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 the upcoming week, followed by a chance for rain late Friday and next weekend.

DISCUSSION

A massive upper-level ridge is forecast to remain parked over the northeastern Pacific through next week. Dry weather is highly probable for NW California (greater than a 90% chance).

Northerlies have been increasing over the coastal ranges this afternoon in the wake of a shortwave trough moving over the Great Basin. A few peak gusts around 25-30 mph will be possible (60% chance) for the exposed coastal ridges and headlands by this evening. Wind directions over land will shift to E-NE later tonight and few gusts to 25-35 mph over exposed ridges in Lake County will be possible (a 70-80% chance).

Northerlies are forecast to ramp up again late Tue into Wed as another dry shortwave trough follows a similar track. Stronger and blustery coastal northerly winds are expected in the wake of this trough by Tue afternoon. ECMWF ensemble mean peak wind gusts have been trending higher for coastal low lands. Gusts around 20-30 mph will be possible. E-NE winds will also develop Tue night-Wed for the higher terrain and over Lake County. E-NE wind gusts to 30-40 mph will be possible over the ridges. Ridge level gusts to 50-55 mph are on the limbs of the distribution (95th percentile and ensemble max) over the high mountain peaks.

Frost and freezing morning temperatures will also be possible for coastal areas, primarily for the Humboldt Bay area, Monday through Thursday. Stratocumulus low cloud cover over Humboldt Bay and Eel delta tonight may hinder the longwave cooling in the Eel delta and around Eureka. Offshore flow is expected later tonight, but does not appear strong enough to completely scour out the low cloud cover. Frost will be most probable, 70-90% chance, for the north bay (Arcata, McKinleyville, Fieldbrook) as light easterlies drive dewpoints down through the night. Chance for a freeze is much lower, only 10-20%.

Chance for frost around Humboldt Bay area Tuesday morning decreases to around 30% as another shortwave trough generates more cloud cover Mon night. Offshore flow resumes Tue night and Wed morning and the chance for frost increases again to around 60-80% for the Humboldt Bay area. Chance for 32F in the north bay increase to about 30-40% Wed morning. Meaningful chances for early morning frost for the North Coast is expected to continue Thu 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...(18Z TAFS)

Low clouds continue to clear for terminals across the region this afternoon. Overnight tonight and into Monday morning, offshore flow across the area will bring gusty winds over ridges. Also, this offshore flow will most likely inhibit marine stratus formation for most coastal terminals. There could still be a chance for some interior valley fog overnight, if winds remain calm. /JLW

MARINE

Moderate northerly winds in the outer waters will continue to increase through the day today with near gale force gusts to 30 kts by later this evening. The inner waters will remain markedly calmer with few gusts over 15 kts near shore. Northerly winds will shunt further offshore by Monday afternoon, but there is good agreement that winds will rapidly return around mid week and push more into the inner waters with high chances (50 to 60%) of gale force conditions.

Aside from the winds, a minor mid period westerly around 8 feet is currently impacting the waters and will quickly decay today. 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 long period swell (up to 22 seconds) will suddenly build into the waters up to 12 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 Monday morning through Tuesday morning for CAZ101-103-104-109.

NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory until 11 PM PST this evening for PZZ455.

Small Craft Advisory until 3 AM PST Tuesday for PZZ470-475.