830 FXUS66 KMFR 250513 AFDMFR Area Forecast Discussion National Weather Service Medford OR 1013 PM PDT Thu Jul 24 2025 .UPDATE...Updated Aviation Discussion. && .AVIATION...25/06Z TAFs...Widespread IFR/LIFR stratus/fog will persist along the coast and into coastal valleys through Friday morning. Areas of IFR/MVFR may spread into the Umpqua Valley, mainly north of Roseburg, early Friday morning. There is a 30% chance for a period of MVFR at Roseburg Friday morning. Elsewhere, mainly VFR prevails. However, another round of scattered thunderstorms is expected Friday afternoon and evening from the Southern Oregon Cascades east and over Northern California with local MVFR visibilities in heavy rain. Any thunderstorms Friday will have the ability to produce strong, gusty outflow wind gusts of 40-60 mph, heavy rain and small hail. && .PREV DISCUSSION... /Issued 847 PM PDT Thu Jul 24 2025/ DISCUSSION...Scattered thunderstorms and showers are occuring east of the Cascades and across Northern California. Some of these storms have been strong to locally severe with strong gusty winds (generally 30 to 40 mph), hail (up to 1 inch) and very heavy rain. These storms have been very slow movers, allowing heavy rain to fall over some areas, including central and western Siskiyou and southern Klamath counties. Small stream and urban flood advisories have been issued this evening for these areas. Thunderstorms are expected to diminish over the next couple hours and small stream and urban flooding impacts are expected to ease late this evening. Then, another round of thunderstorms, similar to today, is expected to develop again Friday afternoon and evening for areas from the Cascades east and Siskiyous southward. Please be alert for the potential of strong to severe storms and for possible flooding. Have multiple ways to receive information and weather alerts. MARINE...Updated 800 PM PDT Thursday, July 24, 2025...Sub- advisory north winds and low seas of 5 ft or less, will persist through the weekend and likely into early next week. Of note, winds will briefly approach small craft advisory levels late Friday afternoon and early Friday evening, between Port Orford and Gold Beach, 2 to 20 nm from shore. Winds then lower Friday night. Areas of fog and low stratus will also persist through this time. PREV DISCUSSION... /Issued 1256 PM PDT Thu Jul 24 2025/ DISCUSSION...In the last couple of hours, satellite imagery reveals cumulus developing in increasing instability due to daytime heating across portions of south central Oregon and norCal/NW Nevada. Radar is showing bulk of the activity in northern Washoe and into Lassen County. These will be primarily over higher terrain initially, but as they build, they`ll propagate toward the WNW since mid-level steering flow is from the ESE around the low near the California coast (just south of SF Bay). Main axis of instability stretches from the NorCal mtns over to portions of southern Klamath and Lake counties. This will be the focus for scattered to numerous showers/thunderstorms this afternoon and evening. Storm cloud bases will be mostly in the 10-12K ft range, so with plenty of downdraft CAPE, many storms will have significant outflow wind gusts, mostly 40-55 mph. But, a stronger cell or two could have severe gusts up to 60 mph and hail. Models are showing fairly weak storm motions, so where they do develop, there is the potential for brief, heavy rainfall as well (PWs are highest across western Siskiyou County, where they are in excess of 1.00"). This is most likely in an arc from the Trinity Horn and SW Siskiyou County over to eastern Siskiyou and western Modoc counties into this evening. Of course, another significant risk will be cloud to ground lightning, and we are expecting abundant lighting over dry fuels. As such, a Red Flag Warning is in effect. Since storm motions are from the ESE, we do have a small risk that any storm that gets going over the Cascades and/or Siskiyou Mtns, drifts out over the south end of the Rogue Valley or the Applegate/Illinois valleys this evening. This is a low probability/confidence event (around 5-15% chance), but could occur, so we`ve allowed for that potential in the forecast. Keep an eye to sky and if thunder roars, go indoors! Activity this evening will wane with the loss of instability and most thunderstorms will be done by around 10 or 11 pm. It`s not out of the question isolated showers linger into the overnight and there is an outside shot at a thunderstorm across southern and eastern sections, but things should mostly quiet down during the night. Coastal stratus will continue to impact most areas from Curry to Coos and western Douglas counties, perhaps to areas just NW of Roseburg (Elkton most likely, but perhaps Sutherlin) tonight into Friday morning. The clouds and/or fog should peel back toward the coast again Friday afternoon. The upper low near the California Coast will edge inland on Friday and we`ll have another active day of showers and thunderstorms with just an ever so slight shift to the south and east of the main focus area. Modoc County looks to be the focus where HREF lightning probability is >90%, but the arc of influence will once again be across much of NorCal and into SE portions of Klamath/Lake counties. These storms should continue to be wetter with time, but due to the potential of abundant lightning again, the Fire Weather Watch has been upgraded to a Red Flag Warning. On Saturday, the low will drift to the Sierra Crest, near or just south of Lake Tahoe. So, this will maintain a chance of showers and thunderstorms across the SE portion of the forecast area (highest probability from around the Warner Mtns eastward). This won`t be as large of an area compared to today and Friday, so we decided against another watch at this time. In addition, and to give us further confidence in less activity, an upstream "kicker" trough will move toward the PacNW coast. This will bring in some drier air and WSW flow aloft. The bulk of the thunderstorm activity will be to our south and east where the deeper moisture is. Sunday and Monday, the orientation of this "kicker" trough will maintain mostly S-SW flow aloft and a somewhat drier air mass than previous days. So, while there is still a slight chance of showers/storms (especially over the East Side), they`ll be more isolated in nature. Flow orientation will shift back to southerly as another disturbance rounds into the base of the trough. This could once again enhance t-storm activity over the area Tue-Thu of next week with some solutions showing the potential for west side storms. We`ll continue to monitor this period and make changes as needed over the coming days. -Spilde && .MFR WATCHES/WARNINGS/ADVISORIES... OR...Red Flag Warning until 11 PM PDT this evening for ORZ624-625. Red Flag Warning from 1 PM to 11 PM PDT Friday for ORZ624-625. CA...Red Flag Warning until 11 PM PDT this evening for CAZ280>282-284- 285. Red Flag Warning from 1 PM to 11 PM PDT Friday for CAZ280>282- 284-285. PACIFIC COASTAL WATERS...None. && $$ CC/CC/CC