textproduct: Eureka

KEY MESSAGES

* Seasonable temperatures along the coast with persistent overnight and morning marine stratus and fog into Monday morning. * Warming trends this week are expected with a 60-70% probability of a stronger warming trend mid- to- late 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 filled in before sunset at the coastal terminals and will continue to be a hindrance to flight operations through the night and early morning hours. KCEC started the LIFR regime Sunday and will trend that way into Monday morning with ceilings 200 feet or lower and vertical visibility in similar quantities at 100-200 feet. Dewpoint approaching overnight temperatures and the switch to southerly winds at calm to light flow could help advected stratus lower visibility with some ground fog but this will primarily be from marine stratus intrusion as overcast skies will limit fog development considerably. Winds will veer westerly by Monday afternoon with IFR/LIFR conditions lingering at KACV and KCEC. KACV may fair better with IFR as the cloud base lifts in the afternoon. Mostly VFR for KUKI with winds picking up by 20z out of the south, likely not as gusty as Sunday. /EYS

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. 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 6 PM PDT Monday for PZZ470-475.