A surprisingly wet October continues to bring gentle rains to the Sacramento region, providing some relief to watersheds parched by five years of drought.
But as scattered showers hit the region Thursday, forecasters and hydrologists said the promising start to the rainy season, while helpful, doesn’t necessarily mean the drought will end this winter.
This October is the 12th wettest in Sacramento in the 139 years tracked by the National Weather Service. As much as 2 more inches of rain might fall before the month is over.
While that’s a good start, October precipitation as a rule isn’t particularly significant to the overall numbers by the end of California’s short wet season. More than half of Sacramento’s annual rain falls between December and February.
So far, 2.39 inches of rain have fallen in Sacramento this month, including small traces during the day Thursday. There was a 90 percent chance of rain Thursday night, with as much as three-quarters of an inch expected.
October’s precipitation more than doubled the historical average of 1.05 inches. Sacramento’s rainiest October recorded was in 1962, when the region was swamped with 6.85 inches of rain.
“After five years of drought, an above-average October is a welcome sight,” said Michelle Mead, a meteorologist at the National Weather Service’s office in Sacramento.
But Mead cautioned that the wet October isn’t necessarily a predictor of what lies ahead. Amid uncertainty about the possibility of a relatively dry La Niña pattern, forecasters still aren’t sure how much precipitation the state will see in the winter months, which mark the most crucial period in the “water year.”
She said there’s a one-third chance of a wet winter, a one-third chance of a normal winter, and a one-third chance of a dry winter.
“What that means is: Get your dart board out,” she said. So far Southern California, which got much less rain last winter than Northern California, has remained exceptionally dry.
That’s not to say the early wet weather isn’t helping. Mountain watersheds and Sacramento Valley groundwater basins are benefiting from having soil saturated early.
“None of it’s hurting. That’s for sure,” said Joseph Hevesi, a hydrologist with the U.S. Geological Survey’s California Water Science Center in Sacramento. “From a recharge point of view, it’s better to go into the winter season with the soils pretty saturated.”
The reason? After a long, dry summer the soil is basically a dry sponge. Early fall rains help soak the soil, allowing for more water to start flowing into reservoirs and groundwater basins when snow and rain fall in earnest later in the season.
Maury Roos, chief hydrologist for the state Department of Water Resources, said that to “really generate the runoff,” it typically takes around 5 to 10 inches of rain to dampen the high-country soils. Roos said so much rain already has fallen this month in the higher elevations that he expects to see a modest increase in the coming days in the amount of runoff washing into reservoirs such as Folsom Lake.
The weekend forecast is mostly wet. The chance of rain will vary between 70 percent and 100 percent Friday, dipping to 50 percent Saturday but then increasing to 80 percent Sunday. Only a “slight chance of showers” is in the cards for Halloween on Monday, according to the weather service.
Temperatures will turn cooler this weekend, and the Sierra Nevada should see snow as low as 5,500 feet. As much as a foot of snow could fall in the northern Sierra and Lassen Volcanic National Park on Sunday.