A pair of atmospheric rivers will spread rounds of rain and snow over the next several days. A pair of potent storm systems known as atmospheric rivers are spreading rounds of rain and snow across the Pacific Northwest and Northern California over the next several days.

The weather will become more active this weekend as a storm system moves into the region. Starting Saturday, breezy to windy conditions are expected, along with rain in the lowlands and a mix of rain and snow in the mountains.

The unsettled weather pattern will remain well on into next week. A continued chance for showers and windy weather at times will be possible. Afternoon highs stay cool, in the 40s to near 40.

In the northern hemisphere, atmospheric rivers typically occur during winter and are often cited for strong storms in the West. According to NASA, they are the largest transport mechanisms of fresh water on Earth.

An active weekend of weather is expected across western Oregon and southwest Washington from the coast to the Cascades.

Temperatures will hover in the upper 30s and mid-40s this week, with a chance for rain and snow starting Wednesday.

Southern California will have a respite from hot, dry weather this weekend as colder temperatures sweep in — bringing with them the possibility of scattered rain showers and snow in the mountains.

A maritime polar air mass is blowing down from the north, bringing cold temperatures and a chance of light rain and snow in some parts of Southern California over the weekend. After the weekend, the Santa Ana winds are expected to return starting Tuesday.