textproduct: Eureka

SYNOPSIS

Light rain and mountain snow return tonight through Wednesday night. High pressure is expected to build in late this week bringing dry conditions to Northwest California. Sneaker waves are expected at the coast on Wednesday transitioning into large surf on Thursday.

DISCUSSION

The heaviest rain has finally come to an end allowing streams and rivers across the region to recede. However, before we can completely dry out, another couple fronts will bring light to moderate precipitation to primarily the northern half of the forecast area tonight and then again on Wednesday. Total precipitation from the two waves of precipitation will likely range from a couple tenths of an inch to around three quarters of an inch for coastal and valley locations of Humboldt, Del Norte, and western Trinity counties with potentially over an inch in the higher terrain. Snow levels will fall behind each front, potentially to as low as 2500 feet in Del Norte county before the snow comes to an end. Total snowfall in the higher terrain will easily reach advisory criteria, but with very little expected down to any highway passes, a winter weather advisory has not been issued at this time. The main concern is highway 199 where light snow may reach the highway Wednesday night for a few hours with up to an inch or two of snow possible. If trends point to heavier snow at the tunnel then a winter weather advisory may need to be introduced in future forecast packages.

In addition to the rain and mountain snow, northwesterly winds will also ramp up behind the front. Wind gusts in excess of 20 mph will be possible along the coast Wednesday afternoon and evening along with many of the ridgetops across the entire region. Locally higher gusts will be possible on the interior mountains, particularly in Lake and eastern Trinity counties. Local gusts over 40 mph will be possible in those areas in the wake of the frontal passage.

Dry conditions are expected beyond Wednesday for the next several days. Overnight lows will be quite cold with lows in the 20s and 30s across the region behind the cold front. The frost/freeze seasons have concluded for all areas with the turn to the new year so no frost headlines will be issued. However, overnight low temperatures may approach 30F in portions of Lake and southern Mendocino counties Thursday and particularly Friday mornings. The need for cold weather advisories will have to be contemplated for those two mornings. A warming trend will likely begin over the weekend. /RPA

AVIATION...(18Z TAFs)

VFR conditions prevail this afternoon with light winds and elevated BKN-OVC ceilings. An approaching weather system tonight will bring light rain and moderate southerly winds to coastal terminals. A break in the rain is forecasted from about 16Z until about 22Z tomorrow when more rainshowers are possible. Ceilings are expected to remain in MVFR/VFR with only a 20% probability of IFR for the North Coast. Inland, light winds remain with lingering clouds. High resolution models show that some fog/low cloud development is possible, yet a PROB30 has been issued for KUKI as far due to forecast uncertainty.

MARINE

Weak high pressure will be briefly settling over the area as the low pressure drifts southward. Winds will switch to 10 to 15 kt south to southwest over the northern waters while farther south, the winds will turn more westerly. Northerly winds are expected to return through the day on Wednesday as high pressure builds back into the area. These are expected to peak around 15 to 25 Wednesday night and Thursday morning.

The 11 second swell moving through the waters is gradually diminishing and will continue to diminish through Wednesday. A large, long period swell is expected to move into the waters Wednesday and Thursday. Initially these waves may be around 3 to 4 feet at 23 seconds. These will build through the day and overnight to around 17 to 19 feet at 18 seconds by Thursday morning. This is about 2 feet over the wave watch 3 model and more in line with the ECMWF wave model. Issued a hazardous seas watch to highlight the potential for a swell over 17 feet.

The winds and seas are expected to diminish Friday, but the swell may remain above 10 feet until Friday night. Calmer conditions are expected on Saturday this coming weekend.

BEACH HAZARDS

Forecast confidence is growing that a large, long period swell is expected to move into the waters Wednesday and Thursday. The forerunners of this wave will start to build in Wednesday around midday. Initially, these waves may be around 3 to 4 feet at 23 seconds before building to 5 to 8 feet by midday. There will likely be set behavior with these long periods creating an increased sneaker wave threat. There will be some background NW swell and increasing northerly winds, but the sets may still be distinct enough to catch some people off guard. After the front runners of this wave group enter the coastal waters, the swell will keep building overnight to around 17 to 19 feet at 18 seconds by Thursday morning. Large breakers of 22 to 25 feet are expected for west and northwest facing beaches. A high surf advisory has been issued from 7 PM PST Wednesday until 4 PM PST on Thursday due to these dangerous shoreline conditions.

EKA WATCHES/WARNINGS/ADVISORIES

CA... Beach Hazards Statement from late tonight through Wednesday afternoon for CAZ101-103-104.

High Surf Advisory from 7 PM Wednesday to 4 PM PST Thursday for CAZ101-103-104-109.

Beach Hazards Statement from Wednesday morning through Wednesday afternoon for CAZ109.

NORTHWEST CALIFORNIA COASTAL WATERS... Hazardous Seas Warning from 7 PM Wednesday to 3 PM PST Thursday for PZZ450-470.

Hazardous Seas Warning from 11 PM Wednesday to 3 PM PST Thursday for PZZ455-475.