241 FXUS66 KEKA 241958 AFDEKA AREA FORECAST DISCUSSION National Weather Service Eureka CA 1258 PM PDT Thu Jul 24 2025 .SYNOPSIS...Thunderstorms are possible in the interior both this afternoon and evening and Friday. Near normal to slightly below normal temperatures expected this week. Temperatures trend slightly upward early next week. && .DISCUSSION...An upper low off the coast of Central California has moved slightly closer to shore. This fairly subtle movement will increase mid-level moisture moving in from the east and allow for thunderstorm development. Model soundings are showing a small capping inversion in the late morning and early afternoon. As of around noon today, fire cameras pointed at the Butler Fire is showing this inversion quite well. The cap is expected to break this afternoon, bringing isolated to scattered thunderstorms to Trinity, eastern Humboldt, and eastern Del Norte. Model soundings also show an inverted-V pattern and DCAPE values near 1000 J/kg. Weak shear of 15- 20 kts suggest storms that will form fast and collapse fast, bringing gusty outflow winds possibly in excess of 50 mph. PWATs are also fairly high, so brief periods of heavy rain are also possible in the strongest cells. There are some hints of remnants of storms moving into coastal Del Norte and Humboldt this evening and overnight. Confidence has diminished on these being thunderstorms, but a stray shower isn`t completely out of the question. Additionally, there are hints of showers from the Sierra moving into Lake or eastern Mendocino counties in the early morning. These are likely not going to be thunderstorms, but a stray shower is possible. Friday, the upper-low inches more northeasterly, bringing a similar setup to today`s storms, but moves slightly south and east. Confidence has increased on thunderstorms forming across Trinity County, eastern Mendocino, and northern Lake Counties. CAPE may be even higher Friday (nearing 1000 J/kg) with DCAPE remaining near 1000 J/kg. Higher shear in the Yolla Bollys may allow for some longer-lasting storms, but elsewhere shear remain weak. Storms will likely form and collapse quickly, bringing gusty outflow winds possibly in excess of 50 mph. PWATs of an inch could support periods of heavy rain. The low moves to the east Saturday, bringing most mid-level moisture with it. Thunderstorm chances significantly decline, and if any form, the Trinity Horn is the most likely area. Sunday and into the middle of next week high pressure is expected to generally remain east of the area. This will keep temperatures near seasonal normals with highs in the upper 80s to low 90s. Thunder potential generally looks to remain low. Ensembles are hinting at another upper-low forming right off the coast, which may return thunderstorm chances mid next week, and this will need to be watched. JB && .AVIATION...(18Z TAFs) Another foggy day today with IFR conditions along the Redwood coastline. Daytime winds show a likely probability (60-70%) for clearing to MVFR/VFR conditions by midday. However, a return to IFR/LIFR categories due to degraded visibilities and low cloud ceilings is expected (>80%) by 03Z. Winds are expected to remain light along the coast. Inland however, VFR conditions are expected with clouds building this afternoon as thunderstorms with downburst of 50kts + lightning potential over Eastern Humboldt and Trinity counties. Fog entering the river valleys this evening shows a 40-50% probability of reaching KUKI up the Russian River leading to potential IFR conditions. && .MARINE...A cutoff low has developed off Central California and will remain in the vicinity through the end of the week. This will continue to weaken the pressure gradient, holding winds to gentle to moderate levels. Seas 2 to 5 feet are expected, with the lightest conditions expected nearest the coast. Winds will be broadly northerly with south/southwest winds likely directly adjacent to the coast, especially overnight. The northerlies will begin to slightly increase Friday, mainly through the outer zones, and likely remaining mainly below 20 kts through the weekend. && .FIRE WEATHER...Isolated to scattered thunderstorms are likely today and Friday in the interior. Today, thunderstorms are most likely in northern Trinity County. There is some model divergence in storm chances for Del Norte and northeastern Humboldt County, where lightning coverage ranges from little to abundant. Therefore, the Red Flag Warning continues in Trinity, NE Humboldt, and eastern Del Norte. Isolated thunderstorms are possible in eastern Mendocino, southern Trinity, and eastern Humboldt. Gusty, erratic outflow winds of 50 mph are possible in the strongest cells and brief periods of heavy rain are also possible. Friday, thunderstorms shift south and east with the highest confidence in Trinity, eastern Mendocino, and northern Lake. Isolated storms are possible in eastern Humboldt as well. Again gusty, erratic outflow winds of 50 mph are possible and a brief heavy downpour is not out of the question. A Red Flag Warning has been issued for abundant lightning in Trinity, eastern Mendocino, and northern Lake Counties. Thunderstorm chances decrease this weekend. Outside of thunderstorms, winds are generally expected to be fairly light and terrain driven. Interior Temperatures are generally expected to be around or slightly below seasonal normals with highs in the 80s to low 90s. Dry afternoon RHs in the 20s are possible in the eastern portions of the area, but good overnight recoveries are likely. JB && .EKA WATCHES/WARNINGS/ADVISORIES... CA... Red Flag Warning until 11 PM PDT this evening for CAZ203- 204-211-283. Red Flag Warning from 11 AM to 11 PM PDT Friday for CAZ212- 277-283. 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