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

Flight categories overnight into Friday morning at the coastal terminals will be influenced by subsidence and light southerly winds, likely to reduce flight categories to LIFR. KCEC has a high probability of ceilings less than 1000 feet during the pre dawn hours and within that timeframe it looks as though GFS guidance is suggesting several hours of sub 500ft ceilings, of which there is about a 30% chance of occurrence around 12z-16z. KACV will have similar conditions with light southerly winds turning westerly by dawn. Both terminals improving to MVFR by Friday afternoon. KUKI may have a few intermittent gusts, similar to Thursday's late afternoon push that only lasted a few hours but VFR mostly expected through Friday. /EYS

MARINE

The surface pressure gradient between an offshore surface high pressure system and an inland surface thermal low is starting to weaken. 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 but should expire by Friday morning due to diminishing 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.

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.

Gale Warning until 8 AM PDT Friday for PZZ475.