Average rainfall amounts at the Paso Robles Municipal Airport, Cal Poly — home of climatology for San Luis Obispo — and the Santa Maria Public Airport all dropped to approximately 27 percent of average at the end of February. The 2018 rainfall season was on track to be one of the driest on record, and optimism was fading.
Nevertheless, those of us with the memory of the “March Miracle” of 1991 or the March floods of 1995, hope springs eternal that the “Spring Equinox” that rolled in last Tuesday would bring a change in the weather — and indeed it did.
This spring came in like a lion.
The most significant Atmospheric River event to hit the Central Coast since December 2010, which flooded areas of Arroyo Grande and Oceano, took aim at a 15-mile-wide line that stretched from Estero Bay (Cayucos, Morro Bay and Los Osos) and onward toward the Atascadero/Paso Robles regions. Yes, this system produced heavy rainfall throughout Central California, but the middle part of this river in the sky, which carried the highest amount of water vapor, produced remarkable amounts of precipitation.
In fact, the communities in the direct path of the Atmospheric River saw terrific gains in seasonal averages. Paso Robles increased 53 percent and is now at 80 percent of average. Usually, Paso Robles only gets about 2.5 inches of rain in March. However, this month, the airport recorded 6.76 inches of rain.
Long Valley Ranches along Cebada Road, in western Atascadero, reported 11.5 inches during this Atmospheric River event, while Rocky Butte near San Simeon recorded 10.5 inches. By the end of this incident on Thursday, the Paso Robles Fire Department and the California Highway Patrol Air Operations unit stationed at the Paso Robles Airport rescued 10 people with their helicopter from Salinas River due to flooding.
The term Atmospheric River hasn’t been around very long. None of my oceanographic and atmospheric textbooks show any reference to it. Turns out, the phrase was coined by researchers Reginald Newell and Yong Zhu of the Massachusetts Institute of Technology in the early 1990s.
These rivers in the sky can stretch for thousands of miles across the world’s oceans but are only a few hundred miles wide. They can draw huge amounts of water vapor into narrow bands ahead of cold fronts and transport fantastic amounts of water across vast expanses. In fact, they can carry more fresh water than the Amazon River.
Along the West Coast, they are informally called the “Pineapple Express.” The Pineapple Express is a subset of an atmospheric river event that originates in the tropical waters near Hawaii — hence the pineapples. In the past, meteorologist simply referred to these as “the hose.”
Away from the middle of the Atmospheric River, rainfall totals were understandably less. Both Cal Poly and Santa Maria also saw significant increases in their seasonal rainfall averages. Cal Poly is now at 61 percent of average; a 33 percent increased since late February. Santa Maria improved to 52 percent of average with 6 inches of precipitation.
Gary Linquist wrote me: “It’s abundantly clear to me, and, I hope to you, that we are smack dab in the middle of a ‘Minor March Miracle!’”
Gary is right, especially the communities near the middle of last week’s Atmospheric River.