textproduct: Eureka

SYNOPSIS

Cooler and drier conditions expected through Wednesday. A quick moving system arrives Wednesday evening, bringing breezy south winds and rain across the area. Drier conditions expected by Thursday afternoon through at least Sunday. Frost possible Friday night into the weekend.

DISCUSSION

A brief period of dry weather is forecast through most of Wednesday as a much drier airmass fills in behind this system tonight, bringing chillier temperatures to the interior areas. Lingering cloud cover is likely to keep high temperatures this afternoon moderated, with even the warmest valleys struggling to reach 60. Ample moisture from recent rains are likely to promote cloud cover and patchy valley fog again tonight. Temperatures could still drop into the mid to high 30s for the coldest valleys of Trinity and northern Mendocino counties. These overnight temperatures will likely be high enough to prevent widespread frost.

Another system is likely to arrive by late Wednesday evening, returning gusty south winds and rain to the area. Most models show this as a quick moving system bringing light to locally moderate rain and breezy south winds. NBM is showing over 50% chances for over 0.5" of rain north of Cape Mendocino. There is around a 40% chances or higher for over 1" in Del Norte the King Range. Generally, forecast amounts range from 0.25-0.5" across the area, with localized areas over 1". South winds are not currently forecast to be strong, though gusts of 25-35 mph are possible especially along the coastal areas and in channeled terrain. 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. Chilly overnight temperatures are likely, which could lead to widespread frost as early as Friday morning if cloud cover clears out. An additional system is possible early next week, but ensembles are starting to trend this system northward. NBM is only showing a 50% chance for 0.1" in Del Norte Monday, with much lower probabilities to the south. Even high-end precipitation amounts (75th percentile) are only showing 0.25-0.50". JB

AVIATION...(18Z TAFS)

VFR conditions are forecast to prevail at coastal aerodromes (KCEC and KACV) through the period. Shallow moist air may result in brief MVFR vsbys this evening once mixing and solar insolation ceases. IFR conditions are expected to redevelop in the interior valleys overnight. Skies have been slow to clear out in Trinity and portions of interior Humboldt this afternoon and may not clear out at all. KUKI has cleared out, but IFR conditions will likely (60% chance) redevelop aft 08Z. Toward the end of the forecast period, MVFR cigs may (50% chance) spread back out over the coastal plain around Humboldt Bay and over KACV after 14-16Z Wed as winds turn south-southeasterly in advance of a front. Low level wind shear and shallow severe turbulence will be possible (20% chance) for over the coastal mountains and coastal airfields after 00z Thu as a 35kt+ low level barrier jet develops.

MARINE

A frontal boundary will rapidly progress across the waters Thu afternoon and evening bringing a brief period of gale force winds by mid to late evening. High resolution 10 member ensemble indicates 60-80% chance for gust > 34 kt, primarily in the outer waters, and nearshore waters north of Trinidad head, around Pt St George and north of Shelter Cove around Cape Mendo. There is a great deal of small scale variability, timing and spatial differences between all the HREF members. Thus a gale watch for gusts > 34 kt has been hoisted after 4-7 PM Wed for the outer waters. Gusts > 34 kt are certainly expected inside 10NM, especially around headlands. Large W-NW swell will begin to build Wed night and reach 15-17 feet at 13-15 seconds by Thu morning. This swell will combine with short period wind waves and seas will once again become quite hazardous. A warning for seas may be necessary. Otherwise, northerly winds and steep wind waves are generally forecast to prevail through the remainder of the week. A series of large W-NW swell groups will also propagate into the waters Thu through Sun.

BEACH HAZARDS

Long period W-NW swell from 8-12 ft with dominant periods near 16 seconds is forecast to build over the weekend. This swell may pose a moderate risk for sneaker waves as well as continued erosion of beach profiles. Stay tuned.

EKA WATCHES/WARNINGS/ADVISORIES

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

Gale Warning until 11 PM PST this evening for PZZ470.

Gale Watch from Wednesday afternoon through Wednesday evening for PZZ470.

Gale Warning until 9 PM PST this evening for PZZ475.

Gale Watch from Wednesday evening through late Wednesday night for PZZ475.