textproduct: Eureka

SYNOPSIS

A weakening front may generate light showers tonight through Friday morning, primarily for Del Norte and northern Humboldt. Otherwise, dry and seasonably cool weather is forecast for the next 7 days. A highly energetic long period west swell will bring an increased risk for hazardous beach conditions Monday through Tuesday next week.

DISCUSSION

Decaying frontal boundary trailing southwestward from a surface low offshore the Pacific NW has been slowly moving toward the North Coast this afternoon. So far only 0.01 to 0.04 inches of rain has occurred, mostly in Del Norte. High resolution models continue to depict a shallow moist layer pushing onshore this evening and overnight for perhaps additional light rain on the order of a few hundredths in the Humboldt Bay area. High resolution ensemble guidance indicates highest chances for 0.10 to 0.20 inches in 24 hours ending 4 AM Fri over Del Norte County and coastal areas of northern Humboldt north of Trinidad.

Above normal 500mb heights will most likely (80% chance) keep much of Northwest California in a long stretch of dry weather all next week.

There are a couple of caveats for light spotty precip, however. A trailing trough and surface low south of 40N will approach 130W on Fri, and then drift southward through the day. All models keep this low too far offshore for precip concerns. Another shortwave trough will swoop down across the Pacific NW into the Great Basin over the weekend. This trough has an overland trajectory and will most likely serve to reinforce the dry offshore flow across our forecast area. Overnight frost and freezing morning temperatures will once again be prime concern for those with sensitive plants.

A third shortwave trough may (10% chance) generate fleeting showers for Del Norte and mountains of Trinity Mon or Tue. This second insider slider trough will carve out a larger scale trough that will promote blustery N and NE winds around mid week. With lower dew points, calm winds in the valleys, clear skies and long nights, the threat for frost or freezing temperatures will once again crop up. A killing freeze has already occurred multiple times in Trinity, northern interior Mendocino and northern Lake Counties. We have suspended issuing frost and freeze products for these areas until spring. Cold weather products for wind chill may be necessary if an unseasonably cold air mass settles over the area around mid next week. There are subtle signs of omega block break down or a westward shift in the longwave the following weekend of Dec 6-7 and consequential precip will be possible.

AVIATION...(18Z TAFS)

General overcast skies will continue to move through the region as a dry weak front progresses east. Chances for light rain will diminish greatly by late this evening for coastal terminals in northern Humboldt and Del Norte counties. MVFR ceilings will continue for coastal terminals through this TAF period with ceilings approaching IFR conditions overnight and into early Friday morning. General cloudiness will continue into late Friday morning. /JLW

MARINE

Winds are shifting northerly this afternoon in the wake of the passing front. Northerlies will increase into Friday, especially in the southern waters. Models support that the strongest winds will be south of Cape Mendocino, with potential gusts up to 20 kts. For the weekend, northerly winds are anticipated to expand northward with gusts to 25 kts across the outer waters by Sunday.

A forerunner mid-period WNW swell around 8 to 12 feet at 11 to 12 seconds will continue to build in this afternoon/evening. Wind waves around 6 to 9 feet at 8 seconds expected on Sunday.

BEACH HAZARDS

A highly energetic long period westerly swell group generated from a Hurricane Force low pressure system near the international dateline (180th meridian) will arrive Sunday night and build through the day on Monday. This high energy swell will bring a high risk for sneaker waves to Northwest California beaches on Monday. The sneaker wave risk will probably persist Monday night and Tuesday, though should decay to moderate levels as swell heights increase to 10 feet or more. 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... None. NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory from 3 PM this afternoon to 9 AM PST Friday for PZZ450-470.

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