Area Forecast Discussion
Issued by NWS Eureka, CA
Issued by NWS Eureka, CA
991 FXUS66 KEKA 122146 AFDEKA AREA FORECAST DISCUSSION National Weather Service Eureka CA 246 PM PDT Fri Jul 12 2024 .SYNOPSIS...Very hot and dry weather will continue in the interior through tomorrow. An offshore low will bring a small chance of dry thunderstorms to the interior tomorrow afternoon and Sunday. Interior heat is forecast to moderate slightly Sunday and early next week. Coastal areas will remain cool with occasional fog and low clouds through the weekend. && .DISCUSSION...Interior heat will continue to build through tomorrow with an excessive heat warning remaining in effect for triple digit temperatures in the interior valleys. Ukiah Municipal Airport could tie or set a new record today and get close to a record tomorrow. As of 2PM today, Ukiah is already at 106F, while todays record high temperature is 107F set in 1927. Tomorrow, the high temperature at Ukiah is forecast to be 107 with the record high temperature being 110F set in 1972. An upper low offshore will begin to break down the persistent ridge by tomorrow, perhaps bringing some spotty clouds, allowing for some very minor relief to the heat in Mendocino and Lake counties. NBM still shows over a 90 percent chance of temperatures being above 100F. NBM probabilities of over 105 actually increase for Trinity and interior Humboldt tomorrow. Major to Extreme HeatRisk continues in most interior valleys, as a result. The heat risk is forecast to abate by Sunday and into early next week as another upper level trough approaches from the NW. It will still be quite hot in the interior for Sunday; 96-103F. High temperatures, according to NBM, are forecast to remain near or above normal early next week; 94- 103F. So the relief from the heat is not going to be all that dramatic, though the heat risk is forecast to become moderate. An upper low developing off the Central California Coast will bring some mid and upper-level moisture into the region by tomorrow afternoon and into Sunday. When combined with very hot daytime temperatures, this could bring instability to the higher terrain. Moisture will be limited in the lower levels, with afternoon RHs in the teens to low 20s, so any thunderstorms that do develop will likely be dry with showers likely remaining as virga. Uncertainty remains high on both available moisture and instability. Probability of thunder for tomorrow remains less than 10 percent, but there will be a slightly higher chance of isolated showers or thunderstorms for Sunday. The position of the low offshore will determine the amount of moisture and what time of day the most moisture arrives. Models seem to be converging on Sunday morning, where the lack of daytime heating could limit instability and thunder potential. The best chance for anything to develop would be early Sunday morning in eastern Lake and Mendocino counties, and Sunday afternoon in Trinity County. There is slightly higher confidence (still less than 15 percent) in northern Trinity County for Sunday afternoon. The coast will continue to have similar conditions to the previous days, with stratus developing overnight, scattering in the afternoon, then redeveloping the following night. Temperatures will stay around seasonal normals through the weekend and into next week. && .AVIATION...The coastal air terminals were impacted by a more robust marine layer today...under a S-SSW wind flow this morning. ACV pireps indicated tops at 1600-1800 feet. Another impact is that the low level inversion is strong and has most likely inhibited or delayed stratus scattering...especially from Prairie Creek to Crescent City. Previous discussion noted a southerly return eddy possibly holding the stratus locally this afternoon. Coastal pressure gradient may be a little weaker today along with slow cloud erosion...thus resulting in less wind speeds. Inland areas remained VFR. Overnight: The marine layer will again increase and cause concern for coastal TAF Sites. /TAA/JJW && .MARINE...Gale force northerlies will continue today in the outer waters, with steep, hazardous seas to 15 ft. Gusts to 40 kts can be expected through tomorrow morning. The Gale Warning for the northern inner waters has been extended to 3pm tomorrow. The steep and hazardous seas will be slower to subside throughout tomorrow and may require a Hazardous Seas Warning behind the ongoing Gale Warning. The inner waters will continue to see steep wind waves around 9-12 ft at 9 s. An area of low pressure will then begin to approach the coast, and this will initiate a weakening trend in the northerlies. By Sunday afternoon, the northerlies will weaken to 15 to 20 kts in western portions of the outer zones, and less than 10 kts elsewhere. Weaker northerlies will likely remain into next week. && .FIRE WEATHER...Afternoon winds will remain breezy, primarily in Lake and Mendocino counties along the rim of the Sacramento Valley. Isolated patches of critical fire conditions are possible in southern Trinity and Lake counties with these breezes as very hot temperatures and low RHs continue. Models are converging on a plume of monsoonal moisture arriving tomorrow afternoon. Moisture along with daytime heating will allow for greater instability and a small chance of dry thunderstorms tomorrow afternoon in Lake, eastern Mendocino, and eastern Trinity counties. Sunday has slightly greater potential for dry thunderstorms in eastern Lake, Mendocino, and Trinity counties. Northern Trinity and Del Norte could see some afternoon convection as well. Broadly, chances of thunderstorms remain low, below 15 percent, and uncertainty remains high on available moisture and instability. Stay tuned for updates. JB && .EKA WATCHES/WARNINGS/ADVISORIES... CA... Heat Advisory until 9 PM PDT Saturday for CAZ104-106-112. Excessive Heat Warning until 9 PM PDT Saturday for CAZ105- 107-108-110-111-113>115. NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory until 9 PM PDT Saturday for PZZ450. Small Craft Advisory until 3 PM PDT this afternoon for PZZ455. Gale Warning until 3 PM PDT Saturday for PZZ470. Gale Warning until 9 AM PDT Saturday for PZZ475. && $$ 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