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AREA FORECAST DISCUSSION

 
 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
 
 
 
 

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