textproduct: Eureka

SYNOPSIS

Chilly overnight temperatures and patchy frost is possible Tuesday and Wednesday. Generally dry weather and warm temperatures through mid week. There is a chance of light rain and sprinkle Day for Del Norte and Northern Humboldt counties on Thanksgiving Day, followed by dry and cooler weather conditions through the weekend.

DISCUSSION.

A weakening front brought light rain and sprinkles across the northern portion of the forecast area early this morning. High pressure quickly builds back in the wake of the front this afternoon and evening, promoting drying northerly flow. Coastal stratus have been stubborn to scattered out early this afternoon. While interior valley low clouds continue slowly lift and clear and keeping temperatures lower than expected in that specific area, especially farther north of Mendocino County. High clouds will continue to stream downslope from the ridge across the area, which may limit the amount of afternoon sunshine.

Tonight, a dry offshore flow (easterly wind) is expected to develop across the area into Tuesday, with some breezy conditions over the higher terrain. Areas of fog and patchy dense fog are anticipated along the shelter valleys, mainly in Humboldt and Mendocino counties. Lingering cold air will promote overnight temperatures to be a few degrees cooler than today's readings, with lows in the upper 30s to mid-40s for the coastal areas and generally in the upper 30s inland. The lowest temperatures are expected for Trinity County, with temperatures as low as 33 degrees in the coldest areas like Hayfork and Ruth. A Frost Advisory is in effect from 9 PM this evening to 9 AM PST Tuesday for Trinity County.

Ridging will continue to build and strengthen over the area Tuesday into Wednesday, promoting quiet weather conditions with a drying and warming trend. Dry offshore flow, especially at nights, keeping the air dry and helping to scour out some of the low-level clouds, which should lead to more afternoon sunshine compared to today. High temperatures are forecast to range from mid- to upper-50s along coast and mid-60s inland. Additional warming is expected Wednesday afternoon, with highs in the upper 60s in the warmest interior valleys. Any areas that do have fog develop overnight will likely be slow to clear and may be lower than forecast.

A subtle shift in the weather pattern is expected for Wednesday night (Thanksgiving Eve) and Thursday (Thanksgiving Day). The high pressure begins to shift eastward as a shortwave trough and its associated surface low move toward the Pacific Northwest. A weakening cold front crossing the area will bring light rain and sprinkles for Thanksgiving Day, for Del Norte and Northern Humboldt counties, with most rainfall total under a tenth of an inch. Elsewhere, increasing cloudiness and mostly dry conditions are expected.

Looking ahead for Friday and through the weekend, the general consensus between ensemble and deterministic models shows an upper-level trough dropping southward while an upper level ridge builds in the Gulf of Alaska. There is, however, high uncertainty in the position of this upper-level trough, with models showing variable solutions, especially over the weekend. The ECMWF, GFS ensemble means and clusters show similar solutions with the upper trough dropping south over land and becoming positively tilted. This solution typically leads to dry and colder weather. Just a 22 percent of the cluster mean are showing widespread precipitation, while the 78 percent of the members suggest dry weather conditions. /ZVS

AVIATION...(18Z TAFs)

Conditions are improving today regarding flight categories, after light rain overnight into the morning TAF period. KCEC likely to remain in VFR/MVFR through the TAF period with mid level clouds, 15000ft at their lowest and scattered to broken until Tuesday evening when the next moisture push clips the northern edge of the CWA, wrapping around a ridge primarily aimed at Oregon. Low probability for KCEC getting any precip and even less for KACV Tuesday. Otherwise, winds turn easterly by the evening at KCEC and KACV. Light winds and VFR categories are expected at KUKI through the TAF period. /EYS

MARINE

Northerly winds return and increase across the area, easing by early Tuesday morning with the southern outer waters retaining most of the higher winds south of Cape Mendocino. Models have trended slightly weaker with these winds, but they still look to be around 15 to 20kt. The swell is gradually dropping, but looks to be dropping slower than expected in the southern waters. So have extended the small craft advisory through Monday evening to highlight the northerly winds as well. There may be a short break between these two, but at this point it looks like the waves will remain close to ten feet until the winds increase.

Tuesday and Wednesday are generally expected to see fairly light winds. Wednesday afternoon these are expected to start becoming southerly again as a frontal boundary approaches the area. The models continue to struggle with the strength of the system on Thursday and how far south it will come. In general it looks like the models have shifted it slightly to the north making the southerly winds a bit lighter. They generally look like they will still peak around 20 kt in the northern outer waters with lighter winds farther south. Some of the models to show a lighter scenario than this. Friday stronger northerly winds are expected to return and models are in fairly good agreement on this. For the weekend the models have trended towards keeping the northerly winds in place. Some of the models show these northerly winds fairly strong at around 30 kt.

The swell is expected to continue to diminish Tuesday to around 6 feet at 12 seconds. Wednesday these swell heights drop to around 4 to 5 feet at 11 seconds. The wind driven waves are expected to diminish Tuesday night setting up a very calm day on the water for Wednesday. Total wave heights look to be around 4 feet with a dominant period of 12 seconds. The next swell is expected to build in Thursday morning, but this is now looking fairly small. MKK /EYS

EKA WATCHES/WARNINGS/ADVISORIES

CA... Frost Advisory from 9 PM this evening to 9 AM PST Tuesday for CAZ107-108.

NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory until 3 PM PST this afternoon for PZZ450.

Small Craft Advisory until 2 AM PST Tuesday for PZZ455.

Small Craft Advisory until 1 AM PST Tuesday for PZZ475.