SLO County weather forecast for the week of March 12: Another storm on the way

Unlike the previous storms where the jet stream came out of Canada and flowed southward toward California, bringing a frigid airmass and snow levels down to 1,000 feet, the upper-level winds are now flowing out of the southwest from Hawaii and raised snow levels to near 10,000 feet.

Consequently, flooding, especially in the foothills of the Sierra Nevada Mountain range and the Northern California coastal mountains, occurred on Friday as relatively warm rain melted a significant amount of the near record-breaking snowpack from the previous frigid low-pressure systems.

Friday’s heavy rain caused the Salinas Reservoir to reach 111 percent capacity. Lopez Lake hit 76.2, while Whale Rock reservoir was 100 percent capacity as of Saturday. Lake San Antonio was 43, and Lake Nacimiento was 83 percent of capacity on Thursday. Currently, water is being released from Nacimiento for flood control.

Upper-level westerly winds across the Pacific will pull and push a plume of subtropical moisture across the Central Coast, producing partly cloudy to mostly overcast skies with pockets of mist and drizzle on Sunday into Monday. Temperatures will remain mild, with overnight lows dropping to the low-50s, with highs in the mid-60s throughout San Luis Obispo County.

An intense 996-millibar low-pressure system and the associated warm and cold fronts will tap into this stream of subtropical moisture as they move southeastward through the Central Coast on Tuesday. This complex system will produce moderate gale-force to fresh-gale force (32 to 46 mph with gusts to 60 mph), southerly winds, and heavy rain throughout the day on Tuesday. With the ground saturated, gale force southerly winds have the potential to topple trees and heavy rain could cause numerous landslides on Tuesday. Snow levels are indicated to be at 8,000 feet.

Rain will turn to rain showers on Wednesday morning, ending by Wednesday afternoon. Total rainfall amounts are forecast to range between 2.5 and 4.5 inches, with higher amounts along the southerly-facing slopes of the coastal mountains. The Santa Lucia Mountains above Cayucos, Cambria, San Simeon, and Big Sur could see as much as 10 inches of rainfall.

Dry weather is expected from Thursday through Friday; however, the marine layer is expected to return along the coastal regions during the night and morning with areas of fog and mist.

Surf Report

A 5- to 7-foot westerly (275-degree, deep-water) swell (with an 8- to 14-second period) is expected along our coastline on Sunday, decreasing to 4 to 6 feet (with an 8- to 14-second period) on Monday.

Increasing southerly winds along the California coastline will generate 10- to 12-foot southerly (180-degree, shallow-water) seas (with a 3- to 7-second period) on Tuesday, followed by a 14- to 16-foot westerly (270-degree, deep-water) swell (with an 8- to 16-second period) on Wednesday.

A 4- to 6-foot northwesterly (300-degree, deep-water) swell (with an 8- to 12-second period) is expected along our coastline on Thursday, decreasing to 3- to 5-feet by Friday.

Seawater temperatures

A northerly flowing current will bring a warmer body of seawater to our coastline.

Seawater temperatures will range between 53 and 55 degrees through Sunday, increasing to 55 to 57 degrees on Monday into Friday.

Weekly temperatures

LOWS AND HIGHS, PASO ROBLES

LOWS AND HIGHS, SAN LUIS OBISPO AND COASTAL VALLEYS

John Lindsey’s is a longtime meteorologist who lives in Los Osos. Email him at JohnLindseyLosOsos@gmail.com.