Santa Barbara County can expect moderate to heavy rainfall most of this week, which could lead to significant runoff into local reservoirs as well as urban flooding, officials say.

This week’s storms are expected to cause Gibraltar Reservoir on the upper Santa Ynez River — at 57.3% of capacity on Monday — to fill and spill, Matt Griffin, engineering manager for the county Flood Control District, told Noozhawk.

That would send considerably more rainwater runoff into the Santa Ynez River.

“Once Gibraltar spills, all that water get directed downstream into Lake Cachuma,”  Griffin said.

Hydrologists will run computer models closer to the arrival of the storms, but Griffin said he expects Cachuma, which was at 31.9% of capacity on Monday, to rise by several feet by the time this week’s storms are done.

On Monday, Lake Cachuma’s water level stood at 693.6 feet, according to the U.S. Reclamation Bureau. The spill level is 753 feet, so there is a long way to go.

It would take several more big storms in order for Cachuma to get close to filling and spilling, Griffin added.

Public Works crews will be monitoring the situation closely, and some flooding is possible, Griffin said, especially in the more-recent burn areas such as the 16,970 acres that were blackened by the Alisal Fire in Refugio Canyon and along the Gaviota Coast in October 2021. 

“We could see some flooding and big flows, but not any debris flows, per se,” he added.

“The upcoming Wednesday and Thursday storm system has the potential to produce considerable runoff and reservoir inflow, given that the watersheds are wet from recent storm activity,” said Lael Wageneck, public information officer for the Santa Barbara County Public Works Department.

The amount of the runoff will be highly dependent on the volume of rain, where it falls, and rainfall intensity, Wageneck said.

“Should moderately high amounts of rain occur in the upper Santa Ynez watershed, the Gibraltar Reservoir can fill and spill fairly rapidly, resulting in additional downstream pass-through into Cachuma,” Wageneck said.

“There could be some small streams overflowing, and urban flooding would not be out of the question,” said Joe Sirard, a meteorologist with the National Weather Service in Oxnard.

“In addition to the strong and gusty winds, we could also see tree limbs down, scattered power outages, and those sorts of things.”

According to Sirard, rainfall will be heaviest in the middle of the week. Wednesday and Thursday will bring moderate to heavy rainfall in most parts of the county.

“It looks like we could get an additional like 2-4 inches of rain along the coast, maybe 3-5 inches up in the Santa Ynez Mountains,” Sirard said.

Winds of 10 to 15 mph are expected Monday night in Santa Barbara, with an 80% chance of rain, according to extended forecasts on the National Weather Service’s website.

Tuesday night could see gusts as high as 20 mph and on Wednesday they could reach 35 mph.

There is an 80% chance of rain and breezy winds on Thursday.

In Santa Maria, gusts could reach up to 20 mph Monday night, with a 90% chance of rain.

On Wednesday, Santa Maria should see winds up to 35 mph and a 90% chance of rain. Conditions will be breezy on Thursday with an 80% chance of rain.

Lompoc can look forward to winds up to 25 mph Monday night and Tuesday, with a 80-90% chance of rain.

On Wednesday, gusts could reach 45 mph, with a 90% chance of rain. Thursday will be breezy with an 80% chance of rain in Lompoc.

In the Santa Ynez Valley, winds could reach 20 mph with an 80% chance of rain Monday Tuesday nights.

On Wednesday, gusts of 40 mph are possible, with a 90% chance of rain.

On Thursday, the chance of rain is 80%, with breezy winds.

» Click here for the latest Santa Barbara weather forecast.

» Click here for the latest Santa Maria forecast.

» Click here for the latest Lompoc forecast.

» Click here for the latest Santa Ynez Valley forecast.

Noozhawk Executive Editor Tom Bolton contributed to this report.