textproduct: Eureka

SYNOPSIS

A quick moving front will bring moderate rainfall and breezy winds this afternoon into Thursday. Drier and cooler weather with a chance for freezing morning temperatures in the interior can be expected toward the end of the week and weekend.

DISCUSSION

An approaching frontal system will increase rain chances throughout the day as southerly winds increase ahead of the front. Wind gusts will reach 20 to 30 mph, with some gusts over 40 mph for coastal Del Norte, the King Range, and the prominent coastal headlands and interior ridges. These stronger winds will be shorter lived and mainly with the frontal passage Wednesday night. NBM is generally showing low chances for gusts over 30 mph, so there is still some question of the magnitude of winds that mix down to the surface.

A burst of widespread moderate to locally heavy rainfall (up to 0.3 inches per hour) is expected with this front. There is a moderate probability (40 to 60%) for 24 hour rainfall over 0.75 inch from Southern Humboldt to Del Norte. The rain shadow from downsloping southeast winds will lower amounts for locations such as around Humboldt Bay. There is better chances and higher confidence for rain amounts over 0.5 inch.

Snow levels will drop Wednesday night to 5000-5500 ft, but lower precipitation potential in Trinity County will only support a dusting at Highway 3 around Scott Mountain Pass. Conditions quickly improve by Thursday morning with only some lingering showers continuing by Thursday afternoon.

Another break in the wet weather returns Friday and into the weekend as high pressure noses in from the west. Daytime high will rebound back to warm values Friday and through the weekend for most of the region. Chilly overnight temperatures are likely, which could lead to widespread frost as early as Friday morning if cloud cover clears out. Interior valley fog would lower chances for colder temperatures however. An additional system is possible early next week, but ensembles are starting to trend this system northward. Even high- end precipitation amounts (75th percentile) are only showing 0.25 amounts clipping Del Norte County.

AVIATION...(18Z TAFS)

Chance for low level wind shear and severe shallow turbulence will increase this evening over Del Norte and Humboldt Counties. Surface winds may initially be too gusty for a sharp drop off in wind speed from 1000-2000 AGL. Max threat will be around 04z to 07z Thu with frontal boundary passage. VFR to MVFR ceilings will likely deteriorate with occasional IFR or 2SM in moderate to locally heavy rain from about 03z to 07z Thu for ACV and CEC. Precip intensity falls off after 07z with generally MVFR conditions. Light rain should also spread over KUKI by 04-05z and MVFR conditions are generally expected. Mixing and cloud cover should limit the risk for IFR due to fog. HREF does show light rain ending after 10-12Z and with light or calm winds. Cloud cover will probably be too extensive for dense fog around daybreak in the valleys.

MARINE

Southerly winds are projected to strengthen ahead of an incoming front that will move through the coastal waters late this afternoon into this evening. Un-calibrated HREF continues to indicate 80-100% chances for gusts > 34 kt late today into this evening, primarily north of Cape Mendo. Individual CAMS show a wide range of possible outcomes across time and space. Wind gusts over 40 kt from the W-NW with mini occlusions along the front could also develop by mid to late evening or shortly after midnight, Both north and south of Cape Mendo. Even the inner waters could have gust > 34 kt from about Trinidad Head to the Oregon border around Pt St George this evening. Winds at KCEC are already above model guidance, but the flow remains stable and laminar with no gusts. Instability and mixing will increase this evening as a 925mb speed max around 35 kt develops near and along the front. If deeper convection or elevated thunderstorms develop, wind gusts to 40 kt may even occur. A marine weather statement has been issued for this. On Thu, a large W-NW swell will begin to build and reach 15-17 feet at 13-15 seconds Thu afternoon and evening. This swell may combine with short period wind waves and seas will once again become quite hazardous. A warning for seas may be necessary. At this time, the wind waves appear to dwindle and the swell looks to be the dominant energy. For the remainder of the week, northerly winds and steep wind waves are generally forecast to prevail. Wind gusts to 35 kt or more are certainly possible downwind of Cape Mendo. Another large W-NW swell group will propagate into the waters this weekend and may pose a threat for sneaker waves once the shorter period wave groups subside.

BEACH HAZARDS

A large W-NW swell will bring a risk for dangerous surf Thursday afternoon through Friday morning. Breakers from 16 to 20 feet are expected assuming an ideal and average beach profile. Larger breakers will be possible if the swell ends up coming bigger than forecast by GFSwaves. For now will call attention to this risk via weather story post and on social media. The swell is too large for sneaker wave criteria and too low to warrant a high surf advisory. A longer period W-NW swell group from 8-12 ft with dominant periods near 16 seconds is forecast to build over the weekend. This swell may pose a greater risk for sneaker waves and continued erosion of beach profiles. Stay tuned.

EKA WATCHES/WARNINGS/ADVISORIES

CA... None. NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory from 4 PM this afternoon to 10 PM PST this evening for PZZ450-475.

Small Craft Advisory until 10 PM PST this evening for PZZ470.