‘May gray’ along the SLO County coast will give way to warmer weather this week

Persistent onshore winds and below-normal seasonal temperatures will continue through Memorial Day across the Central Coast. Along the coastline, extensive marine low clouds will persist during the night and morning, followed by partial afternoon clearing in some areas.

Beginning Tuesday and continuing into next weekend, strengthening northwesterly winds are expected to bring slightly warmer temperatures along with increased sunshine and improved clearing across coastal regions.

A stubborn trough of low pressure parked over the Central Coast will continue to generate gentle to moderate (8 to 18 mph) west to northwesterly winds through Sunday, increasing to moderate to fresh (13 to 24 mph) levels on Memorial Day.

This persistent onshore flow will maintain widespread marine low clouds, along with pockets of mist and drizzle in the coastal valleys such as San Luis Obispo during the night and morning, followed by afternoon clearing. Beaches may remain mostly overcast through much of the weekend under typical “May gray” conditions, although partial afternoon clearing is expected on Memorial Day for the “Lost at Sea” memorial in Cayucos.

Daytime highs will generally reach the mid-70s across inland valleys, including Paso Robles, while coastal valleys such as San Luis Obispo will remain cooler in the mid- to upper 60s. Along the beaches, temperatures will range from the upper 50s to lower 60s.

A pair of cold fronts moving through Northern California from late Monday through Wednesday will not bring rainfall to the Central Coast, but they will tighten pressure gradients along the coastline and generate strong to gale-force (25 to 38 mph with gusts up to 45 mph) northwesterly winds along the coast from Tuesday through Wednesday.

These stronger winds should be sufficient to erode the marine inversion layer, resulting in mostly clear skies and somewhat warmer temperatures.

During this period, inland valleys are expected to warm into the low 80s, while coastal valleys rise into the upper 60s and low 70s. Beach communities will generally remain in the low 60s, although south-facing beaches such as Cayucos, Avila Beach, and Shell Beach could warm into the upper 60s.

The trailing edge of one of these cold fronts will move across the Central Coast on Thursday, bringing decreasing winds and increasing cloud cover. Another round of gale-force northwesterly winds along the coastline is then expected Friday into next weekend. Meanwhile, unsettled weather is forecast for the Sierra Nevada, where thunderstorms and higher-elevation snow are possible Wednesday night through Thursday.

If the latest numerical weather models verify, winds next weekend could strengthen to moderate gale-force to fresh gale-force (32 to 46 mph with gusts to 50 mph) levels in the coastal regions.

Looking farther ahead, dry weather is expected to continue into the first week of June, which is typical as California’s rainy season draws to a close.

Surf report

A 2- to 4-foot northwesterly (300-degree deep-water) swell (with an 8- to 11-second period) is expected this Saturday through Monday morning.

Moderate to fresh (13 to 24 mph) northwesterly winds along the Central California coastline will produce a 3- to 5-foot northwesterly (305-degree deep-water) sea and swell (with a 5- to 15-second period) Monday afternoon through Tuesday morning, increasing to 7- to 9-feet (with a 7- to 13-second period) on Tuesday afternoon through Wednesday.

A 5- to 7-foot northwesterly (290-degree deep-water) swell (with an 8- to 20-second period) is expected on Thursday as the local winds decrease and a long-period swell arrives from the Gulf of Alaska.

Northwesterly gales will generate a 6- to 8-foot northwesterly (300-degree deep-water) sea and swell (with a 5- to 16-second period) on Friday, building to 11 to 13 feet (with a 5- to 14-second period) next weekend.

A 2- to 3-foot Southern Hemisphere (220-degree deep-water) swell (with a 15- to 17-second period) is forecast to arrive along the Central Coast on Monday through Tuesday.

Another 2- to 3-foot Southern Hemisphere (210-degree deep-water) swell (with an 18- to 20-second period) is forecast next weekend.

Seawater temperatures will range between 52 and 54 degrees through Thursday, decreasing to 49 and 51 degrees on Friday into next Sunday.

On this date in weather history, May 24

1894: Six inches of snow blanketed Kentucky. Just four days earlier as much as 10 inches of snow had fallen across Kentucky, Tennessee and Virginia. Six days earlier a violent storm had wrecked nine ships on Lake Michigan. (David Ludlum)

1930: A tornado touched down near the town of Pratt, Kansas, and traveled at an incredibly slow speed of just 5 mph. (David Ludlum)

1940: Hail fell near Ada, Oklahoma, to a depth of 6 to 8 inches, with drifts of hail up to 5 feet high.

2012: The northwesterly winds reached 43-mph sustained with gusts to 59-mph at Diablo Canyon. Wind gust peaked at 60-mph at Point Buchon. Very windy indeed!

This week’s temperatures

LOWS AND HIGHS, PASO ROBLES

SUNDAY: 47, 76

MONDAY: 47, 76

TUESDAY: 46, 75

WEDNESDAY: 46, 78

THURSDAY: 48, 80

FRIDAY: 50, 81

SATURDAY: 51, 83

SUNDAY: 52, 84

LOWS AND HIGHS, SAN LUIS OBISPO AND COASTAL VALLEYS

SUNDAY: 50, 68

MONDAY: 49, 67

TUESDAY: 49, 66

WEDNESDAY: 48, 70

THURSDAY: 50, 68

FRIDAY: 51, 70

SATURDAY: 52, 74

SUNDAY: 53, 75

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