San Francisco Chronicle
Atmospheric river storm may hit Bay Area this week
Northern California could be in for a new atmospheric river storm by the end of the week, potentially blasting the Bay Area with substantial rain, and the Sierra with even more heavy snow, but likely not as fierce as the wet storms that wreaked damage across the region at the start of the year, forecasters say.
Although still an early forecast, weather models show that an atmospheric river — a band of moisture that can travel thousands of miles — could flow into Northern California on Friday and Saturday, focused along the coast, including the Bay Area, said Gerry Díaz, Chronicle meteorologist.
“This will be a challenging forecast, because the only way that plays out is if the high pressure off the coast breaks down by Thursday of this week,” Díaz explained. “Think of the high-pressure like a big rock in a flowing stream. If you remove the rock from the stream, then plenty of water will make it downstream to California. If it stays put, then less water will make it here.”
If the weather models play out, the storm could drop 2 to 6 inches of rain across the Bay Area, with the highest rainfall totals predicted for the region’s highest peaks, Díaz said.
The National Weather Service tweeted late Sunday afternoon that confidence was increasing about the possibility of the atmospheric river hitting late in the week, with flooding possible, and street flooding likely where drainage is poor.
The last time atmospheric river-enhanced storms battered the Bay Area was in late December and early January, when back-toback storms led to evacuations, mudslides, downed trees, flooding, road closures and more.
The potential atmospheric river headed toward Northern California this week, however, will probably not be as strong as those storms, Díaz said.
Daniel Swain, a climate scientist at UCLA and the Nature Conservancy, said Sunday that an atmospheric river could be a concern regarding the state’s snowpack, which on Friday reached its highest level this century for the start of March. Such rain-onsnow events — when heavy rain falls on snowpack in higher elevations — could result in snow melting faster, flooding downstream areas and overwhelming rivers, weather experts say.
“There’s just too much uncertainty still to discuss potential impacts. We still don’t know where this potential atmospheric river would be focused, nor how intense it might be (or whether it’ll occur at all!),” Swain wrote on Twitter.