textproduct: Eureka

SYNOPSIS

Coastal cloud cover kept temperatures mild this afternoon, meanwhile inland temperatures reached into the 90's. A cooling trend starts this weekend and continues into early next week. Isolated thunderstorms possible in Trinity County late afternoon/early evening. There is a chances of wetting rain for Del Norte and northern Humboldt counties Monday through Tuesday. Northerly winds will begin turning strong again by Monday afternoon, and likely remaining breezy through mid next week.

KEY MESSAGES

- Chance (10-15%) of isolated mountain showers and thunderstorms across Trinity County, late this afternoon and early evening.

- Gradual cooling trend and lighter winds this weekend and into early next week.

- Coastal stratus will become more stubborn to scatter out through the weekend.

- Light to locally moderate showers are forecast on Monday/Monday night, with lingering showers through Tuesday.

- Breezy to gusty northwest winds returns next Tuesday.

DISCUSSION

High pressure over the PACNW is starting to weaken, while a low amplitude shortwave trough develops over Northern California overnight. Coastal stratus and patchy fog around Humboldt Bay and along much of the immediate coast will likely return tonight and are expected to become more stubborn to scatter through the weekend.

The aforementioned weak shortwave will bring a slight chances (10- 15%) of isolated thunderstorms for Trinity County later this afternoon and early evening, with the west-northwest flow keeping the cells over the eastern portion.

Cooler temperatures are expected for this weekend and early next as the shortwave trough persist over the area and the flow aloft become more zonal. A lingering chance (below 10%) for convective activity may carry into Saturday afternoon for far northern Trinity County if the cap can break.

A deeper trough will work farther south Monday. A late season, weak front off the low has been forecast to clip the area and deliver some light rainfall or drizzle to the northern portion of the region Monday and possibly Tuesday. With a slightly more southerly track modeled, chances for a wetting rainfall (over 0.1 inch) have increased to 30-50%; however, these types of systems usually under perform when arriving into such dry antecedent conditions. Ensemble spread is still quite high, ranging form nothing to 0.4 inches for Del Norte, and this is typical modeling for late season systems.

The deep trough will progress SE through the Pacific Northwest/Great Basin region later Monday through Wednesday. With Northern Pacific high pressure strengthening against it, the northerly to westerly winds will once again begin turning strong by Monday afternoon. The strongest winds will initially be focused over the eastern portion of the area, through Trinity and Lake Counties. Chances for gusts over 35 mph are notably high for Lake County Monday afternoon and evening, at 60-75%. Wind gusts over 40 mph are also looking probable (40 to 50%) for the ridges and locations around Clearlake. On Tuesday, these strong northerlies expand westward over the coastal regions. Chances for wind gusts over 30 mph are pretty solid for the exposed coastal headlands Tuesday afternoon, at 40 to 60%. This pattern will not likely quickly breakdown through Wednesday, but chances for stronger gusts are much lower Thursday. /ZVS&JJW&EYS

AVIATION...(18Z TAFs)

Stratus has partially eroded and lifted early this afternoon, bringing VFR conditions at all terminals. Stratus is likely to return again this afternoon and overnight. Models are pointing at a slightly deeper marine layer as high pressure weakens, but ceilings along the coast are still likely to be LIFR to IFR with occasional visibility reductions, especially near sunrise. Interior areas could see further stratus intrusion tonight as the marine layer deepens. KUKI has about a 40% chance of seeing at least MVFR ceilings overnight. JB

MARINE

Strong near-gale to gale-force winds continue in the outer waters, especially north of Cape Mendocino. Nearshore winds remain much weaker, aside from around Cape Mendocino and Pt. St. George. Still, strong winds in the outer waters continue to generate steep to very steep, hazardous seas.

Northerly winds diminish this weekend as the high pressure shifts eastward and the pressure gradient relaxes. Seas will also subside this weekend and into early next week, and are forecast to be below 5 feet across the waters by Sunday night.

Monday, winds shift to west-northwest as a cold front from the Northeastern Pacific (NEPAC) moves through. Seas for Memorial Day will be relatively mild around 4-6ft expected. Winds shift to northerly and increase in the wake of the front Monday night through Tuesday. A NW swell around 7-11 feet at 12 seconds is expected to build in Tuesday. This NW swell is forecasted to be up to 14-16 feet at 12 seconds at its peak on Tuesday/Tuesday night. High confidence (80-100% chance) for gale- force gusts redeveloping on Tuesday for the southern waters. The chances for gale-force gusts increase to the northern waters Tuesday night/Wednesday. /ZVS&JB

EKA WATCHES/WARNINGS/ADVISORIES

CA... None. NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory until 3 AM PDT Saturday for PZZ450-455.

Gale Warning until 11 PM PDT this evening for PZZ470.

Hazardous Seas Warning from 11 PM this evening to 9 AM PDT Saturday for PZZ470.

Hazardous Seas Warning until 9 AM PDT Saturday for PZZ475.