textproduct: Eureka

KEY MESSAGES

* Localized frost across wind-sheltered interior valleys early this morning.

* High pressure builds mid-to-late week, bringing an extended dry period with interior valley high temperatures warming into the 80s and 90s.

* An arriving long-period west-northwest swell brings an elevated risk for sneaker waves along ocean beaches today.

* Fresh northerly winds continue south of Cape Mendocino, where a Gale Warning remains in effect for the southern outer waters.

SYNOPSIS

An exiting upper trough will allow strong overnight radiational cooling to trigger localized frost across sheltered interior valleys early today. Upper-level ridging builds over the West Coast mid-to-late week, supporting a progressive inland warming trend and dry conditions through next weekend.

DISCUSSION

Water vapor satellite loops show the primary 500 mb shortwave trough axis advancing east toward the Great Basin. Light boundary layer winds and post-frontal dry air will maximize radiational cooling through daybreak, keeping localized frost risks focused within sheltered interior valleys. Broad mid-level ridging over the eastern Pacific will expand inland Tuesday through Friday, establishing high confidence in dry conditions across the region.

At the surface, the onshore pressure gradient between the offshore eastern Pacific high and the interior thermal low will drive fresh northerly winds, strongest south of Cape Mendocino. Strong atmospheric sinking beneath the upper ridge will steadily warm the air mass aloft. Thermal profiles across interior valleys will support afternoon maximum temperatures climbing into the 80s and 90s mid-week. Ensemble guidance highlights an 80% probability of interior valley highs exceeding 90F Wednesday and Thursday.

AVIATION

A shallow marine layer will bring intermittent MVFR to IFR ceilings to coastal terminals (KACV and KCEC) overnight, with a 2030% chance of brief LIFR visibilities in patchy fog around dawn. Ceilings will clear to VFR by late Monday morning as northerly boundary layer flow increases mixing. Inland areas, including regional terminal KUKI, will maintain prevailing VFR conditions under clear skies. Due to an ongoing ASOS comms outage at KUKI, automated observations are unavailable and amendments are not scheduled.

MARINE

Fresh northerlies continue due to the pressure gradient between offshore high pressure and the interior thermal trough.

* Northern Inner Waters: Northerlies of 10 to 20 kt will generate steep short-period seas. A west-northwest swell at 15 to 17 seconds arrives today. A Small Craft Advisory remains in effect through late tonight.

* Northern Outer Waters: Northerlies of 20 to 25 kt with gusts to 35 kt will build combined seas to 1112 ft. A Small Craft Advisory remains active through late tonight.

* Southern Inner Waters: Fresh to strong northwest winds of 20 to 25 kt with gusts to 35 kt will maintain steep seas. A Small Craft Advisory remains in effect through Tuesday morning.

* Southern Outer Waters: Gale force conditions develop in the lee of Cape Mendocino, where northerly winds of 25 to 30 kt with gusts up to 40 kt will yield steep, hazardous combined seas of 13 to 15 ft. A Gale Warning remains in effect this afternoon through Tuesday afternoon.

BEACH HAZARDS

A long period west northwest swell at 3 to 6 ft with a period up to 17 seconds will build in today. This swell will bring a moderate risk for sneaker waves. A smaller 3 ft long period south swell will also bring some risk for sneaker waves for south facing beaches. High astronomical tides will increase the danger, especially over rocks and jetties.

Sneaker waves are a unique hazard, with up to 30 minutes between waves. Large, unexpected waves can sweep across the beach without warning, sweeping people into the sea from rocks, jetties, and beaches. These sneaker waves can also move large objects such as logs, crushing anyone caught underneath. Even ankle to knee deep water can knock you down and drag you out when a sneaker wave hits. Pay attention and stay above the high water line and any wet sand to stay safe. If the ground is wet, waves have surged.

EKA WATCHES/WARNINGS/ADVISORIES

CA... None. NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory until 3 AM PDT Tuesday for PZZ450-470.

Small Craft Advisory until 9 AM PDT Tuesday for PZZ455.

Small Craft Advisory until 3 PM PDT this afternoon for PZZ475.

Gale Warning from 3 PM this afternoon to 3 PM PDT Tuesday for PZZ475.