More rain ahead for San Luis Obispo County

Holiday shoppers will likely have to slosh through the final weekend before Christmas as rain is expected to drench San Luis Obispo County today and Sunday.

Forecasters expect an even more powerful storm Tuesday, just in time for the official start of winter. Computer forecast models are now showing that Christmas Day could be wet as well.

Motorists should be careful, as the National Weather Service expects there to be areas of standing water on roadways because of all the rain. People in low-lying areas will need to be on alert for possible flooding.

John Lindsey, a San Luis Obispo forecaster with more than 20 years of experience monitoring local conditions, said that from today to Thursday, San Luis Obispo could receive 5 inches or more of rain. That would exceed the city’s historical average for the entire month of December, which is 3.79 inches.

Two key factors are behind the coming stormy week, according to Lindsey.

The jet stream — the river of air in the upper atmosphere — is centered over the Central Coast. As a result, it is directing storm systems from the Pacific toward the region.

A low-pressure system now off the Pacific Northwest is tapping into moisture-laden subtropical air from Hawaii and spinning it toward California — meaning abundant rainfall once the clouds get here.

The heaviest rain this weekend is expected this morning, Lindsey said. But there will be more rain “Saturday afternoon, rain on Sunday morning, rain late Sunday morning, rain on Sunday afternoon,” Lindsey said.

A slight break will come Monday before the next heavy wave of precipitation arrives. Rain from that storm will linger through Thursday, with the next break occurring on Christmas Eve. Rain could return Christmas morning, Lindsey said.

Daytime temperatures will be in the low 60s throughout the period, and overnight lows will be in the 50s until the end of next week, when nights cool into the 40s.