SLO County could see 3 days of rain this week. Here’s the forecast

Get ready to curl up and settle into autumn, San Luis Obispo County, we’re in for some rain this week.

Clear skies and windy conditions are expected through Monday afternoon. Then, rain will blow in on Monday night and linger until Wednesday morning. Gentle winds, partly cloudy skies and warmer temperatures will follow on Thursday and Friday.

Afternoon highs will reach the low to mid-70s in the inland valleys (Paso Robles) and the coastal valleys (San Luis Obispo). Beaches will remain cooler, ranging from the mid- to upper 60s.

All eyes are on a 940-decameter, upper-level, low-pressure system off the Oregon coastline that will create vigorous upper-level winds that carve out a 1,004-millibar surface, low-pressure system 200 miles west of San Francisco.

Expect increasing mid- to high-level clouds later Monday, with scattered rain showers developing by Monday night. The associated cold front will move southward, passing over the Central Coast on Tuesday with strong to gale-force (25 to 38 mph) southerly winds and moderate to heavy rain.

An upper-level trough will follow later Tuesday into Wednesday morning with scattered rain showers and a chance of thunderstorms.

Temperatures will struggle to reach the 60s on Tuesday. Snow levels in the Sierra Nevada could drop as low as 4,500 feet.

Because most trees still have their leaves, trees and large limbs could fall across the Central Coast, causing hazardous driving conditions and possible power outages.

NOAA’s Global Forecast System model predicted 0.5 to 1.5 inches of rain, with higher amounts in the Santa Lucia mountains due to orographic enhancement. Meanwhile, the European Center for Medium-Range Weather Forecast predicted between 1.5 and 2.5 inches of rain, with even higher amounts in the coastal mountains.

Gentle variable winds, slightly warmer conditions and partly cloudy skies, along with the marine layer returning along the coastline, are expected Thursday into Friday.

Increasing northwesterly winds and clear skies are forecast for next weekend, with another chance of rain developing on Oct. 20 and 21.

Surf report

Increasing northwesterly winds will generate 6- to 8-foot northwesterly (300-degree, deep water) sea and swell (with a 5- to 11-second period) through Monday morning, decreasing Monday afternoon and night.

Strong to gale-force (25 to 38 mph) southerly winds on Tuesday will generate 5- to 7-foot southerly (190-degree, shallow water) seas (with a 4- to 6-second period).

A 4- to 6-foot northwesterly (290-degree, deep water) swell (with an 8- to 16-second period) is forecast along our coastline Wednesday, decreasing to 3 to 5 feet (with an 8- to 15-second period) on Thursday through Friday.

Seawater temperatures will range between 59 and 62 degrees through Friday.

On this date in weather history (Oct. 12)

One of the most powerful weather systems ever observed during October brought stormy conditions to the Central Coast in 2009. A deep 974-millibar, low-pressure system located about 600 miles off the Oregon coastline rapidly intensified to 966 millibars before tracking northward into the Gulf of Alaska.

As the system’s cold front pushed south, it passed over the Central Coast with gusty southerly winds. The southerly winds at Diablo Canyon peaked at 37.8 mph sustained, with gusts up to 48.5 mph. Hundreds of trees and large limbs came down across northern San Luis Obispo County, causing widespread power outages.

Record rainfall accompanied the storm from the night of Oct. 12 to 13. The Santa Maria Municipal Airport received 0.5 inches of rain, the Diablo Canyon Ocean Lab recorded 2.5 inches and the San Luis Obispo County Regional Airport measured 3.7 inches.

The strong southerly flow produced exceptional orographic enhancement over the Santa Lucia Mountains, dramatically increasing rainfall totals. Cottontail Creek northwest of Cayucos measured 5.6 inches, while Highway 41 at Toro Creek (“Paul’s House”) recorded 7.8 inches — another nearby gauge measured an astonishing 9.3 inches.

Even farther north, the coastal mountains south of Monterey received more than 21 inches of rain.

It was a remarkable early-season storm — an unforgettable reminder of the Central Coast’s capacity for powerful autumn weather.

The last time that we received over an inch of rain in one day in October occurred on Oct. 19, 2004, when a cold front passed over the Central Coast. The Diablo Canyon Ocean Lab rain gauge recorded 1.5 inches of precipitation in just six hours. That rain season produced 35.71 inches of rain. The previous largest one-day total in October was 2.21 inches, which occurred on Oct. 1, 1983.

This week’s temperatures

LOWS AND HIGHS, PASO ROBLES

SUNDAY: 43, 76

MONDAY: 43, 70

TUESDAY: 50, 58

WEDNESDAY: 47, 68

THURSDAY: 47, 70

FRIDAY: 48, 72

SATURDAY: 48, 73

SUNDAY: 49, 77

LOWS AND HIGHS, SAN LUIS OBISPO AND COASTAL VALLEYS

SUNDAY: 48, 73

MONDAY: 47, 68

TUESDAY: 50, 57

WEDNESDAY: 50, 65

THURSDAY: 49, 67

FRIDAY: 51, 68

SATURDAY: 51, 70

SUNDAY: 52, 72

John Lindsey is a retired PG&E marine meteorologist. Email him at JohnLindseyLosOsos@gmail.com or follow him on X @PGE_John.