FXUS66 KMFR 090438 AFDMFR Area Forecast Discussion National Weather Service Medford OR 838 PM PST Wed Jan 8 2025 .UPDATE...The main weather concern tonight into tomorrow morning will be around fog developing in valleys. This evening, satellite observations indicate areas of fog developing in valleys in Jackson, Josephine, Douglas and Coos counties. Areas of fog are also likely for other valleys, including across northern California and for valleys east of the Cascades. Similar to last night, fog may be locally dense, and create travel difficulties with low visibilities. Have updated the forecast to add more fog to areas, based on current observations. We will continue to monitor fog and visibility conditions and update as needed. && .PREV DISCUSSION... /Issued 330 PM PST Wed Jan 8 2025/ DISCUSSION...Quiet weather is in store for the next 24-36 hours. High pressure over the eastern Pacific Ocean will gradually nudge over the region Thursday into early Friday. A quick moving trough and front will knock down the ridge and pass through the area on Friday, bringing a quick shot of precipitation. The ridge will quickly rebound over the weekend, but the ridge axis will be offshore again, and this will allow for a few "inside sliders" Sunday into Monday. Eventually the ridge nudges back overhead early next week while one of the inside sliders undercuts this ridge and retrogrades westward over southern California. With the exception of Friday, this pattern will overall lead to dry conditions with minimal weather impacts. High pressure aloft is resulting in strong valley inversions, leading to persistent fog/low clouds in West Side Valleys as well as stagnant air across the region. An Air Stagnation Advisory is in place through Friday morning until the front arrives to mix out the stagnant air. Above the inversions, a thermal trough at the surface is bringing gusty northeast through southeast winds (15 to 25 kt), warmer temperatures and unseasonably low relative humidities to the higher elevations. This pattern will continue through Thursday night before a front arrives at the coast Friday morning. This front isn't particularly strong, especially compared to the systems we experienced over the holidays, and it'll be washing out as it moves inland during the day Friday. We do expect wetting rains along the coast and along and north of the Rogue-Umpqua Divide to the Cascades, but areas south and east will likely only get a few hundreths if that with this system. Snow levels will be above 5000 with this precipitation, so we don't anticipate any winter weather impacts with this front. It will, however, provide enough mixing to clear out the stagnant air and bring some gusty winds to the coast, mountains and areas east of the Cascades. These winds don't look headline worthy, but gusts of 25-35 mph will be common in these areas. In the northerly flow behind this front, gusty northerly winds will continue and this should keep stagnant conditions from returning until early next week. The inside sliders that follow on Sunday are likely to be dry, though some very light precipitation is possible across far northern areas Sunday afternoon/evening. High pressure returns by the early part of next week, and this is when we could see the return of persistent valley fog/low clouds and stagnant conditions. /BR-y AVIATION...09/00Z TAFS...VFR prevails area wide this evening with a broken mid-level deck moving south-southeastward in NNW flow aloft. Expect low clouds and fog to develop in the west side valleys again later this evening/overnight reducing conditions to LIFR at both Roseburg and Medford. These should break up again Thursday morning or, at the latest, early Thursday afternoon. VFR will prevail elsewhere. -Spilde MARINE...Updated 200 PM PST Wednesday, January 8, 2025...Advisory level conditions are expected to persist through this evening across most of the waters. Residual west swell and breezy north winds will bring steep seas of 8 to 11 feet. While north winds (10-20 kt) continue tonight into Thursday, the swell will decay and conditions briefly improve. A cold front is expected to pass through the region on Friday. Steep seas are likely to accompany this front. Then, north winds strengthen Saturday into Sunday as high pressure builds offshore and a thermal trough develops near the coast. Winds may reach gale force south of Gold Beach during the weekend. -Spilde && .MFR WATCHES/WARNINGS/ADVISORIES... OR...Air Stagnation Advisory until noon PST Friday for ORZ023>026- 029>031. CA...None. PACIFIC COASTAL WATERS...Small Craft Advisory until 10 PM PST this evening for PZZ350-356-370-376. && $$ CC/CC/CC