Santa Rosa received 6.46 inches over the same four days, AccuWeather reported.
Typically, the runoff from this kind of storm would take about a week to find its way into local reservoirs, though thirsty ground from months of dry weather would absorb a large amount first, water officials said.
But already, the storage in the two reservoirs had risen more than 12,000 acre feet beyond what lay behind the dams as of Friday, said Mike Dillabough, chief of the Operations and Readiness Division for the U.S. Army Corps of Engineer's San Francisco District.
Water flowing into Lake Mendocino, measured Friday morning at just 31 cubic feet per second, had increased by a factor of 32 over the weekend, measuring 996 cfs on Monday morning, Dillabough said.
At Lake Sonoma, the in-flow rate rose from 168 cfs to 1,462 cfs over the four-day period, he said.
"That's good," Dillabough said. "That means a lot more water's coming in."
Lake Mendocino was at nearly 41 percent capacity Monday at 7 p.m., up from almost 37 percent Thursday. Lake Sonoma was just shy of 68 percent capacity, up from 66 percent Thursday.
"We need at least six more storms like this," Sonoma County Water Agency spokesman Brad Sherwood said.
The expanding reach of the Laguna de Santa Rosa would suggest a few days break might be beneficial, however.
Even as creeks and rivers around the area were beginning to recede, the Laguna, a 14-mile waterway that empties into the Russian River, remained a flood zone that overflowed pastures and oak woodlands in the rural area between west Santa Rosa and Sebastopol, turning Sanford Road near Occidental Road into a water trap passable only by some four-wheel drive vehicles.