Area Forecast Discussion
Issued by NWS Eureka, CA

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000
FXUS66 KEKA 212148
AFDEKA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE EUREKA CA
248 PM PDT THU AUG 21 2014

.SYNOPSIS...HIGH PRESSURE OFFSHORE WILL MAINTAIN DRY WEATHER
CONDITIONS THROUGH THE WEEKEND. AREAS ALONG THE COAST WILL
CONTINUE TO SEE NIGHT AND MORNING LOW CLOUDS AND FOG.

&&

.DISCUSSION...HIGH PRESSURE OVER THE EASTERN PACIFIC WILL
MAINTAIN DRY AND STABLE WEATHER CONDITIONS ACROSS NW CAL THE NEXT
SEVERAL DAYS. COASTAL STRATUS AND FOG WILL REGENERATE EACH NIGHT
AND MORNING. FOR THE MOST PART THE STRATUS AND FOG WILL MIX OUT
EACH AFTERNOON. HOWEVER...PESKY LITTLE VORTICES TRAPPED IN THE
BOUNDARY LAYER NEAR THE COASTLINE WILL MAKE COMPLETE CLEARING
DIFFICULT...WITH CLEARING ALONG THE IMMEDIATE COAST LESS LIKELY
SOUTH OF CAPE MENDOCINO.

AN UPPER TROUGH OVER THE PAC NW WILL DIG SE TONIGHT AND THEN
INTO THE NORTHERN GREAT BASIN ON FRI. MAIN IMPACT WILL BE SLIGHT
COOLING ACROSS THE INTERIOR AS 850MB DECREASE A TAD AND AFTERNOON
WESTERLY WINDS DEVELOP SOONER. NAM12 AND GFS CROSS SECTIONS
INDICATE THE STRONGEST WINDS (40-50KT) LATE TONIGHT ABOVE
600-500MB...WITH A DISCONTINUITY OR STABLE LAYER NEAR 700MB. THIS
DOES NOT BODE WELL FOR STRONG WINDS MIXING DOWN EVEN OVER THE
HIGHER TERRAIN. NAM12 DOES HAVE 700MB WINDS REACHING 10-20KT LATE
TONIGHT INTO EARLY FRI...SO THERE COULD BE A PERIOD OF GUSTY W-NW
WINDS AROUND 20 MPH OVER THE EXPOSED RIDGE TOPS LATE TONIGHT AS THE
TROUGH DIGS DOWN FROM THE NORTH. CONFIDENCE WE WILL SEE DRIZZLE
AND WIDESPREAD LOW LEVEL CLOUDS NORTH OF THE CAPE TONIGHT INTO
FRIDAY IS NOT HIGH...SO DID NOT MAKE VERY MANY CHANGES TO THE
FORECAST HERE. THE NAM12 DOES HAVE 950-850MB RH`S INCREASING LATE
TONIGHT INTO FRIDAY MORNING. THIS MAY PROMOTE MORE LOW CLOUD
GROWTH. THE SMALL SCALE EDDIES TRAPPED NEAR THE COASTLINE SOUTH OF
THE CAPE LOOK TO DISSIPATE PER THE GFS AND HIGHER RESOLUTION NAM.
HOWEVER THE MODELS DO HORRIBLE WITH THESE SMALL SCALE FEATURES.
I BLENDED IN SOME PERSISTENCE INTO THE FORECAST SOUTH OF THE CAPE
TONIGHT AND FRIDAY MORNING...WITH NEW COASTAL EDDIES LIKELY FORMING.

MODELS WERE IN DECENT AGREEMENT WITH THE TROUGH ALOFT PROGRESSING
EASTWARD THIS WEEKEND ALLOWING HIGH PRESSURE OVER THE NE PAC TO
EDGE CLOSER TO THE COAST. ADDITIONAL PERTURBATIONS WILL DROP DOWN
IN N-NW FLOW ALOFT...BUT OVERALL THIS DOES NOT LOOK TO HAVE MUCH
OF AN IMPACT ON SENSIBLE WEATHER. WE SHOULD SEE MORE WARMING AND
PERHAPS MORE OFFSHORE FLOW NORTH OF THE CAPE THIS WEEKEND.

GOING INTO NEXT WEEK THE MODELS HAVE BEEN FAIRLY CONSISTENT SHOWING
ADDITIONAL WARMING WITH SLIGHTLY HIGHER TEMPERATURES THROUGH MID WEEK.
SHORT WAVE FEATURES IN DRY N-NW FLOW WILL KEEP THE RIDGE AT BAY...WITH
MODERATE WARMING EXPECTED FOR THE INTERIOR THROUGH MID WEEK. THE
NEW 12Z ECMWF DOES HAVE A DRY UPPER LOW NEAR OR OVER THE AREA WED
INTO THU. THIS WILL NEED TO BE WATCHED FOR THE POSSIBILITY OF
CONVECTION IF TROPICAL MOISTURE GETS INCORPORATED INTO THE LOW. THE
700-500MB MEAN RH FROM THE ECMWF IS TOO DRY TO SUPPORT CONVECTION.
CONFIDENCE WE WILL SEE SHOWERS OR TSTMS IS NOT HIGH ENOUGH AT THIS
PT TO INTRODUCE STORMS INTO THE FORECAST AND WILL HOLD OFF TIL THE
MODELS ARE MORE CONSISTENT AND IN BETTER AGREEMENT.

&&

.AVIATION...VFR TO MVFR CONDITIONS AND LIGHT TO MODERATE WINDS WILL
CONTINUE AT KCEC THROUGH THIS AFTERNOON. VFR TO IFR CONDITIONS AND
LIGHT TO MODERATE WINDS WILL CONTINUE AT KACV THROUGH THIS
EVENING. THE LOWER CONDITIONS AT KACV ARE DUE TO REDUCED CEILINGS.
STRATUS WILL MOVE INTO COASTAL AREAS LATE THIS EVENING AND OVERNIGHT
REDUCING CEILINGS TO IFR CONDITIONS AT KCEC AND KACV. PATCHY FOG
WILL ALSO REDUCE VISIBILITIES AT KCEC AND KACV EARLY FRIDAY
MORNING. LIGHT WINDS TO CALM CONDITIONS WILL OCCUR OVERNIGHT AT KCEC
AND KACV. VFR CONDITIONS AND LIGHT WINDS TO CALM CONDITIONS WILL
CONTINUE AT KUKI THROUGH SATURDAY.

&&

.MARINE...THE WINDS AND SHORT PERIOD SEAS WILL DIMINISH THE NEXT FEW
DAYS AS A LOW PRESSURE TROUGH MOVES NORTH OF THE AREA ALLOWING THE
PRESSURE GRADIENT TO RELAX. HOWEVER THE WINDS AND SEAS WILL INCREASE
THIS WEEKEND AS THE OFFSHORE HIGH PRESSURE RIDGE STRENGTHENS AND
INTERACTS WITH AN INLAND THERMAL LOW PRESSURE TROUGH. A LONG PERIOD
SOUTHWESTERLY SWELL WILL PERSIST THROUGH THIS WEEKEND. THE WINDS AND
SEAS WILL BE HIGHER ACROSS THE OUTER WATERS.

&&

.EKA WATCHES/WARNINGS/ADVISORIES...CA...NONE.

NORTHWEST CALIFORNIA COASTAL WATERS...
SMALL CRAFT ADVISORY UNTIL 3 PM PDT THIS AFTERNOON PZZ470.
SMALL CRAFT ADVISORY UNTIL 4 PM PDT SATURDAY PZZ475.

&&

$$

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