000 FXUS66 KMFR 180520 AFDMFR Area Forecast Discussion National Weather Service Medford OR 1020 PM PDT Sat Jul 17 2021 Updated AVIATION Section .DISCUSSION...18/00Z NAM in. Mostly clear skies prevail across the Medford forecast area this evening, but there is a lot of smoke streaming from the Bootleg fire and, to a lesser degree, from the Jack fire. There is also some cumulus over northern Lake County and a pyrocumulus over the Bootleg. The pas de deux between a strong ridge over the four corners area and a long wave trough offshore will continue through the week with mostly southwest flow aloft over the Medford forecast area. The ridge will gain the upper hand Sunday with rising heights over the area. A thermal trough along the coast will move inland Monday afternoon. This will make Sunday the hottest day of the coming week over the inland areas, while the marine layer cools the coast. The trough will fight back and deepen a bit Monday. 500 mb heights will fall a bit and surface temperatures will be a bit cooler inland, but flow aloft will also become more southerly, allowing monsoonal moisture to filter into the area. At this time, it looks like any thunderstorm activity will be limited to the far eastern portions of the Medford forecast area, mostly Modoc and Lake counties. The forecast area of isolated thunderstorms will be close to the eastern boundary of the Bootleg fire. The trough will gain the upper hand Tuesday as it approaches the coast. Expect more cooling inland then and the area of possible isolated thunderstorms will also move east, to southeast Lake and eastern Modoc counties. A short wave ejecting from the trough will move onshore well to the north of the forecast area Wednesday. The inland cooling trend will continue into Wednesday, which currently looks to be thunderstorm-free with near normal high temperatures. Once that short wave moves inland, ridging will return to the area and temperatures will warm inland Thursday into Saturday. No thunderstorms are forecast during this interval. However, the medium range models are hinting at possible thunderstorms next Sunday. No end in sight to this hot and dry pattern. The Climate Prediction Centers 6 to 10 and 8 to 14 day outlook both indicate above normal temperatures and near normal to below normal precipitation. Of course, normal this time of year is near zero. That is good through the end of July. && .AVIATION...For the 18/06Z TAF Cycle...For all inland areas, VFR conditions prevail through the TAF period. The only exception will be reduced visibility due to smoke from numerous wildfires in the area. The main visibility reduction and smoke layers will be emanating from the Bootleg Fire northeast of Klamath Falls. The smoke is not affecting terminals currently and probably will not for the next 24 hours, though patchy smoke could drift back toward Klamath Falls late tonight or early Sunday morning before shifting back to the northeast. Along the coast and just offshore, VFR this evening will give way to areas of IFR marine stratus/fog overnight into Sunday morning. Expect these lower conditions to erode to VFR by late morning/early afternoon in most areas, but then return again Sunday evening. -Spilde && .MARINE...Updated 800 PM PDT Saturday 17 July 2021...A thermal trough will strengthen tonight and persist through much of next week. While the strength of this thermal trough will ebb and flow, it won't be as strong as some of the thermal troughs that can occur at this time of year. Rather, it will remain strong enough and endure to keep conditions hazardous to small craft south of Cape Blanco for several days. Winds in those areas will mostly be 15-25 kt with some gusts to 30 kt and seas of 6-9 feet. It appears there will be a peak in strength of the thermal trough sometime Wednesday or Thursday, when seas could exceed 10 feet for a while, especially south of Gold Beach. Meantime, areas farther north, north of Cape Blanco, will have some northerly afternoon breezy conditions and seas generally running in the 3-6 foot range. -Spilde && .FIRE WEATHER...Updated 800 PM Saturday 17 July 2021...Dry and breezy conditions will persist through Sunday, with the lowest humidities and strongest winds east of the Cascades. This happens to be where the vegetation is driest in a historical context, with Energy Release Component values maxing out compared to recent years for Northeast California and Southern Oregon east of the Cascades. Sunday will be the most critical day with the combination of the strongest winds and lowest humidities in the forecast for the next several days. A Red Flag Warning is in effect from the Shasta Valley eastward (FWZs 281, 282, 284, 285, 624), including the Bootleg, Lava, and Tennant fires. In addition to strong winds and low humidities, very unstable and dry conditions are expected over the Bootleg Fire on Sunday when Haines Index values will be close to maxing out, indicating favorable conditions for plume-dominated fire. Considering we've observed plume-dominated behavior the past several days on the Bootleg wildfire, weather conditions will certainly support that that kind of extreme behavior Sunday. See RFWMFR for details. The wind and humidity situation will improve slightly Monday, but then thunderstorms enter the forecast. The most favorable area for thunderstorms will be over the eastern portions of FWZ 625 and 285. Thunderstorms could be dry initially on Monday afternoon. Afternoon and evening thunderstorms may also develop again Tuesday, but the area will be shifted farther east, over far eastern 625 and 285. This situation will be monitored closely over the coming days. && .MFR WATCHES/WARNINGS/ADVISORIES... OR...Red Flag Warning until 8 PM PDT this evening for ORZ624. CA...Red Flag Warning from 2 PM to 8 PM PDT Sunday for CAZ281-282. Red Flag Warning from 2 PM to 8 PM PDT Sunday for CAZ284-285. Pacific Coastal Waters...Small Craft Advisory until 5 PM PDT Tuesday for PZZ356-376. $$ 15/15/18