textproduct: Eureka

KEY MESSAGES

* Seasonable temperatures along the coast with persistent overnight and morning marine stratus and fog. * Warm conditions across the interior valleys today, with a 60-70% probability of a stronger warming trend mid-to- late this coming week week. * Up to 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 early this coming 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 cloud layer across coastal sectors, yielding regular diurnal cycles of low clouds and localized beach fog. Inland, a building high pressure system in the Four Corners region 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 up to a 10% chance of 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

Coastal stratus will continue to affect coastal terminals of Northwest California through at least mid afternoon. Light onshore flow today has aided in reinforcing this. There is a possibility of some lifting and scattering for some coastal terminals early this evening with a high likelihood of LIFR/IFR conditions returning late this evening and overnight. VFR conditions are anticipated for interior terminals. Early tomorrow morning, southerly flow could help bring stratus into KUKI.

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 today, 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 this coming week.

EKA WATCHES/WARNINGS/ADVISORIES

CA... None. NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory until 9 AM PDT Monday for PZZ470-475.