Area Forecast Discussion
Issued by NWS Eureka, CA

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000 FXUS66 KEKA 042251 AFDEKA AREA FORECAST DISCUSSION National Weather Service Eureka CA 251 PM PST Thu Mar 4 2021 .SYNOPSIS...Gusty south winds will occur across much of the region through Friday morning. A front will then move onshore Friday afternoon and evening. Moderate to heavy precipitation will be possible with the frontal passage, as well as snow for elevations above 2000 feet. A period of relatively drier weather is expected Saturday afternoon, followed by more rain Saturday night through early next week. && .DISCUSSION...Water vapor imagery showed a cold upper-level trough situated over the NERN PAC Thursday afternoon. A surface frontal boundary associated with the trough will approach the Redwood Coast tonight, but is not expected to make landfall until Friday morning. As the front moves onshore, precipitation intensity will gradually increase...potentially becoming moderate to locally heavy over portions of Del Norte and Humboldt Counties by late afternoon. In addition, a tight pressure gradient will exist ahead of the front, and when combined with a 40-60 kt low-level coastal barrier jet, will favor periods of advisory level wind gusts through Friday morning for low elevation sites such as Crescent City, and higher elevations above 1500 feet across Del Norte and Humboldt Counties. Heavy precipitation rates associated with a zone of intense 925 mb frontogenesis is forecast to dynamically cool the airmass in the 1000 to 5000 foot layer during Friday evening. Model forecast soundings show a saturated near-freezing isothermal layer developing as a result over Humboldt and Del Norte Counties. Snow levels will subsequently fall to 2000 feet ASL, and possibly even lower for a brief period of time between 4pm Friday and 4am Saturday. Snow accumulations from 2 to 6 inches will occur as a result across interior ridges and mountains. Reference the latest winter weather advisory for more information. Otherwise, model guidance indicates precipitation will become light and scattered Saturday morning into the afternoon. Thereafter, a second frontal boundary is forecast to move across NWRN CA Saturday night and will aid in another period of rain. Drier weather is forecast to redevelop during Sunday afternoon. Then, a large upper trough accompanied by an expansive area of 500 mb temperatures from -30 to -35 C is forecast to dig over the NERN PAC early next week. Impacts related to winter weather will be possible with that storm system over portions of NRN CA. Garner && .AVIATION...A very broad strip of MVFR CIGS extended along the reach of the North Coast from Trinidad and southward until mid- morning. Over Mendocino, MVFR CIGS pushed into southern interior areas as UKI reported MVFR CIGS in the latter morning; lasting into early afternoon. Southerly gusty winds ramped up before daybreak at CEC and the Del Norte Coast; then after daybreak, ACV and the Humboldt Coast started reporting "not quite as strong" gusty winds. Gusty winds also increased over interior Mendocino in the late afternoon. The winds will remain gusty through afternoon/evening/overnight ahead of Friday`s approaching cold front. The above ground winds are really strong; there is a potential threat for Low Level Wind Shear (LLWS) at coastal locations. By 18z (10L), standing wave clouds were evident on VIS Satellite Imagery along Coastal Humboldt County. Through the 00z TAF period, upper level clouds will continue to advect into Northern California through evening. All models are in general agreement that VFR CIGS/VIS will prevail into Friday morning. Rain data also indicates that rain will begin in the far north after 12z (4AM) but most likely in mid-late morning. /TA && .MARINE...A front will slowly approach the coast today, bringing a slow-moving, wide, and robust band of southerly winds. Gale force winds will continue to spread across most of the waters through this evening, with storm force gusts continuing to ramp up in the N outer waters. These winds will continue to build up short period southerly seas tonight, with heights in the lower to mid teens expected for the outer waters. Meanwhile, another slightly longer period 10 to 12 ft NW swell will fill in through the evening and last through the weekend, bringing chaotic combined seas in the high teens to lower 20s by this evening and lasting through Friday. Winds will significantly weaken late Friday, possibly going light and variable Friday night before another shortwave brings relatively light southerlies on Saturday. Southerly winds are generally expected to continue into next week, with speeds occasionally reaching advisory level, particularly across the N outer waters. Seas will gradually subside Friday night and Saturday. Then, a WNW swell is expected to fill in on Sunday, currently forecast to peak around 18 ft at 16 seconds Sunday night. /TJ&SEC && .EKA WATCHES/WARNINGS/ADVISORIES... CA...Winter Weather Advisory from 4 PM Friday to 4 AM PST Saturday for CAZ102-105>108. Wind Advisory until 10 AM PST Friday for CAZ101. Wind Advisory until 10 AM PST Friday for CAZ102-104>106. NORTHWEST CALIFORNIA COASTAL WATERS...Storm Warning until 8 AM PST Friday for PZZ470. Small Craft Advisory until 9 PM PST this evening for PZZ455. Gale Warning from 9 PM this evening to 9 AM PST Friday for PZZ455. Small Craft Advisory until 3 PM PST this afternoon for PZZ450. Gale Warning until 6 AM PST Friday for PZZ450. Gale Warning until 9 AM PST Friday 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

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