896 FXUS66 KMFR 030541 AFDMFR Area Forecast Discussion National Weather Service Medford OR 940 PM PST Sat Mar 2 2024 ...Updated AVIATION discussion... .DISCUSSION...Main change to the forecast for this evening was to lower the Winter Weather Advisory west of the Cascades down to 1500 ft and to also include the Klamath River Valley in western Siskiyou County in the advisory as well. The main reason for this adjustment was to include portions of Interstate 5 north of Grants Pass, including the Sexton/Smith/Stage Road/Canyon Mountain Passes in the Advisory. While shower coverage is expected to be less overall compared to last night, cold air is in place and accumulating snow will be a travel concern tonight as road surfaces reach freezing temperatures. Even locations that don't see additional snow accumulation tonight, wet roads are very likely to freeze tonight and black ice will be a hazard to watch out for if traveling tonight into Sunday morning. The showery nature of the pattern and the varying intensity of the showers themselves make it challenging to pinpoint exact amounts over valley floors, but it won't take much to create hazardous driving conditions. We do expect snow levels to bottom out around 400 ft, but with snow levels that low, it's not out of the question for a heavier shower to drop snow levels down the beaches at times, although snow is unlikely to stick to the warmer road surfaces there. Outside of the lower elevations, snow will continue to pile up in the mountains and all area passes will continue to be affected tonight. Driving in the region will continue to be challenging and should be avoided if possible. A number of winter weather headlines are in effect for this winter storm and details can be found at WSWMFR. For more details on the remainder of the weekend and into next, see the previous discussion below. /BR-y && .AVIATION...03/06Z TAFs...Scattered rain and snow showers have moved inland across northern California and southern Oregon. Snow levels are expected to be 500 at 500 feet tonight. A brief snow shower has already been observed at the Medford airport. Chances for precipitation will remain high (70-90%) over the Oregon coast and the Cascades, but will drop (10-40%) for west side valleys and east ofthe Cascades through early Sunday morning. As always, even an isolated shower can locally lower ceilings and visibilities as well as obscure terrain. Another weak front is expected to bring widespread activity late Sunday morning and into the afternoon. With snow levels at 1500 to 2000 feet at this point, low elevation snow is less of a concern. For this period, moderate showers are likely over Coos and Curry counties and light showers may affect other areas. Moderate to heavy snowfall is forecast over coastal ranges, the Siskiyou Mountains, the Mount Shasta area, and the Cascades. -TAD && .MARINE...Updated 815 PM Saturday March 02, 2024...Steep, swell- built seas continue for all marine waters. A Small Craft Advisory will remain in effect until Monday at 10 AM to highlight this continuing hazard. Unsettled atmospheric conditions will also continue to support scattered showers and 25-35% chances of thunderstorms over the water. The best chances for thunderstorms are from the shore to 30 nm out, with lesser chances out to 60 nm. These chances will gradually diminish through Monday evening. A weak front approaching the Oregon coast on Sunday afternoon will bring some moderate gusty winds to waters north of Cape Blanco, with gusts up to 25 kts possible through Sunday evening. These winds may build localized areas of very steep and hazardous seas in those northern waters. Waters look to calm after the Small Craft Advisory expires on Monday and look to remain generally calm through the week. Brief and limited periods of steep seas may return during the week, but further guidance is needed to properly forecast the timing and area of any returning disturbed seas. -TAD && .PREV DISCUSSION... /Issued 405 PM PST Sat Mar 2 2024/ SYNOPSIS... A long duration winter storm will continue to bring moderate impacts to southern Oregon and northern California with the biggest snow accumulations closer to the coast. Another low and warm front will bring additional significant snowfall to the area Monday into early Tuesday. Major travel disruptions are possible on Monday evening and Monday night. SHORT TERM... A very cold and unstable airmass persists over the forecast region this afternoon and not much will change over the next 24 hours or so. A deep low bringing all this cool and unstable air remains well offshore and isn't moving anywhere anytime soon. Snow on the valley floors still remains a concern tonight as snow levels crash down to 500 feet, although models appear a little drier for this next wave with less than 1 inch of snow on the valley floors and slightly higher totals above 2000 feet. By late Sunday morning and afternoon, a short wave embedded in this low will push onshore later Sunday afternoon, which should lead into another jump of precipitation and more coverage in showers. However, breaks in the showers and the sun briefly hitting the valley floors will hopefully diminish the risk of significant accumulating snow at lower elevations, which has happened the last two days. We are forecasting highs in the lower 40's within the west side valleys on Sunday. Snow levels will rise to ~ 2000 feet with what weak surface heating we do have and any impacts should really be above that level. Therefore, we opted to keep the winter weather advisory at 2000 feet through most of Sunday for valleys west of the Cascades. Closer to the coast in eastern Curry and western Josephine County, snowfall will remain heavy tonight, especially at elevation. We opted to continue the winter storm warning for those locations as well as western Siskiyou County. The valleys in western Siskiyou County are difficult as it could be cold enough that heavy snow makes it to the valley floors. So that warning could be pushed down to a lower elevation on an update later this evening. However, things become a little more interesting on Monday as a warm front and perhaps weak surface low hit southern Oregon and northern California. That is discussed in more detail below. LONG TERM...(Monday 3/4 through Friday 3/8)...The long term starts with yest another in the long line of winter storms moving into the region. The GEFS ensembles start Monday in remarkably good agreement with over 90% of the GEFS solutions showing a deeper and continued cold upper trough over the area with a shortwave moving down around the base of the trough. This pattern would result in light to moderate showers across the area while the deeper moisture remains just to the south on Monday. Almost all of the ensemble solutions are indicating another winter storm moving into the region with the upper trough positioned slightly further north and a low moving in from the west bringing a front and additional moisture into the area Monday into Tuesday. This will likely result in more rain and snow across the area. Both solutions favor snow levels rising during the day Monday, starting out around 1000 to 2000 feet Monday morning then rising to between 2500 to 3500 feet Monday afternoon. Then further west while all of the ensemble plots indicate an upper trough moving towards to coast, around 40% of the ensemble plots indicate a weak upper low winging in with it. Either way a frontal system approaches remains just south of the area as it moves inland, with the upper low to the south wrapping moisture into mostly northern California later Tuesday. The majority of the GEFS solutions favor lower snow levels but favor lighter rain and snow amounts, with limited to moderate impacts from snow showers over the area. Heading into mid next week ensemble 500 plots begin to diverge more, but the vast majority (>90%) indicate a ridge building over the region and remaining into the end of next work week before shifting east with another system moving in next weekend. Ensemble meteograms for both the EC and the GFS are also in agreement with over 90% member indicating no precipitation for the majority of the region during this time period. -Sven && .MFR WATCHES/WARNINGS/ADVISORIES... OR...Winter Weather Advisory until 10 PM PST Sunday above 1500 feet for ORZ023>026. Winter Storm Warning until 10 PM PST Sunday for ORZ024. Winter Weather Advisory until 10 PM PST Sunday for ORZ027-028. Winter Storm Watch from Monday morning through Tuesday afternoon above 4500 feet for ORZ027-028. Winter Storm Watch from Monday morning through Tuesday afternoon above 4500 feet for ORZ029. CA...Winter Storm Warning until 10 PM PST Sunday above 3500 feet for CAZ080. Winter Weather Advisory until 10 PM PST Sunday for CAZ080. Winter Storm Watch from Monday morning through Tuesday afternoon above 4500 feet for CAZ080>084. Winter Weather Advisory until 10 PM PST Sunday above 4500 feet for CAZ082-083-085. PACIFIC COASTAL WATERS...Small Craft Advisory until 10 AM PST Monday for PZZ350-356-370-376. && $$ MNF/TAD/CZS