textproduct: Eureka

SYNOPSIS

Shallow coastal stratus and fog will persist along the immediate coast with limited afternoon clearing through Friday, with areas only slightly further inland than the beaches experiencing periodic afternoon clearing. Inland areas will remain dry and hot under a building upper- level ridge.

DISCUSSION

An upper-level ridge over the Southwest US is expanding westward over Northwest California. Subsidence aloft is compressing the marine layer, keeping it shallow and confined to the coast and adjacent lower valleys overnight to early/mid morning. Inland areas will experience warming, with afternoon high temperatures in the mid to upper 90s becoming widespread across the interior valleys of Trinity, Mendocino, and Lake counties this afternoon.

Early next week, the placement of the upper ridge will determine the track of potential monsoonal moisture. Current guidance indicates a continuing warming trend for the interior, with a low probability of thunderstorm development over northeastern Trinity County.

AVIATION

As high pressure builds into the area, a very typical summer pattern will take hold of terminals in Northwest California. Shallow, diurnal coastal stratus will continue to affect coastal terminals with overnight and early morning conditions at LIFR/IFR and afternoon/evening conditions at VFR. Winds along the northern Humboldt and Del Norte coasts will most likely have nightly reversal winds (winds from the south). Inland terminals will remain VFR through the TAF period.

MARINE

The surface pressure gradient between an offshore surface high pressure system and an inland surface thermal low is tightening. South of Cape Mendocino, sustained northwest winds of 20 to 25 knots are generating steep, wind-driven seas. A Gale Warning for the southern outer waters is out starting at 5pm today to 8am Friday morning due to potential gusts up to 40 knots. For the northern outer waters, winds of 20 to 25 knots combined with steep 9-foot waves at short 8-second periods satisfy advisory criteria. All coastal marine zones are currently under a Small Craft Advisory.

EKA WATCHES/WARNINGS/ADVISORIES

CA... None. NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory until 11 AM PDT Friday for PZZ415-450.

Small Craft Advisory until 10 PM PDT Friday for PZZ455-470.

Small Craft Advisory until 5 PM PDT this afternoon for PZZ475.

Gale Warning from 5 PM this afternoon to 8 AM PDT Friday for PZZ475.