688 FXUS66 KMFR 052141 AFDMFR Area Forecast Discussion National Weather Service Medford OR 241 PM PDT Fri Aug 5 2022 .DISCUSSION...Our forecast area remains wedged between an upper trough to the north and a closed low off the California coast with a weak frontal boundary extending from Idaho back across SE Oregon into NorCal. Isolated to scattered thunderstorms are developing along this boundary in portions of northern California and also south-central Oregon early this afternoon. These will continue in the same general areas into this evening with a focus out east near the Warners and Hart Mtn Wildlife refuge. North and west of the boundary, fair weather prevails with sunshine and temperatures a few degrees above normal. While an isolated shower or thunderstorm could affect SE portions of the forecast area overnight, most of the convection will wane and dissipate later this evening. A thermal trough and upper ridging will move in overhead this weekend, resulting in a period of hot weather. This latest hot spell does NOT look nearly as strong as last weeks heat wave and will be of much shorter duration. It looks like the peak of the heat will be Sunday into Monday, and there'll probably be some variability in temperatures due to the potential for convection -- more on that later. Right now, we're forecasting 102F here in Medford on Sunday, then 100F on Monday with highs in the mid to upper 90s over most of the east side and in NE Cal. On Saturday, with the ridge axis at its closest, it'll likely be our least active day in terms of thunderstorms. That being said, latest CAMs continue to show at least a slight chance of thunderstorms over portions of the east side and in Modoc County, so we have added that to the forecast. We think the activity should remain east of the current larger fires burning across the area -- the McKinney, Yeti and Windigo. By Sunday and Monday, the closed low offshore will wobble to a position very near 40N and 130W. This places the area in a diffluent flow aloft and is a pretty classic pattern for producing some of the better thunderstorm outbreaks in these parts. The tricky part of the forecast, though, is that the model data is at odds with just how much moisture, instability and forcing can come together (if at all) and produce a significant outbreak. Sunday, for instance, we are seemingly in a good position for convection to form, but models aren't showing much, likely due to a capping inversion and lack of trigger. NBM thunder probabilities are fairly low, 10 percent or less, but SSE flow aloft an minor disturbances in the flow should be enough to trigger some build- ups near the Cascades, over the East Side/Warner Mtns along with a slight chance of thunderstorms. We have deviated from the NBM here to increase the thunder probabilities, due to pattern recognition and enough indices indicating the potential for at least a slight chance. Farther west, including western Siskiyou County and most of the west side, moisture is more limited, so we have maintained a dry forecast there. There is a better chance of thunderstorms in a similar area (Cascades eastward and into Modoc) on Monday afternoon/evening, so we have once again bumped up POPs/thunder probs to introduce that wording to the forecast. Monday night-Tuesday night, the closed low is expected to move northeastward off the coast and then onshore Wednesday. This will result in a chance of additional showers and thunderstorms over parts of the area Tuesday and into Wednesday, but at this point, it's too early to say just exactly where and when. Some guidance is pegging an area near the coast (N&W), but also another east of the Cascades, while southern and western areas get little or nothing. We'll see. Models are showing very low PWs in the SW part of the CWA, which would account for limited convection. Keep checking the forecasts for updates, because forecaster confidence at this time is low. After the low moves onshore, we should get a respite from thunderstorms late next week with temperatures near to slightly above normal. -Spilde && .AVIATION...05/18Z TAFs...Stratus and some patchy fog persist south of Cape Blanco this afternoon keeping Brookings in LIFR thresholds. Those low ceilings will likely persist through the day as the southerly stratus continues to push in. Elsewhere, thunderstorms are in the forecast east of the Cascades with broken ceilings and MVFR to IFR ceilings at times. VFR will prevail west of the Cascades through the TAF period. In northern California, visibilities will be low around the fires as they are still burning with some intensity. Any low level flights around those fires should expect LIFR visibilities at times. By tonight, LIFR ceilings will move back in along the coast later tonight. Visibilities are also expected to fall down to IFR levels. -Smith && .MARINE...Updated 245 PM PDT Friday, 5 August, 2022... Winds and seas will begin to ease a bit this afternoon through tonight, but seas are expected to remain steep into Saturday. By late Saturday morning advisory level conditions are likely to have ended within 10NM of the coast as a southerly surge makes its way northward along and near the coast. Southerly winds are then likely for all of the coastal waters area by Sunday afternoon as low pressure becomes established west of the area. ~BTL/Smith && .FIRE WEATHER...200 PM PDT Friday, 5 August, 2022...Southern Oregon and northern California remain locked between upper level troughing to the north, a persistent and troublesome closed upper level low to the southwest, and ridging with monsoonal inflow to the southeast. This morning, at least a part of the remnants of tropical storm Frank made their way into the area, bringing enough moisture to fire off a few isolated thunderstorms before and just after sunrise. This same lobe of moisture and instability has gradually made its way to the east, and by this afternoon and evening, it will likely help produce isolated to scattered thunderstorms over Modoc and southern Lake and Klamath counties. A Red Flag Warning remains in effect through this evening for these areas. Isolated thunderstorms are possible again Saturday afternoon due to residual moisture, but will likely be relegated to portions of Lake County and points east. Meanwhile, with an upper trough to the north, expect breezy to gusty winds across the region, strongest east of the Cascades where gusts of 25 to 35 mph will be common during the afternoons today and Friday. While it doesn't look like humidities will be a concern with these winds, the concern lies with the wind's potential effects for any hold over fires. The northern trough will depart the area Saturday, and the ridge will expand west and northward. This will produce a warming and drying trend Saturday into Monday, with the warmest temperatures expected Sunday for areas west of the Cascades, and MOnday to the east. Meanwhile, offshore low pressure will slowly approach the coastline, perhaps finally crossing onshore or leaving the area middle to late next week. Typically, a low such as this would result in wind and lightning concerns, and while models have been depicting the increased winds, they seem very reluctant to produce any thunderstorm chances. It seems difficult to follow, given the moisture inflow and instability this low would bring with it, that no lightning is possible. Although confidence in timing and location are low, we are introducing a mention for afternoon thunderstorms along and east of the Cascades beginning Sunday, to get some lead time on what we suspect will begin to show up in the models over the coming days. As for the wind concerns with the low, we do expect to see gusty south to southwest winds Monday into Wedensday. Mid level winds in various models are ranging between 30 and 45 mph, and this is usually a good indicator of gust speeds. These types of winds, occuring after/during lightning and with the ongoing fires in the area, may become a significant concern. We will keep a sharp eye on the wind and lightning threat over the coming days, and will update the forecast when confidence increases. -BPN && .MFR WATCHES/WARNINGS/ADVISORIES... OR...Red Flag Warning until 8 PM PDT this evening for ORZ624-625. CA...Red Flag Warning until 8 PM PDT this evening for CAZ285. Pacific Coastal Waters... Small Craft Advisory until 11 AM PDT Saturday for PZZ350-356. Hazardous Seas Warning until 2 PM PDT this afternoon for PZZ356-376. Small Craft Advisory until 8 PM PDT Saturday for PZZ370-376. $$ MAS/BPN/CZS