textproduct: Eureka

SYNOPSIS

Another strong storm system will bring additional moderate to heavy rain, mountain snow, and strong winds this evening into Friday. Showers activity will gradually to diminish throughout the day on Friday. Drier and colder weather is forecast for the weekend.

KEY MESSAGES

* Strong to very strong southerly winds, with moderate to heavy rain, and embedded thunderstorms area expected from this evening and into Friday. * Flood Watch in effect through Friday evening for Del Norte, Humboldt, Trinity, Mendocino and Lake counties.

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

* Hazardous marine and coastal conditions ere expected late this afternoon through Thursday.

DISCUSSION

Conditions improved today as the previous potent Storm system exited east-northeast of the area. Attention turns to a second storm system associated with a large-scale trough offshore the West Coast. This system is expected to tack northeast, impacting NW California this evening through Friday with renewed winds, rain and mountain snow. Current satellite and Doppler radar imagery depict a moisture plume, with a band of showers and embedded thunderstorms approaching the coastal waters quickly from the southwest. Strong to very strong southerly winds are expected this evening as the surface pressure gradient tightens this evening and a low level jet at 925mb from 60 to 70 kts develops along the coast. It will be more unstable and strong winds aloft will most likely mix down to the surface, especially near or along the surface front. Southerly winds are expected to gradually increase this evening, and peak up after midnight. The strong winds area expected to develop from south to north, impacting first Mendocino County tonight and spreading northward into Del Norte County late tonight/early morning. Gusts from 45 to 60 mph are expected for the Mendocino Coast tonight through Thursday morning; up to 50 mph is expected for lowest elevations in Mendocino Interior, Lake, Northern Humboldt Coast, and Del Norte Interior. While 50 to 70 mph is forecast over the coastal headlands and higher terrain of interior Del Norte and Humboldt... although locally higher gusts are possible over the highest terrain. A High Wind Warning is in effect for Coastal Del Norte, southwest Humboldt, Humboldt Interior and Mendocino Coast from this evening/tonight through Thursday. Wind Advisory is in effect for Northern Humboldt Coast, Del Norte Interior, Mendocino Interior and Lake counties through Thursday morning.

CAMs shows a line of organized convection activity along the frontal system translating from southwest to northeast around midnight, as the low remain spinning off the coast. Periods of moderate to locally heavy rain rates is expected. Colder air aloft will bring increasing instability tonight through Thursday. This will bring a potential for isolated to scattered thunderstorms, lightning strikes, some small hail, locally heavy downpours of rain and erratic gusty winds to the coast through the day Thursday, possibly into Friday.

Cold air moving in from the deep trough will support lower snow levels. Snow levels may drop further to 3500- 4000 ft. Total snow amounts of 2-3 ft through Friday is possible at Scott Mountain pass, while up to a foot is possible above at the highest passes of Highway 36 (around 4000 ft), depending on how much the snow levels lower. A Winter Storm Warning is in effect from Wednesday evening to Friday evening for elevations above 4000 feet in Trinity County.

Friday the models are in general agreement that the low will start to move out of the area. Another surface low could develop and strong westerly or northwesterly winds will be possible on the backside of the surface low. This will need to be watched.

High pressure is expected to start to move into the area bringing a break in the rain and wind for the weekend. The valleys will likely see widespread fog and low clouds each night and through at least the morning. Frost and freezing temperatures will also be possible for the North Coast, especially Sunday morning. Cooler weather and perhaps some precip around mid next week, other mainly dry weather is in for a change. /ZVS

AVIATION

A period of mostly VFR conditions will persist today into early this evening with Northwest California situated in between storm systems. Another very strong system will approach the area tonight and bring a return of rain, chances for thunderstorms, and strong wind gusts to the TAF sites. Wind gusts could once again exceed 40kt, particularly during periods of strong shower or thunderstorm activity. The current best chance of thunderstorms looks to be between 8Z and 12Z overnight followed by additional storms through the day on Thursday. Strong wind shear is likely tonight before the winds become gusty at the TAF sites. /RPA

MARINE

Seas continue to subside behind the departing storm force system that moved through the waters last night. Some seas are still above 10 ft, but generally the steepest seas have subsided so the hazardous seas warning has been replaced with small craft advisories. Quickly tonight winds will ramp up sharply again back into gale and then storm force across all zones. Unlike the last system that moved through quickly, this one will be much slower with an area of low pressure likely to spin off the Northwest California coast for about 18 hour or so. While the low remains strong, gale to storm force wind gusts are likely along with periods of strong showers or thunderstorms focusing some of the stronger wind gusts. A few waterspouts will be possible with the stronger storms later tonight and through the day Thursday. Very steep seas, exceeding 20 feet in some areas, are expected from this persistent wind.

As the storm fills and weakens on Friday the winds will subside and seas will decrease into Saturday. It is likely that some additional headlines will be needed as the weakening process occurs and seas remain elevated, but generally conditions will improve over the weekend as light to moderate northerlies develop. /RPA

HYDROLOGY

Latest observations shows the Elk River around 15.22 feet this afternoon, and slowly receding. Small stream flooding continues on Highway 36 near Carlotta and in Ferndale area this afternoon as result. Additional rainfall is expected this evening through Friday. Convective signature shows up tonight and thursday morning with HREF max rates 0.30 to 0.50 in/hr associated with isolated cores. All main stem rivers are forecast to remain below Monitor or Action Stage through Friday. 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. /ZVS

EKA WATCHES/WARNINGS/ADVISORIES

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

High Wind Warning from 2 AM to 8 PM PST Thursday for CAZ101.

Wind Advisory from 2 AM to 8 PM PST Thursday for CAZ102.

Wind Advisory from 10 PM this evening to 2 PM PST Thursday for CAZ103.

High Wind Warning from 7 PM this evening to 2 PM PST Thursday for CAZ104>106.

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

High Wind Warning from 7 PM this evening to 10 AM PST Friday for CAZ109.

Wind Advisory from 8 PM this evening to 10 AM PST Thursday for CAZ110>115.

NORTHWEST CALIFORNIA COASTAL WATERS... Storm Warning from 11 PM this evening to 3 PM PST Thursday for PZZ450.

Storm Warning until 3 PM PST Thursday for PZZ455-475.

Small Craft Advisory until 7 PM PST this evening for PZZ470.

Storm Warning from 7 PM this evening to 11 PM PST Thursday for PZZ470.