584
FXUS66 KEKA 212105
AFDEKA
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE EUREKA CA
205 PM PDT TUE OCT 21 2025
SYNOPSIS
SNEAKER WAVE AND LARGE SURF RISK CONTINUES THROUGH THE
WEEK. WARM AND DRY CONDITIONS CONTINUE TODAY WITH SLIGHTLY COOLER
WEATHER FORECAST WEDNESDAY AND THURSDAY. CONFIDENCE REMAINS HIGH FOR
AN ATMOSPHERIC RIVER STORM IMPACTING NORTHERN CALIFORNIA FRIDAY INTO
THE WEEKEND.
KEY MESSAGES:
* RISK OF SNEAKER WAVES AND LARGE SURF CONTINUES THROUGH THE WEEK.
* COASTAL DRIZZLE AND STRATUS LIKELY TO RETURN TONIGHT. SLIGHT
CHANCE FOR LIGHT RAIN SHOWERS IN LAKE COUNTY TONIGHT.
* ATMOSPHERIC RIVER ARRIVES TO THE AREA FRIDAY INTO THE WEEKEND,
BRINGING PERIODS OF MODERATE TO HEAVY RAIN, MOUNTAIN SNOW, AND
GUSTY SOUTHERLY WINDS.
DISCUSSION
MOSTLY CLEAR SKIES OVERNIGHT AND OFFSHORE FLOW
PROMOTED A CHILLY MORNING ACROSS THE AREA, WITH SOME VALLEYS OF
TRINITY COUNTY REACHING THE LOW 30S. DESPITE THE COLD START,
OFFSHORE FLOW AND DRIER AIR WILL SUPPORT A FAIRLY WARM TODAY.
HIGH TEMPERATURES IN THE 70S ARE BEING OBSERVED ALONG THE COASTAL
AREAS AND THE WARMEST INTERIOR VALLEYS ARE FORECAST TO SEE LOW TO
MID 80S.
THIS PATTERN BEGINS TO CHANGE TONIGHT AS AN UPPER LOW OFF THE COAST
OF SOUTHERN CALIFORNIA MOVES NORTHWARD TONIGHT. THIS WILL WEAKEN
HIGH PRESSURE AND BRING A MUCH DEEPER MARINE LAYER, RETURNING
STRATUS TO THE COASTAL AREAS AND PERHAPS THE RUSSIAN RIVER AND
SURROUNDING RIVER VALLEYS. CAMS ARE SHOWING A POSSIBILITY FOR A FEW
LIGHT SHOWERS IN LAKE COUNTY OVERNIGHT, BUT THESE MAY JUST BE
REALIZED AS VIRGA. OTHERWISE, STRATUS SURGING UP THE COAST COULD
BRING SOME AREAS OF DRIZZLE.
WEDNESDAY, HIGH PRESSURE CONTINUES TO WEAKEN AS THE CUTOFF LOW MOVES
NORTH AND EAST TOWARD CENTRAL CALIFORNIA, WHILE AN UPPER-TROUGH
MOVES THROUGH THE PACIFIC NORTHWEST. THIS WILL CONTINUE TO SUPPORT A
DEEP MARINE LAYER AND POTENTIALLY RETURN MORE LOW CLOUDS INTO THE
INTERIOR VALLEYS WEDNESDAY NIGHT INTO THURSDAY. TEMPERATURES TREND
DOWNWARD WEDNESDAY AND THURSDAY INTO THE 70S FOR MUCH OF THE
INTERIOR VALLEYS AND HIGH 50S TO LOW 60S FOR THE COASTAL AREAS.
MODEL AGREEMENT CONTINUES TO INCREASE FOR A SERIES OF LARGER SYSTEMS
ARRIVING TO THE AREA FRIDAY AND CONTINUING INTO THE WEEKEND.
DETERMINISTIC MODELS ARE IN GOOD AGREEMENT OF THE FIRST ROUND OF
RAIN PRESENTING AS A COLD FRONT ARRIVING FRIDAY AFTERNOON AND
EVENING PROVIDING MUCH OF THE AREA WITH PERIODS OF MODERATE TO HEAVY
RAIN. THE MAIN LOW PRESSURE TO THE NORTHEAST SLOWLY MOVES TOWARD THE
PACIFIC NORTHWEST COAST, WITH ZONAL FLOW KEEPING A NARROW BAND OF
MOISTURE MOVING INTO THE AREA SATURDAY AND SUNDAY, WHICH DOES
PRESENT SOME UNCERTAINTY IN EXPECTED PRECIPITATION AS SUBTLE SHIFTS
NORTH OR SOUTH CAN MAKE A LARGE DIFFERENCE. PRECIPITATION RANGES
FROM THE NBM (COMPARING THE 25TH AND 75TH PERCENTILES) REMAIN
REMARKABLY STABLE WITH 4-6 INCHES FORECAST FOR DEL NORTE COUNTY, 1.5-
3.5 INCHES FORECAST FOR HUMBOLDT AND TRINITY COUNTIES. THE LARGEST
VARIABILITY IS IN SOUTHERN MENDOCINO AND LAKE WHERE THE RANGE IS
JUST 0.25-1.5 INCHES. WITH THIS MUCH RAIN, RAPID RISES IN SMALL
STREAMS AND RIVERS, MINOR FLOOD IMPACTS TO URBAN AREAS, AND DEBRIS
ON ROADWAYS ARE ALL POSSIBLE. SNOW LEVELS ARE INITIALLY FORECAST TO
REMAIN HIGH, ABOVE 7000 FT, BUT TREND DOWNWARD SATURDAY INTO SUNDAY
MORNING, DROPPING AS LOW AS 5000 FT. SNOW IMPACTS ARE POSSIBLE ALONG
SCOTT MOUNTAIN PASS ON HIGHWAY 3 IN TRINITY COUNTY SATURDAY AND
SUNDAY, BUT THERE IS STILL SOME UNCERTAINTY ON HOW COLD THIS SYSTEM
WILL BE. CURRENTLY 1-3 INCHES ARE FORECAST ABOVE 5500 FT, WHILE 6-12
INCHES ARE FORECAST ABOVE 7000 FT.
GUSTY SOUTH WINDS ARE LIKELY WITH THESE SYSTEMS AS WELL. NBM IS
SHOWING HIGH CHANCES FOR GUSTS OVER 40 MPH OVER EXPOSED RIDGES OF
THE KING RANGE AND DEL NORTE, WITH LOW CHANCES ELSEWHERE. CHANCES
FOR GUSTS OVER 30 MPH ARE MUCH HIGHER, ESPECIALLY SATURDAY WHERE
ESSENTIALLY THE ENTIRE AREA HAS 40-50% CHANCES TO SEE THESE GUSTS.
ENSEMBLE MEMBERS ARE DIVIDED ON IF PRECIPITATION WILL CONTINUE LATE
SUNDAY INTO EARLY NEXT WEEK. AROUND 50% OF MEMBERS CONTINUE SHOWING
NEAR-ZONAL FLOW OVER THE AREA, WHICH LIKELY TRANSLATES TO RAIN
CONTINUING FOR THE NORTHERN PORTIONS OF THE AREA (HUMBOLDT, DEL
NORTE, AND TRINITY). FURTHER PRECIPITATION AMOUNTS DON'T CURRENTLY
LOOK IMPRESSIVE, BUT ANY ADDITIONAL RAIN COULD BRING OR CONTINUE
MINOR IMPACTS. HIGHER CONFIDENCE FOR RIDGING ARISES MID NEXT WEEK. JB
AVIATION...(18Z TAFS)
VFR CONDITIONS WILL DETERIORATE TO LIFR FOR
COASTAL TERMINALS LATE TONIGHT INTO WED MORNING. VISIBLE SATELLITE
IMAGERY SHOWED A SHALLOW BANK OF STRATUS AND FOG SURGING NORTHWARD
ONTO MENDOCINO SHORELINE THIS AFTERNOON. HIGH RESOLUTION MODEL
GUIDANCE CONTINUES TO INDICATE INCREASING PROBABILITIES FOR LIFR
CONDITIONS IN FOG (1/4SM OR LESS) AND LOW CIGS (300 FT OR LESS)
ROUNDING CAPE MENDOCINO AND SPREADING TOWARD THE COASTAL AERODROMES
AFTER 08Z. UNTIL THEN ONLY SHALLOW MIST AND HAZE ARE EXPECTED FOR
THE COASTAL AIRPORTS. SOME OF THE HIGH RESOLUTION MODELS (ARW) ALSO
DEPICT MUCH HIGHER BOUNDARY LAYER HUMIDITY RAMPING UP AND PUSHING
INTO SOUTHERN MENDOCINO AND OVER KUKI BY EARLY WED MORNING. THIS
RAMP UP IN HUMIDITY APPEARS TO BE IN RESPONSE TO A CUT-OFF LOW
EJECTING EASTWARD INTO CENTRAL AND SOUTHERN CALIFORNIA OVERNIGHT.
SOME LIGHT SHOWERS OR SPRINKLES ALSO SEEM POSSIBLE NEARBY KUKI BASED
ON THE HREF COMPOSITE REFLECTIVITIES AND GFS/ECMWF QPF OUTPUT. RAPID
MARINE LAYER DEEPENING WILL LIKELY BE NECESSARY FOR MVFR OR IFR CIGS
TO PUSH OVER THE COASTAL RANGES INTO UKI BY DAYBREAK WED. CONFIDENCE
IS BY NO MEANS HIGH WITH STATISTICAL GUIDANCE INDICATING ONLY MID
AND HIGH CLOUDS.
MARINE
A SERIES OF LONG PERIOD NW SWELL GROUPS WILL IMPACT THE
WATERS FOR THE REMAINDER OF THE WEEK AND THIS WEEKEND. A LONG PERIOD
NW SWELL WILL CONTINUE TO BUILD THIS EVENING AND EVENTUALLY BECOME
THE DOMINATE SWELL GROUP BY EARLY WED MORNING. THIS SWELL WILL
LIKELY PEAK TO AROUND 14 TO 16 FT BY EARLY WED MORNING. SWELL
HEIGHTS WILL REMAIN SUFFICIENTLY ELEVATED, 10 FT OR MORE, TO WARRANT
A SMALL CRAFT ADVISORY FOR ALL WATERS THROUGH THE DAY ON WED. THERE
MAY BE LULL IN ELEVATED SEAS ON THU, HOWEVER ANOTHER LONG PERIOD
SWELL GROUP WILL BUILD INTO NW CA WATERS LATER ON THU, EVENTUALLY
PEAKING TO 11-13 FT THU NIGHT AND FRI. INCREASING SOUTHERLY WINDS ON
FRIDAY IN ADVANCE OF A FRONTAL SYSTEM WILL RESULT IN STEEPER S-SW
WIND WAVE GENERATION. SEAS WILL LIKELY BECOME MUCH ROUGHER WITH N-NW
SWELL SUPERIMPOSED ON SHORTER PERIOD WIND WAVES FROM THE S-SW. GALE
FORCE WIND GUSTS WITH THE INCOMING FRONT REMAINS POSSIBLE (ABOUT 20%
TO 40% CHANCE AROUND PT ST GEORGE AND CAPE MENDOCINO) ON FRI.
GREATER UNCERTAINTY ARISES WITH SURFACE LOW DEVELOPMENT FRI-SAT. GFS
IS DEEPER AND FARTHER SOUTH WITH THE LOW AND HAS SEAS BUILDING TO
20+ FEET OFFSHORE THE OREGON COAST. ECMWF WAVE MODEL WAS NOT AS HIGH
(16-18FT) WITH A WEAKER SURFACE LOW TRACKING FARTHER NORTH TOWARD
THE B.C. COAST. A MORE SOUTHERLY TRACK WOULD ALSO RESULT IN STRONGER
SOUTHERLIES AND LARGE S-SW WIND WAVES ON SAT.
BEACH HAZARDS
A NEW LONG PERIOD W-NW SWELL GROUP WILL CONTINUE TO
BUILD THROUGH THIS EVENING, PEAKING TO AROUND 14 TO 16 FT BY EARLY
WED MORNING. BUOY OBSERVATIONS HAVE BEEN REGISTERING A MIX OF
DOMINATE SWELL PERIODS FROM 13 TO 21 SECONDS. THE NEW SWELL GROUP
WILL BUILD TO OVER 10 FEET OR MORE AND HAZARDOUS SURF IS EXPECTED
LATE TONIGHT INTO WED MORNING. A SECOND SWELL TRAIN IS FORECAST TO
ARRIVE ON THU MAY ALSO POSE A RISK FOR SNEAKER WAVES. THE SWELL DOES
NOT APPEAR TO ARRIVE UNTIL LATE IN THE DAY AND DURING THE OVERNIGHT
HOURS THU. ONCE AGAIN EXPECT A MIX OF WAVES IN THE SPECTRUM WITH
SHORTER PERIOD BANDS DIMINISHING THU NIGHT. LARGER SHORTER PERIOD W-
NW SWELL FROM 14 TO 20 FT IS EXPECTED TO ARRIVE OVER THE WEEKEND.
EKA WATCHES/WARNINGS/ADVISORIES
CA...
BEACH HAZARDS STATEMENT THROUGH LATE TONIGHT FOR CAZ101-103-
104-109.
NORTHWEST CALIFORNIA COASTAL WATERS...
SMALL CRAFT ADVISORY UNTIL 5 PM PDT WEDNESDAY FOR PZZ450-
455.
SMALL CRAFT ADVISORY UNTIL 2 PM PDT WEDNESDAY FOR PZZ470-
475.
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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