450 FXUS66 KMFR 191014 AFDMFR Area Forecast Discussion National Weather Service Medford OR 314 AM PDT Tue Mar 19 2019 .SHORT TERM...Today may not seem too different from yesterday for most of us, however, changes are afoot. A system off California will spread clouds toward our area today and eventually rain will follow. The atmosphere will actually be a little warmer today than yesterday, but this will likely be countered by increasing mid and high cloud, so high temperatures are expected to end up similar to yesterday. Gusty south-southeast winds are also expected to develop in many areas again this afternoon. Surface heating and weak upper cooling as the upper trough edges in later today and this evening will produce modest instability. There will also be some weak vorticity advection to provide a triggering mechanism for convection, and moisture aloft increases. If this were to occur in the summer, we'd probably be getting excited about thunderstorm potential. And the thought did cross our minds this morning. But forecast soundings shows that the lifting condensation level and freezing level will be very close together, which will limit or prevent any liquid water and ice interactions, which is a necessary ingredient to produce lightning. Thus, we don't expect any. That said, guidance is in good agreement that there will be some convection aloft, and this will likely produce some virga this afternoon and evening as precipitation falls into the very dry air mass in the low levels. Eventually, this will moisten the column and allow rain showers to get to the ground later tonight and into Wednesday. The upper trough then gradually morphs into a closed low and moves into the northern California coast. The resulting deep, moist southeast flow over our area will keep the chance for showers going into at least early Thursday. -Wright .LONG TERM...Friday through Monday night...A cold front will be approaching the coast Friday morning, and south winds will increase across the forecast area Friday afternoon. When looking at NAEFS climatological data for this time of year, the winds ahead of this front don't look very remarkable, so we're not expecting strong winds with this system. What we'll likely get with this front is about a 24 hour period of rain and mountain snow across the forecast area Friday afternoon to Saturday morning. Models suggest moisture will make it across the Cascades and bring a tenth to quarter inch of precipitation to areas east of the Cascades. A half inch to inch of precipitation is expected at the coast and in Siskiyou County, with around a quarter inch in West Side valleys. Some lingering showers are expected Saturday, and dry conditions are expected Sunday as upper ridging transits west to east across the area. Operational models suggest another front could spread precipitation inland by Monday afternoon, but there's enough spread in ensemble data that Monday could very well be dry too. By Tuesday wetter and cooler conditions likely return...with the National Blend of Models (suite of many operational models and ensemble members) outputting 70 percent chances of precipitation from the Cascades westward on Tuesday. You may be wondering if any of this precipitation will fall as snow in the mountains. Long answer short is...yes. The more nuanced answer is that snow levels will range from about 4000 feet to 6000 feet during the periods of precipitation. 5 to 10 inches of snow are expected in the Cascades, Siskiyous, and high terrain of Siskiyou County above 5000 feet Friday into Saturday. && .AVIATION...For the 19/06Z TAFS...VFR conditions will continue through Tuesday afternoon for most areas. The first exception will be along the coast south of Cape Blanco, where areas of IFR/LIFR cigs/vsbys in marine stratus and fog will persist this evening and may expand northward to Cape Arago tonight. Areas of IFR/LIFR in fog may continue into early Tuesday morning, especially along the southern coast. The second exception will be the more sheltered valleys of the coastal range and lower Umqpua basin, where IFR fog is possible late tonight and early Tuesday morning. VFR will continue for inland areas Tuesday evening but at the coast, expect areas of MVFR cigs to develop, mainly south of Cape Blanco, as showers move into the southern Oregon coast. -CC && .MARINE...Updated 300 AM PDT Tuesday, 19 March 2019... Low clouds and fog cover most of the coastal waters from Coos Bay southward early this morning. This widespread area of low clouds and fog is expected to slow its progression northward this morning and then push back southward as it encounters drier easterly flow. Areas of drizzle and greatly lowered visibilities should be expected within/under it. A gradual weather transition period is expected today, marked by building long period west swell and increasing clouds. Seas will approach, but not meet Small Craft Advisory criteria today through Wednesday. Bar conditions are likely be on the rougher side due to the longer period swell. Conditions will deteriorate Thursday night as a front approaches the region, with gusty south winds and steep to very steep seas expected as the front makes its way onshore Friday. Long period west swell of around 15 feet at 15 seconds is expected into the weekend, before gradually subsiding through Sunday afternoon. BTL/CC && .MFR WATCHES/WARNINGS/ADVISORIES... OR...Beach Hazards Statement through this afternoon for ORZ021-022. CA...None. Pacific Coastal Waters...None. $$