Get ready for the ‘heat dome,’ SLO County. Triple-digit temps to hit California

Much like June, slightly below seasonal temperatures will persist through Tuesday. However, a shift in the pattern begins midweek.

As a strong high-pressure system — commonly referred to as a “heat dome” — develops over the Four Corners region and expands westward, triple-digit heat is expected to return to the inland valleys from Wednesday through next Sunday.

Sunday forecast

Fresh to strong (19 to 31 mph) afternoon northwesterly winds will develop along the coastline. These winds will help erode the marine inversion layer along southerly facing beaches such as Cayucos, Avila Beach and Shell Beach, allowing temperatures to climb into the mid-70s there.

In contrast, other beaches will remain cooler, ranging from the low to mid-60s. Coastal valleys (San Luis Obispo) will warm into the low 70s, while inland valleys (Paso Robles) rise into the upper 80s.

Expect mostly clear skies by afternoon, but areas of low clouds, mist and drizzle will push inland overnight.

Monday and Tuesday

Northwesterly winds will ease to gentle to moderate (8 to 18 mph), levels allowing the marine layer to persist along the coastline.

Expect continued overcast skies along the beaches with pockets of fog and occasional drizzle throughout the day. Clearing is likely in the coastal valleys, while inland areas remain mostly sunny. High temperatures will range from the low to mid-60s at the beaches, low to mid-70s in coastal valleys like San Luis Obispo, and upper 80s to low 90s in inland valleys such as Paso Robles.

Wednesday through next Sunday

A significant warm-up is expected as the Four Corners high-pressure system strengthens and extends westward. Inland valley (Paso Robles) temperatures will soar into the triple digits, with the Central Valley of California reaching highs between 105 degrees Fahrenheit and 111 degrees Fahrenheit.

Coastal valleys (San Luis Obispo) will warm into the low to mid-80s.

Strong afternoon northwest winds along the coast will help maintain cooler conditions at most beaches, holding temperatures in the 60s — though southerly-facing beaches like Cayucos, Avila and Shell Beach may reach the upper 70s to low 80s.

Additionally, the Four Corners high-pressure system could draw subtropical moisture into the region, particularly over the far eastern portions of San Luis Obispo and Santa Barbara counties.

This setup is associated with the North American Monsoon, which occasionally brings isolated thunderstorms, increased humidity, and virga— rainfall that evaporates before reaching the ground.

Looking ahead, long-range models indicate warmer-than-normal weather as we head toward the Mid-State Fair, which starts on Wednesday, July 16.

Surf report

A 5- to 7-foot northwesterly (310-degree deep-water) sea and swell (with a 5- to 10-second period) is forecast along our coastline through Sunday, becoming a 3- to 4-foot northwesterly (290-degree deep-water) swell (with an 8- to 11-second period) Monday into Wednesday morning.

Fresh to strong (19 to 31 mph) northwesterly winds along the California Coastline will generate a 4- to 6-foot northwesterly (305-degree deep-water) sea and swell (with a 5-to 9-second period) on Wednesday afternoon through Thursday morning, increasing to 5- to 7-feet on Thursday afternoon and night.

This northwesterly sea and swell will lower to 4- to 6-feet with the same period Friday into Saturday.

A 2- to 3-foot southern hemisphere (200-degree deep-water) swell (with a 15- to 17- second period) will arrive along our coastline on Sunday and will remain at this level through Tuesday, gradually fading away Wednesday.

Surface seawater temperatures will range between 54 and 56 degrees through next Sunday.

On this date in weather history (July 6)

1928: A hailstorm at Potter, Nebraska, produced a stone which was 5.5 inches in diameter, and 17 inches in circumference, weighing a pound and a half. (David Ludlum)

1985: Lightning struck a large transformer in Salt Lake County sending a 200-foot fireball into the air and blacking out almost the entire state of Utah for up to five hours.

1989: Unseasonably hot weather prevailed in the southwestern United States. Ten cities reported record-high temperatures for the date, including Las Vegas, with a reading of 115 degrees. Hanksville, Utah, reached 112 degrees; Bullhead City, Arizona, hit 120 degrees; and Death Valley soared to 126 degrees.

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.

This story was originally published July 6, 2025 at 5:00 AM.