632
FXUS66 KEKA 202048
AFDEKA
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE EUREKA CA
148 PM PDT MON OCT 20 2025
SYNOPSIS
DRYING AND WARMING WEATHER TODAY AND TUESDAY. A SERIES
OF LARGE SWELL WILL BRING DANGEROUS BREAKING WAVES ALONG THE WEST
AND NORTHWEST FACING BEACHES THIS WEEK. CONFIDENCE CONTINUES TO
INCREASE FOR A MODERATE ATMOSPHERIC RIVER (AR) IMPACTING NORTHERN
CALIFORNIA FRIDAY INTO THE WEEKEND, BRINGING PERIODS OF HEAVY
RAINFALL, HIGH-ELEVATION HEAVY SNOW, AND STRONG SOUTH WINDS.
DISCUSSION
HIGH PRESSURE CONTINUES TO BUILD ACROSS THE PACIFIC
NORTHWEST AND NORTHERN CALIFORNIA. THIS IS PROMOTING A DRIER DAY
THAN SUNDAY. TEMPERATURES ARE CURRENTLY RUNNING NEARLY 5-10 DEGREES
COOLER THAN YESTERDAY IN SOME INTERIOR VALLEYS, WITH COLD
NIGHTTIME TEMPERATURES AND SLOW DISPERSAL OF VALLEY CLOUDS TO
BLAME. LOW TO MID 30S WERE OBSERVED AROUND HAYFORK AND WEAVERVILLE
EARLY THIS MORNING. CHILLY TEMPERATURES ARE POSSIBLE AGAIN
TONIGHT, WITH LOWS DIPPING INTO THE MID 30S IN TRINITY COUNTY,
INCLUDING HAYFORK AND WEAVERVILLE. A FROST ADVISORY HAS BEEN
ISSUED BETWEEN 2 AM AND 9 AM TUESDAY MORNING FOR TRINITY COUNTY.
TAKE STEPS TO PROTECT ANY SENSITIVE PLANTS. OTHER COLD VALLEYS IN
MENDOCINO COUNTY, INCLUDING COVELO AND WILLITS COULD AGAIN SEE 30S
TONIGHT, BUT FROST POTENTIAL THERE IS LOWER.
HIGH PRESSURE CONTINUES TO BUILD TUESDAY. INTERIOR TEMPERATURES ARE
FORECAST TO WARM UP TO THE HIGH 70S TO LOW 80S. EVEN THE COASTAL
AREAS COULD SEE HIGH 60S TO LOW 70S ON TUESDAY AS OFFSHORE FLOW
KEEPS SKIES CLEAR WHILE WINDS REMAIN LIGHT. WEDNESDAY, THE HIGH
PRESSURE WEAKENS AND BEGIN TO SHIFT EASTWARD, WHILE AN UPPER-LEVEL
TROUGH MOVES TOWARD THE PACIFIC NORTHWEST, AND A CUTOFF LOW OFF THE
SOUTHERN CALIFORNIA MOVES ONSHORE. A WEAK SURFACE LOW OFFSHORE
CENTRAL CALIFORNIA WILL BRING A SOUTHERLY REVERSAL STRATUS SURGE
TUESDAY NIGHT INTO WEDNESDAY, WITH LOW CLOUDS AND PATCHY FOG
CHARGING UP AND LAPPING THE COASTAL AREAS. THIS WILL BRING A PUSH OF
MARINE AIR TO THE INTERIOR ON WEDNESDAY. SOME COOLING IS EXPECTED ON
WEDNESDAY, WITH HIGH TEMPERATURES WILL LIKELY AROUND SEASONAL
AVERAGE. THURSDAY, A WEAK HIGH PRESSURE BUILDS IN, HOWEVER
INCREASING CLOUDINESS WILL KEEP HIGH TEMPERATURES SIMILAR TO
WEDNESDAY.
THERE CONTINUES TO BE STRONG SIGNALS IN ENSEMBLE AND DETERMINISTIC
MODELS FOR A GOOD CHANCE OF WIDESPREAD EARLY WINTER WEATHER FRIDAY
AND WEEKEND. CW3E TOOLS FOR GEFS AND ECMWF EPS INDICATE THERE IS A
75-85% CHANCE OF IVT GREATER THAN 500 KG/MS IMPACTING THE AREA.
THE ATMOSPHERIC RIVER (AR) IMPACTING NORTHERN CALIFORNIA HAS THE
POTENTIAL TO BRING PERIODS OF HEAVY RAINFALL, HIGH-ELEVATION HEAVY
SNOW, AND STRONG SOUTH WINDS. NBM CHANCES FOR 72 HR STORM TOTAL
PRECIPITATION, FRIDAY THROUGH SUNDAY, OF OVER AN INCH ARE NEAR
100% NORTH OF CAPE MENDOCINO AND 60% IN SOUTHERN MENDOCINO AND
LAKE. NBM CHANCES FOR OVER 3 INCHES OF PRECIPITATION ARE OVER 90%
IN DEL NORTE AND AROUND 50% NORTH OF CAPE MENDOCINO WITH MUCH
LOWER CHANCES (30% OR LESS) IN MENDOCINO AND LAKE. HIGH ELEVATION
AREAS OF DEL NORTE AND THE KING RANGE COULD SEE OVER 6 INCHES
TOTAL. RAPID RISES IN SMALL STREAMS AND RIVERS, MINOR FLOOD
IMPACTS TO URBAN AREAS, AND DEBRIS ON ROADWAYS ARE ALL POSSIBLE.
NBM IS ALSO SHOWING HIGH CHANCES FOR WIND GUSTS OF OVER 40 MPH
OVER EXPOSED RIDGES AND COASTAL HEADLANDS WITH SMALL (~15%), BUT
NONZERO, CHANCES FOR WINDS THIS STRONG ESSENTIALLY EVERYWHERE
ACROSS THE AREA. IMPACTS WILL BECOME CLEARER AS THE STORM TRACK
SOLIDIFIES IN THE COMING DAYS. /ZVS /JB
AVIATION...(18Z TAFS)
VFR CONDITIONS ARE FORECAST TO PREVAIL AT
ALL FORECAST TERMINALS. AREAS OF LOW CLOUDS AND FOG MAY FORM IN THE
INTERIOR VALLEYS AGAIN TONIGHT THROUGH EARLY TUE. ALSO, SHALLOW MIST
AND HAZE MAY RESULT IN BRIEF LIFR FOR COASTAL TERMINALS THIS
EVENING. ONSHORE WINDS ARE EXPECTED TO BE LESS TODAY AND EAST AND
NORTHEAST BREEZES OVERNIGHT SHOULD RESULT IN DRYING WITH MUCH LESS
POTENTIAL FOR SHALLOW GROUND FOG AT THE TERMINALS. SOUTHERLY WINDS
WILL BEGIN TO DEVELOP THROUGH THE DAY ON TUE. STRATUS AND FOG
TRAPPED SOUTH OF MONTEREY BAY WILL PROBABLY BEGIN TO CREEP NORTHWARD
THROUGH THE DAY, BRINGING AN INCREASED RISK FOR FOG AND LOW CLOUDS
TO THE MENDOCINO COASTLINE AND PERHAPS UP TO SOUTHERN HUMBOLDT BY
LATE IN THE AFTERNOON OR EVENING ON TUE.
MARINE
MODERATE NORTHERLY BREEZES AND STEEP WIND WAVES ARE
FORECAST TO EASE UP OVERNIGHT INTO TUESDAY MORNING. OTHERWISE, NW
SWILL IS FORECAST TO SLOWLY SUBSIDE TONIGHT THROUGH THE DAY ON TUE.
A NEW LONG PERIOD W TO NW SWELL GROUP WILL BUILD ON TUE AND PEAK TO
AROUND 14-16 FT BY TUE NIGHT OR EARLY WED. 20+ SECOND FORERUNNERS
WILL ARRIVE BY MID TO LATE MORNING ON TUESDAY. THIS NEW SWELL WILL
BE SUPERIMPOSED ON AN OLDER DECAYING SWELL GROUP. THIS SWELL
COMBINATION MAY MITIGATE THE RISK FOR SNEAKER WAVES. OTHERWISE,
SOUTHERLY WIND ARE FORECAST TO DEVELOP THROUGH THE DAY ON TUE AND
STRENGTHEN TUESDAY NIGHT INTO EARLY WED. STRONGER SOUTHERLY WINDS
(GUSTS OVER 35 KT) WILL BE POSSIBLE (40% CHANCE) WITH A SERIES OF
FRONTAL SYSTEMS THURSDAY THROUGH SATURDAY. ADDITIONAL REINFORCING
WEST TO NORTHWEST SWELL GROUPS FROM A SERIES OF NORTH PACIFIC STORMS
ARE FORECAST TO IMPACT THE COAST AND COASTAL WATERS DURING THE LATER
PORTION OF THE WEEK INTO THE WEEKEND.
BEACH HAZARDS
A NEW LONG PERIOD W-NW SWELL GROUP WILL BUILD ON
TUESDAY. SWELL FORERUNNERS FROM 18-22 SECONDS MAY POSE A RISK FOR
SNEAKER WAVES AND SURF RUNNING FARTHER UP THE BEACHES BY MID TO LATE
MORNING. SHORTER PERIOD SWELL FROM AN OLDER SWELL GROUP WILL BE
DECAY THROUGH THE DAY ON TUE AND MAY MITIGATE THE INITIAL RISK. BY
TUESDAY EVENING, THE SWELL WILL BUILD TO OVER 10 FEET AND LARGE AND
HAZARDOUS SURF IS EXPECTED WITH SNEAKER WAVE RISK OR SET BEHAVIOR
DECREASING BY MIDNIGHT.
EKA WATCHES/WARNINGS/ADVISORIES
CA...
BEACH HAZARDS STATEMENT FROM TUESDAY MORNING THROUGH
TUESDAY AFTERNOON FOR CAZ101-103-104.
FROST ADVISORY FROM 2 AM TO 9 AM PDT TUESDAY FOR CAZ107-108.
BEACH HAZARDS STATEMENT FROM TUESDAY AFTERNOON THROUGH
TUESDAY EVENING FOR CAZ109.
NORTHWEST CALIFORNIA COASTAL WATERS...
SMALL CRAFT ADVISORY UNTIL 11 PM PDT THIS EVENING FOR
PZZ450.
SMALL CRAFT ADVISORY UNTIL 6 PM PDT THIS EVENING FOR PZZ455.
SMALL CRAFT ADVISORY UNTIL 11 AM PDT WEDNESDAY FOR PZZ470.
SMALL CRAFT ADVISORY UNTIL 2 PM PDT WEDNESDAY FOR PZZ475.
NOTE: THE FULL FORECAST DISCUSSION IS NOW REGULARLY ISSUED BETWEEN
10 AM/PM AND 1 PM/AM. ADDITIONAL UPDATES WILL BE ISSUED AS NEEDED.
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