Back in December 2020, Jim from Avila Beach asked, “Do you know what the record is for the driest rain season that we have experienced? I have a feeling we may challenge it this year.”
Jim’s intuition is correct, this rain season (July 1, 2020, through June 30, 2021) rainfall amounts are well below average. It may not be the driest rain season on record, 1897 only saw 7.20 inches at Cal Poly, but this year could be one of the most parched.
Historically, the four months with the most rainfall amount are December, January, February, and March, with the greatest chance of rain peaking on February 20 at 24 percent.
Unfortunately, the driest back-to-back Februarys (2020/21) in 152 years of rainfall records at Cal Poly’s Irrigation Training & Research Center pushed most of San Luis Obispo, Santa Barbara, and Ventura counties from D0 (Abnormally Dry) to D1 (Moderate Drought) last week except for North Coast and Big Sur that were most impacted by the Atmospheric River (AR) at the end of January according to the U.S. Drought Monitor Map (https://droughtmonitor.unl.edu/)
The map is updated weekly and is a joint effort by the National Drought Mitigation Center (NDMC) at the University of Nebraska-Lincoln, the National Oceanic and Atmospheric Administration (NOAA), and the U.S. Department of Agriculture (USDA).
So far, the Paso Robles Municipal Airport has recorded only 6 inches of rain. By now, it should be at 10.5 inches. This rain season, San Luis Obispo County Regional Airport is at 8 inches. On average, San Luis Obispo should have received about 19 inches of the wet stuff at this point. Farther south, the Santa Maria Airport has reported about 6 inches of rain, but much like Paso Robles, it should be at 11 inches by now. The Santa Ynez Airport has 7.3 inches but should be at 11 inches by March. Overall, Santa Barbara County is at 54 percent of normal to date.
Along with the low rainfall amounts, our local lake and reservoir totals are well below average. Nacimiento Lake is at 41% of capacity, while Lake San Antonio reported 20% of capacity. Lopez Lake is at 40% of capacity, Salinas Reservoir near Santa Margarita is at 73%, and Whale Rock Reservoir near Cayucos is at 79%. In Santa Barbara County, Cachuma Reservoir is at 63% of capacity, and Gibraltar Reservoir is 14%.
Looking into the future, the 0.75 to 1.50 inches of rain forecasted this Tuesday and Wednesday will help, but the rest of March is looking dry.
Overall, the chance of a “March Miracle” or even a “Mini March Miracle” is fading.
The current La Nina condition, combined with the cool phase of the basin-wide Pacific Decadal Oscillation (PDO), points to below-average rainfall through the end of the month.
The Climate Prediction Center is advertising neutral condition — the infamous El Nothing or El Nada developing this spring and continuing through summer.
It is interesting to note that several of the numerical model runs are indicating a moderate El Niño developing next winter while others are showing a La Nina condition.
At this time of the year, these predictions often change. Here is why: We’re in front of the so-called “spring predictability barrier.” In spring, the El Niño Southern Oscillation (ENSO) is often in transition from one phase to another. For example, a La Niña phase could be decaying and passing through neutral condition to a El Niño condition, or vice versa. Of course, as you get closer to winter, the models become more accurate because there is less time for inaccurate oceanographic and atmospheric data to be amplified at model initialization. At this time of the year many climate scientists think the most reliable strategy is -- WAS (wait and see).