textproduct: Eureka

SYNOPSIS

A weakening cold front is expected to bring a chance for light rain primarily to Del Norte and northern Humboldt counties on Thanksgiving Day. A cooling trend follows for the weekend with dry conditions and a chance for freezing temperatures during the morning hours. Additionally, a long period swell is expected to bring hazardous beach conditions late Sunday into early next week.

DISCUSSION

High pressure is forecast to shift eastward as a shortwave trough and associated surface low moves toward the PacNW tonight through Thursday (Thanksgiving Day). A weakening cold front is forecast to move onto the North Coast during the day on Thursday. A shallow push of moist air with this decaying front will likely bring some light rain to mostly Del Norte and northern Humboldt. Per HREF guidance, greatest amounts will be over Del Norte and far northern Humboldt Counties. Chance for 0.10-0.25 inches in 24 hours ending 4 AM Friday is 60-80% for coastal portions of Del Norte, 30-40% for coastal northern Humboldt north of Trinidad and 20-30% for the higher terrain around Humboldt Bay. Otherwise, generally less a tenth is expected. Now for the bulk of the forecast area, mostly dry conditions are expected Thu-Fri.

Temperature bottomed out in the lower to mid 30's for many of the colder interior valleys early this morning. In southern Trinity, early morning minimums were in the mid to upper 20's. Frost and freeze products have been discontinued for southern Trinity, NE Mendocino and northern Lake Counties for the remainder of fall and through the upcoming winter months. Elsewhere, a widespread killing freeze (at 50% coverage) has not occurred yet and frost and freezing temperatures continues to be a concern for growers and those with sensitive plants.

Cloud cover is forecast to increase tonight and will likely hinder the longwave cooling into early Thu across the area. The air mass is much warmer, but remains dry. Frost appears less likely tonight for portions of interior Mendocino, southern Lake and northern Trinity where a widespread killing freeze has not been recorded yet. Early morning minimums on Thu will likely vary widely under a warmer air mass and clouds. Forecast minimum temperature have been nudged toward persistence (low to mid 30's) in the interior valleys. Higher elevations will likely warm up tonight. Any mixing in the valleys may keep temperatures in the lower to mid 40's.

Another shortwave trough will drop down from the NW over the weekend. Current indications are for this trough to take an over land trajectory as a ridge builds over the Gulf of AK. Potential for more light precip is not completely out of question just yet. General consensus is for continued dry weather Fri-Sun. Only about 20% of the cluster means are showing some light rain, while 80% suggest dry weather. Repetitive frost advisories and/or freeze warnings will most likely be forthcoming over the next several nights and early mornings as this trough reinforces the dry offshore flow over the area. Another inside slider type trough is expected early to mid next week. This trough may bring a greater chance for blustery north and northeast winds by mid week. Once again there is a range of possible outcomes, however the overall blocking pattern suggest predominately dry weather only with a 10-20% chance for fleeting precipitation for Del Norte and Trinity Counties.

AVIATION...(18Z TAFS)

VFR conditions will continue for terminals in Northwest California until this evening. High clouds will begin moving into the area this evening ahead of a weak cold front that'll clip the northern areas of the CWA. MVFR ceilings could occur for Del Norte and northern Humboldt terminals by late Thursday morning and into the afternoon. Light rain is possible for these same areas Thursday afternoon and into Thursday evening. /JLW

MARINE

Relatively calm conditions with light to gentle breezes and seas up to 5 feet will continue through today. Winds continue to shift southerly north of Cape Mendocino this afternoon as a weak frontal boundary approaches. Southerly winds are expected to increase to around 10 to 15 kt across the northern outer waters late tonight and into Thursday. Northerly winds are forecast to redevelop Thursday afternoon in the wake of the front, before strengthening on Friday. Models suggests the strongest winds will be south of Cape Mendocino, with potential gusts up to 25 kts. For the weekend, northerly winds are anticipated to expand northward with gusts up to around 30 kts across the outer waters by Sunday.

A forerunner mid-period WNW swell around 8 to 12 feet at 12 seconds will build in on Thursday. Wind waves around 6 to 9 feet at 8 seconds expected on Sunday. /ZVS

BEACH HAZARDS

A W-NW swell around with periods from 18-22 seconds will move through the waters Sunday evening through Monday, resulting in building surf along the beaches and increasing the potential of sneaker waves. Breaking waves will increase Sunday evening into Monday morning, reaching 14 feet by Monday morning along the northwest facing beaches. Sneaker waves are a unique hazard, with many minutes between waves. Pay attention and stay above the high water line and any wet sand to stay safe. If the ground is wet, waves have surged there recently. Stay safe and never turn your back on the ocean! /ZVS

EKA WATCHES/WARNINGS/ADVISORIES

CA... Frost Advisory from 2 AM to 9 AM PST Thursday for CAZ107- 110-112-113-115.

NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory from 3 PM Thursday to 9 AM PST Friday for PZZ450-470.

Small Craft Advisory from 11 PM Thursday to 9 AM PST Friday for PZZ455-475.