Southern Oregon will move from warm, dry late-summer weather into a considerably cooler and wetter pattern during the first week of September, with the largest change expected between Tuesday and Thursday. Travelers can expect generally favorable highway conditions early in the week before rain, cooler mountain temperatures and periods of reduced visibility affect portions of the region.
The forecast covers communities throughout Josephine, Jackson, Klamath and surrounding counties, including Grants Pass, Medford, Ashland, Cave Junction and Klamath Falls, along with the Interstate 5 corridor, U.S. 199, Highway 62, Highway 140, U.S. 97 and mountain routes through the Cascades and Siskiyous.
Sunday, August 30
Sunday will remain sunny and dry across most of Southern Oregon, with seasonable temperatures and favorable conditions for most regional travel. Interior valleys will warm considerably during the afternoon, while higher elevations and areas east of the Cascades will remain cooler.
The Rogue Valley will experience sunshine throughout the day, with Medford reaching around 90 degrees and similar warm conditions extending through portions of Jackson and Josephine counties. The Klamath Basin will remain cooler, with afternoon temperatures generally reaching the upper 70s to lower 80s.
Interstate 5 through Grants Pass, Medford and Ashland should remain dry, as will U.S. 199 through the Illinois Valley and most major routes crossing Southern Oregon. Temperatures will be considerably lower at higher elevations, particularly during the morning and overnight hours.
Monday, August 31
Monday will be the warmest day of the week for many Southern Oregon communities. Sunshine will continue across the Rogue Valley, where afternoon temperatures are expected to climb into the lower 90s. Higher elevations will remain cooler, while Klamath Falls and surrounding portions of the Klamath Basin should reach the lower to middle 80s.
Winds will increase during the afternoon, particularly east of the Cascades. Southerly to southwesterly winds combined with dry vegetation will produce elevated fire-weather conditions across portions of the region.
Most highways will remain dry, although travelers should be prepared for gustier crosswinds along exposed sections of U.S. 97, Highway 140 and other routes east of the Cascades.
Construction continues along Interstate 5 in the Grants Pass area, where intermittent lane, ramp and shoulder closures are scheduled between approximately mileposts 58 and 67. Motorists traveling through the corridor should allow additional time, particularly during active construction periods.
Tuesday, September 1
A noticeable weather change begins Tuesday as a Pacific weather system approaches Southern Oregon. Temperatures will fall from Monday’s highs, clouds will increase and the possibility of rain will develop during the afternoon.
Western valleys are expected to reach the middle 70s to lower 80s, while temperatures across the Cascades will generally remain in the 60s and lower 70s. The Klamath Basin should reach the lower to middle 70s.
Rain chances will initially be scattered, with a slight possibility of thunderstorms in portions of the region. Conditions may vary considerably over relatively short distances as the system begins moving inland.
Travel conditions will become increasingly variable during the afternoon and evening. Interstate 5, U.S. 199, Highway 62 and Highway 140 could transition between dry and wet pavement as showers develop. Motorists crossing Siskiyou Summit or the Cascade passes should expect cooler temperatures and increasing cloud cover.
Wednesday, September 2
Wednesday will bring the most substantial weather change of the week as a cold front moves through Southern Oregon. Temperatures will fall sharply compared with Monday, and rain will become increasingly widespread, particularly west of the Cascades.
The Rogue Valley should remain substantially cooler, with afternoon temperatures generally in the 60s and 70s depending on location and elevation. Mountain temperatures will fall into the 50s and lower 60s, while the Klamath Basin is expected to reach the lower to middle 60s.
Rain will be most likely across southwestern Oregon and the Cascades, with lower but continuing chances east of the mountains. A slight possibility of thunderstorms will accompany portions of the system.
Wet pavement will become a more widespread travel concern Wednesday. Interstate 5 through Josephine and Jackson counties, U.S. 199 through the Illinois Valley, Highway 62 toward the Cascades and Highway 140 between the Rogue Valley and Klamath Basin could experience periods of rain and reduced visibility.
Siskiyou Summit and the higher Cascade routes will be considerably cooler than the valleys, with changing weather possible throughout the day.
Thursday, September 3
Cool and unsettled conditions will continue Thursday, with rain likely across portions of southwestern Oregon and the Cascades. Scattered showers will remain possible east of the Cascades, including portions of Klamath County.
Mountain temperatures will generally remain in the 50s and lower 60s. The western valleys will remain considerably cooler than they were at the beginning of the week, with afternoon temperatures largely confined to the 60s and 70s.
Travelers should continue to expect wet pavement on portions of Interstate 5, U.S. 199, Highway 62 and Highway 140. Mountain highways could encounter periods of heavier showers and reduced visibility, particularly where clouds settle across higher terrain.
Morning temperatures will also be significantly colder east of the Cascades and at higher elevations, with some locations falling into the 30s.
Friday, September 4
Friday will remain cool, with scattered rain continuing across portions of Southern Oregon. Precipitation should become less widespread as the week progresses, although showers will remain possible in the western valleys, Cascades and Klamath Basin.
Temperatures will remain below the levels recorded Sunday and Monday. Western valleys should generally remain in the 60s and 70s, while mountain locations could remain in the 50s and lower 60s.
Travel conditions should gradually improve as precipitation becomes more scattered, although motorists should continue to anticipate isolated areas of wet pavement and reduced visibility in the mountains.
Saturday, September 5
Saturday currently carries the possibility of lingering showers as the weather system slowly exits the region. Conditions should begin trending drier, although considerable cloud cover may remain over portions of Southern Oregon.
Temperatures will begin recovering in the western valleys while remaining relatively cool across the Cascades and Klamath Basin. Morning temperatures at higher elevations and east of the Cascades could again fall into the 30s and lower 40s.
Highway conditions should improve compared with Wednesday and Thursday, although isolated showers could continue to affect mountain routes.
Sunday, September 6
Sunday is expected to continue the transition toward drier conditions across Southern Oregon, although forecast confidence decreases this far into the period and lingering clouds or isolated showers remain possible depending on the movement of the departing weather system.
Temperatures should begin recovering across the Rogue Valley and other western interior locations while mornings remain cool throughout the mountains and Klamath Basin.
Regional travel conditions are expected to improve as the weekend progresses. Motorists traveling Interstate 5, U.S. 199, Highway 62, Highway 140 or U.S. 97 should continue checking current highway conditions before departure because construction, maintenance, wildfire activity and changing weather can alter travel conditions throughout Southern Oregon.
The primary weather transition for the week will occur between Tuesday and Thursday, when Southern Oregon moves from Monday’s warm and dry conditions into substantially cooler temperatures, widespread cloud cover and periods of rain. Wednesday and Thursday currently carry the greatest potential for weather-related travel impacts, particularly across the Cascades, Siskiyou Mountains and major highways west of the Cascades.