Unlike the wild weather throughout the rest of United States last year, San Luis Obispo County enjoyed a relatively tranquil 2012. While we await the “official” announcement from NOAA that 2012 will become the warmest year in United States history, San Luis Obispo County enjoyed near average temperatures.
Historically, the annual mean temperature in Paso Robles is 59.7 degrees. In 2012 it averaged 60.9 degrees. However, closer to the coast San Luis Obispo saw colder than normal temperatures that averaged two degrees cooler.
The 2011-12 California rain season, which runs from July 1 through June 30, saw Cal Poly — home of climatology for San Luis Obispo — record 14.6 inches of precipitation, or about 65 percent of normal. In the North County, Paso Robles received 8.7 inches of rain, or about 68 percent of normal.
So what caused 2012’s low rainfall amounts and cooler than normal temperatures along the beaches and coastal valleys? The La Niña cycle was probably to blame. La Niña cycles produce stronger-than-normal trade winds across the equatorial Pacific. This condition triggers a greater amount of upwelling along the North and South American Pacific coastlines, which gives rise to cooler surface seawater temperatures.
These cooler waters tend to keep a persistent ridge of high pressure over California that often forces the storm track toward the Pacific Northwest, leaving the Central Coast with less rain and cooler beach temperatures.
January 2012 started dry, extending the dry spell that started the previous December when only 0.18 inches of rain was recorded at Cal Poly.
Thankfully, two low pressure systems on January 21 and 23 produced much needed rainfall throughout the Central Coast. The Walter Ranch near Cambria recorded 7 inches of rain. Other locations in the Santa Rosa and San Simeon watershed ranged from 6 and 12 inches. Cal Poly reported 3.27 inches. All that rain woke Pacific tree frogs from their hibernation. The booming chorus of thousands of high-pitched “kreek-eecks” from a gathering of small but tenacious frogs filled San Luis Obispo County as they sang their hearts out.
Unfortunately, February turned nearly dry. The months of December, January and February, historically the wettest months of the year, only produced a combined total of 4.46 inches of rain at Cal Poly. Normally, the rainfall total for that period should be about 13.90 inches. That was one of the driest three-month totals since 1976-77 or 1990-91. February saw the average seawater temperatures reach about 52 degrees at Diablo Canyon. These were some of the coldest February seawater temperatures since record-keeping began in 1976. Normally, seawater in February averages 55 degrees.
The mostly dry weather continued through most of March. Bob Blanchard of Old Creek Ranch near Cayucos gazed at the dry coastal hillsides with great concern. The Santa Lucia Mountains and Irish Hills took on a bronze hue that looked more like their appearance during summer than the Celtic green normally visible during winter.
“This winter’s dry spell was grim.” Blanchard told me at the time. The Blanchards and many other coastal ranchers were evaluating purchasing feed, selling their cattle or even moving their herds northward along the Oregon coast.
A weather pattern reminiscent of the one that produced the miracle rains of March 1991 allowed a series of storms to produce much-needed rain. About 3 inches of rain fell at Cal Poly. In the North County, Paso Robles saw 2.3 inches of precipitation. Not only was this rain beneficial for local ranchers, but on March 1, the statewide snowpack was only about 30 percent of normal. However, by the first part April the snowpack has increased to 50 percent of normal. That was a 20 percent increase in the snowpack in just one month, according to PG&E hydrologist Gary Freeman.
April saw mostly clear skies that produced warmer than usual temperatures during the afternoon, extra chilly at night, which put the well-known microclimates of San Luis Obispo County in sharp focus.
Former county Supervisor Bill Coy, who grows avocados on his Cottontail Ranch near Cayucos, told me this was one of the coldest winters he can remember, with plenty of nights in the high 20s and low 30s. “When the winds were blowing, our overnight temperatures were mostly in the low 40s, while just a short distance away, our neighbors reported high 20s or low 30s,” Coy said.
John Salisbury of Salisbury Vineyards in Avila Valley said the great number of nights that dropped below the freezing temperature this year delayed the wine grape bud break. Consequently, most of San Luis Obispo County’s vineyards escaped the ravages of frost this spring, unlike the previous year.
April also saw the largest ocean waves of the year, in fact the biggest since January 2010.
The swell peaked at 15.8 feet with an 18-second period at the Diablo Canyon waverider buoy.
After April, a long dry spell developed. It wouldn't rain again until October. A large and slow-moving cutoff low in the upper levels of the atmosphere moved south along the California coast and progressed into Southern California. A band of potent cumulonimbus clouds with the slate gray bases and tall billowing towers moved toward the Cuesta Grade from the east. The air turned electric and fashioned an intense display of lightning. Flashes of light were seen in the eastern sky and the distant rumble of thunder was followed by hail and rain showers.
A 30-mile-wide band of moderate rain stretched from Creston southwestward over San Luis Obispo toward Los Osos and out over the Pacific Ocean. Cal Poly recorded 1.05 inches of rain, ending the long dry spell. Southeast of Creston on Highway 58, a rain gauge at Jennifer Best’s home reported 1.5 inches.
Areas north and south of this band of rain recorded only a few hundredths of an inch. For example, the rain gauge in south Atascadero at Mickey’s home recorded 1.12 inches of rain, while the Templeton rain gauge at the Sheriff’s Office station only recorded 0.04 inches of rain.
The La Niña cycle that persisted through most of 2012 transition to a neutral condition in October. The Eastern Pacific high shifted southward allowing a series of low pressure systems and associate cold fronts to pass over San Luis Obispo County. These systems produced above normal rainfall. Cal Poly recorded 3.07 inches of rain in November and an impressive 6.42 inches in December.
Chris Arndt of SLOweather.com in western San Luis Obispo reported his season’s rain totals at about 150 percent of normal at the end of December.
In late December, the phenomenon of “king tides” developed along the California coast. “King tides” refers to tides that are the highest and lowest of the year. The term originated in Australia and has since spread throughout the rest of the nations that border the Pacific Ocean. The high tide reached 7 feet at Port San Luis. The tide hasn’t been that high since Jan. 10, 2009.
So what does 2013 hold for San Luis Obispo? The Climate Prediction Center in Camp Springs, Md., recently predicted that the current neutral conditions will continue through this winter and combined with the negative phase of the Pacific Decadal Oscillation should produce below-normal rainfall and average temperatures over the next three months.
Thank you for all the insightful stories and wonderful names suggestions for our local katabatic winds. At the end of the day, Santa Lucias received the majority of the vote. An appropriate name indeed!
Sunday’s weather report
A cold front passed San Luis Obispo County last night. An upper-level low supported by a strong jet stream will produce widely scattered rain showers throughout San Luis Obispo County through tonight. This upper-level low will also produce a chance of thunderstorms today.
A strong 1,034 millibar area of high pressure will build in behind the front and produce a steep pressure gradient. This pressure gradient will produce strong to gale force (24- to 38-mph) northwesterly winds along the coastline. Overall, it’s going to be a blustery day.
Rainfall amounts will range between one tenth to half an inch with higher amounts along the northwesterly slopes of the Santa Lucia Mountains. Snow levels are expected to drop to 3,000 feet across the southern Sierra and Tehachapi Mountains, although significant accumulations are not anticipated.
High pressure then sets up over California on Monday. This area of high pressure will produce gentle to moderate (8- to 18-mph) and at times gusty northeasterly (Santa Lucias) winds during the night and morning hours. These winds will give fair and dry conditions on Monday through Wednesday.
A cold front will move into San Luis Obispo County Wednesday night bringing rain showers and colder temperatures. This system has the potential to produce moderate gale to fresh gale force (32 to 46-mph) northwesterly post frontal winds on Thursday.
This system will be followed by a period of dry and gusty Santa Lucias winds on Friday through Sunday. Fair and dry weather expected the following week.
Sunday’s surf report
Increasing northwesterly winds will generate 6- to 8-foot northwesterly (295-degree deep-water) sea and swell (with a 7- to 15-second period) later this morning, increasing to 10 to 12 feet (with an 8- to 15-second period) this afternoon through tonight.
A 6 to 8 foot northwesterly (300-degree deep-water) swell (with an 11- to 14-second period) is forecast along our coastline on Monday, decreasing to 5 to 7 feet (with a 12- to 14-second period) on Wednesday.
Increasing northwesterly winds along the coastline will generate a 9 to11 foot northwesterly (300-degree deep-water) sea and swell (with a 5- to 15-second period) on Thursday, decreasing 8 to 10 feet (with an 11- to 14-second period) on Friday into Saturday.
Seawater temperatures will range between 54 and 56 degrees Wednesday, decreasing on Thursday into Friday.
If you have any questions about weather or this column, I would love to hear from you. You can also subscribe to my daily weather forecast by emailing me at PGEweather@pge.com.