Marine Weather and Tide Forecast for Mendocino, CA

KEY MESSAGES:

* Elevated to locally critical fire weather conditions through Friday evening for Lake, eastern Mendocino and eastern Trinity Counties due to low RH's and stronger west and northwest winds.

* Gusty and locally strong coastal northerlies this evening.

* Much cooler Friday and Saturday in the interior, followed by a warming and drying trend early to mid next week.

* Light rain possible for Del Norte and northern Humbodlt Friday afternoon and evening.


DISCUSSION

Prime concern tonight through Friday evening will be strong and gusty west and northwest winds across the interior. Gusts to 20-30 mph are probable (60-70% chance). Higher terrain and ridges may even gusts 35-45 mph as an unseasonably cold 500mb low drops down from the Gulf of AK on Friday. Friday looks to be the strongest wind day while humidity generally increases. Portions of Lake, eastern Mendocino and eastern Trinty will likely have low humidity around 20-25% on Friday. With the trough enhancing diurnally westerly and northwesterlies breezes on Friday, elevated to locally critical fire weather conditions are forecast. Risk for small and fast spreading grass or brush fires will increase.
Winds may not line up exactly with low RH's for 8 hours or more for a red flag warning. Now a few windier higher elevations will probably reach or exceed 8 hours with these stronger winds on Friday even with slightly higher humidities. We will message this fire weather threat in weather story graphic and social post.

This upper trough/surface front will probably generate some light rain for Del Norte and northern Humboldt Friday afternoon and evening. Around 0.10 to 0.25 inches of rain are forecast for Del Norte County with a few hundredths for northern Humboldt. This is not very much rain, but just enough to have impacts on outdoor activities and projects Friday afternoon and evening. We will message this low impact light rain episode in a weather story graphic and social media post. GFS and ECMWF deterministic models continue to differ substantially with rain amounts. GFS has barely a tenth to only a few hundredths of an inch while the ECMWF has 0.50 to 1.0 inches over 24 hours from 11 AM Fri to 11 AM Sat. NBM 24 hour interquartile spreads are on the order of 0.30in for Crescent City and 0.04in for Eureka with means around 0.25in and 0.04in, respectively.

Model soundings continue to show low CAPE along the far northern portion of our coastal waters and Del Norte county as 500mb temps dip down to minus 25C or less. Soundings continue to show low EL's (equilibrium levels) and very narrow CAPE with WNW flow through the column. Thus not convinced there will be any thunder in our area. Calibrated guidance (HRRR and SREF) continues to show much higher chances north of the ORCA border with passages of a shorter wavelength trough Friday afternoon and evening.

Additional perturbations in N-NW flow on the backside of an upper level trough may generate isolated showers over the weekend, primarily for Del Norte and Trinity. Otherwise, dry and cooler weather is forecast to prevail into the weekend.

If skies clear out and winds go calm, patchy early morning frost will be possible (45% chance) for Trinity County (Hayfork and Ruth) and NE Mendo (Covelo) Friday and again on Sunday. With temperatures falling to 36F or less for a few hours right before sunrise, we will message the potential for frost in a weather story graphic and social media post.

A warming trend is forecast early to mid next week with highs in the lower to mid 90's by Wed. Also of note is the possibility (10% chance or less) for thunderstorms over the interior mountains Sunday and Monday as perturbations pin-wheel around the upper trough or the trough develops into a sem-closed circulation.
GFS indicate inverted V profiles which suggests high based storms.
There is considerable run-to-run and model-to- model variability and no clear signs of moisture import into the area. At this point, there is no compelling reason to deviate from the National Blend of Models (NBM) thunder chances.

AVIATION

19/18Z TAFs...VFR conditions at all TAFs terminals with mid-high level clouds streaming across the northern portion of the weather forecast area. Increasing NNW winds up to 15-20 kts with higher gusts until around 20/04Z, decreasing to around 10 kts after.
Winds are expected to remain breezy at CEC through late tonight.
Stratus will gradually to redeveloped after 02Z around Humboldt Bay, promoting MVFR to IFR ceilings at ACV with a deepen marine layer. VFR conditions should prevail at CEC and UKI. After 15Z, SHRA likely at CEC.

MARINE

Strong to gale force gusts winds across the outer waters and southern inner waters today, with the strongest winds south of Cape Mendocino. Meanwhile, gentle to moderate breezes over the northern inner waters. Waves will be mainly steep and wind driven.
Winds and seas will ease on Friday as a low pressure system approaches the Pacific NW region, becoming gentle to moderate west- northwest breezes. Winds shift back to northerlies Friday night, before increasing to moderate to strong breeze this weekend...with the strongest over the southern waters.

FIRE WEATHER

Stronger westerly and northwesterly winds are forecast through Friday across the interior as an unseasonably cold upper trough moves across the Pacific NW (Washington and Oregon). With minimum RH's around 20-25% on Friday and gusty afternoon and evening winds, elevated to locally critical fire weather conditions are anticipated for eastern Trinity, eastern Mendocino and Lake Counties. Duration of these red flag conditions are not forecast to be long-lived for most of the area. A few higher elevation exposed ridges will likely remain very dry and windy with 8 hours or longer of red flag conditions.

A low level northerly speed max (925mb) will likely develop over the Sacramento valley and clip the eastern peripheries of Mendocino and Lake Counties this weekend. Lower overnight humidity and gusty N-NE winds are likely over the higher terrain of Lake and eastern Mendocino (fire weather zones 264 and 277). Once again we may be flirting with locally cortical fire weather conditions. Our neighboring NWS office in Sacramento has a fire weather watch out for cured grassy fuels for elevations below 1000 feet. Otherwise, daytime minimum humidities are forecast to trend drier over the latter portion of the weekend (Sunday) into early next week as temperatures increase each day.

Also of note is the possibility (10% chance or less) for thunderstorms over the interior mountains Sunday and Monday as perturbations pin-wheel around the upper trough. There is considerable run-to- run and model-to-model variability. At this point, there is no compelling reason to deviate from the National Blend of Models (NBM).

EKA WATCHES/WARNINGS/ADVISORIES
CA...
None.
NORTHWEST CALIFORNIA COASTAL WATERS...
Small Craft Advisory until 3 AM PDT Friday for PZZ450-470.

Gale Warning until 9 PM PDT this evening for PZZ455.

Gale Warning until 3 PM PDT this afternoon for PZZ475.