Slight chance of thunderstorms this week as muggy weather comes to SLO County

We are indeed a land of microclimates!

So far this July, the high temperature at the Paso Robles Airport has averaged 106 degrees, 13 degrees above normal. In contrast, the weather station in Baywood Park has recorded an average high temperature of 58 degrees.

This highlights a remarkable 48-degree difference within just 24 miles as the crow flies between the coast and the inland valleys. Closer to the coastline, the Santa Maria Airport has seen an average high of 75 degrees, only a few degrees warmer than usual, while the San Luis Obispo Airport reported an average high of 86 degrees or 8 degrees above historical high temperatures for this month.

Subtropical moisture will stream over the Central Coast this weekend, producing variable mid- to high-level clouds and a slight chance of rain showers and thunderstorms, primarily in the eastern regions of San Luis Obispo and Santa Barbara counties.

This condition will create lower maximum daytime temperatures but warmer overnight lows with higher humidity levels. The inland valleys (Paso Robles) will reach the high 90s, while the coastal valleys (San Luis Obispo) will reach the high 70s. The beaches will range between the high 50s and the low 60s.

A thermal trough of low pressure over the Central Valley of California will produce persistent northwesterly winds that will continue to produce marine low clouds with pockets of fog and drizzle overnight into the morning in the coastal valleys and along the beaches.

While the coastal valleys will clear by the late morning and afternoon, the beaches will remain mostly overcast from Monday into Tuesday.

Along the coastline, fresh to strong (19 to 31 mph) northwesterly winds will develop during the afternoon on Wednesday through next Sunday.

These winds will mix out the temperature inversion layer, leaving behind mostly clear skies during the afternoon; however, marine clouds with pockets of fog and mist will continue to develop overnight and in the morning.

Over this period, temperatures along the beaches will reach the 60s, except for Cayucos, Avila Beach and Shell Beach, which will reach the mid-70s.

For the start of the Mid-State Fair, temperatures are expected to climb back into triple digits and remain at this level through the following week.

Surf report

A 4- to 6-foot northwesterly swell (with an 8- to 11-second period) is forecast along our coastline through Sunday, decreasing to 2 to 4 feet with the same period on Monday through Wednesday morning.

Fresh to strong (19 to 31 mph) northwesterly winds along the coastline will generate a 3- to 5-foot northwesterly sea and swell (with a 4- to 10-second period) Wednesday afternoon through Thursday, building to 6 to 8 feet (with a 5- to 9-second period) on Friday through next Sunday.

Combined with this northwesterly sea and swell, will be the largest southern hemisphere swell of the year. This southern hemisphere wave train will arrive along our coastline on Monday at 1 to 2 feet (with a 17- to 19-second period), peaking at 3 to 5 feet (with 15- to 17-second period) on Tuesday through Wednesday. This swell gradually decrease on Thursday through Friday.

Surface seawater temperatures will range from the low to mid-50s through Saturday.

On this date in Weather History (July 14)

1936: Extreme heat prevailed across the central U.S. as severe drought raged from Texas to the Dakotas. Record high temperatures were established in 16 states that summer, including readings as high as 120 degrees in the Great Plains Region. On this particular date, afternoon highs for 113 stations across the state of Iowa averaged 108.7 degrees. (David Ludlum)

1957: Hail, with some stones up to an inch in diameter, covered the ground to a depth of 3 inches ruining crops in the Bath area of New Hampshire.

2005: Death Valley had seven consecutive days (July 14-20) with high temperatures equal to or above 125 degrees.

2021: Paso Robles reached 88 degrees, the first day since July 6 that the temperature didn’t hit triple-digits levels.

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.