Area Forecast Discussion
Issued by NWS Eureka, CA

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000
FXUS66 KEKA 171141
AFDEKA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE EUREKA CA
441 AM PDT WED SEP 17 2014

.SYNOPSIS...AN APPROACHING LOW PRESSURE SYSTEM WILL BRING RAIN
SHOWERS TO NORTHWEST CALIFORNIA THIS AFTERNOON THROUGH THURSDAY.
THEN BUILDING HIGH PRESSURE WILL RESULT IN WARM AND DRY WEATHER OVER
THE WEEKEND.


&&

.DISCUSSION...
.SHORT TERM (THROUGH THUR)...EARLY MORNING SATELLITE IMAGERY
SHOWS THE FRONTAL BOUNDARY MAKING A PUSH TOWARDS THE WEST COAST
WITH VERY LIGHT RADAR REFLECTIVITY JUST BEGINNING TO IMPACT THE
OUTER FRINGES OF THE EUREKA COASTAL WATERS. IN ADDITION, LIGHTNING
SENSORS SHOWED A FEW STRIKES WELL OFFSHORE BETWEEN 135W AND 130W
LONGITUDE. AREAS NORTH OF CAPE MENDOCINO MAY OBSERVE SOME
SPRINKLES THIS MORNING HOWEVER THE FRONT WILL NOT ARRIVE UNTIL
LATE THIS MORNING BRINGING LIGHT RAIN SHOWERS THROUGH THURSDAY.
MODELS STILL VARY WITH RAINFALL TOTALS ACROSS THE REGION YET THEY
STILL AGREE ON A FEW KEY AREAS RECEIVING THE BULK OF THE RAIN
INCLUDING: COASTAL DEL NORTE COUNTY, THE SISKIYOU RANGE, AND THE
KING RANGE. WITH STRONG SOUTHERLY FLOW OFFSHORE, THE HUMBOLDT BAY
AREA WILL LIKELY EXPERIENCE THE RAIN SHADOW EFFECT AS DOWNSLOPING
WINDS DRY OUT THE ATMOSPHERE. AS A RESULT, LIGHTER RAINFALL
AMOUNTS WERE MAINTAINED FOR THIS AREA. HIGHEST RAINFALL AMOUNTS
COULD REACH THE HALF INCH MARK WHILE OTHER LESS FORTUNATE AREAS
(MOSTLY FARTHER SOUTH) MAY SEE A FEW HUNDRETHS TO ONE TENCH OF AN
INCH.

THUNDERSTORMS WITH A LIGHTNING STRIKE OR TWO WILL POSE A POTENTIAL
THREAT WITH THE FRONTAL PASSAGE THIS AFTERNOON. THUNDER WAS ADDED
OVER COASTAL WATERS AS A SPOKE OF ENERGY WRAPS UP ALONG THE COAST
THIS AFTERNOON. ANOTHER AREA OF CONCERN IS THE YOLLA BOLLY RANGE
ALONG EASTERN MENDOCINO COUNTY. WITH IMPROVING CAPE VALUES AND
MARGINAL INSTABILITY, THUNDERSTORMS HAVE THE POTENTIAL TO IGNITE
LATER THIS EVENING. HOWEVER, WITH UNCERTAINTY IN THE ALIGNMENT OF
CONVECTIVE PARAMETERS HAVE LEFT THUNDER OUT OF THE FORECAST.
THURSDAY AFTERNOON REMAINS ON TRACK WITH POST FRONTAL INSTABILITY
ENCOURAGING THUNDERSTORM ACTIVITY. THE ONLY THING TO CONSIDER IS
WHETHER STORMS NEED TO BE ADDED EARLIER IN THE DAY.

TEMPERATURES THROUGH THURSDAY WILL BE SEVERAL DEGREES BELOW NORMAL
WITH COOLER AIR ALOFT AND ABUNDANT CLOUD COVER. THE ONLY EXCEPTION
WILL BE ALONG THE HUMBOLDT AND DEL NORTE COASTS WHERE DOWNSLOPE FLOW
WILL LIKELY ALLOW TEMPERATURES TO SPIKE INTO THE MIDDLE TO UPPER 60S
AND POSSIBLY LOW 70S IN SOME LOCATIONS. KMLRPA

.LONG TERM (FRI THRU TUE)...HIGH PRESSURE WILL BUILD IN OVER
NORTHWEST CALIFORNIA ON FRIDAY AS THE UPPER TROUGH SLIDES OFF TO THE
SOUTH AND EAST...TRANSITIONING INTO A CUT OFF LOW THAT THEN DIVES
SOUTH...SETTLING OVER SOUTHERN CALIFORNIA...AND MOVING OFF TO THE
EAST BY MONDAY. BOTH THE GFS AND ECMWF HAVE NOW COME INTO GOOD
AGREEMENT WITH THIS SOLUTION. DRY CONDITIONS ALONG WITH LIGHT
OFFSHORE FLOW AND ABOVE NORMAL TEMPERATURES WILL RETURN TO
CALIFORNIA AND DOMINATE THE WEATHER PATTERN INTO EARLY NEXT WEEK AS
HEIGHTS BUILD. WITH THE LIGHT OFFSHORE FLOW...COASTAL LOCATIONS
COULD SEE HIGH TEMPERATURES INTO THE 70S...WITH THE WARMEST DAY
LOOKING LIKE SATURDAY. STP

&&

.AVIATION...IR SAT SHOWS HIGH CLOUDS STREAMING ACROSS THE AREA THIS
MORNING IN ASSOCIATION WITH THE UPPER LEVEL TROUGH AND ASSOCIATED
FRONT APPROACHING THE AREA. CIGS WILL GRADUALLY DROP THROUGH THE
DAY AS THE FRONT BRINGS SOME LIGHT RAIN TO THE AREA. IT IS POSSIBLE
THERE COULD BE A THUNDERSTORM OR TWO WITH THE FRONT...BUT CONFIDENCE
IS TOO LOW TO ADD THEM TO THE FORECAST. THE FRONT WILL LIKELY DROP
CIGS TO MVFR CONDITIONS WITH LOCAL IFR CONDITIONS THESE EVENING.
TONIGHT BEHIND THE FRONT SKIES WILL LIKELY CLEAR OUT...BUT SHOWERS
WILL BE MOVING THROUGH THE AREA. THIS MAY BRING SOME LOCAL IFR
CONDITIONS IN THE HEAVIER SHOWERS. MKK


&&

.MARINE...AN UPPER LEVEL TROUGH APPROACHING THE AREA THIS MORNING IS
BRINGING SOME LIGHT SOUTHERLY WINDS TO THE WATERS. AN ASCAT PASS
FROM 05Z INDICATED ALL WINDS WERE LESS THAN 5 KT. WINDS WILL REMAIN
OUT OF THE SOUTH AND LESS THAN 10 KT UNTIL THE TROUGH PASSES ON
THURSDAY. FRIDAY NORTHERLY WINDS WILL RETURN AND INCREASE TO 15 TO
25 KT BY FRIDAY AFTERNOON. WAVES WILL BUILD IN RESPONSE TO THESE
WINDS. WINDS TO THE NORTH OF THE AREA WILL BE A BIT STRONGER SO
WAVES WILL BUILD TO AROUND 8 FT AT 7 SECONDS OVER THE NORTHERN
OUTER WAVES. A SMALL CRAFT ADVISORY MAY BE NEEDED. SATURDAY
MODELS ARE SHOWING A SOUTHERLY SURGE OF WINDS RETURN. THIS IS DUE
TO THE TROUGH BECOMING A CUT OFF LOW AND DRIFTING BACK TOWARDS THE
WEST. WINDS LOOK TO REMAIN FAIRLY LIGHT THROUGH THE EARLY NEXT
WEAK WITH WEAK ZONAL FLOW OVER THE AREA ONCE THE LOW MOVES OUT OF
THE AREA.

THE LONG PERIODS WAVES ARE A BIT MORE COMPLICATED. THE DOMINANT WAVE
IS THE NORTHWESTERLY WAVE AT 12 TO 14 SECONDS. THIS HAS BEGUN TO
INCREASE RATHER QUICKLY. IT HAS BUILT TO AROUND 6 AT AT 13 SECONDS.
THIS WAVE WILL PEAK THIS MORNING AND SLOWLY DIMINISH OVER THE NEXT
COUPLE DAYS. THE OTHER WAVE IS A LONG PERIOD SOUTHWESTERLY AROUND 3
FT AT 20 SECONDS. THIS WILL PEAK AROUND 4 FT TODAY AND THEN SLOWLY
DIMINISH THROUGH THE WEEK. ANOTHER NORTHWESTERLY WAVE AROUND 14
SECONDS STARTS TO MOVE INTO THE WATERS ON SATURDAY. HEIGHTS
QUICKLY BUILD TO 8 FT AT 12 SECONDS AND THEN SLOWLY DIMINISH
THROUGH THE WEEK. MKK


&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
NORTHWEST CALIFORNIA COASTAL WATERS...NONE.
&&

$$

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