La Niña is here. What does it mean for rest of SLO County rain season?

It’s official. After months of speculation about the potential onset of a La Niña climate pattern, NOAA’s Climate Prediction Center announced last week that surface seawater temperatures in the Equatorial Pacific Ocean had finally met the criteria for La Niña.

Historically, about 75% of the time, this pattern produces below-average rainfall for San Luis Obispo and Santa Barbara counties.

This rain season, spanning July 1, 2024, to June 30, 2025, has followed a classic La Niña pattern, where the storm track shifts northward into the Pacific Northwest.

So far, the San Luis Obispo County Regional Airport has received 2.95 inches of rain. Most of the longer-range models indicate dry weather conditions continuing through the end of January.

Typically, January is the wettest month of the year at 5 inches of rain, followed by February at 4.6 inches.

The driest rain season (since 1869) occurred well over a century ago, in 1897, when only 7.2 inches of precipitation was recorded in San Luis Obispo.

Much like last week, the Eastern Pacific High off the Northern California coastline will act as a roadblock, forcing the storm track into the Pacific Northwest, keeping the Central Coast dry. At the same time, high pressure over the Great Basin will continue to generate Santa Lucia (northeasterly) winds, mainly bringing clear skies, low relative humidity levels, chilly mornings, and mild afternoons.

Further south, strong Santa Ana wind events will continue through Wednesday.

A pattern of moderate to fresh (13 to 24 mph with gusts up to 35 mph) Santa Lucia (northeasterly) winds are expected during the night and morning, decreasing and shifting out of the northwest during the afternoon through Friday.

Due to the low relative humidity levels, temperatures will rapidly cool after sunset and quickly warm after sunrise. Overnight temperatures will dip into the high-20s to low-30s in inland valleys like Paso Robles and the low to mid-40s in coastal valleys such as San Luis Obispo and along the beaches.

High temperatures will reach the mid-60s throughout the region.

Fresh to strong (19 to 31 mph) northwesterly winds may develop on Saturday, shifting back out of the northeast next Sunday into the following week.

For the following week, some models suggest a cut-off low-pressure system might bring rain. As the late great Dr. George Fischbeck, longtime KABC Los Angeles meteorologist, would say, a cut-off low is a weatherman’s woe.

A cut-off low-pressure system is detached from the primary airflow, making it difficult for weather forecasters to accurately predict. Anyway, the latest runs of the American and European numerical models indicate dry conditions persisting through the end of January.

Surf report

This Saturday and Sunday, a 6- to 8-foot northwesterly (290-degree deep-water) swell (with a 13- to 15-second period) is expected along our coastline.

A 5- to 7-foot (290-degree deep-water) swell (with an 11- to 20-second period) will arrive along our coastline on Monday and will remain at this height but with a gradually shorter period through Friday.

Strengthening northwesterly winds on Saturday will generate a 6- to 8-foot northwesterly (300-degree deep-water) sea and swell (with a 5- to 13-second period).

Surface seawater temperatures will range between 52 and 54 degrees through next Saturday.

On this date in weather history (Jan. 12)

1888: A sharp cold front swept southward from the Dakotas to Texas in just 24 hours, spawning a severe blizzard over the Great Plains. More than 200 pioneers perished in the storm. Subzero temperatures and mountainous snow drifts killed tens of thousands of cattle. (David Ludlum)

2009: High pressure over California produced Santa Lucia (northeasterly /offshore) winds. These winds created bone dry conditions with the San Luis Obispo County Regional Airport reaching a relative humidity level of only 14%. The high temperature hit 82 degrees, breaking the previous daily record of 78.

2017: The month’s rains increased Lake Nacimiento percentage of capacity (%) from 25% Jan. 3, 2017 to 51% . The Rocky Butte rain gauge near San Simeon reached 40 inches of rain.

2019: A cold front produced 1.87 inches of rain at Davis Peak and 1.43 inches at Diablo Canyon.

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.