For months, the rain just didn’t go away in San Luis Obispo County

The North Beach Campground in Pismo Beach flooded Dec. 20 after heavy rains.
The North Beach Campground in Pismo Beach flooded Dec. 20 after heavy rains. jmellom@thetribunenews.com

A rain year marked by historic events, unseasonable contradictions and just plain weirdness came to an official close Thursday, with San Luis Obispo finishing well ahead of normal for total inches of precipitation.

The city received 27.38 inches at Cal Poly, where official records for San Luis Obispo are kept. That bested the historical average of 22.61, the National Weather Service said.

On the west side of the city in the Los Osos Valley, 38.05 inches fell, according to SLOWeather.com, which keeps totals for The Tribune.

The rain year as determined by the National Weather Service runs from July 1 through June 30.

A review of highlights from the year shows the following:

Nothing much notable occurred through the fall and early December. Then, on the weekend of Dec. 18 and 19, a powerful storm system planted itself off the Oregon coastline. It pumped band after band of rain toward the Central Coast. By the time the month was done, 9.66 inches had fallen at Cal Poly, mostly on that one weekend. That was the second-wettest December on record; San Luis Obispo normally gets 3.79 inches for the month.

One negative aspect of the December rains was flooding in part of Oceano when water backed up near Arroyo Grande Creek. Several homes sustained first-floor damage.

The county’s most important rain month — January — ended up drier than normal. From Jan. 3 to Jan. 29, no rain was measured. The month totaled just 2.56 inches — half of the 5.17 inches that is normal. It was the longest stretch of dry weather in January since 1984.

Rain returned in mid-February when a series of storms battered the county with strong winds and cold temperatures.

The first day of spring on March 20 featured not warm, sunny conditions, but a storm from the Gulf of Alaska that brought heavy rain and wind.

Rains continued well into spring. The first weekend of June, normally a great outdoors time for weddings and the annual Greek Festival in San Luis Obispo, instead featured dreary, wet skies. Brides and festival organizers were distraught. For that one weekend, the rain gauge at Cal Poly measured 1.05 inches. That shattered the record of 0.80 inches for the month of June, which was set in 1991.

The wackiness continued to this week, when a late-season storm dropped 0.02 inches early Wednesday morning in San Luis Obispo. For the month, June received 1.77 inches. It will likely be quite a while until a wetter June rolls around, said John Lindsey, who has more than 20 years of forecasting experience along the Central Coast.

Some places received truly generous amounts of rain. Rocky Butte near San Simeon, for example, recorded more than 50 inches for the year.

Reservoirs throughout the region were greatly boosted. Nacimiento Lake, a key water source for the county, spilled for only the fourth time in its 55-year history.

While the year was characterized by the La Niña weather phenomenon, it proved much wetter than a typical La Niña year.

Normally, La Niñas make for drier, cooler winters and springs. Lindsey noted that when La Niñas are in place, rainfall is 87 percent of normal.

“But not all La Niñas are created equal,” he said. This year, “for some reason, the storm track shifted a little farther south than a usual La Niña.”

Totals for the 2010-2011 rain year, in inches

San Luis Obispo: 27.38

Paso Robles: 16.00

Atascadero: 33.52

Pismo Beach: 30.95

Arroyo Grande: 30.02

Morro Bay: 23.23

Grover Beach: 29.92

Sources: National Weather Service, Weather Central