Area Forecast Discussion
Issued by NWS Eureka, CA
Issued by NWS Eureka, CA
958 FXUS66 KEKA 272141 AFDEKA AREA FORECAST DISCUSSION National Weather Service Eureka CA 241 PM PDT Wed Aug 27 2025 .SYNOPSIS...Isolated thunderstorms are possible this afternoon over the Trinity Horn. Generally cooler and calmer conditions will build for the end of the week with some more afternoon sun possible for the coastal areas. && .DISCUSSION...Model soundings show the typical coastal inversion for Thursday morning yet the marine layer will likely continue to deepen into the late week. Inland soundings look as if the potential for isolated thunderstorms are still a possiblility today, even with the eastward shifting of monsoonal moisture there still exists cape in the upper column of the skewT. The low level inversion does look to trend weaker late in the weak and particularly when a trough clips the region through the weekend. This will bring better chances for sunshine. Moisture begins to move to the east today as a trough slowly moves toward the Pacific Northwest. Thunderstorm chances decrease considerably this afternoon, but isolated storms are still possible in the mountains of far northern Trinity County. A deeper marine layer will support slightly cooler high temperatures in the river valleys. High temperatures still remain near or slightly below seasonal normals, with high 80`s and 90`s likely for most interior valleys. Smoke and haze from area wildfires is likely, particularly in eastern Trinity and Lake Counties. Ensembles start to wildly diverge into early to mid next week. Around 30% of the members are showing ridging (dry with hot interior temperatures), while the remaining 70% show some variety of a troughing pattern, whether that be broad troughing continuing like this weekend, or a cutoff low moving offshore and possibly returning the monsoon pattern. More details will become clearer as we get closer. JB/JJW/EYS && .AVIATION...(18Z TAFs)...LIFR conditions inundate the coastline today from Gualala to Crescent City as stratus filled eddies line the shore. Little clearing beyond IFR is expected today as stratus ebbs and flows over the coast and in the coastal river valleys. If there is clearing however, it should occur between 19Z and 03Z leading to SCT-CLR with the only cloud layer being low coastal stratus. Coastal winds are expected to remain light with variable directions (primarily 180-270 or S/SW/W) due to the eddy`s flow. LIFR to return tonight due to low cloud ceilings. Inland, winds are expected to increase as daytime warming takes effect. Afternoon gusts are possible, especially in Mendocino and Lake County, as higher winds mix down to the surface. Satellite imagery shows smoke plumes around wildfire areas. In NE Trinity County, afternoon thunderstorms are possible creating potential hazardous and gusty updraft and outflow winds. Skies are expected to remain clear and VFR inland through the day away from T-Storm areas. && .MARINE...Light winds and seas dominate today as zonal winds flow in the upper atmosphere. This zonal flow has weakened the surface pressure gradient and allows for the current southerly eddies to form. These southerly winds were gusting to 15-20 kt along the coast yesterday, yet have diminished overnight and are not currently forecast to reach that strength again today. Light (<10kt) and variable winds are expected through Friday. Waves continue to diminish as well with wind waves generally below 5 feet. Further calming is expected through the end of the week. A small long period southerly swell is still in places, but it is only around 2 feet at 18 seconds. Northerly winds will reform Saturday with the higher speeds (~20kts) expected downwind of Cape Mendocino. This is expected to begin in the southern waters and expand north through the weekend and currently it doesn`t look like there will be gales. Wind waves will dominate again with the southerly swell. && .FIRE WEATHER...The bulk of the monsoonal moisture pulls east. The ingredients for some isolated thunderstorms over northeast Trinity County will still exist, but the activity may mostly stay east of the county boundary. Westerly winds increase this afternoon with minimum RH lowering to the low 20s to upper teens. Minimum RH will continue to lower Thursday, down to the mid to low teens for the far interior. Southwesterly to southerly winds will also increase Thursday as a shortwave trough nears offshore to increase to fire weather threat, particularly in Lake County where locally critical conditions may develop in some isolated locations. Breezy westerly to southerly winds will likely develop Friday as the trough clips the region while passing north, but minimum RH will have begun generally trending higher and the amount of influence from the trough is still in question. && .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