Scientific Forecaster Discussion
000 FXUS66 KMFR 152245 AFDMFR Area Forecast Discussion National Weather Service Medford OR 245 PM PST Fri Nov 15 2019 .DISCUSSION...Short-term...Tonight through Monday....A weak front has passed through the forecast area, and some rain with the front has been observed over the past 24 hours, primarily from Cascades westward. The highest rainfall (0.88in) was observed in northwestern Douglas County. No rainfall was observed east of the Cascades and in northern California...or in the Rogue Valley. Tonight, rain is not expected, and skies will clear some. We expect fog in the coastal, Umpqua, and Illinois Valley tonight. Farther east where there has been no measurable rainfall, we don't expect much if any fog tonight. Quiet weather continues after the front on Saturday through Monday under low amplitude upper ridging. Fog will impact travel more Saturday and Sunday night as high pressure builds some and inversions strengthen. Some dense fog is possible in the aforementioned valleys. Regarding the Air Stagnation Advisory, the current hazard area looks fine with stagnant air expected to continue in the Rogue Valley and most valleys east of the Cascades. Mixing heights will be close to the thresholds, but without any rain today and light winds continuing, we don't expect the air mass to change much. Farther north, the rain has helped to clear the air some in the Umpqua Basin, and we expect mixing heights to be higher than 1000 ft AGL through the weekend. Therefore we won't be re-issuing the Air Stagnation Advisory for that area. Long-term...(Monday evening through Friday)...The frontal boundary moving through on Tuesday will continue through southern Oregon and northern California through the day. This front is not expected to bring significant rainfall. Maybe a quarter of an inch of rain for the coast, with a tenth of an inch or less for the Cascades with a couple hundreths of an inch in the West Side Valleys with much less east of the Cascades. Snow levels will start off around 7000 feet and drop to around 4000 feet by Wednesday night, after the front goes through. Precipitation should end by the time by the snow levels reach the passes. As such, limited travel impacts, if any, are expected. (Roads may become slippery due to oils washing away-- especially in areas that did not see rain today.) Then we move towards another ridge pattern with gusty east winds and dry air aloft. This means that we'll get some cold temperatures (near or below freezing for most of our valleys in southern Oregon and northern California) at night with some rapid drying out, especially on ridges. This pattern will continue for the next several days. Temperatures will moderate out into the weekend, being closer to normal or slightly above normal. -Schaaf && .AVIATION...For the 15/18Z TAFs...Over the coastal waters, along the coast, in the Coast Range, and in the Umpqua Basin...Areas of MVFR cigs/vsbys in low clouds and rain with higher terrain obscured will persist through this morning. The precipitation will end this afternoon but the lower cigs will persist into this evening. Areas of IFR cigs/vsbys in low clouds and fog will develop tonight, persisting into Saturday morning. Over the remainder of the area...VFR conditions will persist into this evening with scattered light precipitation. Areas of higher terrain will be obscured. Areas of MVFR cigs will develop in the valleys tonight, and persist into Saturday morning. -BPN && .MARINE...Updated 800 AM PST Friday 15 November 2019...Despite light and variable winds, steep and hazardous seas will persist through Saturday evening. Meanwhile, long period west swell could create hazardous bar conditions through Saturday. A weak thermal trough will build along the coast Sunday, producing a brief period of north winds south of Cape Blanco through Monday morning. The next front will move onshore Monday night, followed by gusty north winds and steep to very steep seas Tuesday into Wednesday night. -BPN && .MFR WATCHES/WARNINGS/ADVISORIES... OR...Air Stagnation Advisory until noon PST Tuesday for ORZ026-029>031. CA...None.