SLO County weather forecast: Transition into fall patterns, cold and crisp mornings

Last week, gusty Santa Lucia (northeasterly) winds helped to produce record-breaking temperatures in the coastal regions. The San Luis Obispo County Airport hit 100 degrees on October 19, smashing the previous daily record of 93 degrees set in 2018. This was also the high temperature for the entire United States on that day.

This week, a significant change in the weather pattern will develop as a series of dry cold fronts move through the Central Coast with strong to gale-force (25 to 38 mph) afternoon northwesterly (onshore) winds and much cooler temperatures. In other words, it’s going to feel more like fall with cold and crisp mornings.

Overnight lows will drop to the mid to high-30s in the Inland Valleys (Paso Robles), the coastal valleys (San Luis Obispo) will lower to the mid-40s, while daytime highs this week will range from the low to mid-70s always from the ocean. The beaches are forecast to reach into the mid-60s.

A pattern of moderate to fresh (13 to 24 mph) Santa Lucia (northeasterly) winds developing during the morning, shifting out of the northwest and increasing to strong to gale-force levels during the afternoon will start on Sunday and will continue through Tuesday. In the upper levels of the atmosphere, the jet stream, flowing from Pacific Northwest southward through California, will bring a cooler air mass to the state, keeping temperatures below seasonal averages.

Another dry cold front is forecast to move to the Central Coast on Wednesday with moderate gale-force to fresh gale-force (32 to 46 mph) afternoon northwesterly winds, clear to partly cloudy skies, and cool temperatures.

The winds are forecast to decrease to fresh to strong (19 to 31 mph) levels on Thursday into Saturday which should allow the marine layer to redevelop along the coastline with areas of fog and drizzle.

Long-range models are advertising the chance of rain developing on November 7; otherwise, a dry weather pattern is expected to continue.

Surf report

The roughest oceanographic conditions of the fall season are forecast this week, please practice caution.

Strong to gale-force (25 to 38 mph) northwesterly winds along the Northern and Central California coastline will generate a 6- to 8-foot northwesterly (310-degree, deep-water) sea and swell (with a 5- to 11-second period) on Sunday.

A 5- to 7-foot northwesterly (300-degree, deep-water) sea and swell (with a 5- to 13-second period) is forecast on Monday into Tuesday, increasing to 8- to 10-feet with the same period on Wednesday.

A 5- to 7-foot northwesterly (290-degree, deep-water) swell (with an 8- to 11-second period) will develop on Thursday into Saturday.

A 1- to 2-foot Southern Hemisphere (200-degree, deep-water) swell (with a 15- to 18-second period) is expected along our coastline on Sunday through Tuesday.

Seawater temperatures will range between 53 and 65 degrees through Friday.

This Date in Weather History (October 23):

1843 - “Indian Summer” was routed by cold and snow that brought sleighing from the Poconos to Vermont. A foot of snow blanketed Haverhill NH and Newberry VT, and 18 to 24 inches were reported in some of the higher elevations. Snow stayed on the ground until the next spring. (22nd-23rd) (Sandra and TI Richard Sanders - 1987) (The Weather Channel)

2016 - San Luis Obispo Airport tied the record high of 97 degrees on Thursday. The old record was set in 1964.

2017 - Gale-force Santa Lucia winds have developed during the morning hours over the last two days. Sunday morning saw wind gust of 57 mph, while this morning saw 50 mph wind gust at Diablo Canyon.

These winds will produce dry and hot conditions throughout the Central Coast, including the beaches. In fact, most stations in the coastal valleys and beaches are reporting triple-digit readings. As of 2:15 p.m. today, temperature records were already broken with San Luis Obispo at 102 degrees, the old record for was 99° set in 1965, Santa Maria reached 100°, the previous record of 98° was also set in 1965.

2021 - All the eyes of the meteorological community are on a storm with hurricane-force winds that is rapidly intensifying as it travels eastward across the southern Gulf of Alaska from 989 millibars to 943 millibars today.

This storm’s explosive development is classified as a “bomb cyclone.” A low-pressure system needs to lower 24 millibars in 24 hours to be classified as a meteorological bomb.

The associated cold front is forecast to tap into subtropical moisture and take on the characteristics of an Atmospheric River (AR) as it moves into Northern California with heavy rain on Sunday. Expected precipitation totals in Northern California will range from five-plus inches in the northern coastal mountains and the northern/central Sierra Nevada; three to five inches in lower elevations of the Bay Area and Sacramento Valley.

The ECMWF and GFS models continue to indicate that this intense cold front, strengthened by vigorous upper-level winds, will move through the Central Coast Sunday night into Monday morning. This storm is forecast to produce moderate gale-force to fresh gale-force (32 to 46 mph with gusts to 60 mph) southerly winds and between one and three inches of rain in San Luis Obispo County. The Santa Lucia mountains above Cambria could see as much as four inches.

This week’s temperatures

LOWS AND HIGHS, PASO ROBLES

LOWS AND HIGHS, SAN LUIS OBISPO AND COASTAL VALLEYS

John Lindsey is a longtime meteorologist who lives in Los Osos. Email him at JohnLindseyLosOsos@gmail.com.