textproduct: Eureka

SYNOPSIS

High risk for sneaker waves Monday through Tuesday. King Tides return on Tuesday and then peak Thursday and Friday. Frost and freezing temperatures possible during the morning hours for the Humboldt Bay area Monday through Thursday. Dry weather expected to prevail for this week, followed by a chance for rain late Friday and next weekend.

KEY MESSAGES

* High risk of sneaker waves is expected along the Northwest California beaches from this morning through Tuesday morning.

* King Tides from December 2nd-7th, and may lead to minor coastal flooding in low-lying areas around Humboldt Bay, Crescent City and Arena Cove.

* Dry and seasonably cool weather expected through Friday, followed by a chance of rain over the weekend.

DISCUSSION

High pressure is forecast to remain parked over the northeastern Pacific through Friday. Dry weather is highly probable for NW California.

Offshore flow (E-NE winds) has been increasing across the interior ridges overnight, especially in Lake County. Gusts from 25 to 35 mph are most likely into this morning over the exposed ridges in the eastern portion of Lake County. Winds are expected to diminish throughout the day as the surface pressure gradient relaxes. Satellite imagery depicts patchy low clouds near the coastal areas and patchy fog developing along the river valleys overnight. As of 12 AM PST, high dewpoints in the upper 30s to low 40s have been precluding frost conditions along the coast north of Humboldt Bay. However, frost remain probable, 70-90% chance, for the north bay (Arcata, McKinleyville, Fieldbrook) as light easterlies drive dewpoints down into early this morning. Chance for a freeze is much lower, only 10-20%.

Another "insider trough" will drive southward across the Great Basin toward southern California Tuesday through Wednesday. This will bring increasing high clouds across the area on Tuesday. Ridging strengthen and upper-level heights rises across the Pacific Northwest in the wake of the "insider trough". Stronger and blustery coastal northerly winds are expected in the wake of this trough by Tuesday afternoon. Gusts around 20-30 mph will be possible. East-northeast winds will also develop Tuesday night into Wednesday for the higher terrain and over Lake County, where gusts from 30-40 mph will be possible over the ridges. Ridge level gusts to 40-45 mph are on the limbs of the distribution (95th percentile and ensemble max) over the high mountain peaks.

Chance for frost around Humboldt Bay area Tuesday morning decreases to around 30% as another shortwave trough generates more cloud cover tonight. Offshore flow resumes Tuesday night into Wednesday morning and the chance for frost increases again to around 40-80% for the Humboldt Bay area. Chance for 32F in the north of Humboldt Bay increase to about 30-50% Wednesday morning. Meaningful chances for early morning frost for the North Coast is expected to continue Thursday morning.

The air mass is not forecast to be exceptionally cold next week. With dew points in the 20s, calm winds in the valleys and clear skies overnight, frost and freezing temperatures will once again be a forecast challenge for inland areas that have not had a freeze yet. Cold weather advisories for wind chill may also be a factor with winds around around 5-10 mph and minimum temperatures in the lower to mid 30s. Fog and low clouds will form each and every night (100% chance), though the coverage will decrease as the air mass slowly dries out each day this week.

Massive 500mb ridge appears to flatten out Friday and into next weekend. All global ensemble prediction systems continue to indicate increasing chances for 0.10 to 0.25 inches of rain in 24 hours through the weekend. 24 hour chance for > 1 inch is no more than 20%. It is interesting to note that the majority of WPC ensemble clusters are drier than the grand ensemble. The ensemble mean is by no stretch very wet either. It could be wet or it could be dry or both over multiple days. Stay tuned.

AVIATION...(6Z TAFs)

VFR conditions are expected for the coastal terminals as offshore flow limits stratus impacts. The interior valleys, including UKI, could once again see LIFR stratus and fog early Monday morning. Ceilings and visibilities are likely to improve after sunrise, with generally VFR conditions likely by the afternoon. JB

MARINE

Northerly winds have started to ease slightly and pull away from the coast. Steep seas will largely be confined to the outer waters for much of the day Monday. This will combine with a long period westerly swell which will gradually build to up to 8 ft by Tuesday. Combined seas of 8-12 ft are possible. Stronger northerly winds return Tuesday, with gales possible south of Cape Mendocino. Nearshore winds will be lighter, but peak gusts of 15-25 kts are still possible. North winds ease slightly and pull offshore by Wednesday. Conditions gradually improve through the end of the week. JB

BEACH HAZARDS

A long period swell (up to 22 seconds) will suddenly build into the waters up to 8 feet midday Monday and continue into Tuesday. With calm winds near shore, this swell will pose a high sneaker wave risk with sudden high surf on beaches in otherwise calm seeming conditions. Take extra care to keep distance from the water. Building short period seas and shortening swell period will decrease the risk by Tuesday afternoon. /JHW

COASTAL FLOODING

King Tides return on Tuesday. High astronomical tides are predicted from Tuesday through Sunday for Northwest California. The combination of a high astronomical tides and steep, short-period northerly waves will increase the risk of minor coastal flooding around Humboldt Bay on Wednesday, including King Salmon and low-lying roads near Arcata Bottoms. Minor flooding potential in low-lying areas around Humboldt Bay, and along much of the coast is then expected through next Sunday. /ZVS

EKA WATCHES/WARNINGS/ADVISORIES

CA... Beach Hazards Statement from 8 AM PST Monday through Tuesday morning for CAZ101-103-104-109.

Frost Advisory from 4 AM to 9 AM PST Monday for CAZ103.

NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory until 4 PM PST Tuesday for PZZ470-475.

Gale Watch from Tuesday afternoon through Wednesday morning for PZZ475.