Area Forecast Discussion
Issued by NWS Eureka, CA

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000
FXUS66 KEKA 232247
AFDEKA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE EUREKA CA
347 PM PDT WED APR 23 2014

.SYNOPSIS...WET WEATHER WILL CONTINUE INTO THURSDAY AS A WEAK
FRONT IMPACTS NORTHERN CALIFORNIA. AN UPPER LEVEL TROUGH WILL
INTRODUCE A COLDER AND MORE UNSTABLE AIRMASS TO THE
REGION...RESULTING IN A SLIGHT CHANCE FOR THUNDERSTORMS ON FRIDAY.
DRY WEATHER WILL RETURN LATE THIS WEEK AS HIGH PRESSURE BUILDS
BACK OVER CALIFORNIA.

&&

.DISCUSSION...

.SHORT TERM (TONIGHT THROUGH FRIDAY MORNING)...UPPER LEVEL RIDGING
TOOK PLACE TODAY AS AN EASTERN PACIFIC RIDGE OF HIGH PRESSURE
SHIFTED TOWARDS THE WEST COAST. OVERRIDING CLOUD COVER AND WARM
FRONTAL SHOWERS INCREASED INTO THE AFTERNOON AS AN UPPER LEVEL
TROUGH APPROACHES THE PACIFIC NW. SCATTERED WARM FRONTAL SHOWERS
FIRST IMPACTED THE COAST AROUND 20Z WITH MORE WIDESPREAD
STRATIFORM PRECIPITATION TO IMPACT NORTHERN CALIFORNIA INTO THE
EVENING. SHOWERS WILL PERSIST OVERNIGHT BEFORE A COLD FRONT
ARRIVES EARLY THURSDAY MORNING BRINGING MORE RAINY WEATHER TO
NORTHERN CALIFORNIA AS IT SLIDES TO THE SOUTHEAST.

THE UPPER LEVEL TROUGH WILL CONTINUE DIG SOUTHWARD OVER NORTHERN
CALIFORNIA INTRODUCING A COLDER AND MORE UNSTABLE AIRMASS CONDUCIVE
TO THUNDERSTORM DEVELOPMENT ON FRIDAY. UPPER LEVEL DYNAMICS FAVOR A
MORE UNSTABLE ENVIRONMENT WITH POSITIONING OF THE UPPER LEVEL JET
PROMOTING DIVERGENCE ALOFT. THE BEST LOW LEVEL FORCING WILL OCCUR
EARLY FRIDAY MORNING THROUGH THE LATE MORNING AS THE TROUGH AXIS
TRAVERSES NORTHERN CALIFORNIA. MUCAPE REMAINS IN THE LOWER
HUNDREDS WITH MARGINAL LIFTED INDICES BARELY DROPPING TO -1 C.
THE COLDER AIRMASS WILL ENCOURAGE HAIL DEVELOPMENT WITH 500 MB
TEMPERATURES RANGING FROM -28 TO -31 DEGREES CELSIUS WITH THE
PASSAGE OF THE TROUGH. AS A RESULT, SMALL HAIL WAS ADDED TO THE
FORECAST ON FRIDAY. CONDITIONS WILL QUICKLY STABILIZE AS RIDGING
BUILDS BEHIND THE TROUGH AXIS PUTTING A HALT TO THUNDERSTORM
DEVELOPMENT BY FRIDAY EVENING. KML

.LONG TERM (FRI NIGHT-WED)...MODELS APPEAR TO BE IN GOOD AGREEMENT
WITH PRECIP WINDING DOWN FRIDAY NIGHT THROUGH SATURDAY AS A BROAD
FLAT RIDGE DEVELOPS IN THE WAKE OF THE TROUGH. HOWEVER...ANOTHER
WEAKER FRONT MAY BRING LIGHT AMOUNTS OF PRECIP SATURDAY NIGHT INTO
EARLY SUNDAY MORNING. WE SHOULD SEE BETTER DRYING AND WARMING
EARLY NEXT WEEK AS STRONGER RIDGING DEVELOPS BOTH AT THE SURFACE
AND ALOFT. MODELS GO OUT OF SYNC AROUND MID WEEK WITH ANOTHER
TROUGH. THE GFS HAS BEEN HINTING AT THE POSSIBILITY OF LIGHT
SPOTTY PRECIP ON WEDNESDAY WHILE THE ECMWF INDICATES DRY/STABLE
CONDITIONS PREVAILING...SO CONFIDENCE IS NOT HIGH. &&

.AVIATION...AFTERNOON RADAR SHOWS PRECIPITATION OVER PORTIONS OF
NORTHWEST CALIFORNIA. THIS IS BRINGING MVFR AND LOCAL IFR, MAINLY
TO LOCATIONS NORTH OF CAPE MENDOCINO. THIS WILL CONTINUE THIS
EVENING AND TONIGHT AS A DISTURBANCE IMPACTS OUR AREA. SOUTH OF
CAPE MENDOCINO, WHERE THE PRECIPITATION THREAT IS LOWER, EXPECT
BORDERLINE VFR/MVFR.

&&

.MARINE...NEARSHORE BUOY OBSERVATIONS THIS AFTERNOON ARE REPORTING A
STRONG BREEZE NORTH OF CAPE MENDOCINO, LIGHT WINDS SOUTH OF CAPE
MENDOCINO, AND SEAS AROUND 8-10 FT. THE 1830Z ASCAT PASS SHOWED
WINDS OF 15-25 KT NORTH OF CAPE MENDOCINO AND CALM TO AROUND 15 KT
SOUTH OF CAPE MENDOCINO. THIS IS SLIGHTLY STRONGER THAN FORECAST,
SO BUMPED UP THE WINDS SLIGHTLY OVER THE NEXT FEW HOURS, MAINLY
NORTH OF CAPE MENDOCINO. LEFT THE SCA HEADLINES UNCHANGED. MODELS
REMAIN IN GOOD AGREEMENT SHOWING A SERIES OF SYSTEMS PASSING TO OUR
NORTH OVER THE NEXT WEEK AND BRINGING PERIODS OF MODERATE WINDS TO
OUR WATERS. LONG PERIOD WESTERLY SWELL GENERATED FROM A DISTANT
STORM SHOULD BEGIN MOVING THROUGH OUR WATERS LATE THURSDAY INTO
FRIDAY. WE WILL KNOW MORE WHEN IT PASSES OFFSHORE BUOY #2. THE LONG
PERIOD SOUTHERLY SWELL THE MODELS ARE SHOWING FOR THIS WEEKEND STILL
SEEMS HIGH. FOLLOWING COORDINATION INTERNALLY AND WITH OPC, DECIDED
TO CAP IT AT 3 FT. THIS MAY BE CHANGED IF IT IS LARGER THAN EXPECTED
WHEN IT STARTS PASSING THE SOUTHERN CALIFORNIA BUOYS.


&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
NORTHWEST CALIFORNIA COASTAL WATERS...SMALL CRAFT ADVISORY UNTIL 9 PM PDT THIS EVENING PZZ450.

     SMALL CRAFT ADVISORY UNTIL 2 PM PDT THURSDAY PZZ470.

     SMALL CRAFT ADVISORY UNTIL 9 PM PDT THIS EVENING PZZ475.

&&

$$

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