SLO County should expect chilly, foggy weather on Halloween. What’s next in the forecast?

Weather watches and warnings

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Although it’s not officially confirmed, this rainy season shows characteristics of a typical La Niña pattern.

The storm track is delivering abundant precipitation to the Pacific Northwest, while Central California is expected to stay mostly dry through mid-November.

With that said, it may be a good time to break out those sweaters and jackets, as much windier and cooler weather is expected this week as a trough of low pressure develops along the California coastline.

A pattern of gentle to moderate (8 to 18 mph) Santa Lucia (northeasterly/offshore) winds will develop during the overnight and morning and shift out of the northwest in the afternoon this weekend.

This condition should keep most of the low marine clouds out at sea. However, cloudy skies are expected this weekend as mid- to high level remnant moisture from Hurricane Kristy streams northward over the Central Coast.

The inland valleys (Paso Robles) will reach the low to mid-80s, while the coastal valleys (San Luis Obispo) will hit the mid-70s. The beaches will range between the low to mid-70s this weekend.

A series of Gulf of Alaska storms will move northeastward toward the Pacific Northwest this weekend.

The associated cold fronts will move southward through the Central Coast on Monday into Tuesday, with partly cloudy skies and a chance of a few scattered rain showers — primarily in the eastern regions of San Luis Obispo and Santa Barbara counties.

The main impact of these systems will be strong to gale-force (25 to 38 mph) northwesterly winds and much cooler temperatures.

In fact, temperatures will only reach the mid-60s throughout the region.

On Wednesday and Thursday, the afternoon northwesterly winds will lower to fresh to strong (19 to 31 mph) levels, and temperatures will warm to the 70s.

During this time frame, low marine clouds with pockets of fog and mist will develop overnight into the morning.

The fog and mist could make it a spooky Halloween night.

A cooler air mass will filter into the Central Coast as the trough of low pressure deepens along the coastline during the first week of November. This condition will create stronger northwesterly winds, and high temperatures will struggle to reach the 60s throughout our area.

The long-range models do not indicate any significant rain through mid-November.

Surf report

A 5- to 7-foot west northwesterly (285-degree deep-water) sea and swell (with a 7- to 11-second period) is forecast along our coastline through Sunday, building to 8 to 10 feet (with a 5- to 15-second period) on Monday into Tuesday.

A 4- to 6-foot northwesterly (300-degree deep-water) sea and swell (with a 5- to 12- second period) is forecast on Wednesday through Thursday, increasing to 6 to 8 feet with the same period on Friday into next Sunday.

Combined with this northwesterly sea and swell will be 3- to 4-foot southerly (195-degree deep water) swell (with a 12- to 15-second period) from Hurricane Kristy, centered about 1,000 miles west of Baja, California, on Monday and decreasing on Tuesday.

Surface seawater temperatures will range between 56 and 58 degrees through Sunday, cooling to 52 to 54 degrees on Monday through next Sunday.

On this date in weather history (Oct. 27)

1764: A “very remarkable storm of snow with high winds” produced 22 inches at Rutland in central Massachusetts. (David Ludlum)

1929: A snowstorm dumped 27 inches upon Ishpeming, Michigan, in 24 hours to establish a state record. (David Ludlum)

2014: Paso Robles reached a low of 38 degrees, the coolest temperature since early April. Calvin French reported a low temperature of 31.8 degrees in Adelaida that morning. “It would have been our first frost, had there been any dew,” he said.

2017: Former Typhoon Lan become extra tropical and intensified to 936 millibars near the Aleutian Islands with hurricane-force winds the Tuesday prior. Very long-period swells from this storm reached NOAA’s northwest Hawaii marine buoy the night before at 9 feet with a 24-second period and increased to 12 feet with a 21-second period that morning. At Diablo Canyon’s intake cove, “forecast forerunners” waves were manually being timed at 28 seconds. Due to the very long wavelength of the day’s swell, the accelerometers in the NOAA marine buoys and Scripps waverider buoys were not able to measure much of the wave energy in the long period spectral bands more than 22 seconds. The group velocity of those waves in deep water was about 50 mph versus 30 miles mph for waves with a 17-second period.

2019: The Santa Lucia (northeasterly/offshore) winds increased sharply the night before, with many lower elevation locations reporting gusts above 40 to 50 mph and many higher elevation locations seeing gusts above 60 mph throughout the Central Coast. The strongest winds were in the elevated terrain of the North Bay Area where gusts above 80 mph occurred. The Mount Saint Helena west PG&E weather station at 4,340 feet of elevation reported sustained winds of 72 mph with gusts to 84 mph that morning.

2020: Paso Robles reached a low of 35 degrees that morning, the coolest temperature since April 7, 2020.

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 [email protected] or follow him on Twitter @PGE_John.