT TIMES. CLOUDY SKIES AND OCCASIONAL RAIN SHOWERS WILL KEEP TEMPERATURES FROM WARMING AS PREVIOUSLY ANTICIPATED. EXPECT HIGHS IN THE VALLEYS TO REMAIN SLIGHTLY BELOW NORMAL TRANSLATING TO LOWER TO MID 40S THIS TIME OF YEAR. CLOUDY SKIES AND A FEW RAIN SHOWERS FROM TIME TO TIME. WEDNESDAY AND THURSDAY...LONGER RANGE MODELS ARE TRENDING TOWARD A DEVELOPING RIDGE WHICH WOULD HELP TO BRING DRIER CONDITIONS AND AT OR SLIGHTLY ABOVE NORMAL TEMPERATURES. && .AVIATION...PATCHY FOG DEVELOPMENT IS POSSIBLE THIS MORNING IN SOME VALLEY LOCATIONS ACROSS NORTHWEST MONTANA AND NORTH CENTRAL IDAHO. ANY FOG THAT DEVELOPS SHOULD DISSIPATE BY MID-MORNING. OTHERWISE...VFR CONDITIONS WILL PREVAIL FOR THE NEXT 24 HRS. CLOUD COVER WILL BEGIN TO INCREASE AND LOWER FROM THE NORTHWEST BY SATURDAY MORNING AS A MOIST PACIFIC LOW PRESSURE SYSTEM BEGINS TO IMPACT THE NORTHERN ROCKIES. && .MSO WATCHES/WARNINGS/ADVISORIES... MT...NONE. ID...NONE. && $$ SHORT TERM...DEROSA LONG TERM....RPN AVIATION...DEROSA
