textproduct: Eureka

SYNOPSIS

Scattered showers and thunderstorms are expected across the area today. More widespread rain and mountain snow is expected Saturday. Sunday the showers are expected to come to an end as the cold air moves in. A chilly start to the week is expected with near- freezing temperatures possible in the colder valleys.

DISCUSSION

An upper low continues to move towards the California coast, while another upper low is quickly moving south towards northern California. Showers and thunderstorms are likely again this afternoon and evening across the area, but have been delayed slightly due to ample cloud cover. Similar CAPE values to yesterday (800-1000 J/kg) are expected, but shear is weaker at around 20-30 kts. This should prevent these storms from being as strong. Still, gusty winds of up to 40 mph, small hail, and localized heavy rain are possible with the strongest of these storms. Should training storms develop, flash flooding may become a risk.

The secondary upper low moves into the area tonight into Saturday, bringing more widespread moderate to heavy rain across the area. Gusty south winds of 30 to 40 mph in Mendocino & Lake Counties are possible Saturday morning and afternoon with this system. CAMs are starting to show a convective line Saturday afternoon that could bring locally higher winds, perhaps to 45 mph to southern Mendocino and southern Lake Counties, but the bulk of the winds appear to the to the south of the area. Thunderstorms are possible with this convective line. Showers will follow into the evening and overnight Saturday. This could bring more thunderstorms, mainly for Mendocino and Lake Counties, which could contain small hail. Total rain amounts of 1-2" are expected from this rain Saturday and the following showers Sunday, with some locally higher amounts possible within thunderstorms.

Snow levels will fall dramatically from 5500 to 6000 ft down to 3500 to 4000 ft Saturday night into Sunday. This will bring snow down to Highway 3 at Scott Mountain Pass and along the highest passes on Highway 36. Scott Mountain Pass could see 3 to 7 inches, while South Fork Mountain could see up to an inch. The highest elevations could see over a foot of new snow. A Winter Weather Advisory has been issued for northern Trinity County above 5000 ft from Saturday evening to Sunday evening.

Much colder temperatures are likely during and and behind this frontal passage. Near-freezing temperatures are forecast, especially Monday & Tuesday mornings. Frost advisories and/or freeze warnings might be needed. Looking towards next week, more ensemble members are showing another system approaching the area by Wednesday. NBM is showing around a 50-70% chance for wetting rain (>0.1") for the North Coast Wednesday, with much smaller chances inland and into Mendocino & Lake. The chance for over 1" is low, around 20% in the mountains of Del Norte, and near zero elsewhere. Stay tuned!

AVIATION...(10/18Z TAFs)

LIFR conditions with low ceilings and visibility in mist have been observed across the coastal terminals, becoming variable with passing showers. While conditions for UKI are mostly VFR. Otherwise, conditions will vary widely this afternoon as SHRA activity increases across the forecast area. There is a potential for VCTS between 10/19Z-11/01Z for the TAF sites, especially for KUKI. Expect gusty and erratic winds and possible hail with any TSRA (thunderstorm). Showers are expected to diminish in coverage tonight, allowing IFR/LIFR conditions before a stronger frontal system approaches the area early Saturday, bringing increasing SHRA. Surface south winds are expected to increase after 11/15Z as the frontal boundary approaches, with the highest chances of gusts up to 25 mph in UKI. /ZVS

MARINE

Light south and variable winds along with low seas below 3 feet persist as a cut-off low moves across the coastal waters. However, showers with embedded thunderstorms have the potential to generate hazardous conditions through the day today. These should promote frequent lightning, small hail, and gusty and erratic winds greater than 30 kts. A stronger frontal system is expected to approaches the area late tonight through Saturday. A rapid and brief increase of southerly winds is expected on Saturday as a frontal system approaches the area. Expect gusts up to around 25 kts over the southern waters and around Cape Mendocino, with isolated gust up to 34 knots. After the frontal passage, breezy northerly winds will develop early Sunday. A period of steep seas around 6-7 feet at 6-7 seconds is possible Saturday night. A west-nortwest seas around 5-7 feet at 9-10 seconds and some small swells will dominated the waters on Sunday.

Monday, northerly winds returns as high pressure starts to build into the area. This will promote moderate to strong northerly breezes across the waters Monday into Tuesday, with the strongest winds south of Cape Mendocino. Model guidances suggest a brief wind shift to south over the northern waters by mid-next week as a frontal system moves through. /ZVS

EKA WATCHES/WARNINGS/ADVISORIES

CA... Winter Weather Advisory from 5 PM Saturday to 11 PM PDT Sunday for CAZ107.

NORTHWEST CALIFORNIA COASTAL WATERS... None.