FXUS66 KEKA 291139 AFDEKA AREA FORECAST DISCUSSION National Weather Service Eureka CA 439 AM PDT Fri Mar 29 2024 .SYNOPSIS...Another round of showers a gusty south to east wind remains on track today focused in southern Mendocino and Lake Counties. Calmer and drier weather will then build in through the weekend. && .DISCUSSION...An occluded and strengthening low pressure system is well resolved in water vapor imagery this morning positioned a few hundred miles off of Cape Mendocino. This low is rapidly dipping southeast towards shore and will continue to zip south along the coast today. Weak showers are already evident on radar along the Mendocino Coast. As the low approaches shore, southerly winds will increase, especially in Mendocino and Lake Counties. Deterministic models are showing only modest maximum winds aloft of 45 to 55 mph early this afternoon, but instability with the low and terrain forcing as the wind turns east will likely help efficiently mix winds down to lower elevations. The NBM finally has increased confidence with a 50 to 70% chance of wind gusts over 45 mph in exposed areas of Mendocino and Lake Counties including along the coast. There is stark divergence in model ensembles with the GFS showing mean wind gusts of 20 mph and the ECMWF closer to 40 mph. In line with this, only the ECMWF EFI shows climatologically unusual winds with a value of 0.7 to 0.8 over the southern half of the area today. A short fuse wind advisory has been issued for these winds. Though not super strong, the uncertainty and unusual direction of the wind could lead to greater impacts than other events of a similar magnitude. Beyond wind, rain showers will build through the afternoon with generally light rain of 0.7 to 1.2 inches most likely over high terrain, particularly along east facing slopes around the rim of the Sacramento Valley. Downsloping down into places such as Lakeport and Ukiah will generally reduce rainfall to most likely amounts of 0.3 to 0.6 inches. Temperatures are cold enough this morning for snow as low as 2500 feet in many areas and will remain as low as 3000 feet into the afternoon in Trinity County. That said, east wind will bring little moisture over the coldest areas with the most snowfall on the eastern slopes of the Coast Range. That said, 1 to 2 inches of light snow is most likely on high portions of Highways 36 and 299 with 2 to 4 inches at Scott Mountain. Locally heavy snow is possible on the east side of the Trinity Alps during the strongest wind this afternoon. As low pressure itself skirts shore late tonight, isolated thunder is possible (10 to 20% chance) but any storms will be weak and remain close to shore in far southern Mendocino County. As low pressure eeks south through the weekend, a very positively titled ridge of high pressure will build over the Eastern pacific and stretch across the area. This will help with clearing skies and calmer weather, most likely allowing for widespread valley fog and patchy frost early Sunday and Monday morning. A strong pressure gradient is expected thanks to interactions with the low pressure, brining gusty onshore wind during the afternoon Sunday and Monday. Gusts along shore will most likely reach 35 mph but unlikely (10 to 20% chance) to reach 45 mph even on exposed headlands. High pressure will aid in some of the warmest temperatures of the spring so far inland with most valleys forecast to reach the upper 70s to low 80 by Tuesday afternoon. Significant uncertainty remains in the forecast midweek with the vast majority of model ensemble members showing high pressure breaking down sometime between next Wednesday and Friday. Most (80%) show a trough sweeping across the area but few (less than 20%) show anything more than 0.5 inches of rain and weak wind. /JHW && .AVIATION...Conditions at the terminals tonight have largely been VFR, with some lower ceilings briefly experienced at UKI. A low approaching the area this morning will increase cloudiness and bring rain impacts, primarily in Mendocino and Lake counties, where gusty wind and low level wind shear is forecasted. The coastal terminals are expected to miss the brunt of the system, with some light rain showers possible in the evening. A brief gust of wind is possible at ACV with these showers. The system will move out by tomorrow night, calming winds and clearing skies. && .MARINE...A steep mid-period swell still persists in the waters tonight, though it continues to diminish from it's peak yesterday. A low approaching the northern California coast will bring increasing southeasterlies that will peak as strong gales, with gusts up to 45 kts possible in the water south of Cape Mendocino. This low will move southward by the evening and winds will shift northeasterly as a ridge builds in. Winds in the outer waters will remain breezy, with gusts up to 25 kts possible but calmer winds and wave heights of 7-9 feet in the inner waters are forecast Wednesday morning. Saturday night northerly winds increase to gale force to near storm force gusts in the outer waters. Very steep wind waves of up to 15 ft are forecast to develop Saturday night and Sunday morning. Northerlies and steep wind waves will continue into Sunday, but is forecast to diminish slightly by Monday. && .EKA WATCHES/WARNINGS/ADVISORIES... CA... Wind Advisory from 8 AM this morning to 8 PM PDT this evening for CAZ109>115. NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory until 3 PM PDT this afternoon for PZZ450. Small Craft Advisory until 9 PM PDT this evening for PZZ455- 470. Gale Watch from Saturday afternoon through Sunday afternoon for PZZ470. Small Craft Advisory until 7 AM PDT this morning for PZZ475. Gale Warning until 7 PM PDT this evening 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