SLO County weather forecast: Expect foggy coastline, high inland temperatures

A typical late summer weather pattern will continue through this week with Chamber of Commerce conditions in the coastal regions and above normal temperatures in the inland valleys.

Strong to gale-force (25 to 38 mph) northwesterly winds will develop along the coastline on Sunday afternoon, decreasing to fresh to strong (19 to 31 mph) on Monday. These winds will mix out the marine layer, leaving behind mostly clear skies.

High temperatures will range from the high-70s to the low-80s in the coastal valleys (San Luis Obispo) and the mid to high-90s in the inland valleys (Paso Robles). The beaches will remain in the low to mid-60s, except the southerly facing beaches of Cayucos, Avila Beach and Shell Beach which will reach the 70s.

The afternoon northwesterly winds will further decrease to gentle to moderate (8 to 18 mph) levels on Tuesday into Friday; consequently, the marine layer will be more persistent (Fogust) along the immediate coastline. The marine low clouds will spread inland during the night and morning with areas of fog and pockets of mist, clearing by the late afternoon.

Periods of monsoonal moisture will continue the stream over the Central Coast Central with variable mid to high-level clouds. This condition may bring rain and thunderstorms to the Sierra Nevada Mountains.

Surf report

Strong to gale-force (25 to 38 mph) northwesterly winds will generate a 5- to 7-foot northwesterly (300-degree, deep-water) sea and swell (with a 5- to 8-second period) on Sunday, decreasing to 4- to 6-feet with the same period on Monday.

A 3- to 5-foot northwesterly (290-degree, deep-water) swell (with an 8- to 11-second period) will develop on Tuesday and will remain at his level through Friday.

Sunday’s 1- to 3-foot Southern Hemisphere swell (210-degree, deep-water) swell (with a 14- to 16-second period) will continue at this level through Monday.

Seawater temperatures will range between 54 to 58 degrees through Friday.

This day in weather history

1987 - Slow moving thunderstorms deluged northern and western suburbs of Chicago IL with torrential rains. O’Hare Airport reported 9.35 inches in 18 hours, easily exceeding the previous 24 hour record of 6.24 inches. Flooding over a five-day period resulted in 221 million dollars damage. It was Chicago’s worst flash flood event, particularly for northern and western sections of the city. Kennedy Expressway became a footpath for thousands of travelers to O’Hare Airport as roads were closed. The heavy rains swelled the Des Plaines River above flood stage, and many persons had to be rescued from stalled vehicles on flooded roads.

2018 - The Prefumo Crest Inn of top of the Irish Hills at 1,400 feet of elevation reported a temperature of 78 degrees at 4:45 a.m., while just a short distance away, Diablo Canyon reported 52 degrees in dense fog. A shallow 800-foot marine/temperature inversion layer covers the coastal regions and is producing dense fog along the coastline and a few of the coastal valleys this morning.

2020 - The month of August typically averages only a few hundreds of an inch of rain in San Luis Obispo. Yesterday’s subtropical system produced thunderstorms and rain throughout the Central Coast. Many locations recorded around a tenth of an inch of rain on Thursday. Jim at Oak Shores and I in Los Osos both saw a tenth. Larry on Surf Street in Morro Bay saw nearly two tenths and two readers reported over a quarter of an inch of rain in Cayucos.

This week’s temperatures

LOWS AND HIGHS, PASO ROBLES

LOWS AND HIGHS, SAN LUIS OBISPO AND COASTAL VALLEYS

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