SLO County weather: Scattered rain, thunderstorms and cold temperatures

A significant change in the weather pattern will develop next week as a dry-cold front passes through the Central Coast, followed by a robust upper-level low-pressure system that will produce much cooler temperatures, scattered rain showers, and a good chance of thunderstorms.

A weak cold front will move through the Central Coast on Sunday morning with gentle to moderate (8 to 18 mph) northeasterly winds and a deep marine layer with pockets of fog and mist. In the front’s wake, strong to gale-force (25 to 38 mph) northwesterly winds and clearing skies with cooler temperatures will develop on Sunday afternoon into Monday. Temperatures will reach the high-70s in the inland valleys (Paso Robles), the mid-70s in the coastal valleys (San Luis Obispo), and the high-50s along the beaches on Sunday.

A 542 decameter late-season upper-level low-pressure system will travel southward along the California coastline, moving through San Luis Obispo and Santa Barbara Counties on Tuesday into Thursday with fresh to strong (19 to 31 mph) southerly winds and scattered rain showers. The longer days of late spring can produce more instability in the atmosphere, creating a good chance of thunderstorms. The southerly winds will decrease to moderate to fresh (13 to 24 mph) levels by Thursday, but scattered rain showers and a chance of thunderstorms will continue into Friday morning.

These convective storms can produce lightning, short periods of heavy rainfall, hail, microburst, and even the possibility of tornadic activity. On May 6, 1998, a similar system produced a tornado in San Luis Obispo.

This system will bring in a much cooler air mass; consequently, temperatures throughout the Central Coast will struggle to reach the low- 60s, with overnight lows in the 40s. Snow levels will lower to 4,500 feet. Total rainfall amounts are expected to range between 0.10 and 0.50 of an inch.

Surf report

A 4- to 6-foot northwesterly (290-degree, deep-water) swell (with an 8- to 18-second period) is expected along our coastline on Sunday morning.

Gale-force northwesterly winds along the coastline will generate an 8- to 10-foot northwesterly (310-degree, deep-water) sea and swell (with a 5- to 15-second period) on Sunday afternoon and night, decreasing to 5- to 7-feet (with a 7- to 12-second period) on Monday through Friday.

Keep your thickest wetsuits available; seawater temperatures will range between 49 and 52 degrees through Wednesday, increasing to 54 to 55 degrees on Thursday into Friday.

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.