textproduct: Eureka

SYNOPSIS

Shower activity will continue to gradually diminish today and tonight, with some lingering showers into Saturday. Breezy to gusty northerly winds this evening, with the strongest winds in the exposed ridges in Cape Mendocino. Drier and colder weather is forecast for the weekend and should last into mid next week.

DISCUSSION

A convective line of strong showers and isolated thundertorms moved across the area this morning through midday. The strongest showers produced locally heavy rain, small hail, and gusty winds. Reports of small stream and creek flooding, rock/mudslides, and downed trees have been received, with the highest concentration of impacts noted in Humboldt and Mendocino counties.

A surface low is centered near the Humboldt coast this afternoon, positioned approximately 18 miles northwest of Eureka. The low is expected to move onshore and shift southeast this evening into Saturday. Meanwhile, high pressure rebuilds offshore and into the West Coast, promoting a drying northerly flow aloft. Shower activity will continue to gradually diminish for the remainder of today and tonight, though lingering showers possible into Saturday.

Surface ridging will quickly build in the wake of the low this evening, resulting in a tightening pressure gradient for the coastal areas. Breezy to gusty northerly winds are expected to developed over the coastal headlands and exposed ridges. Overall, this northerly wind surge does not look very strong with very minimal impacts except over the coastal waters and coastal headland where isolated gusts greater than 45 mph are possible (30-60% chance), especially over the exposed terrain in Cape Mendocino. Lower elevations along the coast most likely in the 25-35 mph range this evening.

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 mid next week. The dry weather will likely begin to come to an end as early as Thursday (New Year's Day), but more likely across a greater portion of the area late week. A general consensus between ensemble and deterministic models shows an upper level trough developing over the Gulf of Alaska and digging southward mid to late next week, while the high pressure weakens and shift eastward. WPC/CPC 8-14 day outlook already has NW California back in a slight risk for heavy rain and heavy mountain snow. /ZVS

AVIATION

This afternoon there are some lingering light showers as the upper level trough moves overhead. These are expected to bring occasional MFR or IFR conditions this evening. Winds are expected to switch to the north late this afternoon or evening. Tonight offshore flow sets up and the coastal areas are expected to see generally VFR conditions. However with the recent rain there may be some low clouds or fog that develops towards morning. Inland areas will be a different story. Most areas are expected to see the mid-level clouds clear out. This is expected to allow widespread fog in the valleys later tonight. Saturday this will likely take until midday or early to clear out. MKK

MARINE

The upper level low is moving inland and this has started to shift the winds to north. These are expected to increase to near gale force later this afternoon and tonight with gale force gusts. So have extended the gale warning through the evening in the north and to midnight in the southern waters. The swell is continue to move through the waters at around 7 to 10 feet at 111 to 13 seconds. Southerly wind driven waves are diminishing and will become northwesterly tonight as the winds shift.

Northerly winds of 15 to 25 kt are generally expected through the weekend. Some of the models indicate that there may be some near gale or gale force gusts on Sunday, but so far confidence is not high enough to warrant a gale watch. 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. Thursday or Friday some of the models are now indicating that southerly winds will return. Overall the winds appear to be mainly wind driven through the weekend and into next week with notable swells not expected. The model is showing a small northwest swell building in on Monday. MKK

HYDROLOGY

Latest observations shows Elk River near Falk around 18.28 ft this afternoon, and near to crest. Small stream flooding have been reported on Highway 36 near Carlotta and in Ferndale area this afternoon as result. Additional rainfall is expected this evening into Saturday morning, but this will be mainly light with 12-hour rain range from 0.10" to 0.30". The Eel River at Fernbridge and Mad River near Arcata are both exceeding action stage this afternoon. These are expected to crest this evening, though well below flood stage. California Nevada River Forecast Center (CNRFC) are forecasting the Mad River near Arcata and the Eel River near Ferndale gradually receding later this evening and tonight and reaching below monitor stage Saturday morning. The remainder of the main stem river stages are forecast to remain below Monitor or Action stages. /ZVS

EKA WATCHES/WARNINGS/ADVISORIES

CA... Flood Watch until 10 PM PST this evening for CAZ101>115.

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

Wind Advisory until 2 PM PST this afternoon for CAZ109- 111>115.

NORTHWEST CALIFORNIA COASTAL WATERS... Gale Warning until 7 PM PST this evening for PZZ450-470.

Gale Warning until midnight PST tonight for PZZ455-475.