276
FXUS66 KEKA 062133
AFDEKA
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE EUREKA CA
233 PM PDT SUN SEP 6 2026
KEY MESSAGES
* CONVECTIVE POTENTIAL REMAINS LOW (UP TO 15% CHANCE) AND LIMITED TO
NORTHERN TRINITY AND FAR INTERIOR DEL NORTE THROUGH EARLY EVENING.
* EXPANDING HIGH PRESSURE ALOFT AND COMPRESSING MARINE AIR WILL
DRIVE A SHARP WARMING TREND TUESDAY THROUGH THURSDAY, BRINGING H
HEATRISK POTENTIAL AND TEMPERATURES 10-15 DEGREES ABOVE EARLY
SEPTEMBER NORMALS ACROSS INTERIOR VALLEYS.
SYNOPSIS
AN EXITING MID-LEVEL DISTURBANCE MOVING INTO SISKIYOU
COUNTY IS KEEPING ISOLATED SHOWER AND THUNDERSTORM CHANCES NEAR THE
OREGON BORDER THROUGH THIS EVENING. ATMOSPHERIC HIGH PRESSURE
CENTERED OVER THE DESERT SOUTHWEST WILL BUILD WESTWARD STARTING
MONDAY, INITIATING A PRONOUNCED WARMING TREND THROUGH MID-WEEK.
OFFSHORE FLOW ON WEDNESDAY WILL CLEAR COASTAL LOW CLOUDS TEMPORARILY
BEFORE MARINE AIR MODERATES CONDITIONS LATE IN THE WEEK.
DISCUSSION
WATER VAPOR IMAGERY SHOWS A SHORTWAVE TROUGH AXIS
SHIFTING EAST OF THE FORECAST AREA. MID-LEVEL LAPSE RATES AROUND 7.5
C/KM ACROSS NORTHEASTERN TRINITY AND INTERIOR DEL NORTE ARE
PROVIDING MODEST MID-LEVEL INSTABILITY. THE NBM MAINTAINS A LOW
PROBABILITY (UNDER 15%) FOR RAINFALL UP TO 0.05 INCHES, WITH
MODERATE WEST-SOUTHWESTERLY STEERING FLOW CARRYING ISOLATED
CONVECTIVE CORES RAPIDLY INTO ADJACENT FORECAST AREAS.
AS THE TROUGH EXITS TONIGHT, UPPER-LEVEL HEIGHTS BUILD ACROSS
NORTHERN CALIFORNIA UNDER THE EXPANDING RIDGE. SUBSIDENCE UNDER THE
RIDGE WILL COMPRESS THE COASTAL INVERSION WHILE INTERIOR SURFACE
PRESSURE FALLS STEEPEN THE ZONAL ONSHORE PRESSURE GRADIENT BETWEEN
THE EASTERN PACIFIC SURFACE HIGH AND THE INTERIOR THERMAL LOW.
INLAND VALLEY MAXIMUM TEMPERATURES WILL RISE INTO THE 98 TO 102
DEGREE RANGE TUESDAY THROUGH THURSDAY.
FOLLOWING OPERATIONAL COORDINATION WITH THE WEATHER PREDICTION
CENTER, INTERIOR MAXIMUM TEMPERATURE GRIDS FOR TUESDAY THROUGH
THURSDAY WERE LOWERED 3-5 DEGREES RELATIVE TO RAW NBM GUIDANCE TO
ALIGN WITH ENSEMBLE BIAS TRENDS. BY WEDNESDAY, A THERMAL TROUGH
POSITIONING NEAR THE COAST TURNS LOW-LEVEL FLOW OFFSHORE, BRINGING
AN 80% PROBABILITY OF COASTAL HIGHS EXCEEDING 70 DEGREES AROUND
HUMBOLDT BAY BEFORE THE MARINE LAYER RE-ESTABLISHES LATE THURSDAY.
AVIATION
COASTAL TERMINALS KCEC AND KACV ARE EXPERIENCING
TEMPORARY CLEARING THIS AFTERNOON FOLLOWING MORNING MVFR/IFR
STRATUS. MARINE LOW CLOUDS WILL RETURN ALONG THE COAST AFTER 04Z,
WITH A 60-70% PROBABILITY OF LIFR CONDITIONS LATE TONIGHT INTO
MONDAY MORNING. LIGHT ONSHORE SURFACE WINDS WILL SHIFT TO WEAK
NORTHEASTERLY DRAINAGE FLOW OVERNIGHT. REGIONAL TERMINAL KUKI WILL
REMAIN VFR THROUGHOUT THE PERIOD WITH DAYTIME NORTHWEST WIND GUSTS
AROUND 15 KNOTS DIMINISHING AFTER SUNSET.
MARINE
AN OFFSHORE HIGH-PRESSURE SYSTEM INTERACTING WITH THE
COASTAL THERMAL LOW CONTINUES TO DRIVE NORTHERLY WINDS, STRONGEST
ACROSS THE SOUTHERN MARINE ZONES.
FOR THE NORTHERN INNER WATERS, NORTH WINDS OF 10 TO 15 KNOTS WITH
GUSTS TO 20 KNOTS WILL PERSIST THROUGH MONDAY. COMBINED SEAS WILL
AVERAGE 4 TO 6 FEET, COMPOSED OF A DOMINANT NORTHWEST WIND WAVE OF 4
FEET AT 8 SECONDS AND A LONG-PERIOD SOUTHERLY SWELL OF 2 TO 3 FEET
AT 15 SECONDS.
FOR THE NORTHERN OUTER WATERS, NORTHERLY WINDS WILL RANGE FROM 15 TO
20 KNOTS. WAVE STEEPNESS REMAINS MARGINAL WITH DOMINANT PERIODS
AROUND 9 SECONDS. THIS DECISION IS DEFERRED TO THE UPCOMING MIDNIGHT
SHIFT AS SEA STATE CRITERIA REMAIN MARGINAL.
FOR THE SOUTHERN INNER WATERS, A SMALL CRAFT ADVISORY REMAINS ACTIVE
THROUGH 5 AM MONDAY FOR NORTH-NORTHWEST WINDS OF 15 TO 25 KNOTS AND
WAVE HEIGHTS OF 6 TO 8 FEET AT 8 SECONDS.
FOR THE SOUTHERN OUTER WATERS, A SMALL CRAFT ADVISORY CONTINUES
THROUGH 5 PM MONDAY FOR NORTH WINDS OF 20 TO 25 KNOTS, GUSTS TO 30
KNOTS, AND STEEP SEAS OF 7 TO 9 FEET AT 9 SECONDS.
ADDITIONALLY, A SOUTH-SOUTHWEST SWELL OF 3 TO 5 FEET AT 15-16
SECONDS FROM HURRICANE MARIE WILL DECAY ACROSS ALL WATERS THROUGH
MONDAY NIGHT. A THERMAL TROUGH POSITIONING OVER THE COASTLINE
WEDNESDAY WILL BRIEFLY REDUCE WIND SPEEDS ACROSS ALL WATERS BEFORE
NORTHERLY FLOW RE-STRENGTHENS THURSDAY EVENING.
EKA WATCHES/WARNINGS/ADVISORIES
CA...
BEACH HAZARDS STATEMENT THROUGH MONDAY EVENING FOR CAZ104-
109.
NORTHWEST CALIFORNIA COASTAL WATERS...
SMALL CRAFT ADVISORY UNTIL 5 AM PDT MONDAY FOR PZZ455.
SMALL CRAFT ADVISORY UNTIL 5 PM PDT MONDAY 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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