Area Forecast Discussion
Issued by NWS Eureka, CA
Issued by NWS Eureka, CA
078 FXUS66 KEKA 221228 AFDEKA AREA FORECAST DISCUSSION National Weather Service Eureka CA 528 AM PDT Sun Sep 22 2024 .SYNOPSIS...Warm and dry conditions will continue to gradually settle in today with weakening north winds along the coast. Heat will peak early this week with above average temperatures pushing out even along the coast. && .DISCUSSION...Continued high pressure and diurnal offshore flow has allowed for another mostly clear night, though shallow marine stratus has managed to form in an area of calmer wind right along the Mendocino Coast. Most low elevation areas have managed to cool into the 40s while strong thermal belts have maintained upper elevation lows in the 60s. The gradually building heat dome will allow temperatures to continue creeping upwards today with hot interior valleys reaching the upper 90s, which is a solid 10 to 15 degrees above normal for most locations. Like yesterday, lingering offshore flow this morning may aid in some brief warming near 70 along the coast, especially with clear skies. Generally weakening north winds along shore will most likely allow for slightly stronger heating than Saturday, but should still be sufficient to bring strong marine influence in the afternoon with gusts near 20 mph. High pressure will build and peak early this week with the hottest temperatures most likely Monday and Tuesday. There is a 70 to 90% chance of highs above 100 along the Russian and Trinity River Valleys. In addition, most models are placing a closed low off the Central California Coast during this time. This low will encourage offshore wind which, combined with the high pressure, will help push particularly warm conditions very close to the coast. Thanks to this pattern NBM has a 50 to 70% chance of highs over 100 in Garberville and a 40 to 60% chance of highs in the mid 70s around Humboldt Bay. Such above normal temperatures, combined with little overnight relief will help support moderate and very localized major heat risk. None the expected temperatures, however, are near record breaking. There is high model agreement that high pressure will weaken by mid week and give way to a broad, shallow trough across the Pacific Northwest. About 30% of model ensemble members have the trough dip just south enough to bring light wetting rain right along the North Coast. Should rain occur, however, the timing is very uncertain varying anywhere from Thursday to Saturday, which is contributing to a generally washed out signal in the NBM. Essentially no model members show any rain more than a couple tenths of an inch at the most. Most model ensemble members show no precipitation beyond coastal drizzle with the trough just bringing generally cooler temperatures and increased clouds cover, especially with a marine layer along the coast. There is high confidence in a generally benign, dry, and seasonable patten continuing through the end of the week. By next weekend there is wide model disagreement. About 10% of cluster ensembles show a widespread wetting rain event while 20% show the total opposite with a moderate heat wave. The majority (70%) show weak high pressure and generally dry but seasonable conditions. /JHW && .AVIATION...Gentle offshore flow and very dry air aloft have continued to promote clear skies and VFR conditions all across the area this morning. The only exception being shallow marine stratus right along the Mendocino Coast and patchy areas of surface radiation fog, most notably around Crescent City. Any fog induced IFR should be short lived and quickly lift by mid morning. Otherwise, clear VFR conditions will prevail again today with continued gusty north wind near shore continuing to be the only real notable feature. /JHW && .MARINE...North Winds have very slightly calmed overnight but gusts in the outer waters have still remained near gale force. In concert with the winds, steep short period waves have persisted around 10 feet at 9 seconds. Even closer to shore where winds are more moderate, steep short period seas over 8 feet currently dominate the sea state, especially around Cape Mendocino and in the northern inner waters. North winds will most likely slightly rebound again today during peak afternoon mixing with a short period of gale force gusts in the outer waters, especially fanning south of both Pt. St. George and Cape Mendocino this afternoon and evening. This will maintain a steep and dangerous sea state through the evening with only the most protected parts of the southern inner waters most likely avoiding steep seas. North winds will finally weaken and pull further offshore late Monday afternoon through Tuesday with mostly gentle winds by Tuesday evening. Seas will shortly follow with short period waves falling below 5 feet by Tuesday afternoon. As short period seas fall, the sea state will become mostly dominated by a moderate northwest mid period swell around 9 feet at 14 second by Wednesday. /JHW && .FIRE WEATHER...Building high pressure has again generated enhanced thermal belts overnight. While protected valleys have continued to see very high RH recovery above 80 percent, midslope and high elevation locations are generally between 30 and 50 percent early this morning. Diurnal northeast flow has weakened slight this morning with only isolated gusts over 20 mph, mostly just at the high elevations of the western Klamath Mountains. Building heat and high pressure this week will continue to enhance fire weather conditions with daytime highs in the mid 90s to low 100s and minimum RH in the teens. Overnight recoveries will continue to be poor at mid and high elevations with recoveries of 20 to 40 percent though Tuesday morning. Except for some enhanced north wind right along shore and channeled along the Eel river valley Sunday, daytime winds will be mostly gentle and terrain driven. Low pressure off the central California coast combined with high pressure will help enhance night time northeast flow at high elevations. Northeast wind gusting up to 25 mph should be expected a high elevations late each night early this week. This risk will be focused in the usual areas of Del Norte and Lake Counties but will also include the usually calmer ridges of Southern Humboldt and northern Mendocino Counties. Generally more mild conditions will build in late in the week with increasing marine influence. /JHW && .EKA WATCHES/WARNINGS/ADVISORIES... CA... None. NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory until 3 AM PDT Monday for PZZ450. Hazardous Seas Warning until 9 AM PDT this morning for PZZ470-475. && $$ 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