textproduct: Eureka

SYNOPSIS

Scattered storms will continue through Sunday evening. Some weaker storms may linger on Monday under generally cool and cloudy conditions. Warmer and drier conditions build midweek.

KEY MESSAGES

-Scattered and some isolated strong thunderstorms (15-25% chance) over the the interior through Sunday evening.

-Cooler and cloudy conditions Monday followed by warmer and generally calm conditions by midweek.

DISCUSSION

Scattered thunderstorms have already built across the area early Sunday afternoon, a few hours earlier than high resolution models forecast. A particularly strong storm produced and estimated 0.5 inches of rain and 0.5 inch hail. A cutoff low offshore will continue to pull moisture over the area and support moderate instability through Sunday evening. Easterly wind will push any storms that form over interior mountains towards the coast. At the same time, broad coverage of high clouds has generally reduced surface heating and might limit overall storm coverage. Despite the instability, a stubborn albeit very lifted marine layer has maintained grey skies all along shore.

High resolution models suggest thunderstorm activity will peak between 3 pm and 8 pm. Chances remain greatest (25% chance) in Humboldt, Trinity, and Del Norte counties with little chance (< 10% chance) in Mendocino and Lake Counties. Though storm coverage may be scattered, only a few isolated storms have much chance of approaching severe conditions. That said, any storms will have the potential to generate gusty winds and dangerous lightning.

Drier conditions will quickly return by Monday and Tuesday. That said, there is a very slight (10%) chance of some weak lingering thunderstorms over the interior on Tuesday. Colder air being pulled from the northeast aided by lingering clouds will briefly cool interior temperatures into the 60s Monday. Clouds and valley moisture will limit any frost concerns. The east wind will likely help erode and shallow the marine layer, but most models show stratus persisting through the early week.

Benign and weak high pressure will build late in the week, bringing slightly warmer than average temperatures but otherwise dry, seasonable, and calm weather. There is chance for marine layer clearing out around Wednesday before rebounding later in the week as a marine inversion reforms under the interior heat. /JHW

AVIATION

Ceilings remain steady along the North Coast today. Above this maritime cloud deck, convection is occurring. This increases the likelihood of thunderstorms passing over coastal terminals through the evening. These thunderstorms are forecasted to be above the stubborn stratus along the coastline. Rainshowers are possible through the evening and tomorrow morning as a low pressure center funnels moisture over NW CA. Southerly winds continue for the coast as gusty winds exist inland. Expected LIFR-IFR for coastal terminals and MVFR-VFR for inland terminals.

MARINE

Overnight into Sunday morning, a cold air mass entered the western seaboard, this cold air will disrupt the surface pressure gradient allowing the northerly winds to weaken down to gentle breezy conditions. This will begin an extended period of lighter winds and smaller seas through next week as relatively light winds flow over the coastal waters. From Sunday through the week, the GFS wave model shows two main swells impacting the coastal waters, the first is a long period, westerly swell building up to 6ft@15s and another is a NW swell of 4ft@8s. Minimal impact is expected next week from fresh, short period waves.

BEACH HAZARDS

This morning, a long period northwest swell with periods between 17-20 seconds arrived, posing a moderate increase to the risk of sneaker waves for coastal areas. A Beach Hazards Statement has been issued for the Del Norte, Humboldt, and Mendocino coast Sunday. Sneaker waves are anomalously large, unexpected waves that sweep across beaches without warning. There can be up to 30 minutes of smaller waves before a sneaker wave arrives to the shoreline. Choose your recreation wisely by avoiding steep beaches and jetties as well as staying much farther back from the ocean than normal. Never turn your back on the ocean!

EKA WATCHES/WARNINGS/ADVISORIES

CA... Beach Hazards Statement until 11 PM PDT this evening for CAZ101-103-104-109.

NORTHWEST CALIFORNIA COASTAL WATERS... None.