Weather Pattern Shifts Bring Smoke Risks, Temperature Swings Across Region

Medford, Oregon- A “messy” upper-level weather pattern is expected to keep temperatures above normal through the end of the week before a cooling trend arrives over the weekend, forecasters said Thursday.

High pressure over the western states and a weak low pressure system moving in from the eastern Pacific are interacting in a way that will sustain warm, dry conditions across southern Oregon and northern California. Temperatures are expected to reach the mid- to upper 90s west of the Cascades and mid- to upper 80s east of the mountains.

While dry weather is likely to continue through the weekend, forecasters said a stray afternoon shower cannot be ruled out as some cumulus clouds build over higher terrain. Lightning chances remain low, between 5% and 10%. Breezy winds are also expected, particularly in the Shasta Valley, where southerly gusts could reach up to 25 mph.

By Saturday and Sunday, a low-pressure system offshore is expected to bring cooler weather, dropping temperatures by 5 to 10 degrees. The cooler trend may allow moisture and instability to reach eastern portions of the region by late weekend into early next week, possibly opening the door for thunderstorm chances between Sunday and Tuesday.

Early next week, the upper-level ridge is expected to amplify over the Intermountain West, sending offshore low pressure north toward the Gulf of Alaska. This shift will bring a warming trend beginning Monday, with highs likely climbing back into the upper 90s west of the Cascades and upper 80s east. There is a 70% to 80% chance of triple-digit heat in West Side valleys by the middle of next week, though forecasters expect the heat to be short-lived, with another cool-down possible late next week.

Smoke impacts are also in play. With a general southwest-to-southerly flow, the bulk of smoke from the Emigrant Fire is expected to remain north of the region. However, late evening northerly winds could push some smoke into northern Klamath County, with conditions improving during the day as winds increase. Smoke from the Dillon Fire in Siskiyou County is forecast to remain mostly confined to western Siskiyou, with valley concentrations at night that clear with afternoon breezes.

Fire weather concerns remain relatively low through the weekend despite warm, dry afternoons and breezy winds in the Rogue Valley, Umpqua Basin, Shasta Valley and east of the Cascades. The Shasta Valley could see brief periods of near-critical fire conditions Friday and again Saturday.

Forecasters said thunderstorm chances remain minimal through the weekend but could increase slightly by Tuesday as a weak upper trough approaches, potentially boosting mid-level moisture and instability.