textproduct: Eureka

SYNOPSIS

Isolated to scattered rain showers continue today ahead of a cold frontal passage tonight. Gusty south winds are likely tonight as a front moves approaches the area. Widespread rain returns Wednesday. Mountain snow and coastal small hail are possible Wednesday night and Thursday morning.

DISCUSSION

Light to locally moderate rain showers continue to move across the area, primarily focused in Del Norte, northern Mendocino, and southern Trinity Counties. Increased instability this afternoon might be able to support a thunderstorm in a stronger shower, though confidence is low on this.

A stronger frontal system moves through the PacNW tonight into Wednesday. Southerly winds will increase ahead of the main frontal passage Wednesday morning. The higher elevations of Humboldt and Del Norte could see gusts up to 50 mph. Coastal Del Norte could see gusts up to 45 mph. Further south, peak gusts of 30 to 40 mph are likely for much of Humboldt and western Trinity. Lake County will also be breezy, however this will mostly be in the afternoon with west winds of 30 to 40 mph possible. The highest mountains and coastal headlands could see locally higher gusts up to 60 mph.

Widespread light to moderate rain is likely across the area. Periods of heavy rain are possible for the North Coast, and especially in the King Range and the mountains of Del Norte and northern Humboldt. Total rain amounts range from around 2.0-3.0" in Del Norte, 1.0-2.5" in Humboldt and Trinity Counties, and 0.25-1.00" in Mendocino and Lake Counties. This will largely be beneficial rain, but some minor impacts (flooding in poor drainage areas and mud/rock slides) are possible in Humboldt and Del Norte with the heaviest rain. Snow levels will drop with this system, down to 5,000-5,500 ft Wednesday morning during the period of most precipitation. This will bring some snow down to Scott Mountain Pass. Snow totals there range from around 2 to 6 inches, depending on how low snow levels drop.

Snow levels continue to drop into Thursday, and could be as low as 2,500 ft as stratiform rain turns showery. While precipitation is likely to be meager by this point, some light snowfall is possible on the highest passes of Highways 3, 36, 199, and 299. A Winter Weather Advisory has been issued for the Trinity Horn above 4,000ft due to melted snow freezing overnight while snow levels plummet, creating icy, hazardous roads.

Additionally, with much colder air aloft, atmospheric instability will increase, particularly along the coast. Showers capable of producing accumulating small hail are possible, along with isolated thunderstorms. Much cooler temperatures are expected Friday morning with widespread near-freezing or freezing temperatures. Temperatures will generally trend warmer as high pressure begins to rebuild into the weekend. JB

AVIATION...18Z TAFs

Southerly winds will increase late Tuesday through Wednesday while rainfall moves in with an approaching front. Winds near 925 mb (2000 ft AGL) will increase to 40 to 50 kts from the S to SSW starting 13Z Wednesday. Ceilings will mainly hold to MVFR levels. A well defined front will create a sharp windshift to a westerly direction beginning around 17Z in Del Norte and then pushing eastward through the afternoon as it passes.

MARINE

Southerly winds are increasing across the waters Tuesday ahead of a frontal system, while seas range in the 4 to 6 area. Southerly winds will further increase Wednesday morning when localized areas of gale strength gusts spread through the northern waters.

There will be a abrupt shift in wind direction to westerly as the front passes late Wednesday morning and into the afternoon. A steep westerly swell will start building in Wednesday night, reaching 10- 14 feet at 12 seconds on Thursday. Westerly winds will ease Thursday before northerlies quickly strengthen starting Thursday afternoon. The northerlies increase more Friday, and localized gales are forecast south of Cape Mendocino Friday afternoon through Friday evening. Calmer conditions are forecast to begin by late Saturday.

EKA WATCHES/WARNINGS/ADVISORIES

CA... Wind Advisory from 8 AM to 1 PM PDT Wednesday for CAZ101- 102.

Winter Weather Advisory from 8 PM Wednesday to 11 AM PDT Thursday for CAZ107.

NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory from 5 AM to 3 PM PDT Wednesday for PZZ450.

Small Craft Advisory from 2 AM to 10 PM PDT Wednesday for PZZ470.