Light rain and cloudy skies moved over Marysville on Sept. 4 as cooler-than-normal weather gave the Yuba-Sutter area an early taste of fall. Photo courtesy of Shamaya Sutton

 

YUBA-SUTTER, CA (MPG) - For a few days at the beginning of September, summer seemed to switch off almost overnight in the Yuba-Sutter area.

After weeks of hot, sunny weather, residents woke to cloudier skies, breezy conditions and afternoon temperatures in the 70s — weather more reminiscent of fall than the final weeks of a Sacramento Valley summer.

The abrupt change was caused by a shift in the weather pattern over Northern California. According to the National Weather Service in Sacramento, a trough of low pressure moved into the region during the first week of September, replacing the warmer pattern that had dominated much of the summer. On Sept. 1, forecasters said Sacramento Valley high temperatures were running about 15 to 20 degrees below normal, with many locations only reaching the 70s.

A trough is an elongated area of lower atmospheric pressure that can allow cooler air from the Pacific and farther north to move inland. The system also strengthened onshore winds, bringing cooler, more humid air into the Sacramento Valley and increasing cloud cover. That combination helped explain why the transition felt so sudden.

Yuba-Sutter’s summer heat is often associated with strong high pressure, clear skies and sinking air that warms as it descends. When that pattern weakens and a trough moves in, temperatures can fall noticeably within a day or two.

The cooler spell was felt across the region. Sacramento reached only 77 degrees Sept. 1, about 14 degrees below normal, and 78 degrees Sept. 2, about 13 degrees below normal The unsettled pattern also brought chances for rain to portions of Northern California, particularly north of Interstate 80 and in the mountains.

Residents may also have noticed hazier skies during the weather change. The National Weather Service Sacramento office reported that smoke from the Timber and Plaskett wildfires in the Big Sur area was being carried northward by onshore winds. Much of the smoke remained aloft, though some could reach the surface in foothill and mountain areas. The smoke did not cause the cooler temperatures. Instead, both the haze and the sudden chill were influenced by the changing wind pattern.

Although the cooler spell arrived right at the start of September, it did not necessarily mean summer was over. Meteorological fall begins Sept. 1, but September in the Yuba-Sutter region can still bring periods of 90-degree or even triple-digit heat.