textproduct: Eureka

KEY MESSAGES

* High confidence (90 percent chance) that post-frontal rain showers across Del Norte and northern Humboldt completely diminish by Sunday afternoon. * High pressure offshore builds Sunday night into Monday, increasing northerly winds and bringing hazardous marine conditions to the outer waters.

SYNOPSIS

An upper-level trough over the Pacific Northwest continues to exit eastward, allowing light shower activity over northern areas to taper off completely by Sunday afternoon. Surface high pressure building offshore will strengthen the onshore pressure gradient against the interior thermal low into early next week. This pattern will keep a shallow marine layer pinned along the coast while bringing dry, seasonable warmth back to interior valleys.

DISCUSSION

Water vapor imagery shows the 500 mb shortwave trough axis shifting east of the region early this morning. High-resolution ensemble guidance indicates that light shower activity over Del Norte and northern Humboldt will gradually wane through the morning hours, with the 90th percentile for shower cessation pointing to a complete end by Sunday afternoon. In the wake of this departing trough, mid-level ridging will build off the West Coast, establishing a high-pressure pattern that will linger through mid- week.

At the surface, the onshore pressure gradient between the offshore eastern Pacific high-pressure system and the interior thermal low will tighten notably by Sunday afternoon. Inland maximum temperatures will reach the 70s to lower 80s across interior valleys on Sunday, with moderate warming continuing Monday. Meanwhile, a shallow marine layer will remain anchored along the immediate coast, maintaining cool conditions with high temperatures held in the 60s. Probabilistic ensemble output indicates that maximum temperatures reaching 90 degrees have a 60 to 80 percent probability on Wednesday for the warmest interior valleys.

AVIATION

KCEC: VFR conditions will give way to MVFR ceilings starting around 10Z under low stratus, persisting through late morning before clearing to VFR as low-level moisture departs and winds turn westerly.

KACV: MVFR ceilings will persist overnight under low stratus before lifting to VFR around mid-morning. A brief period of IFR visibility is expected mid-to-late morning before clearing to VFR as winds shift southwesterly to westerly.

KUKI: VFR conditions will prevail through the period at this regional terminal. West-northwest wind gusts up to 18-19 kts are expected during the afternoon and early evening hours.

MARINE

Gentle to moderate breezes persist early Sunday before north winds ramp up sharply Sunday evening into Monday as the onshore pressure gradient tightens between the eastern Pacific high and the interior thermal low.

* Northern Inner Waters: Southerly winds shift southwesterly Sunday afternoon before turning northerly Sunday night. Combined seas remain low, and low wave steepness will keep conditions below advisory criteria. * Northern Outer Waters: Winds turn northerly Sunday evening and strengthen into Monday. Short-period wave steepness increases as winds build, creating hazardous conditions for small craft late Sunday night through Monday evening. A Small Craft Advisory is in effect starting late Sunday night (3 AM Monday). * Southern Inner Waters: Onshore breezes build into moderate northerlies Sunday night and Monday, with localized strong gusts around Cape Mendocino. Wave steepness increases Monday as short- period northerly wind waves build. * Southern Outer Waters: Fresh to strong northerly winds develop Sunday evening, accompanied by near-gale gusts. Steep, hazardous seas develop as short dominant wave periods combine with building wave heights. A Small Craft Advisory is in effect starting 6 PM Sunday.

EKA WATCHES/WARNINGS/ADVISORIES

CA... Red Flag Warning until 2 AM PDT early this morning for CAZ418>421.

NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory from 3 AM to 9 PM PDT Monday for PZZ470.

Small Craft Advisory from 6 PM this evening to 9 PM PDT Monday for PZZ475.