FXUS66 KEKA 112235 AFDEKA AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE EUREKA CA 235 PM PST THU MAR 11 2010 .SYNOPSIS...A WARM FRONT WILL GENERATE LIGHT RAIN ACROSS NORTHWEST CALIFORNIA THIS EVENING. A COLD FRONT WILL PRODUCE MORE INTENSE RAIN AND HIGH ELEVATION SNOW FRIDAY. THE PRECIPITATION WILL TURN TO SHOWERS FRIDAY NIGHT AS COLDER AIR MOVES ACROSS THE REGION AND LOWERS SNOW LEVELS TO AROUND 2500 FEET. && .DISCUSSION...ISENTROPIC LIFT AHEAD OF AN APPROACHING WARM FRONT HAS GENERATED LIGHT RAIN ACROSS THE EXTREME NW CORNER OF THE STATE TODAY. THE LIGHT RAIN WILL CONTINUE OVER DEL NORTE COUNTY THIS AFTERNOON AND SPREAD SOUTHWARD ACROSS THE EUREKA FORECAST AREA THIS EVENING AS THE WARM FRONT BRUSHES ACROSS THE REGION. WARM AIR ADVECTION HAS RAISED SNOW LEVELS TO AROUND 5500 FEET TODAY. RAIN AND HIGH ELEVATION SNOW WILL INTENSIFY EARLY FRIDAY MORNING AS A COLD FRONT NEARS THE CA COAST...AND CONTINUE THROUGH THE AFTERNOON WITH THE FRONT PASSAGE. HAVE ISSUED A WINTER WEATHER ADVISORY FOR ELEVATIONS ABOVE 4000 FEET THROUGH FRIDAY NIGHT. SATELLITE IMAGERY SHOWS A BROAD AREA OF WIDESPREAD OPEN CELLED CU ASSOCIATED WITH A TROUGH BEHIND THE FRONT. THIS COLDER AIR AND UPPER LEVEL TROUGH WILL MOVE ACROSS NW CA FRIDAY NIGHT...AND LOWER SNOW LEVELS DOWN TO AROUND 2000-2500 FEET LATE FRIDAY NIGHT INTO SATURDAY MORNING. THE PRECIPITATION WILL BECOME MORE SHOWERY WHEN THE COLDER AIR FILTERS IN...AND EXPECT SNOW ACCUMULATIONS BELOW 4000 FEET TO REMAIN UNDER ADVISORY CRITERIA. RAINFALL TOTALS WILL GENERALLY BE 1 TO 1.5 INCHES...WITH 2 TO 3 INCHES ACROSS FAVORED OROGRAPHIC FAVORED AREAS LIKE THE KING AND SOUTH FORK MOUNTAINS. HAVE ADDED ISOLATED THUNDERSTORMS ACROSS THE WATERS FRIDAY NIGHT DUE TO STEEPENING LAPSE RATES WITH THE TROUGH PASSAGE. SKIES WILL CLEAR SATURDAY NIGHT AS HIGH PRESSURE MOVES OVER THE AREA...AND RADIATION FOG WILL LIKELY DEVELOP IN THE VALLEYS EARLY SUNDAY MORNING. HIGH PRESSURE WILL PERSIST THROUGH MONDAY AND EXPECT MOSTLY CLEAR SKIES SUNDAY AND MONDAY...WITH COLD NIGHTTIME TEMPERATURES. NUMERICAL MODELS FORECAST A WEAK COLD FRONT TO BRING ANOTHER SHOT OF RAIN AND HIGH ELEVATION SNOW ON TUESDAY. MODELS ARE CONSISTENT WITH HIGH PRESSURE OVER THE NE PACIFIC EXTENDING OVER THE PACIFIC NW WEDNESDAY AND THURSDAY. OFFSHORE WINDS WILL LIKELY DEVELOP WITH THIS PRESSURE PATTERN WITH SUNNY AND WARMER CONDITIONS EXPECTED TOWARDS THE END OF THE WEEK. TH && .AVIATION...12Z THURSDAY-12Z FRIDAY...A COUPLE OF FRONTAL BOUNDARIES ARE APPROACHING NW CALIFORNIA TODAY. CIGS AND VSBY WILL REMAIN MOSTLY VFR IN SOUTHERLY FLOW THIS AFTERNOON AND TONIGHT...ALTHOUGH WINDS WILL BE A FACTOR WITH GUSTS OF 25 TO 30 KT NEAR CEC AND THE POSSIBILITY OF LOW LEVEL WIND SHEAR DUE TO WINDS INCREASING SIGNIFICANTLY WITH HEIGHT AGL. THE STRONGER SOUTH FLOW WILL SPREAD SOUTHWARD ALONG THE COAST TOWARD ACV IN THE AFTERNOON AHEAD OF THE FIRST BOUNDARY. ANOTHER BOUNDARY WILL INCREASE SOUTH WINDS AGAIN FROM AROUND 07 UTC NEAR CEC AND 1000 UTC NEAR ACV AND THE HUMBOLDT BAY AREA. THE STRONGEST WINDS WILL BE LIMITED TO THE REDWOOD COAST...ESPECIALLY THE NORTHERN PORTION...WITH MORE MODERATE FLOW ALONG THE MENDOCINO COAST AND INLAND AREAS. MOSTLY LIGHT PRECIPITATION IS EXPECTED FOR THE AREA...SPREADING FROM THE NORTHWEST CORNER SOUTH AND SOUTHEAST ACROSS THE AREA. MODERATE TO HEAVY PRECIPITATION WILL INITIATE FRIDAY AFTER 1200 UTC...AND THIS MAY REDUCE BOTH CIGS AND VSBY TO MVFR AT TIMES. CC && .MARINE...AN APPROACHING STORM SYSTEM WILL BRING GUSTY SOUTH WINDS AND CHAOTIC SEAS TO THE NW CALIFORNIA WATERS TONIGHT THROUGH EARLY THIS WEEKEND. SOUTH WINDS WILL GUST TO 40 KT OVER THE NORTHERN WATERS BEYOND 10 NM WITH GUSTS TO 35 KT WITHIN 10 NM. SOUTH OF THE CAPE WINDS WILL REMAIN BELOW GALE CRITERIA ALTHOUGH OCCASIONAL GUSTS TO 35 MAY AFFECT THE WATERS OFFSHORE FROM CAPE MENDOCINO. SHORT PERIOD SOUTHERLY SEAS WILL AFFECT THE WATERS NORTH OF THE CAPE...RISING TO ABOVE 10 FEET LATE THIS EVENING. A MODERATE NW SWELL CURRENTLY DIMINISHING IN THE WATERS WILL BE REPLACED BY ANOTHER NW SWELL BUILDING TO NEAR 16 FEET FRIDAY...AND TO 18 FEET AT 15 SECONDS FRIDAY NIGHT. GALE WARNING IN PLACE FOR NORTHERN WATERS ALONG WITH HAZARDOUS SEAS WARNING. THE SOUTHERN WATERS WILL REMAIN SUB-GALE. THE WATCH IN EFFECT ADDRESSES THE LARGE NW SWELL THAT MAY PEAK AT OR ABOVE 18 FEET. THE SWAN HAS BEEN BACKING OFF ON WAVE HEIGHTS BUT ENP IS STILL HIGHER. IN LIGHT OF THIS UNCERTAINTY DECIDED TO LEAVE WATCH IN PLACE FOR NOW. IN EITHER CASE...THE COMBINATION OF STEEP SOUTHERLY WAVES AND LARGE NW SWELL WILL CREATE A HAZARDOUS MIXED SEA STATE THROUGH FRIDAY. DIMINISHING SOUTH WINDS FRIDAY AFTERNOON WILL ALLOW THE SOUTHERLY SEAS TO SUBSIDE AS WELL...BUT THE NW SWELL WILL REMAIN ABOVE 18 FEET THROUGH SATURDAY...AND ABOVE 10 FEET THROUGH THE WEEKEND. CC && .EKA WATCHES/WARNINGS/ADVISORIES... CA...WINTER WEATHER ADVISORY FROM 4 AM FRIDAY TO 10 PM SATURDAY ABOVE 4000 FEET FOR THE CAZ004. NORTHWEST CALIFORNIA COASTAL WATERS... SMALL CRAFT ADVISORY UNTIL 8 PM PST THIS EVENING PZZ450-470. GALE WARNING FROM 8 PM THIS EVENING TO 10 AM PST FRIDAY PZZ450-470. HAZARDOUS SEAS WARNING FROM 8 PM THIS EVENING TO 4 PM PST SATURDAY PZZ450-470. SMALL CRAFT ADVISORY UNTIL 6 AM PST SATURDAY PZZ455-475. HAZARDOUS SEAS WATCH FROM FRIDAY EVENING THROUGH SATURDAY AFTERNOON PZZ455-475. && $$ VISIT US AT HTTP://WWW.WEATHER.GOV/EUREKA WWWW