FXUS66 KEKA 092259 AFDEKA AREA FORECAST DISCUSSION National Weather Service Eureka CA 259 PM PST Fri Feb 9 2024 .SYNOPSIS...A weak system from the north will bring a chance of light precipitation for Del Norte and northern Humboldt counties this evening and overnight. Otherwise, dry weather is forecast for this weekend and probably into early next week. Rain potential will increase around mid week as a frontal system approaches the Northwest California coast. A stronger storm will approach toward the end of next week, bringing a risk for heavy rain and strong winds. && .DISCUSSION...Surface observations indicated light precipitation occurring at North Bend, Roseburg and Brookings in southern Oregon this afternoon. So far nothing has occurred at Crecent City or at other automated rain gauges. High resolution ensemble (HREF) continues to indicate potential for light precipitation (few hundredths) this afternoon and evening for Del Norte and northern Humboldt as precipitable water increases up to 0.90in or about 150% of normal. Most of the water in the column is in the mid levels, however NAM12 and other higher resolution models continue to indicate moistening up in the lower portion of the atmosphere (below 850mb) this evening. The northerly speed max in advance of the building ridge offshore will exit the region late tonight. Boundary layer humidities increase this evening, but dry overnight for Mendocino and Lake Counties as warmer air aloft arrives. Stronger nocturnal inversion and saturated soils will likely result in extensive fog and low clouds for Trinity, Humboldt, Del Norte and perhaps northern Mendo. The fog and low clouds should clear out with daytime heating and weak mixing on Sat. With the warming aloft and light onshore northerly winds, potential for stratus and fog will also increase for coastal areas this weekend as a weak 500mb shortwave moves over the ridge and into the Pac NW. X-sections from the high resolution models show some potential for light drizzle, but for the most part that should not have much if any impacts and will not include in the forecast at this time. Broad flat ridging aloft and above normal 500mb heights will prevail for early to mid next week. A transient shortwave trough may clip the area around mid week (Tue night or Wed) and knock the ridge down briefly. 24 hour probabilities for more than 0.50in are around 20-30% except closer 40-50% for Del Norte/far northern Humboldt. Ridging will likely spring back up on Thu as the next 500mb cold core over the north Central Pacific edges closer to 130W late next week Friday (Feb 16). Probabilities for more than an inch of rain in 24 hours increases toward the end of next week into next weekend (Feb 16-18). 24 hr probabilities from the RAW ensembles and NBM are now in the 40-60% range ending 4 AM Sat, however there continues to be large 25-75th spreads due mainly to timing differences. This first atmospheric river (AR) storm late next week (Feb 16) may also generate strong winds too (gusts greater than 40 MPH). Right now the ensemble probabilities for gusts more than 50 mph and the ECMWF EFI is not screaming super strong winds (50-70mph), though it is possible (less than a 10% chance). Granted we are still more than 6 days out and there continues to be large ensemble spreads. Additional AR storms will likely follow later next week weekend (Feb 17-18) and beyond (Feb 19-21). Stay tuned for another series of AR storms that'll bring an increasing threat for bouts of heavy rain, high winds and then eventually mountain snow. This is highlighted in CPC's 8-14 day (Feb 17-23) hazardous weather outlook. DB && .AVIATION...VFR ceilings and visibilities have been prevailing today at all terminals with cloud bases above 5000 feet. Potential for MVFR ceilings will increase at the coastal terminals this evening and overnight as low level moisture increases and a slight onshore flow develops. High resolution models continue to indicate potential for light precipitation this evening and visibilities may brief fall to 1SM to 3SM in light precip. Fog and low clouds are also forecast to develop over the interior valleys tonight as winds remain calm and skies partially clear. Fog at Ukiah is not completely out of the question, though multi-layered clouds from 150-250Kft will most likely hinder the long-wave cooling. DB && .MARINE...Conditions have been improving today as northerly winds slackened and mid-long period westerly swell continued to subside. Fresh to strong breezes are expected to persist in the lee of Cape Mendocino through late tonight, however. The northerlies are forecast to continue to wane on Saturday, though a weaker expansion fan (gusts to 25kt) will likely redevelop in the lee of Cape Mendo again during the late afternoon and early evening on Sat. Another long period westerly swell with periods from 18 to 21 seconds will build on Saturday and peak near 10 ft by early Sunday morning. The initial build up of the swell will pose a risk to beachgoers due to increased wave run up on the beaches. A beech hazard statement has been issued. For Sunday, a calmer wind regime with split flow across the waters is forecast as a weak front approaches. A light north-northeast wind regime will then re-emerge by Mon after the passage of this front. Light southerlies will eventually unfold on Tue in response to another front. Seas are forecast to trend down early next week and then rebuild by mid week in response to strengthening southerlies. ZVS/DB && .BEACH HAZARDS...A long period westerly swell will build on Saturday with significant swell heights up to 5 ft with periods from 18-20 seconds by late afternoon. This high energy swell has the potential to bring a high risk of sneaker waves, especially Saturday evening. Shorter period NW swell of 4-5 ft at 10-12 seconds may initially mitigate the risk. A beach hazard statement has been hoisted north of Cape Mendo. DB/ZVS && .EKA WATCHES/WARNINGS/ADVISORIES... CA... Beach Hazards Statement from Saturday afternoon through Saturday evening for CAZ101-103-104. NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory until 3 AM PST Saturday for PZZ455-475. && $$ 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