743
FXUS66 KEKA 131155
AFDEKA
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE EUREKA CA
455 AM PDT THU AUG 13 2026
AVIATION 12Z UPDATE
STRATUS REMAINS ALONG MOST OF THE NORTH
COAST AS WELL AS MOST OF SOUTHERN MENDOCINO COASTLINE LEADING TO
CONTINUED IFR/LIFR CONDITIONS. STRATUS IS ENTERING MOST OF THE
RIVER VALLEYS TONIGHT AS WELL WITH A MARINE LAYER BEGINNING AROUND
2KFT. SOUTHERLY WINDS NEAR THE COAST ARE EXPECTED THROUGH THE
MORNING HOURS WITH BOUTS OF -DZ WITHIN THE FOG. AFTERNOON COASTAL
CLEARING IS POSSIBLE TODAY (~40%), BUT NOT EXPECTED THROUGH MOST
OF THE DAY. INLAND AREAS WILL EXPERIENCE CONTINUED TERRAIN
ENHANCED WINDS AND CLEAR SKIES THROUGH THE EVENING. AREAS WITHIN
THE TRINITY AND KLAMATH RIVER VALLEYS WILL BE SMOKEY LEADING TO
MOUNTAIN OBSCURATION AND SLANT/SFC VISIBILITY ISSUES THROUGH THE
WEEK AS WELL.
PREV DISCUSSION
/ISSUED 250 AM PDT THU AUG 13 2026/
KEY MESSAGES...
* COOLER TEMPERATURES ARE LIKELY LATE WEEK INTO THE WEEKEND.
* SMOKEY CONDITIONS LIKELY FROM THE MP18 FIRE, FOCUSED IN THE
TRINITY RIVER VALLEY AND TRINITY COUNTY.
* SLIGHT CHANCE OF INTERIOR THUNDERSTORMS TODAY INTO SATURDAY.
SYNOPSIS...INTERIOR TEMPERATURES TREND BELOW NORMAL TO END THE
WORK WEEK. COASTAL AREAS CONTINUE TO HAVE OVERNIGHT STRATUS
WITH AFTERNOON CLEARING CHANCES AND BREEZY NORTHWEST WINDS. THERE
IS A SLIGHT CHANCE FOR DRY THUNDERSTORMS EACH AFTERNOON FROM TODAY
AND INTO SATURDAY FOR THE INTERIOR.
DISCUSSION...SMOKE FROM THE MP 18 FIRE CONTINUES TO IMPACT AIR
QUALITY OVER NORTHERN CALIFORNIA, PARTICULARLY IN THE INTERIOR
VALLEYS OF HUMBOLDT AND TRINITY COUNTIES. DEPENDING ON FIRE
CONTAINMENT, EXPECT A SIMILAR PATTERN TO CARRY THROUGH THE WEEK.
THE LOW LEVEL INVERSION IS SHOWING SIGNS OF WEAKENING AS A
SYNOPTIC TROUGH PATTERN DEVELOPS. THIS FEATURE COMBINED WITH SOME
ATMOSPHERIC INSTABILITY WILL HELP CLEAR OUT THE SMOKE MORE
EFFICIENTLY OVER THE COMING AFTERNOONS.
UPPER LEVEL TROUGHING WILL ALSO RESULT LOWER DAYTIME TEMPERATURES
FOR THE INTERIOR. TEMPERATURES WILL BE BELOW NORMALS THROUGH THE
EXTENDED FORECAST. THE MARINE LAYER IS DEEPENING AND EXTENDING
FARTHER INLAND, AND WILL BE CONDUCIVE TO PRODUCING LIGHT DRIZZLE
OVER THE COMING DAYS ESPECIALLY FOR COMMUNITIES DIRECTLY ON THE
COAST.
THE BROAD TROUGHING AND EMBEDDED SHORTWAVE DISTURBANCES WILL ALSO
CREATE LOW CHANCES FOR RAINSHOWERS OR PERHAPS THUNDERSTORM
ACTIVITY THROUGH THE END OF THE WEEK. A WEAK SURGE OF MONSOON
MOISTURE ASSOCIATED WITH A SHORTWAVE DISTURBANCE MAY CLIP PORTIONS
OF THE SOUTHERN ZONES THURSDAY, BUT EVEN THE MOST AGGRESSIVE
MODELS CONTINUE TO KEEP THE BULK OF THE MOISTURE SE OF LAKE COUNTY
AT THIS TIME. HOWEVER, DRY LIGHTNING POTENTIAL EXISTS THROUGH
TRINITY COUNTY (5-10%), ESPECIALLY IF THE MOISTURE FLUX ENDS UP
MORE NORTH THAN THE HIGH RESOLUTION MODELS ARE SUGGESTING.
A SECONDARY WAVE WILL MOVE NE OVER NORTHERN CALIFORNIA FRIDAY INTO
SATURDAY MORNING. THIS DISTURBANCE WILL CARRY HIGHER INSTABILITY AND
MOISTURE (THOUGH STILL MEAGER), GIVING A SLIGHTLY HIGHER CHANCE FOR
SOME THUNDERSTORM ACTIVITY. THIS IS MAINLY EXPECTED IN WESTERN SISKIYOU
COUNTY, BUT COULD IMPACT PORTIONS OF SURROUNDING COUNTIES (5-10%
OVER TRINTY COUNTY NORTHWARD THROUGH FAR EASTERN DEL NORTE COUNTY,
AND 10-15% OVER SISKIYOU COUNTY AND FAR NORTHEAST DEL NORTE).
THERE WOULD BE A POTENTIAL FOR NOCTURNAL ACTIVITY LATE FRIDAY AS
WELL IF STORMS OCCUR AT ALL. THAT SAID, THIS IS STILL A VERY LOW
CONFIDENCE FORECAST; HOWEVER, IT WILL STILL BE WATCHED VERY
CLOSELY DUE TO HISTORICAL POOR MODEL HANDLING OF THE SETUP TYPE
AND THE IMPACT EVEN A LITTLE LIGHTNING WOULD HAVE REGARDING FIRE
POTENTIAL OVER THE VERY DRY VEGETATION. SMOKE FROM THE ONGOING
MP18 FIRE NEAR HOOPA WILL LIKELY DAMPEN INSTABILITY (CAPE) OVER
THE AFTERNOON HOURS.
MARINE...STRONG NORTHERLIES WITH GALE CONDITIONS CONTINUE IN THE
OUTER WATERS. THESE WINDS ARE GENERATED STEEP AND HAZARDOUS SEAS UP
TO 12 FT AT 10 TO 11 SECONDS. THESE LARGER SEAS TRAVEL INTO THE
INNER WATERS CREATING STEEP WAVES AND LEADING TO A SMALL CRAFT
ADVISORY. THIS AFTERNOON,NORTHERLY WINDS WILL DROP BELOW 25KTS
AS TROUGHING ENTERS THE REGION DISRUPTING THE SURFACE PRESSURE
GRADIENT BETWEEN THE SEA AND THE LAND. THE NORTHERLIES WILL DROP
EVEN MORE SUBSTANTIALLY FRIDAY AND ESPECIALLY THROUGH THE WEEKEND
AS TROUGHING CONTINUES TO WEAKEN THE PRESSURE GRADIENT. SEAS WILL
LOWER INTO AND THROUGH THE WEEKEND.
FIRE WEATHER...A TROUGHING PATTERN IS TAKING EFFECT OVER THE
WEST COAST, LEADING TO GOOD RECOVERIES AND ALSO INCREASES CHANCES
FOR A DEEPENED MARINE LAYER TO INFILTRATE FARTHER INTO THE
INTERIOR. INCREASED MIXING WITH LOCAL AND GENERAL WINDS WILL
CREATE CONTINUED AFTERNOON GUSTS, ESPECIALLY FOR MAJOR VALLEYS.
A WEAK SURGE OF MONSOON MOISTURE ASSOCIATED WITH A SHORTWAVE
DISTURBANCE HEADING NORTH UP THE VALLEY HAS THE POTENTIAL TO
INTERACT THE MOUNTAIN CREATING LOCALIZED AFTERNOON STORMS.
HOWEVER, EVEN THE MOST AGGRESSIVE MODELS KEEP THE BULK OF
MOISTURE SE OF LAKE COUNTY AT THIS TIME. THAT SAID IT'S CRUCIAL TO
PAY ATTENTION FOR BUILDING CLOUDS TODAY AS ANY STORMS COULD SEND
WIND GUSTS CHANNELING THROUGH TERRAIN IMPACTING ONGOING FIRE
OPERATIONS. THIS BECOMES ESPECIALLY IF THE MOISTURE FLUX NUDGES
NORTHWEST BEYOND WHAT THE HIGHER RESOLUTION MODELS ARE SUGGESTING.
A SECONDARY SHORTWAVE WILL MOVE NE OVER NORTHERN CALIFORNIA
FRIDAY INTO SATURDAY MORNING. THIS DISTURBANCE WILL CARRY HIGHER
INSTABILITY AND MOISTURE (THOUGH STILL MEAGER), LEADING TO A
SLIGHTLY HIGHER CHANCE FOR SOME THUNDERSTORM ACTIVITY (5-10% OVER
TRINTY COUNTY NORTHWARD THROUGH FAR EASTERN DEL NORTE COUNTY, AND
15% OVER SISKIYOU COUNTY AND FAR NORTHEAST DEL NORTE). THERE WOULD
BE A POTENTIAL FOR NOCTURNAL ACTIVITY LATE FRIDAY AS WELL IF
STORMS OCCUR AT ALL. STORM MOVEMENT FRIDAY WOULD BE TO THE
NORTH/NORTHEAST AROUND 20 MPH. SMOKE FROM THE ONGOING MP18 FIRE
NEAR HOOPA WILL LIKELY DAMPEN INSTABILITY (CAPE) OVER THE
AFTERNOON HOURS, FURTHER LOWERING CONFIDENCE ON THUNDERSTORM
COVERAGE.
EKA WATCHES/WARNINGS/ADVISORIES
CA...
NONE.
NORTHWEST CALIFORNIA COASTAL WATERS...
SMALL CRAFT ADVISORY UNTIL 3 PM PDT THIS AFTERNOON FOR
PZZ450-455.
GALE WARNING UNTIL 9 AM PDT THIS MORNING 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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