textproduct: Eureka

SYNOPSIS

Cold overnight temperatures and patchy frost is possible today 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 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 28 degrees in the coldest areas like Hayfork and Ruth. A Frost Advisory is in effect until 9 AM PST this morning for northern Trinity County and Southern Lake County. A Freeze Warning is also in effect for Southern Trinity, Northern Lake, and NE Mendocino Counties until 9AM.

Ridging will continue to build and strengthen over the area through the day into Wednesday, promoting quiet weather conditions with a drying and warming trend. Dry offshore flow, especially at night, will scour out some of the low-level clouds near the coast, 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 have high temperatures that are lower, leading to lower than usual forecast confidence.

A subtle shift in the weather pattern is expected for Wednesday night and Thursday (Thanksgiving Day). High pressure begins to shift eastward as a shortwave trough and its associated surface low move toward the PacNW. 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 totals 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, leading to additional inland freezing temperatures this weekend. Only ~20% of the cluster mean are showing widespread precipitation, while the ~80% suggest dry weather conditions. /ZVS

AVIATION

High pressure is building in and offshore flow is keeping the coastal areas clear. Inland valleys are seeing fog across many of them. Some fog may creep into UKI towards morning, but confidence is low on this. The fog is expected to take its time clearing once again across the interior valleys. Tonight fog is expected to return across the interior valleys. Offshore flow is expected to be slightly weaker along the coast and it is possible some stratus will develop by Wednesday morning. MKK

MARINE

Northerly winds are continuing to diminish this morning as high pressure moves off to the east of the area. The northwest swell continues to slowly diminish and is expected to be around 6 to 8 feet by sunrise. The winds driven waves are diminishing as the winds do. They may drop off more quickly than forecast making for quiet wind and waves on the water for the remainder of the day. The calm conditions linger through much of Wednesday as well and the swell continues to slowly diminish.

Wednesday afternoon these are expected to start becoming southerly again as a frontal boundary approaches the area. The models continue to weak the southerly winds and keep the system farther north. Now it looks like the stronger southerly winds will only around 10 to 15 kt. Thursday afternoon northerly winds return and are expected to strengthen on Friday. Models are still 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, especially in the southern waters.

The next swell is expected to build in on Thursday. The most recent model runs are showing this building to 8 to 12 feet at 15 seconds. However the GFS and the Global Wave Watch (Waves from GFS winds) have been seeing some fairly big differences from run to run. So confidence is lower than normal on these wave heights. MKK

EKA WATCHES/WARNINGS/ADVISORIES

CA... Frost Advisory until 9 AM PST this morning for CAZ107-115.

Freeze Warning until 9 AM PST this morning for CAZ108-111- 114.

NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory until 2 AM PST early this morning for PZZ455.

Small Craft Advisory until 5 AM PST early this morning for PZZ475.