Area Forecast Discussion
Issued by NWS Eureka, CA
Issued by NWS Eureka, CA
780 FXUS66 KEKA 162256 AFDEKA AREA FORECAST DISCUSSION National Weather Service Eureka CA 256 PM PST Thu Jan 16 2025 .SYNOPSIS...Dry weather is expected to continue for the next 7 days. Chilly nights and mornings with areas of frost and patchy fog are also expected. && .DISCUSSION...Satellite imagery showed patches of low clouds offshore over the coastal waters moving onto portions of the North Coast this afternoon. Otherwise, skies have remained clear across the area today. A decaying dry cold front sliding southward along the NW Oregon coast will likely bring a push of shallow moist air to the North Coast and adjacent river valleys tonight into Friday morning as northerlies strengthen over the coastal waters. The onshore flow will likely increase along the Mendocino coast late tonight into Friday, resulting in low clouds and perhaps some fog. High resolution models as well as NBM guidance show much less potential for gusty northerlies on Friday behind the front. Interior Del Norte county may have gusts to 30 mph, otherwise winds are not likely to have any impacts except over the outer coastal waters. With less northerly winds and higher boundary layer humidities, potential for residual coastal low clouds and fog will persist Fri night and Saturday. Offshore flow should increase over the latter portion of the weekend with less potential for coastal low clouds and fog. NAM12 BUFKIT profiles are showing high boundary layer humidities into Sunday and some coastal low clouds may persist. River valley fog and low clouds will form for sure each night and morning. Large scale flow pattern continues to resemble an omega block with no pronounced signal for rain through much next week. A dry offshore flow regime is forecast to continue all next week, increasing the probability for near or below freezing minimum temperatures for coastal areas and adjacent valleys. Sub-freezing temperatures are a sure thing in interior valleys, especially Trinity and northern Mendocino. Some ensemble members and deterministic outliers indicate shortwave troughs busting down or breaking through the block late next week or next weekend. NBM probabilities for > 0.05 of an inch in 24 hours increases next weekend to 20% for SE Lake and 50% for Del Norte. So perhaps our long stretch of anomalously dry weather with below normal low temperatures may finally come to an end. DB && .BEACH HAZARDS...A new long period westerly swell group emanating from a cyclonic storm in the western north Pacific will spread into the coastal waters late Friday night into Saturday morning. This highly energetic swell with 20+ second periods will build through the day on Saturday, increasing the risk for set behavior and/or sneaker waves by late afternoon into Saturday evening. Threat for set behavior and sneaker waves will persist into the day on Sunday and perhaps Sunday night. Significant swell periods are forecast to eventually drop below 16 seconds on Monday, reducing the risk for sneaker waves. A beach hazard statement will definitely be necessary for this swell. DB && .AVIATION...Throughout much of today`s forecast period, weather conditions across NW California were quite humdrum. The only significant exception that impacted the (coastal) TAF sites was a widespread coastal stratus...that advected along the immediate coast north of Cape Mendocino. The result was LIFR/IFR Cig/Vis at ACV and CEC in the morning. However, a small wedge of marine clouds push back over CEC in the afternoon resulting in IFR clouds. A few cool, inland river valleys had fog overnight. Evening/overnight/Thursday morning...the coastal marine layer (a little deeper) will surely manifest again at the coastal terminals. Inland valleys will be spotty, but as of the 18z TAFs, did introduce some clouds/fog at UKI with some model support. /TA && .MARINE...High pressure is forecast to strengthen tonight after the passage of a dry cold front across the Pac NW. Northerly winds and steep wind waves will increase tonight into Friday. Deterministic and probabilistic guidance continues to point to solid small craft advisory for winds in the northern outer waters. Signal for wind strength to advisory level are much less pronounced for the southern outer waters. NBM and HREF, which typically are overdone with wind gusts over the waters, indicate low probabilities for gusts > 34 k. Even where probabilities are 30%, coverage appears insufficient to warrant upgrading the gale watch to gale warning. Also, considered upgrading to a hazardous seas warning, but coverage of steep seas > 10 ft is also lacking in areal coverage. Thus, the gale watch has been upgraded to a small craft advisory for the northern outer waters. Friday night into Saturday the northerly winds are expected to gradually push farther westward away from the coast and diminish below 20 kt over the outer waters with even lighter and more variable winds for the inner waters. Northerlies may ramp up again for the latter portion of the weekend on Sunday, but speeds will likely remain sub-advisory and under 20 kt. Even into next week, northerlies are not forecast to exceed 15 kt. Wind driven waves are expected to persist over the weekend in association with these winds and will remain steep and uncomfortable into early next week. A series of long period westerly swells will continue to spread into the waters through next week and probably for the rest of winter. Currently, a long period swell group has been slowly subsiding today. This swell will continue to decay to 3 to 5 ft Fri-Sat, before a much more energetic westerly swell group with peak periods of 20+ seconds builds Saturday through Sunday. This new swell group is expected to peak by early Sunday, up to 8 ft, and may pose a risk for offshore shoaling as well as sneaker waves this weekend and early next week. DB && .EKA WATCHES/WARNINGS/ADVISORIES... CA... None. NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory from 10 PM this evening to 3 AM PST Saturday for PZZ470. Small Craft Advisory from midnight tonight to 3 AM PST 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