This fall has seen a ridiculously persistent ridge of high pressure — which has driven the majority of the Gulf of Alaska storms north of the Central Coast over the past six years — give way to a trough of low pressure along the West Coast.
This condition has allowed a plume of subtropical moisture, or an atmospheric river, that stretched past the Hawaiian Islands to bring abundant rainfall to San Luis Obispo County during the first half of December. In fact, above-average rainfall has fallen throughout the Central Coast since October. The hills have turned from shades of golden brown to brilliant, emerald green.
Typically, San Luis Obispo receives about 5.5 inches of rain by mid-December. As of Saturday, Cal Poly and Mission College Prep High School had both recorded 8 inches of precious precipitation this rain season, which started July 1 and will continue through June 30.
Chris Arndt’s SLOweather.com in western San Luis Obispo has recorded 7.11 inches, 130 percent of the area’s average precipitation. The San Luis Obispo County Farm Bureau, near the San Luis Obispo County Regional Airport, has recorded 6.47 inches. The SLOCountyWater.org rain gauge at Camp San Luis Obispo reported 8 inches. Across Highway 1 at the San Luis Obispo Botanical Garden, 9.56 inches have fallen.
On top of the Irish Hills Natural Reserve, Tim’s Place has recorded a little more than 10 inches, while Davis Peak is nearly at 9 inches. A short distance away, Diablo Canyon nuclear power plant recorded 8.09 inches; that total is more rain than what fell during the entire 2013 and 2014 rain seasons along the Pecho Coast. Los Osos, Morro Bay and Cayucos have reported about 7.5 inches.
Along the Santa Lucia Mountains, at locations above Cayucos, Cambria and San Simeon, the news is even better.
Since July, the Walter Ranch near Cambria and Rocky Butte east of Hearst Castle have both recorded more than 14 inches of rain. Bill Coy, who lives above Cayucos, wrote me to say that many of the creeks are now flowing.
In the North County, the Paso Robles Municipal Airport usually receives about 3 inches of rainfall by mid-December. So far this rain season, the airport has recorded 3.34 inches, while 4.75 inches have fallen in Templeton and Atascadero.
Farther south, Pismo Beach, Nipomo, Arroyo Grande and Oceano have recorded nearly 7 inches of rain, while Lopez Lake has over 8 inches.
Unfortunately, the rain hasn’t done much to help with the drought. The National Drought Mitigation Center released its latest drought monitor map for the United States on Thursday. The NDMC classifies drought in five categories of increasing severity: abnormally dry, moderate drought, severe drought, extreme drought or exceptional drought. The latest NDMC maps put nearly all of San Luis Obispo County into the most intense category of exceptional drought. However, it reported that drought conditions no longer apply to about 27 percent of California; all in Northern California.
The Sierra Nevada Mountains in Northern California have recorded nearly 180 percent of average rainfall. However, the warm nature of the atmospheric river condition combined with an ever-warming atmosphere have kept snowpack well below historical norms.
This leads to the question: What will this winter bring? Back in December 2014, the Central Coast enjoyed above-average precipitation, but the following January, February and March — the heart of our rain season — were nearly dry.
Since 1950, the National Oceanic and Atmospheric Administration has used sea surface temperatures in a central equatorial region of the Pacific Ocean called Niño 3.4 as the standard for classifying El Niño (warmer-than-normal SST) and La Niña (cooler-than-normal SST) events.
This year, they are calling for a La Niña condition that historically produces below average rainfall along the Central Coast. However, John Neil of the Atascadero Mutual Water Company discovered that in past years, when this station received more than 2 inches of rain during October, the following months also received above-average rainfall.
If I were a betting man, I would double down on Neil’s observations and hope that above-average rainfall will continue through March. The long-range weather models show the next chance of rain around Christmas.
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Late last week, PG&E workers from Diablo Canyon sponsored 200 underprivileged children through the Salvation Army’s Angel Tree program for San Luis Obispo County. Plant employees filled holiday gift wishes children listed on Angel Tree ornaments.
“This program continues to be a wild success because all the children-in-need were adopted,” said Meagan Wilson, the coordinator of the Angel Tree event at the power plant over the past six years.
John Lindsey’s column is special to The Tribune. He is PG&E’s Diablo Canyon marine meteorologist and a media relations representative. Email him at email@example.com or follow him on Twitter: @PGE_John.