Area Forecast Discussion
Issued by NWS Eureka, CA
Issued by NWS Eureka, CA
308 FXUS66 KEKA 172110 AFDEKA AREA FORECAST DISCUSSION National Weather Service Eureka CA 210 PM PDT Sun Aug 17 2025 .SYNOPSIS...A chance for showers and isolated thunderstorms over eastern Trinity County today. A gradual drying and warming trend will develop this week, with further warming late in the week. && .DISCUSSION...After the frontal passage and light precipitation observed Saturday, extensive stratus remains today. Early afternoon satellite shows the low level clouds blanketing most of Humboldt and Del Norte counties, with also a good portion of Mendocino covered. This is due to a greatly deepened marine layer. There was lower level shallow moisture contributing to patchy locally dense fog, but that generally mixed out. Chances for fog are lower tonight, with less coverage expected. Soundings continue to show moisture at the 700 mb area with some instability today, and forcing exists from passing shortwave energy. Satellite imagery this early afternoon also shows some billowing cumulus over the Yolla Bolly region and through eastern Trinity County. These areas are where isolated afternoon showers and a 10-20% chance for thunderstorms are forecast. Moisture and instability mostly depart to start the work week Monday. This will also mark the start of a gradual warming trend. A shortwave perturbation will clip the northern region Wednesday, but is expected to have little impacts other suppressing the greater inevitable warmup. Beyond the passing of the shortwave, temperatures will indeed further warm late in the week. Probability for isolated warmer valleys to exceed 100 increases Thursday. Chances for temperatures over 100 are highest Friday (75%) for the interior valleys. Chances begin slowly dropping thereafter with a weak signal from clusters of some troughing influence, but the heat may linger longer through the weekend. There are hints of some monsoonal moisture getting pulled in from the SE next weekend. This would increase chances for thunderstorms, but the quality of moisture and instability look poor at this time. /JJW && .AVIATION...Low clouds along the coast have been scattering and lifting as a shortwave approaches. Currently, VFR conditions with OVC layer around 3500-4000 feet, accompanied by some SCT layer around 005 feet at ACV and CEC. Expect fluctuations in conditions at the coastal terminals through 18/03Z, before IFR/LIFR conditions redeveloped along the coast with low clouds and visibility in FG/mist. Winds from W at around 5 kts, becoming very light and variable after 3Z. For inland areas: VFR conditions persist at UKI through the period. Surface winds very light and variable, after 22Z becoming NW at around 10kts with higher occasional gusts. There is the potential for some isolated SHRA/TSRA across the eastern portion of Trinity County this afternoon and early evening. /ZVS && .MARINE...Light to moderate breezes are forecast to continue today across the coastal waters, with isolated gusty winds around 20 to 25 knots leeward of Cape Mendocino this afternoon. A NW swell around 4 to 6 feet at around 10 seconds will persist through today, before slowly subsiding through mid next week. Relatively calm conditions with light to gentle breezes and low seas is expected on Monday. Northerly winds begin to slowly increase on Tuesday as a surface high pressure builds in, especially south of Cape Mendocino. Increasing winds will spread northward and continue strengthening by mid to late week as a thermal trough develop near the coast. Resulting in moderate to strong breezes and steep seas, especially across the outer waters. /ZVS && .FIRE WEATHER...A chance for afternoon showers and thunderstorms over eastern Trinity County this afternoon. Westerly winds are are enhanced this afternoon behind a frontal passage. Winds will be stronger in Mendocino and Lake Counties where gusts over 25 mph are forecast or occurring. RH recoveries are high this afternoon. A gradual warming and drying trend will start Monday, with the driest conditions likely reached at the end of the week. && .EKA WATCHES/WARNINGS/ADVISORIES... CA... None. NORTHWEST CALIFORNIA COASTAL WATERS... None. && $$ NOTE: The full forecast discussion is now regularly issued between 10 am/pm and 1 pm/am. Additional updates will be issued as needed. Visit us at https://www.weather.gov/eureka Follow us on Facebook and Twitter at: https://www.facebook.com/NWSEureka https://www.twitter.com/NWSEureka For forecast zone information see the forecast zone map online: https://www.weather.gov/images/eka/zonemap.png