Area Forecast Discussion
Issued by NWS Eureka, CA
Issued by NWS Eureka, CA
815 FXUS66 KEKA 012214 AFDEKA AREA FORECAST DISCUSSION National Weather Service Eureka CA 314 PM PDT Wed May 1 2024 .SYNOPSIS...Warm and dry weather will be interrupted by a weak frontal passage Thursday. Unsettled conditions will continue through the end of the weak before a more impactful system arrives this weekend, bringing measurable rainfall and gusty winds to the area Friday - Saturday. && .DISCUSSION...Cold morning temperatures have risen to highs in the upper 50`s and mid-60`s this afternoon beneath clear skies and abundant solar insolation. Some valleys approached 70 at the peak of daytime heating. Gusty offshore northerly winds continue to expand inland south of Cape Mendocino - current observations indicate gusts 20-30 mph along the Humboldt and Mendocino coasts and exposed ridges within the coastal ranges. Meanwhile, the interior is still expected to briefly warm and dry out for the next 24 hours. Hi-res models have interior valleys reaching into the mid to upper 60`s while RH values drop to between 30-50%. High to mid level clouds will continue to stream into the PNW as a weak shortwave digs into northern CA, eroding away at the meridional pressure gradient driving northerly winds. Cloud ceilings will lower and thicken ahead of a weak surface front, with HREF indicating light precipitation beginning as early as 3 am Thursday morning in far northern Del Norte county. Precip will gradually expand south through Humboldt county during the day Thursday. Hi-res models are trending toward heavier precip rates, with HREF forecasting between 0.20-0.30 inches/6 hours from 8 am to 12 pm. Accumulations 0.25 to 0.75 inches expected through 11 am Friday, with highest amounts in northern Del Norte county and NW facing slopes tapering off heading south into southern Humboldt County. After some mid level drying with the offshore ridge axis, the descending upper low driven along a broad upper trough complex will usher additional moisture into the area late Thursday into Friday ahead of a larger system arriving this weekend. Some scattered showers are possible in northern counties as the winds turn southerly ahead of the leading warm sector of the low. As the cold upper low descends into the PNW, the associated surface low will produce significant rainfall Friday night into Saturday as the cold front pushes onshore and turns winds WNW. WPC and NBM QPF are currently forecasting 1-2 inches of rain in the 24 hours spanning Friday night to Saturday night for northern Mendocino, Humboldt, Del Norte and eastern Trinity counties, with the higher totals (1.75-2) expected on westward facing slopes. Southern Mendocino and Lake counties are leaning closer to 0.5-0.75 inches over the same period. Long range deterministic models are trending a bit higher across the board due to variations in the surface low track, but are in agreement with NBM that the bulk of precip will taper off early Sunday morning. With snow levels around 3,000-4,000 ft, mountain snow will be possible on the tail end of this system, leaving behind unseasonably cold temperatures in its wake. Late weekend into early next week, model clusters and Euro ensembles are leaning toward a colder, more unsettled pattern at least through Tuesday. && .AVIATION...Mostly VFR conditions have and will persist during the daylight today. Northerlies will continue to be gusty in the afternoon at all the terminals and will diminish by sunset. An approaching frontal system arriving later tonight will bring low clouds and occasional precipitation to the coastal terminals tonight, impacting conditions to IFR or MVFR. At KCEC, ceilings have around a 75% probability of being below 1000ft with a 30% chance of being below 500ft. At KACV, these ceiling height probabilities are 70% at 1000ft and 30% at 500ft. Mist, drizzle, and even light rain have over 90% chance of occurring at both coastal sites according to the National Blend of Models. Visibilities tomorrow morning have a 50% probability of dropping below 5SM and a 15-20% probability of being under 2SM periodically during this front passage. Forecast confidence remains low at this point, and these drops in visibility will be addressed in subsequent TAF publications. Inland, KUKI looks on track to stay mostly clear for the next 24 hours, but a low level wind shear threat due to significantly increased wind speeds about 1-1.5km height compared to the light winds at the surface is forecasted for this evening as the front crosses over the area. DS && .MARINE...Gusty northerly winds have continued through most the day. Gusts have been near or at gale force in the southern waters, particularly south of Cape Mendocino. Winds and waves are already beginning to diminish and are forecasted to continue to do so into tomorrow across all the marine zones. An approaching warm front entering our area will force westerly winds to blow tomorrow. North of Cape Mendocino, the winds will blow towards the north while Mendocino Co. and the southern part of Humboldt Co. will blow towards the south. These winds will remain fairly light (>15kt) during this period of split flow. The light winds and relatively calmer sea state accompanied by them will continue until the beginning of this weekend. On Friday afternoon, winds will increase and shift northerly as a cold front approaches, increasing the wind speeds even more on Saturday. DS && .EKA WATCHES/WARNINGS/ADVISORIES... CA... None. NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory until 3 AM PDT Thursday for PZZ450-470. Gale Warning until 8 PM PDT this evening 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