textproduct: Eureka

SYNOPSIS

Strong high pressure over the area brings dry conditions and warm interior temperatures today. An unseasonably strong cold front will bring rain to Del Norte and northern Humboldt counties on Friday, along with significantly cooler conditions. Chilly and breezy weather continues Saturday before a gradual inland warming trend takes hold Sunday into next week.

DISCUSSION

An upper-level ridge remains established over northwest California early this Thursday morning, but an approaching upper trough will begin to break down the pattern later today. High temperatures this afternoon will cool slightly into the mid to upper 80s for most inland valleys, though lower 90s remain probable in the deeper Klamath and Trinity river canyons. The marine layer stays compressed along the coast today, keeping low clouds and cool temperatures locked in, while tightening gradients create afternoon interior gusts of 15 to 20 mph.

On Friday morning, the upper trough moves onshore, expanding and deepening the marine layer to generate areas of morning drizzle along the north coast. By Friday afternoon and evening, the associated cold front will sweep through, spreading rain across the region. The highest probabilities for a wetting rain (exceeding 0.10 inches) are focused over the mountains of Del Norte County (50 to 60 percent) and taper down to 10 percent at the immediate Del Norte coast. Northern and central Humboldt counties carry a 20 to 40 percent probability of wetting rain, with light totals potentially making it east into the Trinity Alps. Breezy northwest winds accompany the front, with interior ridge gusts reaching up to 30 mph.

Dry air filters in behind the front on Saturday, but the presence of the cold core overhead will maintain chilly and breezy conditions, keeping interior highs mostly in the lower 70s. Localized destabilization beneath the cold pool will support a 10 percent chance of afternoon thunderstorms over the higher terrain of northeastern Trinity County. The trough exits by Sunday, allowing heights to rise and building inland temperatures back into the upper 80s and lower 90s early next week.

AVIATION

A shallow marine layer continues to dictate coastal operations early this Thursday morning, with widespread IFR to LIFR ceilings and visibility restrictions firmly entrenched at KACV and KCEC. Expect some slow, temporary scattering to MVFR/VFR late Thursday afternoon. Inland, KUKI will remain VFR through the period with breezy northwest winds developing late this afternoon, gusting to 21 kt. By Thursday night, the approaching upper trough will lift coastal cloud bases into a more uniform MVFR deck.

MARINE

Northerly winds will temporarily diminish across the northern waters today as the upper trough draws nearer, with lighter winds gradually spreading south into Friday. A fresh northwest swell will build into the waters on Friday, keeping sea heights elevated even as wind speeds bottom out. Strong northerly winds return rapidly Saturday afternoon and evening. Winds are expected to rise to near-gale force by Sunday, with gale-force gusts continuing over the outer waters into early next week as strong high pressure re-establishes itself.

FIRE WEATHER

An upper-level ridge brings one last day of warm and dry conditions to the interior valleys today. Highs on valley floors will reach the 90s, with a 10 percent chance of localized triple-digit heat up to 105 degrees in the lowest elevations of the Klamath and Trinity river corridors. Minimum afternoon relative humidities will drop into the teens across these interior zones today.

A major pattern shift arrives Friday as an unseasonably strong trough and cold front push ashore. Wetting rain is likely across coastal Del Norte County (50 to 60 percent chance of exceeding 0.10 inches), while a 30 to 40 percent chance of wetting rain exists for northern Humboldt County. Southern and eastern zones will remain dry outside of isolated sprinkles. Interior temperatures will drop 15 to 20 degrees by Saturday. As the core of the cold trough positions overhead Saturday afternoon, localized destabilization will support a 10 percent chance of thunderstorms across northern Trinity County.

Winds remain light today with typical afternoon valley breezes. Stronger westerly winds develop behind the front Friday afternoon across Lake and southern Mendocino counties, bringing a 70 percent chance of gusts exceeding 30 mph in lower elevations and a high probability of gusts over 40 mph across exposed ridges. Breezy conditions persist Saturday before winds shift to the northeast across Lake County by Sunday afternoon.

EKA WATCHES/WARNINGS/ADVISORIES

CA... None. NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory until 3 AM PDT Friday for PZZ455-475.

Small Craft Advisory until 9 AM PDT this morning for PZZ470.