Southern Oregon residents should prepare for a significant shift in weather patterns as a dry cold front sweeps eastward today, followed by an approaching upper low that will bring cooler temperatures and a chance of showers throughout the weekend. The effects of this weather system are expected to be most pronounced in Coos, Douglas, and the south-central Oregon Cascades.
On Sunday, the upper low is predicted to move into the northern parts of the Pacific Northwest, resulting in a drop in temperatures and a 20 to 40 percent chance of showers. These showers are most likely to occur in Coos, Douglas counties, and extend into the south-central Cascades. Coastal regions can expect high temperatures in the lower 60s or upper 50s, while inland valleys will see temperatures in the 60s to lower 70s.
As the upper low sinks over the area late on Sunday and into Monday, a notable change in weather patterns is anticipated. Monday will bring very cool conditions, with a possibility of precipitation, including light snowfall in the mountains. The models indicate cold air aloft and unstable conditions, leading to a slight chance (15 to 20 percent) of thunderstorms across most inland areas.
On Monday, the upper low is projected to position itself north over Washington, resulting in chances for showers in northwestern portions of the region due to moist onshore flow. Coos and Douglas counties, as well as the south-central Cascades, are expected to experience the highest chances of light showers. Overall, temperatures will remain cool, with highs in the 60s to lower 70s for inland valleys and lower 60s or upper 50s along the coast.
The upper low is anticipated to shift southward and affect the area from Sunday evening into Monday. This movement will bring a strong cooling trend and increase the probability of showers, ranging from 30% to 70%. There is also a slight chance of thunderstorms on Monday afternoon and evening, specifically east of the Coast Range. Snow levels will drop to between 4000 and 5000 feet, potentially resulting in 1 to 2 inches of snowfall above 4500 feet in the mountains. On Tuesday, the upper low will persist, maintaining chances for showers, particularly in Oregon zones.
Residents should prepare for a significant drop in temperatures as the weather pattern evolves. A decrease of approximately twelve degrees is expected on both Sunday and Monday. Monday, into Tuesday morning, is predicted to be the coldest period, with highs in the lower 60s for valleys west of the Cascades and 50s for valleys east of the Cascades. Some areas, such as southern Klamath, southern Lake, northern/eastern Siskiyou, and Modoc Counties, have a 50-60 percent chance of temperatures at or below freezing, while northern Klamath and northern Lake counties have a 60-100 percent chance of freezing or below temperatures on Tuesday morning.
Valleys west of the Cascades will experience lows in the upper 40’s to upper 50’s on Tuesday morning, and cool temperatures will persist throughout the day, with highs in the upper 50s to upper 60s.
The weather pattern is expected to remain cool, cloudy, and occasionally wet throughout the week as a cool, active, trough-dominated pattern persists. Additional disturbances moving around the trough will continue to bring cooler temperatures, cloudy skies, and intermittent rainfall to the area.