973 FXUS66 KMFR 290408 AFDMFR Area Forecast Discussion National Weather Service Medford OR 808 PM PST Thu Dec 28 2023 ..Updated MARINE discussion... SHORT TERM...Tonight through Saturday night. A slight chance to chance of light showers will continue this evening, ahead of an occluding front. South to southeast winds have begun to increase with 25 mph sustained and gusts to 40 mph reported at Weed, and gusts to 30 mph in the Coast Range. Rain will reach the coast before the end of the night. Rain and gusty winds will be most notable Friday into Friday evening from the coast to the Cascades, with highest rainfall amounts (around a half inch to an inch and a half) for Curry, Josephine, and Siskiyou counties, and strongest southerly winds (gusting to 50 mph) in the southern portions of the Shasta and Rogue valleys. Snow levels will be well above the major passes, at around 7000 to 8000 feet, which will limit the impacts from the frontal passage. Elsewhere, amounts of up to a quarter of an inch in southwest Oregon, a half inch for the Cascades, and up to a tenth of an inch for the east side. The remnants of the front will move across the east side Friday night, while a post-frontal surface trough brings the next dose of rain to the coast. This disturbance will move across inland areas Saturday into Saturday evening with the low level flow shifting from southerly to westerly and snow levels around 5000 to 5500 feet. Though still light with rainfall accumulations of up to a quarter of an inch, some west side areas, particularly Coos, Douglas, Jackson and eastern Josephine counties, including Roseburg, Grants Pass, and Medford, will receive more precipitation with this disturbance late Friday night into Saturday evening than with the stronger Curry and Siskiyou County focused southerly-flow system of Friday into Friday evening. Amounts will be very light on the east side, up to a tenth of an inch. High pressure will build in late Saturday night with valley low clouds and fog becoming more extensive into Sunday morning. LONG TERM...Sunday through Thursday. The extended forecast will start with the large scale pattern calming down a bit after this past week of parading storm systems. An area of low pressure will be cutoff to our south, while a shallow wave will pass to our north through B.C. This will leave SW Oregon and NorCal under quasi-high pressure for at least a 24 hour period. Calm winds, shallow mixing heights, and clearing skies will favor the formation of fog Sunday morning. A proper ridge of high pressure will build in over the entire Pacific coast as the cutoff low drifts into the Desert Southwest. This will create another day of poor ventilation on Monday and again create conditions conducive for fog. It is hard to say for certain just how expansive or dense the fog could be, though because most places inland from the coast range have not received more than a tenth or so of rain in the past 72 hours. Usually, more moisture would help things but, we are also at our longest nights of the year...so stay tuned if fog is a concern for you! The pattern becomes active again on Tuesday as a wave digs south towards the Bay area and the front moving through Tuesday evening/night through Wednesday morning. This will result in a glancing blow for this region, with a similar pattern to our most recent fronts where rain is focused along the Coast Range and over Siskiyou County. Snow levels look promising, in that the possible ranges are from 3500-5500 feet, which would offer a chance for even some mid-slopes to catch some snow. Our official forecasted snow level calls for it to hover between 4000 and 4500 feet, resulting in 1-6 inches of snow in the Cascades and 4-10 in Siskiyou County. Despite snow levels possibly being low enough to reach some mountain passes, the amounts and rates for now look like they will cause no more than a minimal disruption to travel and commutes. Showers will be lingering along the high terrain and coast later on Wednesday. Models show quick moving high pressure building back in on Thursday, with another wave of low pressure quickly kicking that east. Behind this second high pressure ridge is more storm activity that is catching the attention of the Climate Prediction Center. They are calling for a slight chance for heavy rain/snow and strong winds over the Pacific Northwest from Jan. 5-11. -Miles AVIATION...29/00Z TAFs...VFR conditions continue under high ceilings and clear visibilities for northern California and southern Oregon , with little expectation of levels changing through the night. An approaching warm front will bring low level wind shear late tonight, with 30-40 kt southerly winds over most areas and 50- 60 kt winds over higher terrain. Precipitation will start to fall on the Oregon coast later in the morning and will move inland through the day, mostly affecting areas west of the Cascades. Snow levels of 7000-8000 feet will prevent snow from anywhere except the highest terrain. Rainfall should be mostly light, but could still locally lower ceilings and visibilities as well as obscure terrain. -TAD .MARINE...Updated 730 PM Thursday December 28, 2023...Very high and very steep seas are expected through at least Friday night. Swell dominated seas will continue for much of tonight, then quickly transition to wind driven again by early Friday morning. An approaching warm front will bring another round of strong winds with gales expected across the outer waters through Friday afternoon. This will bring another round of very high and very steep wind driven seas of 15 to 20 ft through Friday evening. Winds will ease Friday evening, but another heavy long period swell will build into the waters Friday night and maintain very steep and chaotic seas of 15 to 18 ft into Saturday morning. Seas will gradually subside later Saturday morning and throughout the weekend, eventually lowering to below 10 feet on Sunday. Winds will also become light on Sunday and relatively calm conditions will persist into the start of next week. Another system approaches the region Tuesday into Wednesday, and while this will bring increasing winds and building seas, conditions are currently not expected to reach the levels they have been at for the past week. /BR-y BEACH HAZARDS...Updated 200 PM Thursday December 28, 2023...Large breaking waves are expected to continue through at least today, which will create dangerous conditions along and within the surf zone, and could inundate beaches and low lying shorelines. Increasing the hazards of these breaking waves is the occurrence of King tides. These very high tides peaked early Monday but will continue higher than normal through today. So far the tides have come in 0.3' to 1.2' higher at Port Orford and Charleston respectively. While there still likely won't be coastal flooding, this does increase the chance just a little more; and so some low lying areas especially around Coos Bay and the immediate shoreline at Gold Beach may see high water from tidal overflow combined with the action of the high surf. Regarding high surf, the high surf advisory has been upgraded to a High Surf Warning through early Saturday morning. With the arrival of a very heavy southwest swell and building wind seas, dangerously large breaking waves of 25 to 30 ft are expected to result. This high surf action will increase the inundation of beaches and increase the risk of beach erosion, especially when combined with the effects of King tides. /BR-y/Hermansen && .MFR WATCHES/WARNINGS/ADVISORIES... OR...Wind Advisory until 7 PM PST Friday for ORZ026. High Surf Warning until 7 AM PST Saturday for ORZ021-022. CA...Wind Advisory until 7 PM PST Friday for CAZ081-082. PACIFIC COASTAL WATERS...Hazardous Seas Warning until 4 AM PST Saturday for PZZ350-356-370-376. Gale Warning from 1 AM to 1 PM PST Friday for PZZ370-376. && $$