Area Forecast Discussion
Issued by NWS Eureka, CA

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FXUS66 KEKA 162210
AFDEKA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE EUREKA CA
310 PM PDT TUE SEP 16 2014

.SYNOPSIS...AN APPROACHING LOW PRESSURE SYSTEM OVER THE EASTERN
PACIFIC WILL BRING RAIN SHOWERS WEDNESDAY THROUGH THURSDAY. WARM
AND DRY WEATHER WILL RETURN OVER THE WEEKEND AS HIGH PRESSURE
BUILDS OVER NORTHERN CALIFORNIA.


&&

.SHORT TERM...(THROUGH THU NIGHT) THE MAIN FORECAST ISSUE OVER
THE NEXT COUPLE OF DAYS WILL BE HOW MUCH RAINFALL TO EXPECT
THROUGH THURSDAY. THE FIRST SIGNIFICANT UPPER LEVEL TROUGH FOR THE
SEASON IS NOW ADVANCING TOWARD THE COAST WITH HIGH AND MID LEVEL
CLOUD COVER SPREADING OVER THE REGION. INCREASING SOUTHERLY FLOW
AHEAD OF THE SYSTEM HAS ALLOWED MOISTURE TO STREAM NORTH SETTING
THE STAGE FOR AT LEAST SOME LIGHT RAIN ACROSS THE REGION. THE
FRONT WILL BEGIN TO IMPACT THE AREA ON WEDNESDAY...LIKELY LATE IN
THE MORNING HOURS THROUGH THE AFTERNOON...WITH A BAND OF
PRECIPITATION IMPACTING THE HUMBOLDT AND DEL NORTE COASTLINES AND
SPREADING INLAND. THE ECMWF AND GFS ARE NOW IN GREAT AGREEMENT ON
THE LOCATION AND TIMING OF THE RAINFALL WEDNESDAY THROUGH
THURSDAY...THOUGH THERE IS SOME UNCERTAINTY WITH THE TOTAL
RAINFALL EXPECTED. THE ECMWF HAS ONCE AGAIN COME IN WETTER THAN
ITS PREVIOUS RUNS AND NOW IS PREDICTING OVER A HALF INCH OF RAIN
ON THE REDWOOD COAST. CONSIDERING THE SOUTHERLY WINDS...IT IS
HIGHLY LIKELY THAT THE HUMBOLDT BAY AREA...THE TARGET OF THE ECMWF
RAINFALL...WILL BECOME RAIN SHADOWED AND THUS NOT RECEIVE THE
RAINFALL THE MODEL PREDICTS. HAVE OPTED TO FORECAST THE GREATEST
PRECIPITATION AMOUNTS IN THE KING RANGE AND SISKIYOU MOUNTAINS
ALONG WITH ON THE DEL NORTE COASTLINE...IN OTHER WORDS IN THE MORE
CLIMATOLOGICALLY FAVORED AREAS. THE FRONT WILL ALSO BRING WITH IT
SOME MID LEVEL INSTABILITY WHICH COULD BRING A STRAY RUMBLE OF
THUNDER ON WEDNESDAY. FOR NOW HAVE KEPT THUNDER OUT OF THE
FORECAST ON WEDNESDAY BUT THIS WILL BE SOMETHING THAT NEEDS TO BE
WATCHED CLOSELY.

THE UPPER TROUGH WILL BEGIN TO MOVE INLAND WEDNESDAY NIGHT INTO
THURSDAY WITH A SECONDARY POST FRONTAL TROUGH MOVING INLAND LIKELY
EARLY THURSDAY. WITH COOL AIR ALOFT AND BREAKS EXPECTED IN THE
CLOUDS...IT WILL BE LIKELY THAT DECENT INSTABILITY WILL DEVELOP OVER
THE REGION PARTICULARLY ACROSS THE INTERIOR. IN FACT...THE NAM
INDICATES 100-600 J/KG OF SURFACE BASED CAPE DEVELOPING THURSDAY
AFTERNOON OVER SOUTHERN TRINITY AND NORTHEASTERN MENDOCINO COUNTIES.
THUS THERE IS THE POTENTIAL FOR ISOLATED THUNDERSTORMS THURSDAY
AFTERNOON AND THIS CHANCE HAS BEEN INTRODUCED IN THIS FORECAST
UPDATE. SHOWER ACTIVITY WILL DECREASE THURSDAY EVENING AS THE TROUGH
CONTINUES TO MOVE INLAND AND SKIES SHOULD CLEAR OVERNIGHT.

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. RPA

.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...VFR CONDITIONS AND LIGHT WINDS WILL CONTINUE AT KCEC,
KACV AND KUKI THROUGH THIS EVENING. MVFR CONDITIONS MAY DEVELOP AT
TIMES AT KCEC AND KACV OVERNIGHT. VFR CONDITIONS AND LIGHT WINDS
WILL PREVAIL AT KCEC, KACV AND KUKI WEDNESDAY.


&&

.MARINE...A LOW PRESSURE SYSTEM WILL PRODUCE LIGHT TO MODERATE
SOUTHERLY WINDS ACROSS THE WATERS THROUGH THURSDAY AS IT MOVES INTO
NORTHERN CALIFORNIA. SEAS WILL SLOWLY INCREASE WEDNESDAY AND THIS
WEEKEND AS A HIGH PRESSURE SYSTEM STRENGTHENS OFFSHORE. SEAS WILL BE
HIGHER ACROSS THE OUTER WATERS.


&&

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

$$

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