Storm dumped nearly 8 inches of rain on Rocky Butte in SLO County. Why is it so rainy there?

Last Thursday’s storm brought intense rainfall to Rocky Butte, a fabled peak rising 3,245 feet above sea level between Hearst Castle and Lake Nacimiento in the Santa Lucia Mountain Range.

The storm dumped nearly 8 inches of rain there, while nearby Cambria received only 2.6 inches.

Why does Rocky Butte receive so much more rain than the rest of the Central Coast? The answer lies in the wind patterns.

The Santa Lucia Mountain Range runs in a north-northwesterly direction. When southerly prefrontal winds approach, they force the air mass upward over the mountains. As the air rises, it cools at approximately 5.4 degrees per 1,000 feet of altitude gain.

Once the air reaches its dew point, it becomes saturated, leading to condensation. This process releases latent heat, warming the air and reducing the cooling rate. In other words, like squeezing out a wet sponge.

This phenomenon explains why temperatures often rise just before rain or snow.

Adding to this effect, the winds during this storm came directly from the southwest — a rare event.

Typically, wind data from Diablo Canyon nuclear power plant’s meteorological tower shows that winds blow from the northwest about 60% of the time, from the northeast (Santa Lucia quadrant) about 12% and from the southeast (prefrontal winds) roughly 23%. The remaining 5% of the time, winds are evenly distributed among the other directions.

During the storm, these unusual southwesterly winds reached sustained speeds of 49.4 mph, with gusts peaking at 71.2 mph at the PG&E weather station near the TV Towers on Cuesta Grade.

Mt. Lowe, at 2,628 feet on Cuesta Grade, recorded an even stronger gust of 86.5 mph at 11:20 a.m. on Thursday.

Unlike southeasterly winds, these southwesterly winds were nearly perpendicular to the Santa Lucia Mountains above San Simeon, intensifying the orographic enhancement at Rocky Butte.

This rain significantly improved rainfall totals for the rain season, which runs from July 1, 2024, to June 30, 2025. So far, this season has followed a classic La Niña pattern, with the storm track shifting northward into Northern California, Oregon and Washington.

A nearly dry December and January left much of the Central Coast in moderate drought conditions, as reported by the U.S. Drought Monitor.

But Rocky Butte’s rainfall total climbed to 26.4 inches — 91% of the seasonal average — up from just 48% two weeks ago.

At the Paso Robles Municipal Airport, 4.7 inches of precipitation improved its total to 53% of the seasonal average. The San Luis Obispo County Regional Airport recorded 6.83 inches, reaching 51% of its usual 13.5 inches by February.

Further south, the Santa Maria Airport reported 3.86 inches (41% of average), and Santa Barbara Municipal Airport measured 4.43 inches, rising from 14% to 39% of normal for February.

Looking ahead, long-range forecasts suggest a dry pattern through the first week of March along the Central Coast.

High pressure over the Great Basin will strengthen this weekend, bringing moderate to fresh (13 to 24 mph with gusts to 35 mph) Santa Lucia northeasterly winds at night and in the morning, shifting out of the northwest in the afternoons and increasing to fresh to strong (19 to 32 mph with gusts up to 40 mph) along the coast through Friday.

This pattern will result in mostly clear to partly cloudy skies, with dense fog in valleys and on northeasterly-facing mountain slopes during nighttime and morning.

Morning temperatures will drop to the mid-30s in inland valleys (Paso Robles) and the mid-40s in coastal valleys (San Luis Obispo) and along the beaches. Daytime highs will reach the mid-to-high 70s across the Central Coast.

Long-range models indicate continued dry weather through the first week of March.

Surf report

A 5-to 7-foot northwesterly (290-degree deep water) swell (with an 8- to 17-second period) is forecast along our coastline Saturday into Sunday.

Gale force northwesterly winds along the California coastline will generate an 8- to 10-foot northwesterly (305-degree deep water) sea and swell (with a 5- to 16-second period) on Monday, decreasing to 6- to 8-feet (with a 7- to 17-second period) on Tuesday and will remain at this level through Friday.

Surface seawater temperatures will range between 54 and 56 degrees through Monday, decreasing to 53 to 55 degrees on Tuesday through Friday.

On this date in weather history (Feb. 16)

1852: Between Jan. 15, and Feb. 24, a total of 1,378 railroad cars were drawn by horses across the frozen Susquehanna River to engines waiting at Havre De Grace, Maryland.

1932: Up to 2 inches of snow whitened the Los Angeles Basin in California. The Los Angeles Civic Center reported an inch of snow, and even the beaches of Santa Monica were whitened with snow, in what proved to be a record snowstorm for Los Angeles.

1952: A six-day snowstorm was in progress in the western United States. The storm produced 44 inches of snow at Marlette Lake, Nevada, 52 inches at Sun Valley, Idaho and 149 inches at Tahoe, California, establishing single-storm records for each of those three states. In addition, 24-hour snowfall totaled 22 inches at the University of Nevada and 26 inches at Arco, Idaho, establishing records for those states. The streamliner train called City of San Francisco was snowbound in the Sierra Nevada Range near Donner Summit. (David Ludlum)

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.

This story was originally published February 16, 2025 at 5:00 AM.