textproduct: Eureka

SYNOPSIS

A mid period westerly swell will bring a moderate risk for hazardous beach conditions Saturday afternoon. A much more energetic westerly swell group will bring a high risk for sneaker waves Monday through Tuesday next week. Otherwise, dry and seasonably cool weather is forecast for the next 7 days.

KEY MESSAGE

* Dry and seasonably cool weather expected through the next 7-days, with a mix of sunshine and clouds.

* A Moderate Risk of sneaker waves risk is expected along the Northwest California beaches this afternoon and early evening.

* Sneaker Waves risk increases to High on Monday and continue through Tuesday. * Blustery north and east-northeast winds over the ridges Tuesday night into Wednesday.

DISCUSSION

Latest GOES-West satellite imagery depicts stratocumulus continuing to stream eastward across the area, while coastal low clouds persist overnight. Despite the high-level cloud cover, chilly overnight temperatures in the mid to low 30s have been observed in Trinity, portions of interior Mendocino and Lake counties. Southern Lake County have not seen a widespread killing freeze yet this Fall. A Frost Advisory is now in effect until 9 AM this morning for southern Lake County. Dry weather and seasonably temperatures continue today, with a mix of sunshine and clouds.

A semi-stationay upper-level ridge over the northeastern Pacific will act as a blocking pattern through the next 7-days, forcing any "inside slider" weather disturbance to track southward from the Pacific NW. A dry shortwave trough will swoop down across the Pacific NW into the Great Basin over the weekend and serve to re- establish an offshore wind regime across the area by Sunday. Breezy northerly winds will develop along the coastal headlands and exposed ridges by Sunday. Offshore winds are expected to develop over the higher terrain across the interior Sunday evening and increase into Monday morning, with the strongest winds anticipated over the eastern portion of Lake County where gusts up to 25-35 mph are possible. Frost and freezing morning temperatures will also be possible. Average low temperatures for this time of year are in the low to mid 30s in the interior valleys and agricultural interests have ended. Frost and freezing morning temperatures could kill tender plants left outside in the cold.

A third shortwave trough may (18% chance) generate a few fleeting light showers or sprinkles for Del Norte and mountains of Trinity Monday-Tuesday. This shorter wavelength trough will carve out a larger scale trough that will head southward over central and southern Cal by Wednesday. Another possible outcome is for the trough to dig much farther east over the Great Basin with a massive ridge aloft taking hold over the forecast area by Wednesday. Blustery N and E-NE winds will develop Tuesday night- Wednesday for the higher terrain and perhaps Lake County. E-NE wind gusts to 35-45 mph will be possible over the ridges. The air mass is not forecast to be exceptionally cold next week either. With dew points in the 20s, calm winds in the valleys and clear skies overnight, frost and freezing temperatures will once again crop up for areas that have not had a so called killing freeze yet. Fog and low clouds will no doubt (a 100% chance) be a nightly occurrence in the interior river valleys, especially Humboldt and Trinity. Cold weather advisories for wind chill may also be necessary for wind gusts around 10-15 mph. Our long stretch of dry cool weather may finally come to an end late next week. All global ensemble systems indicate increasing probabilities for 0.10 inches of precip in 24hr over multiple days from Dec 6 to Dec 8.

AVIATION...06z TAFs

Ceilings have gradually dropped through the evening, with mostly MVFR ceilings along the coast around midnight. There is high model disagreement on the exact evolution of conditions into Saturday morning. Most models show at least borderline IFR to MVFR ceilings through the early morning, especially around Humboldt Bay, with IFR to LIFR fog for many interior valleys including Ukiah.

Interior conditions will most likely quickly clear after sunrise. Most ensemble members show lifting to MVFR or VFR along the coast during the day Saturday, but about 30% of models show MVFR ceilings more persistent through the day. A weak trough passing to the north may help lift ceilings Saturday night, but will also promote onshore flow conducive to marine layer formation. With those two competing forces, ensembles continue to show uncertain and mixed conditions, but with little potential for widespread, disruptive LIFR conditions. /JHW

MARINE

Weak to moderate northerly winds have built in all across the waters. Northerly winds will continue to increase in the outer waters with near gale force gusts in the southern outer waters Sunday gradually spreading northwards. North winds and steep short period seas will stay restricted to the outer waters and will briefly weaken again around Monday. There is strong agreement, however, that north winds will push back closer to shore around mid next week with periods of strong gale force gusts.

Aside from the winds, a minor mid period westerly swell will build up to around 8 feet late Saturday into Sunday, but this swell will quickly decay. Another, much longer period swell will build around Monday into Tuesday up to around 12 feet. Neither swell will be particularly steep but will dominate the inner water sea state where short period seas are calm. /JHW

BEACH HAZARDS

A series of mid period westerly swells will continue to impact the waters through the weekend. The next swell will build up to 8 feet at 14 seconds beginning Saturday afternoon into Sunday. With mostly calm short period seas, the forerunners of this swell especially will pose a moderate sneaker wave risk Saturday evening with unexpected and inconsistent surf on area beaches Saturday afternoon.

A second, stronger sneaker wave risk is possible as longer period swell builds Monday into Tuesday. The very long period of this swell up to 22 seconds will make waves particularly deceiving with the swell likely to build in rapidly with little warning. Short period seas building closer to shore will lessen the overall risk by around mid week. /JHW

EKA WATCHES/WARNINGS/ADVISORIES

CA... Beach Hazards Statement Saturday afternoon for CAZ101-103.

Beach Hazards Statement from Saturday afternoon through Saturday evening for CAZ104.

Beach Hazards Statement from Saturday afternoon through Saturday evening for CAZ109.

Frost Advisory until 9 AM PST Saturday for CAZ115.

NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory from 11 AM to 11 PM PST Sunday for PZZ455-470.

Small Craft Advisory from 11 PM Saturday to 5 AM PST Monday for PZZ475.