It’s heating up, SLO County. Look for warm but windy conditions this week

Historically, spring along the Northern and Central California coast is notorious for vigorous and persistent northwesterly winds, and this week will undoubtedly live up to this reputation.

The northwesterly gales of spring often mix out the marine/temperature inversion layer, creating less overcast with more sunshine in the coastal regions.

For this week, a high-pressure ridge over California will produce Santa Lucia (northeasterly) winds during the night and morning. As the Central Valley heats up during the day, a steep pressure gradient will develop between the shoreline and far inland valleys.

This condition will cause the winds to shift out of the northwest and increase to strong to gale-force levels (25 to 38 mph with gusts to 45 mph) along the coastline and many of the coastal valleys during the late morning, afternoon and evening through Wednesday.

This weather pattern will result in clear skies and warmer temperatures across San Luis Obispo and Santa Barbara counties. In fact, temperatures will soar to the low 80s in the inland valleys (Paso Robles) and mid-70s in the coastal valleys (San Luis Obispo), while the beaches will experience high 60s. The coastal communities will experience a drop in temperature during the afternoon; however, the southerly facing beaches of Caucus, Avila Beach and Shell Beach will warm up to the 70s.

A trough of low pressure will form along the California coastline from Thursday through next Saturday. This will lead to a decrease in northwesterly winds and the formation of a deep and persistent marine layer. This layer will bring pockets of drizzle and fog overnight along the beaches and the coastal valleys, while the coastal valleys will clear during the afternoon, with many of the beaches remaining overcast.

Another round of strong to gale-force (25 to 38 mph) northwesterly winds are forecast next Sunday through most of the following week.

Surf report

A 6- to 8-foot northwesterly (310-degree deep-water) sea and swell (with a 5- to 8-second period) is expected on Saturday, building to 8- to 10-feet with the same period on Sunday through Tuesday. This northwesterly sea and swell will decrease to 5 to 7 feet on Wednesday.

A 4- to 6-foot northwesterly (290-degree deep-water) swell (with an 8- to 11-second period) will develop on Thursday, decreasing to 3 to 5 feet on Thursday into next Saturday.

Combined with this northwesterly sea and swell, will be 1- to 2-foot southern hemisphere (215-degree deep-water) swell (with a 15- to 17-second period) on Saturday through Tuesday.

This week’s temperatures

As the winds blow parallel to our coastline, the friction causes ocean surface water to move.

Because of the Coriolis effect, the surface water flows to the right, or offshore. That, in turn, causes upwelling along the coast as cold, clear and nutrient-rich water rises from the ocean’s depths to the surface along the immediate shoreline to replace the shallow water that is pushed out to sea.

Consequently, sea water temperatures will decrease to 50 and 52 degrees on Sunday through Wednesday.

LOWS AND HIGHS, PASO ROBLES

LOWS AND HIGHS, SAN LUIS OBISPO AND COASTAL VALLEYS

On this date in weather history

April 27, 2017: Yesterday’s northwesterly winds reached 46.3 mph sustained with gust to 61.9 mph at the Diablo Canyon Meteorological Tower at the 76-meter anemometer. These are some of the strongest spring northwesterly winds ever recorded.

April 27, 2020: Gusty Santa Lucia (northeasterly) winds last night produced mid- to high-70-degree temperatures at Diablo Canyon around midnight.

April 28, 1921: A severe hailstorm in Anson County, North Carolina, produced hail the size of baseballs. Gardens, grain fields and trees were destroyed. Pine trees in the storm’s path had to be cut for lumber because of the hail damage, The Weather Channel reported.

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