Area Forecast Discussion
Issued by NWS Eureka, CA
Issued by NWS Eureka, CA
853 FXUS66 KEKA 050705 AFDEKA AREA FORECAST DISCUSSION National Weather Service Eureka CA 1205 AM PDT Fri Sep 5 2025 .SYNOPSIS...Drizzle and stratus continues to blanket the coast. Interior temperatures trend downward into the weekend. Wet weather possibly returns late Sunday into early next week, with multiple chances of rain. && .DISCUSSION...The ridge over the western portion of the U.S. has started to move eastward as an upper trough moves toward the area. As it does, it starts to elongate and a shortwave trough forms south of it and starts to rotate towards the coast this evening and overnight. Another trough follows and rotates around on Saturday evening. Finally, on Monday the upper level low starts to become an open wave and move onshore. Today through Sunday these shortwaves rotating around the low is expected to enhance the coastal drizzle. The NBM is still showing a 20 to 30 percent chance of over a tenth of an inch of drizzle for the immediate coastline this morning. These probabilities drop to around 10 to 20 percent along the coast for the weekend. As the air aloft gets cooler and the inversion starts to weaken, the clouds at the coast may break up in the afternoon, but otherwise clearing may be limited. Fairly significant cooling is expected today and into the weekend for interior areas. Highs today are expected to be in the upper 80s to low with a few additional degrees of cooling both Saturday and Sunday. Sunday afternoon and evening, the upper level low starts to get close to the area and may start to bring some showers to the area. A thunderstorm is not completely out of the question, but this is generally not a pattern conducive to thunderstorms. Monday, the upper level trough moves onshore and Tuesday this gets reinforced by a large trough that settles over the west coast and remains in place on Wednesday and Thursday. Overall the ensembles are in pretty good agreement on the trough over the west coast. The challenge lies in where exactly this low goes and this will impact the details of how much rain occurs and where it will be. Here are some probabilities of rainfall totals from 5am Sunday through 5am Wednesday. There is a 70 to 80 percent chance of exceeding an inch in Del Norte county, a 50 to 60 percent chance on the Humboldt Coast, and around 50 percent chance in the mountains of interior Humboldt and Trinity counties. The probabilities drop off quickly to near zero in Mendocino and Lake counties for an inch. However, for a tenth of an inch there is a 40 to 70 percent chance in Mendocino and Lake counties with the highest in the northern Mountains. The NBM is highlighting thunderstorms, especially along the coast, with this system as the trough moves overhead. Confidence is low as instability is meager, but is something to watch. This will also keep temperatures cooler and interior high temperatures will likely be in the 60s to low 70s. MKK/JB && .AVIATION...(06Z TAFs)... A deeper marine layer has developed as an upper level trough approaches from the west. Expect variable conditions between LIFR/IFR/MVFR at coastal terminals through Friday morning. Patchy drizzle is expected to occur along the coast with this saturated layer. Very light S to variable winds will continue into very early Friday morning. For inland areas: Into Friday morning, high-res model guidance suggests low clouds developing in the vicinity of UKI with the deeper marine layer. There is a 20% chance for ceiling height at 1000 feet or lower by early Friday morning. Very light and variable winds will exist through Friday morning; however, any gentle southerly winds that may develop in the Russian River Valley may bring lower clouds to UKI. /ZVS && .MARINE...Gentle to moderate breezes continue across the outer waters, while light to gentle breezes continue over the inner waters. Localized gusty winds up to 20 kts are expected downwind of Cape Mendocino through tonight. Conditions are expected to continue improving into Friday and the weekend as an upper level trough approaches from the west and the surface pressure gradient relaxes. Winds shift to southerly and slightly increase ahead of an associated frontal system this weekend. Small, mid- period NW and SW swells will persist through the weekend. Overall, relatively calm conditions are forecasted for this weekend through early next week. /ZVS && .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