Since we are near the end of our typical rainy season, I thought it would be interesting to take a final look back at it.
San Luis Obispo County is characterized by a Mediterranean climate, which means that most of our rainfall occurs between November and April.
Normally, the rainfall in May quickly tapers off with San Luis Obispo only averaging about 0.4 of an inch, but there have been exceptions. In 2006, on May 21-22, a cold front stalled over the Central Coast and produced 2.8 inches of rain at the Pacific Gas and Electric Co. Diablo Canyon Ocean Lab. This was the highest amount of precipitation over a two-day period in May since records started being kept at Diablo Canyon in 1973.
According to general climate summaries for San Luis Obispo at Cal Poly, the wettest May occurred in 1998, when 3.4 inches of rain were recorded. That year was a strong El Niño and featured large-scale warming of sea-surface temperatures across the central and east-central equatorial Pacific Ocean.
This year, a moderate El Niño occurred, and many locations throughout the county have recorded near to above-average rainfall.
This year’s rainy season started out strong when one of the most intense weather systems I’ve seen during the month of October slammed into the Central Coast on the 13th and produced some of the greatest recorded 24-hour rainfall totals in many locations throughout San Luis Obispo County for the month.
SLOweather.com, with a gauge in the southwestern part of San Luis Obispo, recorded 7.6 inches. A few gauges along Highway 41 between Morro Bay and Atascadero recorded more than 9 inches of rainfall. After three years of drought, the ground literally soaked up most of the rainfall with little runoff.
The promise of October led to the disappointment of November, when only 0.04 of an inch was recorded at the Ocean Lab. December saw a recovery, with nearly 3 inches; the average for the month is about 4 inches. Then the skies opened in January and February and produced above-normal precipitation.
Surprisingly, March turned out to be almost dry, but a series of cold fronts and cut-off lows produced above-normal rainfall in April.
Normally, Camp San Luis Obispo off Highway 1 receives about 22 inches of rainfall. This season it recorded 27 inches. SLOweather.com has recorded more than 34 inches, about 144 percent of normal.
According to San Luis Obispo County Water Resources’ website, SLOCountyWater.org, Nipomo normally records about 18 inches; this year it is above 20 inches. In the North County, Atascadero also normally receives about 18 inches of rainfall. This year, the city has recorded just a little over 19 inches. Rocky Butte near San Simeon has nearly 49 inches of rain; the annual average is 39 inches.
All this rain has helped to increase the water levels at our local lakes and reservoirs. Lake San Antonio is currently at 57 percent of capacity. Nacimiento Lake, which was below 10 percent of capacity last September, has since increased to 68 percent. Salinas Reservoir near Santa Margarita is at 100 percent of capacity, and Lopez Lake is currently at 63 percent.
After three years of below-normal rainfall followed by this year’s near- to above-normal rainfall, is the drought over? It all depends on whom you ask. Careful measurements by PG&E hydrographers and many others in the Sierra this April indicate the snowpack is above normal. According to the National Drought Mitigation Center at the University of Nebraska, the drought has ended for the Central Coast, but abnormally dry conditions persist in the Sacramento and San Joaquin valleys. Many of the state’s lakes and reservoirs are still below where water resource managers would like to see them.
One thing I know for sure, water is a critical resource for California and we should all try to conserve as much as possible whenever it’s a dry or wet year. Dry spells or droughts are a normal part of life in California and can be counted on to occur in the future.
A 1,033-millibar surface high-pressure area about 800 miles to the west of San Luis Obispo will produce strong to gale force (25- to 38-mph) northwesterly winds with gusts reaching 40 mph along the coastline this afternoon through this evening.
At the same time, increasing high pressure in the upper atmosphere will give gradually warmer temperatures and spectacular Central Coast weather through Monday.
A few areas of coastal low clouds and fog this morning will burn off later today.
High temperatures will range from the mid- to high 70s in the interior and coastal valleys. The northwesterly facing (Los Osos) beaches will warm to the low to mid-60s, while the southerly facing (Avila Beach) beaches should reach the low 70s.
A ridge of high pressure will build over the Great Basin and will produce gentle to moderate (8 to 18 mph) northeasterly (offshore) winds Monday. This condition will give even warmer weather Monday with temperatures reaching the high 70s along the beaches and coastal valleys and the low to mid-80s in the interior.
This high-pressure ridge will move eastward and will allow a steep pressure gradient to develop along the California coastline.
This condition will produce relentless springtime northwesterly (onshore) winds Tuesday all the way through the end of the week. These moderate gale to fresh gale force (32 to 46 mph) northwesterly winds with gusts reaching 50 mph along the coastline will produce below-normal temperatures throughout the county, especially along the beaches, and night and morning coastal low clouds. No rain is in sight.
Today’s 8- to-10-foot northwesterly (320-degree deep-water) sea/swell (with a 7- to 11-second period) will remain at this height and period through tonight.
A 5- to 7-foot northwesterly (290-degree deep-water) swell (with an 8- to 11- second period) will develop along our coastline Monday morning, lowering to 4 to 6 feet by Monday afternoon and remaining at this height and period through Tuesday morning.
Increasing northwesterly winds will generate 6- to 8-foot northwesterly (320-degree deep-water) sea/swell (with a 5- to 9-second period) Tuesday afternoon, increasing to 8 to 10 feet with the same period Wednesday.
This northwesterly sea/swell will decrease to 5 to 7 feet Thursday and remain at this height and period through Saturday.
Arriving from the southern hemisphere: A 1- to 2-foot southern hemisphere (200-degree deep-water) swell (with a 17- to 19-second period) will arrive along our coastline late Tuesday, increasing to 2 to 3 feet (with a 16- to 18-second period) Wednesday through Friday.
Seawater temperatures: Increasing northwesterly winds have produced a greater amount of upwelling along our coastline and consequently cooler seawater temperatures, which will range between 48 and 51 degrees through Saturday.
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John Lindsey is a communications representative for Pacific Gas and Electric. He is also a local weather expert and has lived along the Central Coast for more than 23 years. If you have a question, send him an e-mail at firstname.lastname@example.org