textproduct: Eureka

SYNOPSIS

Temperatures will continue to cool today with marine influence deepening and pushing inland. Scattered dry thunderstorms will impact high terrain locations over the interior Friday.

KEY MESSAGES

- Temperatures ease through Saturday with only minor HeatRisk

- Slight chance of dry thunderstorms over higher terrain of northern Humboldt and Trinity counties this morning.

- A lifting but persistent marine layer at the coast.

- Warming trend returns next week.

DISCUSSION

An upper level trough approaching the area will continue to bring cooler and more moist conditions Friday and Saturday. Most interior valleys are expected to have highs in the mid 70s to mid 80s with the hottest valley locations barely getting over 90. Increasing marine influence will also keep RH higher (over 30 for driest valleys). The trough will cross inland today and bring more cloud cover to the region.

The trough will also help increase upper level instability. Combined with a moisture surge up the Sacramento Valley, there is potential for thunderstorms as early as sunrise this morning. High resolution models show a weak convective signature, but chances of actual lightning remain low to moderate at best (15%). Models generally focus convection over northern Humboldt and Trinity counties though just a few want to put storms as far south and west as the King Range. Uncertainty remains high, as many model soundings show moisture too high in the unstable layer with weak forcing, making lightning potential questionable. That said, these setups are typically not well resolved by models. In general, potential for thunderstorms is generally 20 to 30 percent, with the highest potentials for Trinity County (particularly the NE portion of the county).

Otherwise cool conditions will bottom out on Saturday with gradual warming and non-impactful weather next week. Temperatures are anticipated to return to the 90s with only moderate HeatRisk expected. /JHW

AVIATION

A persistent marine layer continues to blanket the coast early this morning causing LIFR/IFR conditions. Approaching instability from an upper level trough continues to deepen the coastal stratus. Another intrusion of low ceilings into the Russian River Valley are expected this morning. Increasing instability will most likely help further lift ceilings today. /JHW

MARINE

Winds have generally dropped to gentle or even calm across all waters. Moderately steep short period seas are gradually falling and will generally fall below 6 feet Friday morning. Beyond the wind waves, there is a minor but persistent mid period northwest swell around 4 feet that may be more obvious with the calmer seas. North winds will gradually increase again this weekend with near gale force gusts in the outer waters by Sunday afternoon. These winds will pull closer to shore brining steep short period seas to all waters through early next week. /JHW

FIRE WEATHER

EKA WATCHES/WARNINGS/ADVISORIES

CA... Red Flag Warning from 8 AM this morning to 7 PM PDT this evening for CAZ403-406-409-410.

NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory until 5 AM PDT early this morning for PZZ470.