Rain season off to a good start, but SLO County shouldn’t expect an exceptional year
After a dry October and nearly a parched November, the storm door finally swung open on Nov. 26 and allowed a series of tempests to produce rain and snow throughout California.
One more low-pressure system is expected to produce much-needed precipitation this weekend, before a stretch of dry weather starts on Monday and is forecast to continue through Dec. 20.
Overall, most of the airports along the Central Coast have recorded between 2 and 3 inches of rain this season.
As of Friday, here are totals from south to north: Santa Ynez Airport, 2.4 inches; Lompoc Airport, 2.1; Vandenberg Air Force Base, 2.3; Santa Maria Airport, 2.6; and San Luis Obispo County Regional Airport, 2.3. The Paso Robles Municipal Airport has recorded the most rain at 3.6 inches.
This weekend’s storm system is forecast to produce between 0.75 and 1.50 inches of additional rainfall. Currently, SLOWeather.com is showing 80 percent of average rainfall.
This weekend’s gale should increase the average precipitation for all these airports to between 80 and 90 percent; however, the Paso Robles Airport could reach 130 percent by Sunday. With all this moisture, our fields and hills will soon turn emerald green.
Weather outlook
So, what will the rest of the season bring?
Like last month, the federal Climate Prediction Center continues to advertise that the infamous neutral condition — known as “El Nothing” or “El Nada” — will continue into spring 2020. Unfortunately, the neutral condition typically produces lower-than-average winter rainfall during the year.
Another large-scale ocean water temperature cycle is the Pacific Decadal Oscillation (PDO), which is found primarily in the North Pacific.
The phases of the PDO are labeled warm or cool. Unlike El Niño–Southern Oscillation (ENSO), which focuses on the sea-surface temperature in the central equatorial region of the Pacific, the PDO is classified by seawater temperatures throughout the northern Pacific Ocean. The December model runs are indicating that it will continue to shift to the cool phase, which can mean a higher chance of below-normal rainfall.
In addition to these oceanographic conditions that can cause lower-than-average precipitation for California, the October polar sea ice extent was the second smallest on record. Current sea surface temperature anomalies are well above normal as the lack of ice caused more solar energy to get absorbed by the Arctic Ocean.
According to PG&E senior meteorologist Ted Schlaepfer, climate model forecasts for that area are showing above typical temperatures during the upcoming winter.
The warmer air mass this winter over the Arctic is favored to produce blocking high pressure at times, which could disrupt the regular jet stream circulation.
The Arctic Oscillation (AO) is a mode of climate variability characterized by winds circulating counterclockwise in the Arctic. In the positive phase, the jet stream moves from west to east with little north/south variability — thus, Arctic cold air stays in the higher latitudes.
During the negative phase, high pressure is present across the polar areas, and the arctic jet stream (aka polar vortex) can move southward into the middle latitudes for cold air outbreaks. These severe cold air outbreaks usually occur in the central and eastern parts of the United States with a dry and warmer high-pressure ridge over California.
The AO is highly variable year to year with the coldest winters in the U.S. almost always occurring when the index is negative.
Overall, warmer-than-average temperatures are forecast for much of California, and seasonal precipitation should be below average. Naturally, the snowpack should also be below average across the Sierra Nevada.
Forecast for the Central Coast
Overall, the precipitation outlook for the Central Coast this winter is expected to range between 75 and 90 percent of normal.
The month of December is expected to get less than 90 percent of typical rainfall, while January is favored to receive more than 110 percent of average precipitation. February should get less than 75 percent of normal, while March rebounds to 90 percent.
John Neil, manager of the Atascadero Mutual Water Co., wrote to me, “(In) the years we had no measurable rainfall for the period July 1 through Oct. 31, surprisingly, annual totals weren’t too bad. The average is 16.13 inches, or about 1.5 inches below the historical average.”
The company has collected rainfall data since 1914 at a rain gauge at the confluence of the Salinas River and Atascadero Creek.
On Sunday, Dec. 15, from 2:30 to 4:30 p.m., I will narrate “’Twas the Night Before Christmas” at the Atascadero Community Band’s Holiday Sampler at the Pavilion on the Lake.
The band will perform popular and traditional holiday music, including an old-fashioned sing-along. Admission, refreshments, and parking are free. This holiday concert will benefit the Toy Bank of Greater Paso Robles, a nonprofit that helps provide approximately 1,500 children with holiday cheer.