textproduct: Eureka

AVIATION 12Z UPDATE

Coastal stratus has filled in over much of the North Coast overnight and should remain stubborn through the TAF period. Southerly winds will dominate today with gusty conditions likely at KCEC. Categories are likely to waiver between MVFR and IFR through the day before settling down to IFR-LIFR Monday night into Tuesday morning. Inland areas can expect VFR and northery afternoon winds.

PREV DISCUSSION

/issued 206 AM PDT Mon Aug 31 2026/

KEY MESSAGES... * Breezy afternoon winds will elevate fire weather conditions in Trinity county this afternoon.

* Warm temperatures to continue today before much cooler temperatures arrive for the remainder of the week.

* Isolated thunderstorms are possible in Trinity County Tuesday afternoon and evening.

* An early season storm is likely to bring widespread rain to the area Wednesday and Thursday.

SYNOPSIS...An approaching upper low will deepen the marine layer today. A few showers and thunderstorms are possible Tuesday and Tuesday night as this low moves overheard. An early season storm is expected to bring widespread wetting rain Wednesday afternoon through Thursday.

DISCUSSION...An approaching trough is expected to deepen the marine layer and bring slightly cooler temperatures to much of the area. This is also expected to bring increased west-southest winds in the afternoon. This will elevate fire weather concerns in Trinity County as afternoon relative humidities remain low. For more details see fire weather section.

Tuesday is expected to see moisture aloft increasing as the trough cuts off and moves towards the coast. A shortwave rotating around the low may provide enough lift with some instability aloft to produce thunderstorms. These may be fairly dry initially with PWATS around 0.6 or 0.7 inches. High resolution models have started to come within range, and some are showing some showers and thunderstorms over the area, primarily northern and eastern Trinity County. The REFS especially is showing a few members with over 40 dBZ along with MUCAPEs over 200 J/kg. Some precipitation is possible with these storms, but the dry lower levels will limit accumulations. A few light showers are possible outside of these thunderstorms over the coastal waters and along the coast.

There will be a short break in precipitation chances Wednesday morning and early afternoon, but the next system arrives by the late afternoon or evening. Gusty south winds are likely ahead of this system with around 50% chances for gusts over 30 mph along the coastal areas and ridges of Del Norte and Humboldt. Locally higher gusts of 40 mph or higher are possible on windward ridges and coastal headlands. Wednesday evening and overnight into Thursday, the system is expected to bring a wetting rain to much of the area. The models are still struggling with how far south this rain will make it. The NBM is showing over an 80% chance for wetting rain (over 0.1") from about Ukiah and northward. Most of Humboldt county is showing a 60 percent chance of over a half inch of rain. Farther north in Del Norte county there is a 70 percent chance of over an inch of rain. Some of the models are still showing drier solutions so this will need to be monitored as it gets closer. Late in the week and over the weekend, an additional colder system looks possible. Precipitation looks limited with this system, however, at this moment, but colder temperatures aloft may be supportive of thunderstorms.

Along with the rainfall, temperatures will fall far below normal with many interior areas in the 60s or 70s mid to late week. Overnight lows could drop into the 30s or 40s should skies clear overnight. Frost may be possible in the coldest interior valleys. JB/MKK

MARINE...Strong northerly winds will diminish today and southerly winds will develop near the coast. Wind driven waves of around 7 to 8 feet will slowly subside today as the winds subside. A southerly swell of 2 to 3 feet at 17 seconds continues as well. This will slowly diminish over the next several days.

Tuesday, an early season weather system starts to approach the area switching winds across the area to southerly. These southerly winds are expected to slowly increase through Wednesday afternoon. Current models showing them peaking around 20 to 25 kt in the northern waters. Some models are showing these southerly winds reaching 30 kt Wednesday afternoon. These southerly winds are expected to continue through the week, although for now it looks like they will remain under 15 kt or so outside of Wednesday. Next weekend northerly winds may return. MKK

FIRE WEATHER...An approaching upper level low will deepen the marine layer, bringing a trend upwards in relative humidities in areas closer to the coast. This will also bring slightly cooler interior temperatures today. Breezy south winds this afternoon in Trinity County along with still low afternoon relative humidity in the teens will bring elevated fire weather conditions.

Late Tuesday afternoon and Tuesday night the upper low moves overhead bringing the potential thunderstorms. High-resolution models are supportive of isolated thunderstorms in Trinity County, with higher chances on the northern and eastern edges. Confidence is still low, at around 10-15%. These thunderstorms are likely to be a mix of wet and dry, but precipitation is expected to be little.

Wednesday afternoon and evening there is the potential for widespread wetting rain. Precipitation continues to trend wetter and farther south, with wetting rain now likely across NW California. Rainfall amounts over an inch are possible in Del Norte and northern Humboldt counties. This will need to be watched if precipitation continues to trend upwards for any potential impacts to recent burn scars. MKK/JB

EKA WATCHES/WARNINGS/ADVISORIES

CA... None. NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory until 9 AM PDT this morning for PZZ455.

Small Craft Advisory until 3 PM PDT this afternoon for PZZ470-475.