493 FXUS66 KMFR 251344 AFDMFR Area Forecast Discussion National Weather Service Medford OR 644 AM PDT Mon Mar 25 2019 .UPDATE...Updated the Aviation and Marine sections. && .AVIATION...For the 25/12Z TAFS...Conditions will remain mainly VFR early this morning. An incoming front has reached the Curry County coast and will bring a mix of MVFR and VFR cigs with precipitation, obscured higher terrain, and gusty low level southerly winds as it tracks to the Cascades by 19Z then across the east side through this afternoon. Winds will be strongest in the Shasta and Rogue Valleys, over the higher terrain, and across the east side this morning into the early afternoon. Post-frontal showers and snow showers will persist during the late afternoon and evening across the area with a slight chance of thunderstorms over the coastal waters to the immediate coast. Conditions will mostly improve tonight, though with patchy valley IFR possible. -DW && .MARINE...Updated 300 AM PDT Monday 25 March 2019...A front will move through the area today, bringing increasing small craft advisory winds and steepening seas. High and steep seas will then linger through this evening. Weak high pressure will bring improving conditions late tonight into Tuesday evening. Another front will move through Wednesday, and low pressure will remain over the waters into Thursday. This will produce an episode of stronger southerly winds with high and steep to very steep seas. High pressure will build in with improving conditions Friday into Saturday. -DW && .PREV DISCUSSION... /Issued 359 AM PDT Mon Mar 25 2019/ DISCUSSION...A hefty spring storm is making its way toward the forecast area this morning. Latest model data has slowed the arrival of the heaviest Northern California precipitation by a few hours compared to yesterday's models. Seemingly a small change, it may have big consequences on the weather. Heavy precipitation will be focused over Northern California, and this is where we have Winter Storm Warnings and Winter Weather Advisories ongoing. Start of heaviest snow will be delayed until around 8am in the Mount Shasta City area per latest data. This makes a tricky forecast even more difficult because post- sunrise really throws into question how much snow will impact roadways, particularly Interstate 5. This is, however, why we have an Advisory out for elevations between 3000 and 4000 feet...and not a Warning...and have communicated that uncertainty to our partner agencies. At higher elevations, March sun angle won't have as much impact, and snow on roadways is possible through the morning and early afternoon. Winds will also impact Siskiyou County, particularly the Shasta Valley, where a Wind Advisory is ongoing. Farther north, precipitation impacts won't be as significant, but it will be windy. We've issued a Wind Advisory for the southern Rogue/Bear Creek Valleys. This is based mainly on consistent HRRR high-resolution wind output, along with current observations and expected trends. 2000- and 5000-foot winds align nicely with the valley this morning, another indicator for gusty winds from Ashland to Medford. East of the Cascades, gusty south winds are expected as well, impacting most areas. We have a Wind Advisory for those areas too. Precipitation in Southern Oregon will be focused at the coast, while inland valleys like the Rogue and Umpqua will likely see a quarter inch or less of rain. Given the strong winds in the Rogue Valley, I wouldn't be surprised to see less than a tenth of an inch and very little to none in the morning. Models have trended away from the potential of significant East Side snow tonight, so we're left with little to no weather impacts tonight into Tuesday. The next frontal system arrives Wednesday, and models have trended stronger with this, in terms of southerly wind field and precipitation. We'll have to consider Winter Weather Advisories for Siskiyou County again, and snow levels will likely be a touch higher than today's system. Wind Advisories will be likely too. Please see the previous long-term discussion from the Sunday dayshift below. Keene Thursday through Sunday...Models are showing good agreement with a closed low moving into the Oregon coast on Thursday. This is expected to bring widespread showers with snow levels of around 3500 feet rising to 4000 to 4500 feet in the afternoon. Weak instability and moist upslope flow may result in some moderate to locally heavy showers during the the day on Thursday, especially over the Cascades and western mountains. Thursday night, an upper trough and moist onshore flow are expected to continue over the area with scattered to numerous showers likely. Friday into Friday night, ensemble forecasts support a weak upper level ridge building offshore and gradually moving into the coast. The ECMWF and ensemble ECMWF are slightly slower to build the ridge into the area and support some continued moist onshore flow and troughing. So may see some continued scattered showers Friday before drier conditions develop over the area Friday night. On Saturday, models and ensembles have trended warmer and drier with an upper ridge in place and the next front remaining offshore. So have lowered the chance for precipitation and increased temperatures during this period. The next front may approach the coast and begin to spread light to moderate precipitation inland on Sunday. However, there is significant variability in the track of this system as it moves into the ridge. So confidence is low on the details of the forecast for timing and amount of precipitation. -CC && .MFR WATCHES/WARNINGS/ADVISORIES... OR...Wind Advisory until 5 PM PDT this afternoon for ORZ029>031. Wind Advisory until 1 PM PDT this afternoon for ORZ026. CA...Wind Advisory until 11 AM PDT this morning for CAZ081. Winter Storm Warning until 5 PM PDT this afternoon above 4000 feet in the for CAZ080. Winter Weather Advisory until 11 AM PDT this morning for CAZ082. Winter Storm Warning until 5 PM PDT this afternoon above 4000 feet in the for CAZ082. Winter Weather Advisory until 11 AM PDT this morning for CAZ083. Winter Storm Warning until 5 PM PDT this afternoon for CAZ083. Pacific Coastal Waters...Small Craft Advisory until 8 PM PDT this evening for PZZ350-356. Small Craft Advisory until 8 PM PDT this evening for PZZ370-376. $$