Issued by NWS Medford, OR
000 FXUS66 KMFR 222250 AFDMFR AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MEDFORD OR 250 PM PST SUN NOV 22 2009 .DISCUSSION...COLD AIR ALOFT COMBINED WITH WEAKENING DYNAMICS AND SOME UPSLOPE FLOW IS CAUSING SNOW SHOWERS OVER THE CASCADES WITH ISOLATED RAIN SHOWERS IN THE COASTAL AREAS. UPSTREAM...A RIDGE IS BUILDING AHEAD OF A STORM SYSTEM THAT WILL RIDE INTO THE GULF OF ALASKA. THIS WILL REFLECT AS HIGH PRESSURE ON THE SURFACE...INCREASING STABILITY OVER THE REGION AND ENDING ANY SHOWERS. LIGHT WINDS...LONG NIGHTS...SURFACE HIGH PRESSURE AND RECENT RAIN AND SNOWFALL IS A PERFECT SCENARIO FOR FOG DEVELOPING IN THE VALLEYS IN THE WEST AND EAST SIDE. MONDAY THROUGH WEDNESDAY WILL FEATURE FOG FORMING AFTER MIDNIGHT IN FAVORED VALLEYS. THE FOG WILL LIFT TO LOW CLOUDS AND EVENTUALLY CLEAR AROUND NOON IN MOST LOCATIONS. TUESDAY A WEAK COLD FRONT BRUSHES THE COASTAL ZONES...BUT RAIN CHANCES ARE VERY LOW. CLEARING TIME WILL DICTATE HOW WARM TEMPERATURES GET DURING THE FIRST HALF OF THE WEEK. CURRENT FORECAST PRESENTS THE IDEA THAT WEDNESDAY WILL BE THE WARMEST DAY AS GFS AND NAM AGREE THAT AIRMASS MAY BE 1-2 STANDARD DEVIATIONS ABOVE AVERAGE BY THAT TIME. CLOUDS WILL BE MOSTLY OF THE MID AND HIGH VARIETY THIS WEEK. WEATHER FOR THANKSGIVING DAY TRAVEL IS GRADUALLY COMING INTO FOCUS. GFS ENSEMBLE MEMBERS ALL INDICATE A SIMILAR IDEA OF AN UPPER TROUGH AND COLD FRONT AFFECTING NORTHERN CALIFORNIA AND OREGON BY THURSDAY AFTERNOON. SNOW LEVELS WILL INITIALLY BE BETWEEN 5000 TO 7000 FEET BUT WILL FALL THURSDAY NIGHT AND END UP AROUND 3500 FEET FRIDAY MORNING. THE ECMWF INDICATES MORE MOISTURE THAN THE GFS SO WILL NEED TO MONITOR TRENDS IN THE NEAR-TERM. SISKIYOU PASS WILL NOT LIKELY HAVE SIGNIFICANT SNOW IMPACTS WITH THIS WEATHER SYSTEM. HOWEVER...AS COLD AIR FOLLOWS THE COLD FRONT...SOME SNOW MAY ACCUMULATE AT PASS LEVEL LATE THURSDAY NIGHT OR EARLY FRIDAY MORNING. && .AVIATION...VFR CONDITIONS ARE EXPECTED TO CONTINUE AT ALL TAF SITES THROUGH LATE TONIGHT WHEN FOG FORMS AT RBG AND MFR...RESULTING IN IFR CONDITIONS THAT SHOULD LAST THROUGH MIDDAY MONDAY. MOUNTAIN OBSCURATION WILL CONTINUE TO IMPACT MOST OF THE HIGH TERRAIN THROUGH ABOUT 06Z WHEN DRY AIR BEGINS TO FILTER INTO THE ELEVATED AREAS AND CLOUDS THERE DIMINISH. && .MFR WATCHES/WARNINGS/ADVISORIES... OR...NONE. CA...NONE. PACIFIC COASTAL WATERS...HAZARDOUS SEAS WARNING UNTIL 4 AM PST MONDAY FOR PZZ350-PZZ356-PZZ370-PZZ376. $$ KEENE
