535 FXUS66 KEKA 121933 AFDEKA AREA FORECAST DISCUSSION National Weather Service Eureka CA 1233 PM PDT Sat Jul 12 2025 .SYNOPSIS...Excessive heat is forecast to persist in the interior Sunday through Monday. Heat risk is forecast to diminish by mid next week. Unhealthy air quality due to nearby wildfires is possible. There is a slight chance for isolated dry thunderstorms Sunday afternoon and evening over the mountains of northern Trinity County. && .DISCUSSION... High pressure has built into the area, bringing a shallow marine layer with dense fog at times along the coast and hot weather to the interior. Smoke from the Butler and Green fires remaining in the valleys will likely pool back in overnight. Smoke models are showing the Trinity and Klamath River valleys with high smoke concentrations overnight with general haziness is possible across the area. As for the heat, high temperatures between 100-110 are possible, with the highest temperatures likely in Trinity County along the Trinity River Valley. Widespread haze may bring highs slightly below what is forecast, but no major impact to temperatures are likely. The overnight lows may actually be a few degrees warmer than forecast (forecast being low to mid 60s) in the valleys as denser smoke could trap some heat the valleys. Regardless, this heat does bring Moderate to Major HeatRisk and is dangerous to those without proper cooling and those sensitive to heat related illness. Sunday, the upper level ridge begins to move east slightly. This could support a slightly deeper marine layer and temperatures a degree or two lower in interior Del Norte and southern Humboldt. Still, temperatures will remain hot. Models are picking up a moisture intrusion from the east by Sunday afternoon. CAMs within range are showing a low chance (15%) for some activity in northern Trinity County. Model soundings do show a weak capping inversion and moisture remains limited, so confidence remains low. Monday, the ridge continues to push further east, which will allow the marine layer to gradually deepen early next week. Triple digit temperatures are likely to continue into at least Monday, with "cooling" finally arriving by Tuesday and Wednesday. Temperatures are likely to remain warm, with 90s expected for much of the interior through the end of next week. && .AVIATION... Coastal stratus layer was quickly scoured out this afternoon by increasing northerly winds offshore. VFR conditions expected through 00Z as daytime temperatures increase. Gusty winds expected again at CEC with gusts 20 to 30 knots possible this afternoon. Similarly, UKI will remain clear with breezy WNW winds 10 to 15 knots. HREF probabilities are 50-70% for IFR ceilings returning to ACV by 06Z as a strong marine inversion develops beneath strong high pressure. A southerly wind reversal is likely adjacent to the coast as the strongest winds move offshore overnight. Southerly winds 5 to 10 knots will advect IFR ceilings into CEC after 06Z. Both coastal terminals expected to see reduced viz with mist/fog through sunrise (HREF 50-60% for viz <4SM). Model soundings show the marine layer reluctant to scatter out on Sunday. && .MARINE... A tight coastal pressure gradient continues to produce strong northerly winds. Gale gusts will retreat into NW PZZ470 this afternoon through Sunday, but steep and hazardous wind driven seas 9 to 14 feet will continue. Winds and seas will still remain elevated in the southern outer waters with moderate to fresh breezes and waves 7 to 9 feet. Conditions will diminish in the inner waters on Sunday as the strongest winds idle further offshore. Gales expected to ramp up again on Monday, expanding into the southern outer waters and pushing closer to shore. Seas expected to respond accordingly with another round of 12 to 16 foot waves. Increasing confidence in high pressure beginning to break down Tuesday, diminishing hazardous conditions by midweek. && .FIRE WEATHER... Building high pressure along with offshore flow has brought warming and drying to the interior and near-coastal areas. Afternoon RHs remain very dry, into the teens and 20s across most the interior. High elevation areas (above 2000-2500 ft or so) continue to see moderate to poor overnight RH recoveries. Lower elevations are largely seeing moderate to good overnight recoveries. Offshore winds in the higher terrain are forecast to remain breezy overnight, especially in Del Norte county, though at least Sunday morning. Some marginal improvement is possible Sunday and Monday nights, before finally easing by Tuesday night. Upper-level moisture arrives from the east Sunday and Monday afternoons. Elevated instability along with some moisture brings a slight chance (10-15%) for isolated dry thunderstorms to northern Trinity County. As of now, moisture looks more limited on Monday, but there is still a 5-10% chance for isolated dry thunderstorms. The ridge begins to weaken Monday into early next week, which will slowly deepen the marine layer into the middle of next week. RHs will improve in the near-coastal areas with moderate to good overnight recoveries possible in the highest terrain by the Tuesday or Wednesday. JB && .EKA WATCHES/WARNINGS/ADVISORIES... CA... Heat Advisory until 11 PM PDT Sunday for CAZ102-105-110-111- 113>115. Extreme Heat Warning until 11 PM PDT Monday for CAZ102-105- 107-108. Heat Advisory until 11 PM PDT Monday for CAZ106. NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory until 5 AM PDT Sunday for PZZ450. Gale Warning until 11 PM PDT this evening for PZZ470. Hazardous Seas Warning from 11 PM this evening to 5 PM PDT Sunday for PZZ470. Small Craft Advisory until 5 AM PDT Monday for PZZ475. && $$ 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