textproduct: Eureka

SYNOPSIS

Drier and colder weather is expected to last into Tuesday. Periods of mostly light rain and high mountain snow are forecast to return Thursday and Friday.

DISCUSSION

Dry and seasonably cold weather is forecast to continue into early next week as a ridge aloft builds over the area. Mean sea level pressure pattern will continue to favor dry offshore flow with chilly nights for the the coast. A few coastal sites may dip down to 32F or less around Humboldt Bay early this Sunday morning. NBM continues to indicate a 96% chance for McKinleyville and a 70% chance for Arcata. Light NE and E winds may keep temperatures from falling to 32F. A frost advisory is in effect until 9 AM Sunday. Frost for coastal areas will be possible again tonight or early Monday morning.

Adiabatic warming is expected to build Mon through Wed. Daytime highs will increase, especially for the higher elevations with southern sun exposure and in broad N-S oriented valleys. High's in the lower to mid 60's are expected. This is above normal for late Dec. Early morning lows will still be near or below freezing, however. After multiple days of rain, fog and low clouds will invariably form each night in the interior valleys. High temperatures may not warm much in valleys with stubborn and persistent low clouds and fog. Coastal areas will generally fair better with only shallow morning ground fog around Humboldt Bay and occasional high clouds.

The ridge will begin to weaken and shift eastward on Wednesday as a Gulf of AK trough interacts with a subtropical cut-off low. A large swath of moisture in advance of the trough will spread northward from Central California on Wed. Some light rain or sprinkles will be possible as early Wed night for Lake and Mendo counties. 6-hourly rain rates increase Thu-Fri generally under 0.10 inches with local maximums perhaps up to 0.35 inches in the King Range Thu night or Fri morning. Highest rain rates will most likely occur with frontal passage on Fri. IVT with most ECMWF and GFS ensemble members are under 250kg/m/s. Impacts from rain or mountains snow appear minor at this point.

AVIATION

With Northwest California solidly between systems and ridging building aloft, winds have become light and radiational cooling is causing temperatures to fall rapidly. With recent rainfall across the region, fog will easily form across the interior valleys. It is highly lightly that LIFR conditions will develop in many valleys including UKI. Less low clouds are expected at the coast, especially with high level clouds spreading over the area. Interior valley fog will slowly mix out on Sunday with some interior valley locations remaining in the fog into the afternoon hours. VFR should prevail at the coast. /RPA

MARINE

Northerly winds will diminish overnight as ridging begins to build over the west coast weakening the surface pressure gradient over the waters. Winds and seas will remain generally low through midweek. The next storm system will approach the waters Wednesday into Thursday allowing winds to turn out of the south. Model guidance is indicating this next storm will not be particularly strong and winds may turn back out of the north rather quickly behind the passing front. The main concern on the horizon is a northwesterly fresh swell that could build into the waters late in the week to possibly next weekend. /RPA

COASTAL FLOODING

King Tides are predicted to return next week. Highest probabilities for salt water inundation of normally dry areas will be around Humboldt Bay during high tide from Tue, December 30th to Mon, January 5th. Highest tidal predictions for Humboldt Bay are expected Fri and Sat. Strong southerly winds and a large tidal anomaly may result in levels near 9.6 feet above MLLW. Other coastal areas are less certain. Noyo harbor, Arena Cove, Crecent City harbor and Shelter Cove may also have minor salt water inundation.

EKA WATCHES/WARNINGS/ADVISORIES

CA... Frost Advisory from 2 AM to 9 AM PST Sunday for CAZ101.

Frost Advisory until 9 AM PST Sunday for CAZ103-109.

NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory until noon PST Sunday for PZZ455.

Small Craft Advisory until 6 PM PST Sunday for PZZ470.

Small Craft Advisory until 8 PM PST Sunday for PZZ475.