textproduct: Eureka

SYNOPSIS

Conditions will greatly begin to moisten and cool Friday and into the weekend. Widespread wetting rain will cross the area around Sunday into next Monday.

DISCUSSION

Over the past few days, high pressure east of the area has promoted consistent offshore flow, generating clear and unseasonably warm conditions even right along the coast. This pattern will begin to significantly change Friday.

Broad, weak low pressure will gradually push into California with a broad lobe of high pressure offshore. This will promote moderate onshore flow Friday into Saturday, bringing a resurgence of marine influence, especially to the coast with some weak marine stratus likely by Friday evening. Marine air pushing inland will greatly cool and moisten conditions each day.

There is high ensemble confidence that a deep trough a strong surface cold front will sweep across the area Sunday into Monday. This front will be focused on the northern half of the area and into Oregon. Widespread wetting rain is expected along the front, though there is still a good amount of uncertainty regarding amounts due to variability in the moisture plume strength and duration, particularly this far south. That said, ensembles consistently place the area in the range for a weak atmospheric river with only very limited high end potential.

Reflecting the moisture plume uncertainty, most likely rainfall amounts vary from about 0.5 to 1.5 inches at low elevations in Humboldt and Del Norte to 1.0 to 2.0 at higher elevations. Rain amounts will be less further south with most likely ranges of 0.1 to 0.5 inches for most of Mendocino and Lake Counties. There is a 15% chance of some wind gusts over 45 mph right along the coast, but any such winds would be very isolated to just the frontal passage itself.

Much colder air will move in behind the front. Snow levels will most likely drop to around 3000 feet by mid next week, but there will most likely be too little moisture at that time to support strong snowfall, with less than an inch or two at any highway passes. Any additional rainfall next week shows very little confidence in specific timing and amount. That said, there is very high ensemble agreement in a generally colder and more moist pattern through at least mid month with additional waves of rain likely over the next couple of weeks. /JHW

AVIATION

Prevailing VFR conditions for all aerodromes through at least 06/12Z. Satellite imagery depicts high-level clouds streaming northward across the area overnight. With a weaker offshore flow, a shallow marine layer is expected to develop along the coast overnight into Friday. After 14Z, HREF suggest there is a 50-60% chance of a shallow marine layer developing along the North Coast. Should stratus develop, IFR to LIFR ceilings are expected. Any low clouds are expected to lift and scatter out by late morning (after 17Z). However, onshore flow is expected to push stratus back inland to the coast and adjacent coastal areas during the afternoon hours. Mainly VFR to MVFR ceilings is expected for the coastal terminals Friday afternoon and evening.

For the interior area, including UKI, prevailing VFR conditions with very light and variable winds are expected to continue through the next 24 hours. /ZVS

MARINE

A mid period westerly swell continue to slowly subside across the waters. However, a larger, long period westerly swell at around 10 to 12 ft at 16 seconds will build overnight and early Friday, keeping seas elevated. This will result in hazardous conditions to small craft through late Friday night/early Saturday. Light to gentle winds southerly winds are expected to continue on Friday. Winds are expected to increase to moderate to fresh breezes over the weekend in advance of an approaching front, especially north of Cape Mendocino. Northerlies returns in the wake of the front Sunday night, with generally moderate to fresh breezes. Seas remain elevated as additional west swells build into early next week. /ZVS

BEACH HAZARDS

A Beach Hazard Statement continue in effect through Friday night due to a moderate risk of sneaker waves along areas beaches. A large long period west swell is forecast to arrive overnight and build into Friday across the coastal waters, with heights around 10 to 12 feet at 15 to 16 seconds. These high energy will bring a moderate risk of sneaker waves on Thursday, resulting in the potential deadly waves that unexpectedly surge much farther up the beach than previous waves, overtaking unaware beachgoers. Remember to never turn your back to the ocean, and to avoid steep beaches, jetties, outcroppings, and rocks during these events./ZVS

EKA WATCHES/WARNINGS/ADVISORIES

CA... Beach Hazards Statement through Friday evening for CAZ101- 103-104-109.

NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory until 3 AM PST Saturday for PZZ450-455- 470-475.