textproduct: Eureka

AVIATION 06Z UPDATE

Stratus remains along most of the North Coast as well as most of southern Mendocino coastline leading to continued IFR/LIFR conditions. Southerly winds near the coast are expected through the overnight hours as is -DZ within the fog. Widespread clearing is possible for Thursday, 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 429 PM PDT Wed Aug 12 2026/

WHAT HAS CHANGED... Decreased forecast thunderstorm coverage, otherwise no significant changes to the forecast/discussion.

KEY MESSAGES...

* Warm, near-normal temperatures expected for the interior today. Cooler temperatures are likely late week into the weekend.

* Smokey conditions likely from the MP18 Fire, focused in the Trinity River Valley.

* Slight chance of interior thunderstorms Thursday into Saturday.

* Minor coastal flooding is possible around Humboldt Bay at the midnight high tide tonight.

SYNOPSIS...Interior temperatures trend below normal late in the week. Coastal areas continue to have near normal temperatures with overnight stratus clearing in the afternoons along with breezy northwest winds. There is a slight chance for dry thunderstorms in the interior thursday and into Saturday.

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 more of a troughing pattern develops, and this combined with some atmospheric instability will help clear out the smoke more efficiently over the coming afternoons.

The troughing will continue to lower interior daytime highs. Temperatures will be lowering to 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.

The broad troughing and embedded disturbances will also bring low chances for some showers or perhaps dry thunderstorm activity. A weak surge of monsoon moisture associated with a shortwave disturbance may clip portions of the southern zones Thursday, but even the most aggressive modes keep the bulk of the moisture SE of Lake County at this time. This day will still be watched regarding any dry lightning potential through Trinity County (5-10%), especially if the moisture flux nudges northwest at all.

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 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 will periodically migrate into the inner waters following the afternoon/evening stronger wind surges. Seas of up to 11 ft have occasionally been observed at the North Spit buoy. Northerly winds will drop below 25kts Thursday afternoon as troughing enters the region. The northerlies will drop more substantially Friday and especially through the weekend as troughing weakens the pressure gradient.

FIRE WEATHER...Minimum RH and overnight recoveries will continue to improve with moistening westerly flow and lower daytime highs from the breakdown of the ridge of high pressure. A troughing pattern then takes shape, which will maintain good recoveries and also increases chances for a deepened marine layer to infiltrate farther into the interior.

A weak surge of monsoon moisture associated with a shortwave disturbance may clip portions of the southern zones Thursday, but even the most aggressive modes keep the bulk of moisture SE of Lake County at this time. This day will still be watched regarding any dry lightning potential through Trinity County (5 to 10%), especially if the moisture flux nudges northwest at all.

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 (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.

COASTAL FLOODING...Measured sea levels continue to run approximately 0.7 to 0.84 ft above the predicted tide level in Humboldt Bay. The tide gage at the North Spit measured 8.82 ft at the highest peak last night with a 0.84 ft anomaly which drove the predicted tide of 7.98 ft near the coastal flood advisory range of 8.9. The predicted high tide overnight will be around 7.84ft and with a similar anomaly it will be just under the criteria for an advisory, but the weakening northerly winds may slightly enhance the anomaly. /EYS

EKA WATCHES/WARNINGS/ADVISORIES

CA... Coastal Flood Advisory until 1 AM PDT Thursday for CAZ103.

NORTHWEST CALIFORNIA COASTAL WATERS... Coastal Flood Advisory until 1 AM PDT Thursday for PZZ415.

Small Craft Advisory until 9 AM PDT Thursday for PZZ450-455.

Gale Warning until 9 AM PDT Thursday for PZZ470-475.