textproduct: Eureka

SYNOPSIS

An extended period of wet and colder weather that will span through next week will begin over the weekend. Significant mountain travel impacts begin from these systems by early next week and continue through much of the week.

DISCUSSION

Shortwave ridging nosing in from the west maintains dry weather Friday. The pattern begins to change Saturday as a closed low begins forming off the CA coast. Potent surface impulses will form and increase rain and winds through the weekend. Models still struggle with the placement of these surface lows. They may initially remain quasi stationary, but chances for breezy to locally strong winds are increasing. The higher end potential wind forecast from NBM show widespread wind gusts of 30 to 40 mph, with higher gusts over the ridges and some prominent coastal headlands.

A stronger and much colder trough will then dive down from the north Monday. The approaching trough will kick a previously mentioned surface low eastward into the CA coast Monday. The southern and eastern periphery of this feature will contain strong winds. Models have been somewhat consistent with landing it south of Mendocino County. Even so, enhanced wind will likely span through Mendocino and Lake counties where wind gusts up to 45 mph will be possible over the ridges and some coastal headlands Monday.

Winds will increase again over a broader area Monday night and Tuesday as the cold trough from the north moves in. At the same time, precipitation rates increase as snow levels quickly lower. Snow levels are forecast to drop to 2000 to 1500 ft Monday night through Tuesday morning. There is moderate to high confidence for snow these snow levels (65% chance for less than 2000ft and 45% chance for levels less than 1500 ft Tuesday and particularly Wednesday). Probabilities for levels less than 1000 ft have even increased (25%), particularly Wednesday. Heavy snow across the higher ridges above 4000 feet could accumulate from 1 to 3 feet from Saturday evening through mid next week. Snow totals over the region have continued to trend higher, so the forecast should be followed closely. A Winter Storm Watch issuance is anticipated, with advisory level conditions likely also to be met. Snowfall may continue through late next week.

Instability will increase Tuesday. Convectively enhanced precipitation rates may temporarily drive down colder air, lowering snow levels. This will not be difficult to achieve with 850 mb temperatures dropping as low as -5C Tuesday. The cold air aloft, instability, and convective showers will also bring a likely threat for accumulating small hail Tuesday. Accumulating small hail over roadways would also pose a significant threat to motorists.

That said, major travel impacts are likely over much of Trinity County, and major impacts will also be possible into Humboldt and Del Norte counties. Travel impacts will also reach the passes of Del Norte, Humboldt and Mendocino counties, particularly if the less than 1500 ft elevation snow levels are maintained. Currently, significant snow accumulations are forecast for highway passes at locations such as Collier Tunnel, Berry Summit and a good portion of Highway 36 through Humboldt County. Higher summits on 101 such as the Laytonville area/Rattlesnake Summit and perhaps even Prairie Creek Summit will also need to be closely watched for travel impacts from snow.

Regarding lower elevation rainfall accumulation, NBM probabilities are predicting a high likelihood for 1.5" to 3" in 72 hours from early Sunday to early Wednesday morning for most of the CWA, with 3 to 5" in the windward facing terrain. Minor flooding of smaller river, creeks and streams, urban areas with poor drainage will be possible, along with sharp rises in some mainstem rivers. JJW

AVIATION

Stratus has moved inland along the coast bringing IFR to MVFR ceilings that will last through the morning. Interior valleys could see fog again this morning as moisture remains available. UKI has around a 40% chance to see fog this morning. Any stratus and fog is likely to lift and scatter by late in the morning. High clouds will also move through the area.

MARINE

Northerly winds continue to diminish today. Steep northerly wind waves will continue to diminish as well, but conditions could still be hazardous to small crafts. A large long period northwest swell continues to build into the coastal waters, peaking early today at around 12 ft at 16 seconds. Combined seas up to 14 ft are possible today.

North winds continue to subside and turn southerly by this afternoon as low pressure approaches the area. The center of the low pressure is likely to be off the northern California coast, and the exact location of the strongest winds is currently uncertain. Strong northerlies are possible on the western edge of this low with moderate to strong southerlies possible on the eastern edge. Winds are likely to remain elevated through the week as the pattern remains active. There is at least a 30% chance for gales in the outer waters each day through Friday of next week. JB

BEACH HAZARDS

A steep, northwest long period swell is building in, bringing a sneaker wave threat Friday. This swell will peak around 12 to 13 feet at 16 seconds during the daytime Friday. This swell will align with beaches in Humboldt, Del Norte, and Mendocino counties, increasing the threat of sneaker waves. The wave is expected to produce set behavior with breakers leading to rapid and unexpected beach run ups of over 18 feet. Calmer winds and few short period seas along the coastline Friday will further enhance this danger making waves more sneaky, especially on steeper beaches. Take care if going to the beach late in the week. Choose flatter beaches if possible. Stay off of rocks, logs, and jetties. Never turn your back to the ocean! DS

EKA WATCHES/WARNINGS/ADVISORIES

CA... Beach Hazards Statement through late tonight for CAZ101-103- 104-109.

NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory from 4 AM early this morning to 3 AM PST Saturday for PZZ450-455.

Small Craft Advisory until 3 AM PST Saturday for PZZ470-475.