textproduct: Eureka

SYNOPSIS

Unseasonable warmth with widespread minor heat risk in the interior is forecast to abate this weekend into early next week. Coastal northerlies will increase on Saturday after passage of a front. Next chance for rain is expected Tuesday into Wednesday.

DISCUSSION

A massive 500mb height anomaly (GPH 594dM) centered over the SW U.S. and extending NW over our forecast area continued to result in max temperatures well above mid March normals (30-year average) today in the interior. High temperatures are forecast to peak into the mid 80s and lower 90s in Mendocino and Lake Counties today. Del Norte, Humboldt and Trinity will most likely peak in the mid 70s to upper 80's again this afternoon. This is 20F or more above mid March averages. Overnight low temperatures have been generally cool under the dry airmass and light wind regime in many of the interior valleys. A few of the colder valleys in our forecast area have been dipping down into lower to mid 30's after warming into the lower to mid 80's. As result the heat risk is forecast to remain minor, but may still impact those extremely sensitive to heat and/or have no way to keep cool. Moderate heat risk is forecast for mostly Lake County again on Friday where overnight low temperatures have been warmer, in the 50s to mid 60s, for the higher terrain and within the thermal belt. The above normal daytime warmth is forecast to continue for one more day, Friday, for the Mendocino and Lake, while daytime highs diminish some for the northern zones in response to an offshore trough. This trough will knock down 500mb heights and induce an onshore flow for the region. Temperatures will cool down more substantially on Saturday after slight air mass cooling with a front, aided by gusty northerlies in the afternoon. Highs are still forecast to remain above normal on Sunday as offshore flow re-emerges and areas of minor heat risk spring up again in the interior; mainly for Lake, Trinity and interior Mendocino.

Coastal areas remained much cooler today even under greater sunshine. Satellite showed stratus and fog just offshore over the coastal waters this afternoon. With less stratus and fog compared to yesterday, temperatures were warmer. As of 2pm, temps were in the lower 60's along the North Coast. Just a few miles further inland it was much warmer, in the lower 70s. The mass of stratus and fog offshore will linger near the coastline tonight and Friday and may push into the adjacent river valleys. Patches of fog with vsby 1/4SM or less will be a distinct possibility again. Fog was locally dense around Humboldt Bay this morning, but not widespread. Offshore winds cleared most of the fog out by mid morning Thu. Onshore breezes this afternoon will likely draw in the cool-damp marine air and fog may once again pose a hazard to navigation.

Broad flat riding with above normal 500mb heights will dominate the weather scene for Northwest California this weekend through early next week. This will ensure dry weather with above normal daytime high temperatures. Patches of mist and coastal drizzle will be possible with a decaying front early Sat, otherwise the next formidable chance for rain will arrive Tue-Wed next week. Deterministic models continue to vary widely with timing and amounts. NBM has quite the 24-hr spread too so stay tuned for updates and more details.

Ridging springs back around mid next week after our brief spat of rain Tue or Wed. Generally dry conditions with above normal interior high temps are expected. Overnight low temps may cool down mid or late next week for perhaps low end frost freeze concerns.

AVIATION

Coastal stratus with patchy dense fog, especially around Humboldt Bay, eroded away from the coast by mid to late morning. VFR conditions are expected to prevail until later this evening. While most terminals in the interior are expected to remain VFR through the TAF period, coastal stratus will once again affect coastal terminals through the overnight hours. The high pressure system over the region will weaken through the night, while a shortwave trough approaches the Pacific NW. This will aid in deepening the coastal stratus which will lead to greater coverage into tomorrow morning. This will most likely mean more widespread MVFR/IFR conditions a bit further inland and less of a chance for areas of dense fog. /JLW

MARINE

As high pressure gradually pushes east, the pressure gradient over the area has reached it weakest, allowing for gentle to mostly calm north winds through today generally below 15 kts. As high pressure finally breaks down, stronger winds will begin to return first to the southern waters Friday afternoon with gusts near 25 kts. Conditions will build to near gale during the day Saturday in the outer waters, with strong winds over 25kts pushing even into the inner waters Saturday afternoon and evening.

Calmer winds will generally limit any meaningful short period seas through today. That said, a minor, long period southerly swell and modest mid period westerly swell combine to create at least some seas up to 6 feet through tonight. Steeper short period seas will return Friday and into the weekend with the wind allowing for wave heights in excess of 10 feet by Saturday. /JHW

EKA WATCHES/WARNINGS/ADVISORIES

CA... None. NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory from 11 PM Friday to 3 PM PDT Saturday for PZZ455.

Small Craft Advisory from 3 AM to 3 PM PDT Saturday for PZZ470.

Small Craft Advisory from 5 PM Friday to 3 PM PDT Saturday for PZZ475.