How hot will the weather get during final week of the CA Mid-State Fair?

The California Mid-State Fair will be open for one more week in San Luis Obispo County, and the heat just might be bearable with lower-than-usual temperatures forecast for Paso Robles.

Over the past few weeks, the atmosphere has been locked in a stubborn pattern: A strong Bermuda High off the East Coast and a robust Eastern Pacific High off the West Coast.

Despite sharing the same latitude, weather along the East and West coasts can feel worlds apart — thanks to the vastly different impacts of these dominant high-pressure systems.

Along the West Coast, the Eastern Pacific High — a semi-permanent, high-pressure system over the northeastern Pacific Ocean — drives a cool onshore flow from the Gulf of Alaska.

This circulation often results in a persistent summer marine layer, which naturally moderates temperatures and reduces the need for air conditioning. In winter, this same flow helps keep coastal temperatures mild.

In contrast, the East Coast is influenced during the summer by the Bermuda High, a large high-pressure system centered near Bermuda. Its clockwise flow pulls warm, humid air from the Gulf of Mexico and Caribbean Sea, resulting in the classic “three H’s” of summer: heat, humidity and haze.

Relief from these oppressive conditions is often hard to find in the southeast.

Thanks to the cool influence of the Eastern Pacific High, California’s Central Coast enjoys some of the most comfortable weather in the country. In fact, according to MyPerfectWeather.com, it is the most comfortable climate anywhere found in the United States.

Much like last week, northwesterly (onshore) winds and warm inland temperatures will continue to fuel widespread marine low clouds along the coast, with areas of night and morning fog, mist and occasional drizzle expected through the upcoming week.

However, the afternoon northwesterly winds will gradually increase through this week, reaching gale-force levels by Thursday into the following weekend.

Moderate to fresh (13 to 24 mph) afternoon northwesterly winds will develop Saturday and Sunday, further building to fresh to strong (19 to 31 mph) levels on Monday into Wednesday. A steep pressure gradient along the California coastline will produce strong to gale force (25 to 38 mph) northwesterly winds starting Thursday and continuing through next Sunday.

There is a chance that these winds could reach moderate gale-force to fresh gale-force (32 to 46 mph) levels on Friday and Saturday.

These winds will be strong enough to mix out the temperature inversion layer during the late morning and afternoon, leaving behind clear skies, except a slug of monsoon moisture that will produce variable mid-to-high-level clouds.

High temperatures will remain near seasonal averages, with the coastal valleys (San Luis Obispo) ranging between the low to mid-70s.

Temperatures in inland areas like Paso Robles will climb into the high 80s to low 90s, resulting in one of the coolest California Mid-State Fairs on record.

Beach temperatures will hover in the low to mid-60s, except for the southerly facing beaches of Cayucos, Avila Beach and Shell Beach, which will hit the low 70s.

Looking ahead, the Climate Prediction Center is forecasting below-normal temperatures from late July into the first week of August, along with an increasing chances of monsoonal moisture reaching Southern California.

Surf report

Fresh to strong (19 to 31 mph) northwesterly winds along the California coastline will generate a 3- to 5-foot northwesterly (296-degree deep water) sea and swell (with a 5- to 8-second period) through Wednesday morning, increasing to 4- to 6-feet with the same period by Wednesday afternoon.

Gale-force northwesterly winds will produce a 5- to 7-foot northwesterly (305-degree deep water) sea and swell (with a 5- to 9-second period) on Thursday, building to 6- to 8-feet with the same period on Friday through next Sunday.

A 1- to 2-foot southern hemisphere (195-degree deep water) swell (with a 15- to 17- second period) will arrive along our coastline on Wednesday and will remain at this level through Thursday, gradually fading away on Friday.

Surface seawater temperatures will range between 58 and 60 degrees through Tuesday, decreasing on Wednesday through next Sunday.

On this date in weather history (July 20)

1930: The temperature at Washington D.C. soared to a record of 106 degrees. The next day, Millsboro, Delaware, reached 110 degrees to set a record for the state. July 1930 was one of the hottest and driest summers in the U.S., particularly in the Missouri Valley where severe drought conditions developed. Toward the end of the month, state records were set for Kentucky at 114 degrees and Mississippi at 115 degrees. (David Ludlum)

1988: The temperature at Redding, California, soared to a record high of 118 degrees.

2015: Monsoon moisture produced periods of heavy rain over the Central Coast, which broke many 24-hour July rainfall totals. Paso Robles recorded the most rain, at 3.55 inches. The San Luis Obispo County Airport reported 1.32 inches, while the Santa Maria Airport recorded 0.14 of an inch.

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.