textproduct: Eureka

SYNOPSIS

A mix of linear bands and cellular convective activity, mountain snow and periods of strong to gusty winds will continue through Friday morning. Shower and isolated thunderstorm activity will gradually to diminish through the day on Friday. Drier and colder weather is forecast for the weekend and should last into early next week.

KEY MESSAGES

* Strong to gusty winds, showers and isolated to scattered thunderstorms with locally heavy rain expected through Friday afternoon. * Flood Watch remains in effect through Friday evening for Humboldt, Trinity, Mendocino and Lake counties.

* Winter Storm Warning for elevations above 4000 ft through Friday evening for Trinity County.

* Hazardous marine and coastal conditions expected through Friday morning.

DISCUSSION

Scattered to numerous showers and isolated thunderstorms under a southwesterly wind flow aloft continues impacting the region. Several lightning strikes and small hail have been detected with the strongest thunderstorms. These showers have been producing moderate to locally heavy rain during the morning and early afternoon hours.

A negatively tilted shortwave trough is pinwheeling into Northern California around a 982mb low pressure currently located just near 42N 129W, just ~260 miles offshore of Oregon Coast. An upstream mid-level jet and associated vorticity maximum will approaches the NW California, specifically the Mendocino Coast late this afternoon and evening. This will bring another peak in winds and an enhanced in showers across the area. A line of organized convection activity with heavy rain and/or thunderstorms is expected to move from southwest to northeast across the region with sudden, strong to gusty south winds from 30 to 50 mph late this afternoon and evening. Heavy rainfall rates up of 0.30" to 0.50" per hour will be likely with these new rounds of heavy showers and thunderstorms activity. The saturated soil conditions along with strong winds will bring an increased risk of downed trees, and will make it easier for tree to uproot. In addition, there is the potential for isolated waterspouts near shore late this afternoon/early evening as well.

A mix of linear bands and cellular convective activity is expected to move across the area from southwest bringing an additional peak in winds tonight into Friday. A brief burst of strong to gusty winds is expected along a 45-60kts coastal barrier jet (925mb) late tonight and early Friday. Strong south winds from 40-50 mph are expected over the coastal headlands and exposed ridges in Southwestern Humboldt, Mendocino and Lake counties, with locally strongest gust up to 60 mph possible.

Snow level will likely drop to 3500-4000 ft tonight into Friday as colder air aloft moves across the area. 48-hour total snow amounts of 2-3 feet are expected through midday Friday. A brief break of showers is expected this afternoon and early evening, but travel over Scott Mtn Pass will be very difficult or impossible if roads are now plowed.

The mid-upper level trough and associated surface low is expected to move overhead Friday afternoon and shift east-souteast across the area Friday night. Showers and thunderstorms activity are expected to gradually diminish by afternoon and evening hours on Friday, with lingering showers into Saturday.

High pressure is expected to start to move over the area on Saturday bringing a break in the prolonged wet spell. Northerly may be a bit breezy and gusty over ridges this weekend. The valleys will likely see widespread fog and low clouds each night and morning. Frost and freezing temperatures will also be possible for the North Coast, especially Sunday morning. Cooler and drier weather should last into early next week. This may be too optimistic this time of year. Chances for more than 4 to 5 days in a row of no possibility of precip is not high. In fact CPC 8-14 day outlook already has us back in a slight risk for heavy rain and high mountain snow. /ZVS

AVIATION

An upper level low off the coast continues to have showers rotating around it. There are some shortwaves that are enhancing these showers periodically and bringing some thunderstorms as well. This low has strong southerly winds ahead of it. Additional shortwaves are expected tonight through Friday morning. Later this afternoon or evening a shortwave is expected to push some stronger showers north into Mendocino county and Ukiah through around 3Z on the 26th. Late tonight it looks like another will bring enhanced showers to the terminals. These showers will generally bring increased wind gusts and brief periods of IFR conditions. Friday afternoon the winds and showers are finally expected to start to diminish. MKK

MARINE

The upper level low off the coast continues to bring strong southerly winds to the waters, although they have diminished slightly from earlier. Gales generally persist in most areas with more storm force gusts in the northern outer waters. Some areas the winds have dropped below gale force, but frequent showers will bring gusts back up to gale force periodically. So have dropped the storm warnings in all but the northern outer zones, but have added gale warnings through Friday morning. This is continuing to product waves of 12 to 18 feet. Tonight and Friday a west to northwest swell is expected to move into the waters and build to around 6 to 12 feet at 12 to 14 seconds. The biggest waves are expected in the southern waters.

Friday afternoon or evening the winds are expected to northwesterly as the the low finally moves inland. Northerly winds of 15 to 25 kt are generally expected through the weekend. Early next week it looks like there will be a weak system breaking down the ridge and bringing lighter winds. However, there is some uncertainty on the timing of the system. Late in the week northerlies are expected to return. MKK

HYDROLOGY

Moderate to locally heavy rain showers are expected to continue across the area through Friday, with max rain rates up of 0.30" to 0.50" per hour likely. Heavy shower could promote minor flooding of smaller rivers, creeks and streams with poor drainage will be possible with grounds saturated and all the water going into run-off. Mad River at Arcata and Eel River at Fernbridge could touch Monitor Stages Friday evening/night. Hopland could also touch or exceed slightly minor flood stage (15% chance) on Friday. Otherwise, all main stem river stages are forecast to remain below Monitor or Action stages through Friday. /ZVS

EKA WATCHES/WARNINGS/ADVISORIES

CA... Flood Watch through Friday evening for CAZ101>115.

High Wind Warning until 8 PM PST this evening for CAZ101.

Wind Advisory until 8 PM PST this evening for CAZ102.

Wind Advisory until 2 PM PST this afternoon for CAZ103.

High Wind Warning until 2 PM PST this afternoon for CAZ104>106.

Winter Storm Warning until 10 PM PST Friday for CAZ107-108.

High Wind Warning until 10 AM PST this morning for CAZ109.

Wind Advisory until 10 AM PST this morning for CAZ110>115.

NORTHWEST CALIFORNIA COASTAL WATERS... Storm Warning until 3 PM PST this afternoon for PZZ450-455- 475.

Storm Warning until 11 PM PST this evening for PZZ470.