Storm Bears Down On Bay Area: Timeline For Downpours And Snow

SAN FRANCISCO, CA — The Bay Area is finally receiving its first significant rainfall in weeks, starting Tuesday, as a high-pressure system that previously brought record heat and dry conditions moves out of the region, the National Weather Service reported.

A cold front brought rain to the coast early Tuesday morning and is expected to last through Thursday morning, with the heaviest precipitation expected Wednesday night, according Dylan Flynn, a meteorologist with the National Weather Service’s Bay Area office.

The rain and snow at higher elevations are expected to wash away what has been the second driest and hottest March in the record books, according to Flynn. The respite may be short-lived as April is expected to remain very dry, he added.

Rain moved into the Bay Area early Tuesday morning as a very light, steady drizzle and is expected to continue in generally light fashion through Wednesday, according to the weather service.

The most significant period of rain is forecast for Wednesday night, with the North Bay seeing the heaviest downpours from the system, possibly beginning by Wednesday evening, Flynn said.

Most of the rain will fall overnight Wednesday. By early Thursday morning, around sunrise, the system should be largely finished, with clearing skies and sunshine returning during the day, Flynn told Patch.

San Francisco is forecast to receive approximately 0.2 inch of rain through Thursday. Radar indicated pockets of heavier rain in the South Bay. Coastal areas in the North Bay are expected to get the most precipitation, with forecasts ranging from 0.5 to 0.75 inch.

The storm is being caused by a cold front moving in from the northwest, interacting with a prefrontal air mass that’s pulling moisture up from the subtropics, according to Flynn.

Behind the storm, a warming trend is likely bringing a dry pattern back to the region, Flynn told Patch.

"After this system moves through, the sun’s going to come back out on Thursday, and we get another warming trend through the weekend," Flynn told Patch. "It’s a little iffy what’s going to happen after that."

Flynn said he expects at least the first half of April is likely to be drier and warmer than normal.

The shift in the weather pattern is also good news for the Sierra Nevada, where the snowpack currently sits at only 30 percent of normal for the central part of the state. This system offers only a modest and short‑lived boost, Flynn said. Most of what falls today will come down as rain rather than snow because of the unusually warm temperatures, with snow confined mainly to the highest elevations, Flynn told Patch.

By tomorrow night, as the cold front pushes through, some additional snow is expected, providing a small but welcome bit of relief for a snowpack that is currently at the lowest levels ever recorded, according to NWS.

By the weekend, temperatures are projected to run about 10 degrees above normal again, speeding up the already rapid melting of the thin snowpack.

The National Weather Service in Sacramento predicts 4 to 8 inches of snow could fall above 6,000 feet, with higher elevations potentially seeing increased totals through Wednesday evening.

Further east, the National Weather Service in Reno has issued a winter weather advisory for Mono County at elevations above 8,000 feet, where 6 to 12 inches of snow is expected to accumulate through early Wednesday morning.