SLO County weather forecast: Mist, clouds expected for Halloween

A 1,025 millibar area of high pressure over the Great Basin will produce Santa Lucia (northeasterly) winds during the night and morning on Sunday through Monday. The condition will create cold and crisp mornings and mild afternoons under primarily clear skies. Later this week, it will be time to batten down the hatches and break out the sweaters and coats as a significant change in the weather pattern develops.

A pattern of moderate to fresh (13 to 24 mph) Santa Lucia (northeasterly) winds developing during the night and morning, shifting out of the northwest and increasing to fresh to strong (19 to 31 mph) levels during the afternoon will start Sunday and will continue through Monday under primarily clear skies.

Overnight lows will drop to the low to mid-40s throughout the Central Coast, while daytime highs will range from the low-60s at the beaches, the low to mid-70s in the coastal valleys (San Luis Obispo), and the high-70s in the inland valleys (Paso Robles).

As if on cue, the marine layer, with pockets of fog and drizzle, will develop along the coastline on Monday night (Halloween) and surge inland by Tuesday morning as a slow-moving cold front is forecast to travel through the Central Coast on Tuesday. Please ensure that your trick-or-treaters are highly visible, especially in misty conditions.

This low-pressure system is forecast to produce partly to mostly cloudy skies and a few scattered rain showers on Tuesday. The main impact of this tempest will be increasing northwesterly winds and cooler temperatures.

In the wake of the cold front, strong to gale-force (25 to 38 mph) northwesterly winds and cooler temperatures will develop on Tuesday afternoon, further increasing to moderate gale-force to fresh gale-force (32 to 46 mph) levels on Wednesday into Thursday along the coastline. Temperatures will struggle to reach the low-60s, with most Central Coast locations only reaching the high-50s on Wednesday and Thursday under hazy skies. The first freezing temperatures of fall could develop on Thursday and Friday morning in the inland valleys.

The long-range models are advertising a decent chance of moderate to heavy rain and gale-force southerly winds developing on November 8th and 9th.

This Date in Weather History (October 30):

1947 - The Donora, PA, smog disaster finally came to an end. For five days an inversion trapped impurities in the lower atmosphere over the Monongahela Valley killing 20 persons, and leaving more than 2000 others sick. (26th-30th) (David Ludlum)

2007 - A strong ridge of high pressure along the California coastline will continue to force the storm track far to the north. This is a very stable condition and except for a chance of a random cut-off low pressure system developing off our coastline, rain is not expected over an extended period.

2019 - In Southern California, one of the strongest Santa Ana wind event in October is underway. Peak winds today could range between 50 and 70 mph with gusts to 80 mph in a few of the mountain passes. Easterly seas could reach 10 feet in the Southern California Bight! Relative humidity levels will drop to single digits in Ventura and Los Angeles counties.

Surf report

Strong to gale-force (25 to 38 mph) northwesterly winds along the Northern and Central California coastline will generate a 5- to 7-foot northwesterly (310-degree, deep-water) sea and swell (with a 5- to 15-second period) on Sunday through Tuesday. The northwesterly sea and swell will further build to 7- to 9-feet (with a 5- to 12-second period) on Wednesday through Friday.

Seawater temperatures will range between 53 and 55 degrees through 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.