SLO County weather: Strong winds, light rain ahead

After days of dry and mild weather, a significant change in the meteorological conditions is expected later this week as a series of low-pressure systems move southward along the California coastline.

Sunday morning’s gusty Santa Lucia (northeasterly) winds will produce clear skies and cool morning temperatures.

Overnight lows will drop to the mid-30s in the inland valleys (Paso Robles) to mid-40s in the coastal valleys (San Luis Obispo). Daytime highs will range from the mid to high-60s throughout the Central Coast on Sunday.

The winds will decrease and shift out of the northwest (onshore) by Sunday afternoon into Monday morning. These onshore winds will allow the marine layer to redevelop along the coastline and surge inland on Sunday night into Monday morning with pockets of fog and mist.

A dry cold front will move through the Central Coast later Monday morning with increasing mid to high-level clouds. In the wake of the cold front, strong to gale force (25 to 38 mph) northwesterly winds, cooler temperatures, and clearing skies will develop Monday afternoon into Tuesday.

The winds will decrease and shift out of the north on Wednesday. A cooler air mass will filter into the Central Coast with temperatures only reaching between the high 50s to the low 60s on Wednesday.

Thursday will be a transition day with gentle southerly winds, increasing clouds and a few rain showers. Moderate to fresh (13 to 24 mph) southerly winds and rain is forecast Friday into Saturday (Dec. 2 and Dec. 3) as a low-pressure system moves southward along the California coastline.

A stronger storm is expected next Sunday (Dec. 4) with increasing southerly winds and moderate to heavy rain.

Surf report

Intense storms in the mid Pacific will continue to generate long-period swells this week.

Sunday’s 5- to 7-foot northwesterly (290-degree, deep-water) sea and swell (with a 7- to 15-second period) will remain at this level through Monday morning.

Strong to gale-force (25 to 38 mph) northwesterly winds along the California coastline will create a 7- to 9-foot northwesterly (305-degree, deep-water) sea and swell (with a 5- to 18-second period) on Monday afternoon and night, decreasing to 6- to 8-feet (with 7- to 16-second period) on Tuesday,

A 4- to 6-foot northwesterly (295-degree, deep-water) swell (with an 8- to 18-second period) will develop along our coastline on Wednesday into Thursday.

Seawater temperatures will range between 53 and 56 degrees through Friday.

This Date in Weather History (November 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, MI, in 24 hours to establish a state record. (David Ludlum)

2017 - Former Typhoon Lan become extratropical and intensified to 936 millibars near the Aleutian islands with hurricane-force winds last Tuesday.

Very long-period swell from this storm reached NOAA’s Northwest Hawaii marine buoy last night at 9 feet with a 24-second period and has since increased to 12-feet with 21-second period this morning.

At Diablo Canyon’s intake cove “forecast forerunners” waves are manually being timed at 28 seconds. Due to the very-long wavelength of today’s swell, the accelerometer’s in the NOAA marine buoys and Scripps waverider buoys are not able to measure much of the wave energy in the long-period spectral bands over 22 seconds. The group velocity of these waves in deep-water is about 50 mph versus 30 miles mph for waves with a 17-second period.

2019 - The northeasterly (offshore) winds increased sharply last night, with many lower elevation locations reporting gusts above 40 to 50 mph and many higher elevation locations seeing gusts above 60 mph. The strongest winds so far have been in the elevated terrain of the North Bay Area where gusts above 80 mph have occurred. The Mount Saint Helena West PG&E Weather Station at 4,340 feet of elevation reported sustained winds of 72 mph with gust to 84 mph this morning.

2021 - The Chair 6 Ridge anemometer on Kirkwood Mountain, with an elevation of 9,186 feet, south of Lake Tahoe, reported sustained east-northeasterly winds of 110 mph with 136 mph gusts early this morning. An anemometer on Mount Saint Helena reported northeasterly wind gusts to 89 mph.

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.