Area Forecast Discussion
Issued by NWS Eureka, CA
Issued by NWS Eureka, CA
878 FXUS66 KEKA 211924 AFDEKA AREA FORECAST DISCUSSION National Weather Service Eureka CA 1224 PM PDT Mon Jul 21 2025 .SYNOPSIS...Cooler interior temperatures expected following a weak frontal boundary this morning. Thunderstorms are possible in the interior through late this week. && .DISCUSSION...A weak cold front moved through the region this morning, bringing high cloud cover and some light drizzle to the north coast. Temperatures in the interior expected to be cooler today, with highs in the upper 70`s and low 80s. The marine layer has deepened along the coast, favoring more widespread cloud cover further inland through the week. Breezy westerly winds 15 to 25 mph expected again this afternoon in Lake and Mendocino county. An upper trough will extend into NorCal and remain fixed over the area through late week, bringing a daily possibility for thunderstorm development across interior Del Norte, Humboldt and eastern Trinity county. Mid-level moisture and cooler upper temperatures show greatest thunder potential beginning Tuesday afternoon - hi-res models show convective initiation over Siskiyou potentially drifting west into eastern Humboldt and Trinity, but confidence is still low on coverage. Convective potential increases Wednesday into Thursday with increasing surface temperatures/instability as the upper trough gradually cuts off and closes off the coast. This may allow storms to develop and push further west into eastern Del Norte and northern Trinity and Humboldt. Thunder potential continues for this area through the end of the week, increasing to 15 to 25% for the latter half of the week. && .AVIATION...A cold front is currently moving through Mendocino County, leaving a more moist and cooler environment in it`s wake. This resulted in a deeper marine layer push this morning in Del Norte and Humboldt counties plus more cloud cover on the Mendocino coast. With this airmass now in place, it is likely that we will see a repeat tonight with IFR to MVFR ceilings at the coast, cloud cover pushing inland over much of Del Norte and Humboldt counties following some clearing this afternoon, plus a potential spillover of clouds from the west into the Ukiah valley impacting the airport. /RPA && .MARINE...An upper trough is beginning to settle over northwest California, disturbing the surface pressure gradient over the coastal waters and weakening the northerly winds. As the trough transitions to a cut-off low pressure system, the pressure gradient will continue to weaken and winds will further decrease into Tuesday and remain light through the week. This will result in rather tranquil seas, some potentially to as low as 2 feet near the immediate coastline mid to later week. /RPA && .FIRE WEATHER...Breezy west-northwesterly winds expected today for the interior areas, with the strongest winds likely in eastern Trinity and Lake counties. In southern Lake County, winds are still breezy but mainly from the west-southwest. Peak gusts of 20-30 mph are possible, bringing locally elevated fire weather conditions. Poor air quality persists for interior Humboldt and northern Trinity County due to the Butler Fire. Some improvement in air quality is possible in the afternoon with greater mixing except immediately downwind of the fire. An inland push of the marine layer followed a weak frontal passage this morning. A few showers are possible this afternoon in the Trinity Horn, but thunderstorm chances remain low at around 5-10%. Tuesday and Wednesday afternoons have increasing confidences (10 to 15%) as storms drift west from Siskiyou County, where higher probabilities persist. Thunderstorm chances increase in coverage and probabilities later in the week, but still confidence remains low. && .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