Hazardous Seas Warning 37, NWS Eureka, CA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE EUREKA CA
255 PM PST WED NOV 25 2009

.SYNOPSIS...DRY WEATHER WILL PERSIST ACROSS THE REGION THROUGH
TONIGHT. A COLD FRONT WILL BRING A CHANCE OF RAIN TO THE REGION
THURSDAY AFTERNOON THROUGH FRIDAY MORNING. HIGH PRESSURE WILL
BUILD FRIDAY AFTERNOON AND RESULT IN DRY AND STABLE WEATHER
THROUGH THE WEEKEND.

&&

.DISCUSSION...ANOTHER NICE DAY ACROSS THE REGION TODAY UNDER
LIGHT OFFSHORE FLOW AND A RIDGE ALOFT. PATCHES OF FOG AND LOW
CLOUDS WERE OFFSHORE OVER THE WATERS AND SHOULD CREEP ONTO THE
COAST THIS AFTERNOON INTO EARLY EVENING. GRADIENTS REMAIN LIGHT
WITH DIURNALLY DRIVEN WINDS...SO THE SHALLOW FOG AND LOW CLOUD
SHOULD PEEL AWAY FROM THE SHORELINE THURSDAY MORNING AS LIGHT
SOUTH WINDS FORM IN RESPONSE TO A DEVELOPING LOW WEST OF OREGON.

PRIMARY FORECAST CONCERN CONTINUES TO REVOLVE AROUND THE TIMING
OF RAIN THURSDAY AFTERNOON THROUGH EARLY FRIDAY MORNING. AS OF
21Z...THE RAIN FRONT WAS NEARING 135W 40N. THE FRONT WILL SLOW
DOWN AS LOW PRESSURE SPINS UP...WEST OF 130W AND NORTH OF 42N
TONIGHT. LIGHT RAIN AND PERHAPS A LITTLE BIT OF DRIZZLE MAY HIT
THE GROUND AS EARLY AS THURSDAY AFTERNOON IN THE WEAK WARM AIR
ADVECTION AND LIGHT SOUTHERLY FLOW IN ADVANCE OF THE MAIN BOUNDARY.
PRIAMRY FRONTAL PASSAGE IS EXPECTED THURSDAY NIGHT AS THE 700-500MB
TROUGH MOVES OVER THE REGION. BY 4 AM FRIDAY...UP TO THREE-QUARTERS
OF AN INCH OF RAIN WILL ACCUMULATE IN DEL NORTE COUNTY...WITH LESS
THAN A TENTH SOUTH TO UKIAH AND EAST TO WEAVERVILLE. SNOW LEVELS
WILL REMAIN ABOVE ALL THE MAJOR PASSES DURING THE BULK OF THE HEAVIER
PRECIP RATES THURSDAY NIGHT...SO WINTER WEATHER TRAVEL CONCERNS
APPEAR TO BE MINIMAL AT THIS TIME. COLD AIR ALOFT AND SHALLOW
INSTABILITY WILL LINGER THROUGH THE DAY ON FRIDAY AND WE MAY SEE
ISOLATED OR SCATTERED WET SNOW ACCUMULATIONS OF 1 INCH OR LESS
FROM 2500 TO 3500 FEET OVER THE COASTAL RANGES. ECMWF AND GFS HAS
MOISTURE RUNNING OVER THE RIDGE IN NORTHERLY FLOW ON SATURDAY.
THIS LOOKS TO BE OVERDONE WITH STRONG HIGH PRESSURE AT THE SURFACE
AND BRISK NORTH FLOW IN THE BOUNDARY LAYER. FOR NOW...LEFT THE
POSSIBILITY OF LIGHT SHOWERS IN THE FORECAST...MAINLY ACROSS DEL
NORTE COUNTY FOR SATURDAY.

HIGH PRESSURE WILL REBUILD BY SATURDAY AND HOLD THROUGH SUNDAY.
THE DRY AND STABLE WEATHER LOOKS TO CONTINUE INTO MONDAY. HOWEVER...
12Z ECMWF AND 12Z GFS DO SHOW A SHORT-WAVE TROUGH MOVING OVER THE
RIDGE MONDAY NIGHT THROUGH TUESDAY FOR AN OUTSIDE CHANCE OF LIGHT
RAIN...MAINLY ACROSS HUMBOLDT AND DEL NORTE COUNTIES. IF THE TIMING
OF THIS SHORT-WAVE IS CORRECT...HIGH PRESSURE AND DRY OFFSHORE
FLOW WILL RETURN ON WED. THIS IS THE FIRST RUN SHOWING RAIN
CREEPING BACK INTO THE PICTURE FOR MON->TUE...SO WILL HOLD OFF ON
ADDING A CHANCE OF RAIN TO THE FORECAST. DJB

&&

.AVIATION...WEAK HIGH PRESSURE WILL MAINTAIN LIGHT WINDS THROUGH THE
NIGHT. SKIES WILL BE MOSTLY CLEAR IN THE EARLY EVENING WITH POCKETS
OF MVFR VISIBILITIES DUE TO HAZE. EXPECT STRATUS AND POSSIBLY PATCHY
FOG ALONG THE COAST LATER THIS EVENING. THERE WILL BE AN INCREASE IN
MID AND HIGH CLOUDS TONIGHT AND THU MORNING AS A FRONTAL SYSTEM
APPROACHES THE REGION. THESE HIGHER CLOUDS WILL REDUCE NOCTURNAL
RADIATION COOLING IN THE EARLY MORNING...AND MAY DETER FOG
DEVELOPMENT ALONG THE COAST AND COASTAL VALLEYS. SKIES SHOULD REMAIN
MOSTLY CLEAR INLAND WITH RADIATION FOG DEVELOPING IN THE INTERIOR
VALLEYS OVERNIGHT AND INTO THU MORNING. TH

&&

.MARINE...THE SHORT TERM MARINE CHALLENGE IS A LARGE WEST SWELL THAT
WILL MOVE THROUGH THE WATERS LATE TONIGHT THROUGH THURSDAY MORNING.
SWELL OBSERVATIONS OF 22 TO 26 FT WITH 17 SECOND PERIODS WERE
OBSERVED AT BUOY #6 THIS MORNING. A SIMPLE SWELL DECAY MODEL
FORECASTS 15 TO 17 FT SWELL WITH 19 SECOND PERIODS IN THE NORTHERN
CA WATERS NEAR MIDNIGHT TONIGHT...WHEREAS THE ENP AND SWAN MODELS
FORECAST 14 TO 16 FT SWELL AT 16 SECONDS. THE 06Z AND 12Z ENP
FORECAST FOR BUOY#6 ALIGNED WELL WITH OBSERVATIONS TODAY AND HAD NO
REASON TO DEVIATE MUCH FROM THE MODEL...BUT HAVE FORECASTED SWELL 1
TO 2 FT ABOVE GUIDANCE DUE TO THE SWELL OBSERVED AT BUOY#6. THE
SWELL WILL REMAIN BELOW WARNING LEVEL...BUT THE SEAS WILL REMAIN
DANGEROUS AND PRODUCE LARGE BREAKERS IN BAYS AND HARBOR ENTRANCES.
WINDS NORTH OF CAPE MENDOCINO WILL SHIFT TO THE SOUTH LATE TONIGHT
AHEAD OF AN APPROACHING FRONT AND INCREASE SLIGHTLY THURSDAY NIGHT
AS THE FRONT NEARS.

NORTH WINDS WILL RAPIDLY INTENSIFY BEHIND THE FRONT ON FRIDAY WITH
GALES POSSIBLE FRIDAY NIGHT AND SATURDAY...MAINLY OVER THE OUTER
WATERS. STEEP SEAS WILL DEVELOP FROM THE STRONG WINDS AND WHEN
COMBINED WITH A MODERATE NW SWELL WILL POSE AN EXTRA THREAT TO
MARINERS FRIDAY...FRIDAY NIGHT...AND POSSIBLY INTO SAT MORNING.
FORECAST MODELS ARE HINTING FOR A BRIEF DECREASE IN WINDS OUT 10 NM
SATURDAY MORNING...BUT THE WINDS STAY STRONG BEYOND 10 NM...AND
INTENSIFY OVER ALL WATERS IN THE AFTERNOON. THE PRESSURE GRADIENT
SHOULD RELAX SATURDAY NIGHT WITH CALMER WINDS BY SUNDAY. A SERIES OF
STORMS MOVING ACROSS THE NE PACIFIC WILL MAINTAIN MODERATE NW SWELL
THROUGH THE WEEKEND. TH

&&

.EKA WATCHES/WARNINGS/ADVISORIES...SMALL CRAFT ADVISORY FROM 3 AM
THURSDAY TO 11 PM PST MONDAY FOR PZZ450-455. SMALL CRAFT ADVISORY
FROM 9 PM THIS EVENING TO 11 PM PST MONDAY FOR PZZ470-475.

&&

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