SLO County is in for a much cooler week after weekend heat wave. See forecast

A transitory upper-level ridge was expected to bring warm to hot weather under mostly clear skies on Saturday, before cooling somewhat on Sunday.

A significant cool-down, accompanied by gale-force northwesterly winds, is expected later Sunday through Friday, before temperatures rebound again next weekend into early next week.

Earlier this weekend, a 586 dm upper-level high-pressure system centered over the Central Coast drove unseasonably warm temperatures.

Inland valleys, such as Paso Robles, were expected to approach triple digits, while coastal valleys like San Luis Obispo will see highs in the upper 70s to low 80s. Most beaches were expected to range from the upper 60s to low 70s, though the southerly facing beaches — Cayucos, Avila Beach, and Shell Beach — would climb into the upper 70s due to down-slope winds.

By late Sunday, a pronounced cooling trend begins as a new upper-level trough develops along the California coast. This will interact with a robust 1,036 mb Eastern Pacific High situated about 1,100 miles west of Cape Mendocino, generating strong to gale-force (25 to 32 mph) northwesterly winds each afternoon.

On Tuesday and Wednesday, winds may intensify to moderate gale-force to fresh gale-force levels (32–46 mph) levels.

These gusty conditions will help scour out the marine inversion, leading to sunny afternoons, but low clouds, fog and mist are expected during the overnight and early morning hours.

Temperatures will drop sharply: Inland valleys will fall to the mid-to-upper 60s, coastal valleys to the low 60s and most beaches will only reach the upper 50s — except for the southern beaches, which should still hit the mid-60s.

Looking ahead, long-range models suggest another warming trend beginning next Sunday, as high pressure builds in from the desert Southwest. Expect widespread triple- digit heat in the inland valleys, with mid-80s likely in the coastal valleys.

Dry conditions are expected to persist through the end of May.

Surf report

Gale-force northwesterly winds along the California coastline will generate a 6- to 8-foot northwesterly (310-degree deep-water) sea and swell (with a 5- to 11-second period) on Saturday, building to 9- to 11-feet on Sunday through Wednesday, rough oceanographic conditions indeed.

A 5- to 7-foot northwesterly (300-degree deep-water) sea and swell (with a 7- to 14- second period) is forecast along our coastline on Thursday through Friday.

Combined with this northwesterly sea and swell will be a 1- to 3-foot Southern Hemisphere (220-degree deep-water) swell (with a 15- to 18-second period) on Tuesday through Thursday.

Surface seawater temperatures will range between 52 and 54 degrees through Sunday, decreasing to 49 to 51 degrees on Monday through Friday.

This date in weather history (May 11):

2011: Elliott who lived north of Creston and east of Paso Robles reported a possible tornado.

“The clouds grew and the sky darkened,” he said.

At about 7:30 p.m. he went outside and saw strong northeasterly winds and smelled rain. He heard a crack, and suspected that a tree had fallen. He turned toward the sound and saw dust and plant debris swirling about a hundred feet away. He wrote, “I could see pollen streaming from pine trees. The dust and debris were swirling around in a column probably 30 feet across. The wind-event snapped the top off a pine tree up the hill from our house.”

He added that, “We see a lot of dust-devils here, but they are generally during hot weather.”

Thunderstorms developed along the San Luis Obispo/Kern County line and produced 0.28 inches of rain at Parkfield. Shandon, New Cuyama and Condor Lookout in eastern San Luis Obispo County reported a few hundreds of an inch of rain. A few sprinkles were reported in Atascadero.

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 X @PGE_John.