textproduct: Eureka

SYNOPSIS

Sneaker waves risk Friday afternoon and overnight. Showers with areas of thunderstorms develop over the weekend. Some showers and thunderstorm will be capable of gusty winds and heavy downpours, mainly over the interior.

DISCUSSION

In the near term, a building long period northwest swell is brining an increased risk for sneaker waves this afternoon and overnight. Water vapor imagery shows a ridge of very dry air over Southern CA, with increasing moisture and cold cloud tops pushing into Northern California from the SW. An upper low and mid level disturbance to the west is increasing deeper moisture and instability. As the mid level disturbance nears, showers will push in from the SW Saturday and especially Saturday afternoon. Soundings show a good amount of convective inhibition (CIN), likely from the increasing mid to high level clouds. Models due project modest elevated CAPE (200 to 300 with isolated areas over 400 J/kg) Saturday afternoon with steepening lapse rates. This environment would be favorable for thunderstorm development as well, particularly from the increasing forcing Saturday afternoon as the mid level disturbance nears.

Isolated to scattered thunderstorms are likely if the cap sufficiently erodes, and some of these storms would be capable of gusty winds and heavy downpours, especially over Trinity County. There is a 50 to 60% chance for over 0.5 inch of rainfall over some higher terrain, likely from terrain enhancement of convective activity. Of note, there is also a 20 to 30% chance for very isolated amounts over 1 inch of rainfall for the Trinity Horn and far northeast Del Norte County. There are still some questions of the trajectory of this system and the best focus of showers and potential thunderstorms.

Additional showers and possible thunderstorms will develop Sunday as the low pushes over N california, with the highest chances for thunderstorms over Trinity County. A small surface low is modeled to form Sunday, and this feature may increase shower and thunderstorm coverage closer to the coast, especially if it arrives in the afternoon. Precipitation chances then fade into mid week beyond the departure of the low. A secondary system looks to at least clip the region mid next week. Current probability for total rainfall amounts do not look impactful. There is a 45% chance for 24 hour totals over 0.5 inch Wednesday over Del Norte and northern Humboldt. JJW

AVIATION

VFR conditions through the day. Light northerlies for coastal terminals. Light variable winds forecasted inland. A fast moving cold front approaches Saturday morning increasing the North Coast's chance of showers beginning at 15Z (+/- 2 hrs). A very slight chance of lighting is possible for terminals as well beginning around 18Z (+/- 1 hr). VFR conditions are expected through this frontal passage with a chance (20-40%) of MVFR due to decreases in visibilities.

MARINE

Winds remain generally light and northerly today, with the only exception being some gusts of up to 20 kts around Cape Mendocino and the far northern outer waters. Seas will build this afternoon and overnight as a long period north-northwest swell of around 8 ft at 15 seconds arrives. Combined seas may briefly exceed 10 ft in the outer waters overnight.

There is greater confidence in details of a weak cold front moving through the waters Saturday morning. High-res models are starting to show a tighter pressure gradient, potentially causing a fast moving band of winds up to gale force (>34kt). There is currently a growing certainty of the magnitude and timing and timing of these winds. REFS and HREF are showing around a 30% chance for Gale Force gusts south of Cape Mendocino Saturday and a 50 to 60% chance for gusts over 25 kts. These winds are forecasted to be quick in and quick out, beginning at 9am and ending at around noon. Due to the quick nature of this band, a gale warning has not been issued because winds will persist for under 2 hours. After this passage, winds will diminish again into Sunday. Winds and seas are likely to remain mild through at least Wednesday of next week before northerlies build in as a fairly weak thermal trof set up looks to form over the waters. DS

BEACH HAZARDS

A long period northerly swell is building into the region. The swell is arriving with a 16 second period, with up to 15 second period energy lingering after Midnight. This will bring a risk for sneaker waves. Oregon buoys show the swell coming in larger than modeled. 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!

COASTAL FLOODING

A nearing full moon phase will bring high than usual tides over the next several days. The worst case forecast tide levels over Saturday and Sunday are high, reaching 8.3ft, but will remain below advisory and impact level for Humboldt Bay.

EKA WATCHES/WARNINGS/ADVISORIES

CA... None. NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory until 10 AM PST Saturday for PZZ470.