Hazardous Seas Warning 20, NWS Eureka, CA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE EUREKA CA
324 PM PDT TUE JUN 23 2009

.SYNOPSIS...A WEAK TROUGH WILL APPROACH NORTHWEST CA TONIGHT. THE
TROUGH WILL MOVE ACROSS THE REGION WEDNESDAY AND THURSDAY...AND
...POSSIBLY TRIGGER A FEW SHOWERS OR THUNDERSTORMS FOR EASTERN
TRINITY COUNTY.  OTHERWISE... DRY AND WARM WEATHER WILL CONTINUE
THROUGH THE WEEKEND.

&&

.DISCUSSION...SATELLITE IMAGERY CONTINUES TO SHOW A WEAK UPPER LEVEL
LOW OFFSHORE OF POINT CONCEPTION WITH AN EXPANSIVE RIDGE OF HIGH
PRESSURE ACROSS THE CENTRAL CONUS. MODELS HAVE SLOWED THE FORECAST
PROGRESSION OF THE LOW AND EXPECT INLAND TEMPERATURES IN THE UPPER
80S/LOWER 90S WED AND THU. WATER VAPOR SATELLITE IMAGERY SHOWS A
BAND OF MID LEVEL MOISTURE ASSOCIATED WITH THE LOW...WITH SATELLITE
DERIVED PRECIPITATION VALUES NEAR BETWEEN 0.5 AND 0.75 INCH. THIS
MOISTURE WILL BEGIN TO MOVE OVER NW CA AS WED THE LOW SLOWLY MOVES
INLAND AND PEAK ON THU. THE LOW WILL WEAKEN THE SURFACE PRESSURE
GRADIENT AND THE WINDS WILL EASE WED INTO THU. WITH THE INCREASE IN
MOISTURE AND DECREASE IN WINDS...EXPECT INCREASINGLY EXTENSIVE
OVERNIGHT COASTAL STRATUS AND PATCHY FOG AS WED NIGHT AND THU NIGHT.

FORECAST CONVECTIVE PARAMETERS SHOW MARGINAL CHANCES FOR
THUNDERSTORMS...BUT THINK THAT THE INCREASED MID LEVEL MOISTURE
COMBINED WITH THE HOT INLAND TEMPERATURES...AND UPPER LEVEL
DIFFLUENCE WILL TRIGGER ONE OR TWO THUNDERSTORMS ACROSS EASTERN
TRINITY COUNTY WED AND THU AFTERNOONS. HAVE THEREFORE KEPT THE
SLIGHT CHANCE OF THUNDERSTORMS FOR WED AND ADDED A SLIGHT CHANCE FOR
THU...MAINLY OVER THE TRINITY ALPS AND YOLLA BOLLYS. DAYTIME
TEMPERATURES WILL LOWER A LITTLE WED AND THU DUE TO THE TROUGH
PASSAGE...BUT REBOUND FRI THROUGH SUN AS AN UPPER LEVEL RIDGE WILL
BUILD ACROSS THE REGION.

MID RANGE MODELS FORECAST ANOTHER UPPER LEVEL TROUGH TO MOVE OVER NW
CA EARLY NEXT WEEK. THE MODELS VARY ON THE STRENGTH AND TIMING OF
THIS FEATURE. THE ECMWF SEEMS TO BE THE OUTLIER AND IS FORECASTING A
DEEPER TROUGH. DUE TO LOW FORECAST CONFIDENCE DEVIATED LITTLE FROM
PREVIOUS FORECAST BEYOND SUNDAY. TH

&&

.AVIATION...THE GRADIENT WAS MUCH WEAKER AS CEC AND ACVS WINDS WERE
NOT NEARLY AS STRONG TODAY VERSES IN THE LAST COUPLE OF DAYS. CEC
KEPT SOUTHERLY LIGHT WINDS DUE TO THE INFLUENCE OF A WEAK EDDY
THROUGH EARLY AFTERNOON.  PATCHY IFR CONDITIONS OCCURRED ALONG THE
NORTH COAST THIS MORNING AND LINGERED OFF HUMBOLDT BAY THROUGH LATE
MORNING. THE GRADIENT WILL FURTHER RELAX AFTER SUNSET. THEN...LATE
NIGHT/EARLY MORNING DEVELOPMENT OF STRATUS/FOG WILL BE MORE
EXTENSIVE NEAR HUMBOLDT BAY AND PATCHY ELSEWHERE ALONG THE COAST.
BRIEF MVFR/IFR CONDITIONS EXPECTED IN THE A.M. FOR ACV/CECS TAF
SUITES. UKI TO REMAIN VFR THROUGH THE PERIOD.   TA

&&

.MARINE...NO QUIKSCAT OR ASCAT DATA THIS MORNING. ONLY ONE SHIP
REPORT IN THE SOUTHERN OUTER WATERS THAT REPORTED N WINDS TO 28 KT
AT 11AM. HAVE KEPT GALE GOING IN OUTER WATERS INTO THIS EVENING AS
WINDS NOW PICKING UP IN NEAR SHORE BUOYS WITH TYPICAL DIURNAL
TIGHTENING OF THE GRADIENT. WITH WEAK FRONT TO APPROACH TONIGHT AND
WED...THE GRADIENT DECREASES AND CONDITIONS DROP INTO SMALL CRAFT OR
BELOW. ONCE FRONT MOVES THROUGH WED NIGHT...PRESSURE GRADIENT
TIGHTENS AGAIN WITH GALE FORCE CONDITIONS TO AGAIN DEVELOP. 35-40 KT
WINDS IN OUTER WATERS THUR-FRI AND ONLY SLIGHT DECREASE OVER THE
WEEKEND. WITH STRONG WINDS AND FETCH INTO SOUTHERN OREGON
WATERS...SEAS BUILD TO 14-16 FEET IN OUTER WATERS AND EXPECT PERIODS
TO BE IN 7-8 SECOND RANGE SO WILL ALSO NEED HAZ SEAS WARNING. CLOSER
TO THE COAST...WINDS IN SMALL CRAFT RANGE BUT SEAS ABOUT 8-11 FT
WITH PERIODS 8-10 SECONDS SO VERY STEEP SEAS AND WILL BE FLIRTING
WITH HAZ SEAS WARNING CRITERIA. WILL WAIT UNTIL AFTER THIS GALE ENDS
BEFORE HOISTING GALE/HAZ SEAS WATCH FOR NEXT EVENT. DEAN

&&

.EKA WATCHES/WARNINGS/ADVISORIES...

SMALL CRAFT ADVISORY UNTIL 9 PM PDT THIS EVENING FOR PZZ450 AND
PZZ455.

GALE AND HAZ SEAS WARNING UNTIL 9 PM PDT THIS EVENING FOR PZZ470 AND
PZZ475.

&&
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