textproduct: Eureka

SYNOPSIS

Cold temperatures this morning for the inland valleys with daytime temperatures mild for the season. Dry conditions will prevail with pleasant effects, similar to previous patterns with ridging in place.

DISCUSSION

The effects of a dry cold air mass will be felt overnight into Monday morning. A maritime polar (mP) air mass will be advecting colder air mostly to the north of our CWA, while the resilient ridging pattern blocks most of the effects, 850mb and surface pressure maps show some of the flow wrapping around the ridge towards our CWA. Low temperatures are expected in the Trinity, Mendocino, and Lake county valleys. Model soundings show cold surface temps with a decoupled inversion/warmer aloft, which is indicative of a stable profile. Deterministic models have temperatures a few degrees warmer than than the National Blend. Decoupled valleys have been observed a few degrees cooler and our forecasts reflect the trend. Some of the cooler areas like Covelo and Hayfork could get as low as 19-20F. Weaverville as low as the mid 20's and Ruth in the upper 20's overnight into Monday. Tuesday morning's low temps will be a few degrees warmer for these locations with a similar set up.

High pressure aloft will build over the West Coast overnight into Monday. A Rex Block pattern is likely to form, with a major 500mb height anomaly setting up over the region on Tuesday, resulting in multiple days of dry and stable weather along warmer temperatures. This will allow dry east-northeasterly winds developing across the area. Moderate breezes are forecast to develop over the higher terrain across the interior late tonight through Monday morning. Areas of low clouds and fog are expected to develop across the interior valleys tonight into Monday morning. Overnight low temperatures are forecast to be in the chilly side with freezing minimums highly probable for valleys in Trinity and perhaps portions of interior Humboldt, interior Mendocino and Lake counties Monday morning.

Dry offshore flow (easterly winds), especially at night, will keep the air very dry and reinforce the warming trend by mid week. Highs are forecast to warm up into the lower to mid 70's in the interior next week. South-facing exposures and higher terrain stand the best chance for highs in the 70's, while valleys trapped under the nocturnal inversion with night and morning fog may not warm up even into the lower 60s, especially in Trinity and northern interior Humboldt. Even the coastal areas are expected to warm up to mid 60s to low 70's before the sea breezes develop, especially on Wednesday.

Global Ensembles and deterministic model guidances are suggesting a break- through in the westerlies or undercutting of the blocking ridge Thursday night into Friday. The forecast becomes more uncertain on Saturday, as some model guidance suggests dry weather will continue while other guidance suggests precipitation will return to the area. There is currently a 25-50% chance of rain will return as early as late Saturday, and a 40-70% chance rain will return as early as Sunday. Stand by for more details as the situation develops. /ZVS /EYS

AVIATION

Clouds formed along much of the coastline during the evening and expanded overnight with LIFR conditions in most locations. Visibilities below airport minimums will be possible at times through the morning. Farther inland some overnight fog will also form with a possibility of a few hours of fog in the UKI area around daybreak. This is not included in the TAF at this time with probabilities less than 20 percent at UKI specifically. Clouds will mix out across the region during the morning hours with VFR returning at the TAF sites by late morning. Another round of low clouds will be possible again Monday night, but light offshore flow could reduce the coastal coverage. /RPA

MARINE

A westerly swell will continue to move through the waters this morning with seas above 10 feet for most locations into Monday afternoon. High pressure will build over the west coast this week with light winds expected over the coastal waters. Seas will subside on Tuesday into Wednesday with conditions likely to remain below small craft. Another large westerly swell will build into the waters Thursday into Friday with heights expected to be around 11-13 feet at 15 seconds. With winds remaining light to moderate, short period seas will remain small and westerly swells should be the dominating wave through the forecast period. /RPA

BEACH HAZARDS

A long period westerly swell train continues today with heights between 10 and 13 feet with periods near 15 seconds. This swell may be too large for sneaker waves, though it could still pose a threat to beachgoers. Breakers up to 16 feet for west and northwest facing beaches are forecast based on average beach slope profiles through Monday. Beachgoers venturing near or in the surf zone tonight or early Monday morning should remain vigilant. Avoid rocks, jetties and steep beaches. Another large swell may bring slight sneaker wave threat Thursday into Friday. /RPA

EKA WATCHES/WARNINGS/ADVISORIES

CA... None. NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory until 4 PM PST this afternoon for PZZ450-455-470-475.