Southern Oregon will open the week under a blast of September heat before temperatures retreat sharply across the Rogue Valley, Cascades and surrounding communities, bringing cooler mornings and a decidedly more autumnlike finish by next weekend.
Sunday, September 20, will deliver the week’s hottest afternoon across much of the interior. Grants Pass and Medford are expected to climb into the lower 90s, with some locations in the Rogue Valley capable of reaching the middle 90s under mostly sunny skies. Ashland will approach 90 degrees, while overnight temperatures across the valleys fall quickly into the lower and middle 50s.
The combination will produce one of Southern Oregon’s familiar early-fall temperature spreads: a hot afternoon followed by a cool night. Residents leaving home early and returning during the afternoon could encounter temperature differences approaching 40 degrees.
Monday will remain warm but will begin the region’s steady retreat from Sunday’s heat. Grants Pass should reach the middle to upper 80s, with Medford also remaining in the upper 80s and Ashland in the middle 80s. Sunshine will continue across most inland communities, while nighttime temperatures return to the lower 50s.
By Tuesday, the Rogue Valley will lose another several degrees. Afternoon readings are expected around the lower 80s from Grants Pass through Medford, accompanied by mostly sunny skies and cool overnight conditions. Wednesday continues the pattern, with daytime temperatures generally hovering near 80 degrees and morning readings around 50.
A brief bump in temperatures remains possible Thursday before substantially cooler air reaches the region Friday. Interior communities that begin the week near or above 90 degrees could struggle to move much beyond the middle and upper 70s by Friday afternoon. Overnight temperatures will become increasingly crisp, dropping into the upper 40s in several valleys.
Saturday, September 26, should remain comfortable but considerably cooler than the opening weekend. Grants Pass and Medford are expected to remain primarily in the 70s, with cool morning temperatures and increasing cloud cover possible. Extended forecasts through Sunday, September 27, continue to favor daytime temperatures in the middle to upper 70s across much of the Rogue Valley.
The weather changes become more pronounced with elevation.
Klamath Falls will spend much of the week in the 70s, with nighttime temperatures routinely dropping into the 40s. Travelers crossing the Cascades should expect significantly cooler conditions than those experienced in Grants Pass or Medford, particularly during the early morning and after sunset.
Crater Lake will be colder still. Daytime temperatures near the park will slide from the lower 60s early in the week toward the lower 50s by next weekend, with nighttime temperatures approaching the upper 30s. Anyone traveling into the higher Cascades from the Rogue Valley will leave summerlike valley temperatures behind within a relatively short drive.
The Southern Oregon coast will escape the dramatic temperature swing occurring inland. Brookings should remain primarily in the upper 60s to around 70 degrees, with North Bend experiencing similar conditions. Coastal clouds and morning marine influence will periodically interrupt the sunshine, while the possibility of precipitation increases modestly late in the week.
Rain does not appear positioned to dominate Southern Oregon’s weather through next Sunday. A weak late-week weather system could introduce clouds and a limited chance of showers in portions of southwest Oregon, but widespread heavy rainfall is not currently indicated.
For highway travelers, construction rather than weather is expected to create the more persistent complications.
Interstate 5 through the Grants Pass area remains affected by ongoing rehabilitation work. Motorists should be prepared for nighttime lane restrictions and intermittent ramp closures around Exits 58 and 61, including work near the Oregon 99, U.S. 199, Scoville Road, Merlin Road and Monument Drive interchanges. Overnight construction between approximately mileposts 58 and 68 can reduce available lanes and produce short delays.
Travel south toward Ashland and Siskiyou Summit should remain free of winter weather based on the current forecast. Drivers crossing the summit during nighttime or early-morning hours will nevertheless encounter much cooler temperatures than those prevailing across the Rogue Valley.
Travel east toward Klamath Falls on Highway 140 will bring an equally noticeable change. Temperatures decrease considerably with elevation, particularly after sunset, making a warm afternoon departure from Medford a poor indication of conditions travelers may encounter later in the Cascades.
U.S. 199 travelers heading toward the coast will experience the reverse transition, moving from Sunday’s interior heat into considerably cooler coastal air. Morning clouds and marine conditions may reduce visibility in some coastal locations even while inland skies remain sunny.
Southern Oregon’s final full week of September will consequently carry two seasons within several days. Sunday arrives with temperatures resembling midsummer across the Rogue Valley. By Friday and the weekend, afternoon readings will have fallen by roughly 15 to 20 degrees in some communities, nighttime temperatures will be dipping into the 40s, and the higher Cascades will be flirting with readings in the 30s.
For residents traveling anywhere from Grants Pass and Medford to the coast, Klamath Basin or Cascade passes, the week begins with heat but finishes with jackets returning to the morning routine.