How much rain has fallen in SLO County? 5 times more than last year to date
A series of storms kicked off winter in a big way in San Luis Obispo County, dropping five times the amount of rain to date compared to last year.
Most of the rain came in the last three weeks of the year, with some areas measuring anywhere from 4 to nearly 20 inches in that period, according to the San Luis Obispo County Department of Public Works.
And some areas have received more rain so far this season than in all of the 2020-21 rain year. The season spans from July 1 to June 30.
“This December was a real blessing for all of us,” PG&E meteorologist John Lindsey said of the unexpected downpours.
From July 1, 2020, to Dec. 31, 2020, the county received on average a little more than 2 inches of rain, according to Public Works. That’s less than a tenth of the county’s average yearly rainfall.
This rain year to date, Public Works data show the county has received on average nearly 11 inches of rain — or more than half the average measured in a typical season.
San Luis Obispo County averages about 20 inches of rain annually.
Locations across the county are off to a great start, thanks to the stream of storms.
So far this season, higher-elevation areas such as Davis Peak and Rocky Butte have seen 66% of their average annual rainfall, according to Public Works.
San Luis Obispo is at 51% of its average for the year.
Other places aren’t quite as high. Atascadero, Santa Margarita, Shandon, Oceano and San Simeon are at about 40% to 45% of their rainfall for a full season.
While the precipitation was welcomed — and helped reduce the severity of local drought conditions — it put a strain on local infrastructure that struggled to keep up with downpours.
City roads and major highways flooded and hillsides turned into flowing mudslides, causing traffic issues for work and holiday travelers.
What caused the stream of rainstorms?
The rainier season this year could be due to the La Niña event occurring throughout the United States, according to Lindsey.
“Usually, La Niña for us is drier than usual, but they can be wetter than normal, too,” Lindsey said, noting the climate pattern can be more variable than its counterpart, El Niño.
A massive warm front bringing lots of moisture to the Pacific northwest was pushed southward into San Luis Obispo County and most of southern California in mid-December, Lindsey said. Last week, a low-pressure system brought cold weather and more rain to the area.
The wet December didn’t just impact San Luis Obispo County.
The Sierra Nevada mountains — whose snow reserves serve as a water bank for the state — have seen record-breaking levels of snowpack.
This week, the UC Berkeley Central Sierra Snow Lab measured 266 inches of snow at its Donner Pass laboratory. That’s 253% of the average to date for the season that begins Oct. 1, according to the university lab.
On average, the lab measures about 377 inches of snowfall in an entire snow year.
What’s ahead in the forecast?
Looking ahead, the first month of 2022 might be dry, Lindsey said, though the forecasts are not completely certain.
Nevertheless, Lindsey noted that a rainy first half of the season may be a good sign for the rest of the year.
“All these seasons where we have particularly wet Decembers ended up having above average rainfall for the season,” he said.
This story was originally published December 31, 2021 at 9:00 AM.
