Bay Area residents should prepare for chilly mornings this week, with temperatures dipping into the 40s inland and around 43 degrees in downtown San Francisco.

Tuesday morning will be brisk, but a slight warming trend is expected by midweek, according to Dial Hoang, a meteorologist with the National Weather Service Bay Area.

Daytime highs will range from the upper 50s to mid-60s, with San Francisco at 59 degrees, San Jose at 64, and Oakland slightly cooler. By Wednesday, temperatures could climb to the lower 70s in some areas as the week progresses.

However, atmospheric river conditions may be on the horizon.

“We’ll see the first real atmospheric river start to impact the North Bay toward the middle of the week, spreading across the Bay Area and Central Coast by the end of the week,” Hoang said.

An atmospheric river is a stream of moisture in the atmosphere that delivers heavy rain when it reaches land. These conditions often bring risks of flooding and other weather-related hazards.

Rain boots, layers, and an umbrella are advisable as residents should prepare for soggy commutes. If atmospheric river conditions fully develop, localized flooding may also occur.