Area Forecast Discussion
Issued by NWS Eureka, CA
Issued by NWS Eureka, CA
004 FXUS66 KEKA 302149 AFDEKA AREA FORECAST DISCUSSION National Weather Service Eureka CA 249 PM PDT Sun Jun 30 2024 .SYNOPSIS...Dry and seasonable conditions will continue through weekend along with gusty northwest wind in the afternoon. A strong heatwave will build early this week. && .DISCUSSION...Seasonable weather will close out the weekend, with highs hovering in the high 80s to low 90s for most interior valleys this afternoon. The coastal marine layer has been bolstered by onshore flow despite a weakened marine inversion, so while stratus has receded this afternoon many coastal locations remain inundated with cloud, primarily the Humboldt Bay region. The along shore pressure gradient will remain strong this afternoon as the trough moves east and high pressure quickly builds on its heels. This will bring gusty northwest wind this afternoon gusting between 20 and 30 mph on exposed ridges and in channeled terrain. Instability aloft will most likely aid in enhanced cumulus build up over high terrain today, but the chances for any lightning are very low (less than 5%). There is high confidence that very strong high pressure will build early this week, generating significantly warmer than normal temperatures by Tuesday. By Wednesday, NBM shows a 90 to 100% chance of highs in excess of 100 throughout inland valleys of Lake, Mendocino, and Trinity Counties. Focused on the Russian River Valley, there is even a 60 to 80% chance of highs above 110 just in time for the 4th of July holiday. Such values will rival the daily high record for Ukiah. Overnight lows will bring little relief, especially along midslope areas of Mendocino and Lake counties where lows are likely to stay above 70. Such high temperatures are expected to bring Major to isolated Extreme HeatRisk around Clear Lake and in the Russian River Valley. With steady confidence, the existing excessive heat watch has be upgraded to a warning. Widespread Moderate to Major HeatRisk is expected throughout the rest of the interior. Despite similar high temperatures, much cooler overnight lows in the 50s for Trinity and northern Mendocino County will help lower the overall HeatRisk. Though there are flagged areas of Extreme HeatRisk beyond Lake and southern Mendocino, the vast majority of the populated areas show only Moderate HeatRisk. At the moment, a heat advisory has been hoisted for the remained of interior Mendocino County where heat is most confident and will start the soonest. Above average temperatures are most likely to persist late into the week. That said, the presence of a surface low pressure off the coast late in the week may disrupt the heat depending on how efficiently it can break up larger scale high pressure and pull in marine influence. It is possible its impact will be negligible, with about 50% of model ensemble members showing Major to Extreme HeatRisk continuing even late into the week. Still, Thursday will most likely bring at least a brief mild relief to the heat. As such, no heat products have been extended beyond Thursday at the moment. /JHW && .AVIATION...A widespread marine layer and stratus are affecting the coastal terminal today. The profilers are showing a deep marine layer up to around 1,000 feet. LIFR conditions with OVC layer at 400ft and visibility around 3-2mi due to mist/fog are currently impacting ACV and CEC as result. Low clouds will burn off with the daytime heating, however stratus are expected to be stubborn to scatter out along the immediate coast this afternoon. KACV and KCEC may have a period MVFR/VFR category during the afternoon, before IFR to LIFR ceilings redevelop. Meanwhile, VFR conditions and breezy NW at 10 kt and strongest gusts continues at UKI. Winds are expected to continue breezy throughout the day at UKI, with strongest gusts after 20Z. Surface winds from NW at 5-10 kt are forecasted for the coastal terminals. && .MARINE...Northerly winds and seas will hold steady in regards to conditions across the waters this morning. However, the southern waters will continue to see strong breezes, with localized near gale force gusts possible south of Cape Mendocino. Wind wave driven seas around 6-8 ft will continue promoting hazardous conditions for small crafts across the southern waters. A mid period WNW swell is moving across the waters, bringing an additional wave group of 4-5 ft @ 12s to the sea state. Monday, winds are forecast to strengthen again as a high pressure offshore begin to builds in quickly in the wake of the trough. A thermal trough is then expected to develop near the coast Monday afternoon and favor moderate to strong pressure gradient along the coast resulting in strong northerly winds. Widespread strong to gale force winds and very steep, hazardous seas can be expected through Wednesday evening. Gusty northerly winds up to around 40 kt and seas around 12-16 feet @ 9-10 seconds are expected for the outer waters. An official Gale Watch for the outer zones from Monday through Wednesday has been enacted due to the increased coverage of these windy conditions. Winds are expected to gradually diminish on Thursday, a southerly wind reversal is forecasted to move north towards the Mendocino Coast and relax the pressure gradient. && .FIRE WEATHER...A strong pressure gradient along shore will continue to promote enhanced northwest wind this afternoon, particularly in Mendocino and Lake Counties with gusts up to 30 mph along exposed ridges. This will lead to elevated fire danger, especially in fine fuels. That said, northwest flow will also increase marine influence, prevent RH from dropping much below 25% except in the driest valleys. This influence and the short lived nature of the wind will limit the over extent of fire weather concerns. As a strong heat wave builds in, critically dry conditions will impact the interior. By Tuesday, afternoon RH will drop into the single digits with very poor overnight recoveries below 40%, especially within midslope thermal belts. Even in the absence of wind, such conditions will rapidly increase fire danger. RH and temperatures aren`t the only concerns, however. As the heat builds in, northeast winds of 10 to 20 mph will impact the rim of the Sacramento Valley. In combination, these two forces will create localized critical fire weather conditions for southeast Lake County on Tuesday. A Red Flag warning has been raised to highlight this hazard. Borderline critical conditions will be present as the heatwave wears on, especially in areas where terrain wind may be enhanced such as the Trinity River Valley. /JHW && .EKA WATCHES/WARNINGS/ADVISORIES... CA... Heat Advisory from 11 AM Tuesday to 5 AM PDT Thursday for CAZ110-111. Excessive Heat Warning from 11 AM Tuesday to 5 AM PDT Thursday for CAZ113>115. Red Flag Warning from 2 AM to 8 PM PDT Tuesday for CAZ264. NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory until 5 AM PDT Tuesday for PZZ455. Small Craft Advisory from 9 AM to 5 PM PDT Monday for PZZ470. Gale Warning from 5 PM Monday to 2 AM PDT Thursday for PZZ470. Small Craft Advisory until 2 PM PDT Monday for PZZ475. Gale Warning from 2 PM Monday to 3 PM PDT Wednesday 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