textproduct: Eureka

KEY MESSAGES

* Seasonable temperatures along the coast with persistent overnight and morning marine stratus and fog. * Warm conditions across the interior valleys through the weekend, with a 60-70% probability of a stronger warming trend mid-to-late next week. * A 10% chance of afternoon thunderstorms over northeastern Trinity County on Monday.

SYNOPSIS

A shallow marine layer will continue to support night and morning low clouds, fog, and seasonal temperatures near the coast. Inland areas will see warm afternoon temperatures over the weekend and early next week before a building high pressure ridge brings hotter conditions to the interior valleys by mid-week.

DISCUSSION

An upper-level trough shifting past the Pacific Northwest will maintain a persistent marine layer depth across coastal sectors, yielding regular diurnal cycles of LIFR/IFR stratus and localized beach fog. Inland, a building four corners high pressure ridge will suppress deep mixing but sustain seasonably hot temperatures, with valley highs reaching into the 90s to near 100 degrees in topographically favored hot spots like Big Bar.

As the upper trough approaches the Pacific Northwest coast on Monday, it will draw a narrow corridor of mid-level moisture northward from tropical system Douglas off Baja California. Weak mid- level lapse rates and limited instability will keep thunderstorm potential highly isolated and locked primarily east of our area, though a 10% chance for an afternoon lightning strike remains warranted across northeastern Trinity County near Trinity Lake. By Wednesday and Thursday, the upstream trough weakens, allowing the interior heat dome to build westward. This transition will initiate a more robust warming trend, pushing daytime valley temperatures deeper into the high 90s and low 100s for late next week.

AVIATION

The marine boundary layer remains highly stratified tonight. Coastal terminals KACV and KCEC will experience persistent IFR to LIFR flight categories due to low stratus ceilings and developing mist/fog. Southerly or variable low-level winds returning after midnight will further lock in the marine moisture, suppressing visibility down to 1/2SM to 1 1/2SM at times through 15Z Sunday before gradual diurnal lifting occurs. Inland, VFR conditions will prevail at KUKI with light diurnal wind shifts and clear skies, interrupted only by sparse high clouds.

MARINE

Northerly winds over the inner coastal waters will stay light at under 10 knots as a thermal trough anchors over the interior and encourages localized nocturnal wind veering. Consequently, Small Craft Advisories remain strictly confined to the outer waters from 10 to 60 nautical miles out. The localized pressure gradient will compress slightly through Sunday morning, generating brief periods of near-gale northerly gusts across the northern outer waters zone. By Monday, an approaching Pacific Northwest trough will weaken the inland thermal gradient, relaxing the marine wind field and allowing hazardous small craft conditions to drop off across the outer zones early next week.

EKA WATCHES/WARNINGS/ADVISORIES

CA... None. NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory until 9 PM PDT this evening for PZZ470- 475.