What’s ahead for the rest of the rainy season in San Luis Obispo County?

Since late November, the jet stream has primarily blown out of the Gulf of Alaska toward California, helping to carve out intense storms off the Pacific Northwest.

At our latitude, the jet stream, aka the steering wind, is typically a tubular ribbon of high-speed winds flowing in wave-like patterns for thousands of miles. It usually blows from west to east some 15,000 to 40,000 feet up. It is often about 300 miles wide at its core and averages about 100 mph in winter and 50 mph in summer. But these speeds may rise to 250 mph or higher.

These upper-level winds have steered a series of upper-level troughs and cold fronts toward the Central Coast, bringing periods of frigid air temperatures, low snow levels, and much-needed rain.

The convective nature of the rain has produced relatively near-uniform amounts of rainfall throughout the Central Coast, from the beaches to the inland, which is not typical.

So far, this rain season, which runs from July 1, 2019, through June 30, 2020, rain gauges along the beaches and coastal valleys have recorded below-average rainfall. Still, locations farther inland have seen above-normal precipitation, and here is why.

Without the vast amounts of orographic enhancement, Rocky Butte, near Hearst Castle, has recorded 16.3 inches of rain this season, or about 85 percent of normal. Inland, the Paso Robles Municipal Airport has reported 6.6 inches of precipitation or 122 percent of average. You see, Paso Robles receives about 13 inches of rain per season, while Rocky Butte gets about 40 inches.

Typically, by this time, the Santa Maria Public Airport would have recorded over 5.4 inches of precipitation. However, this season, the weather station there has recorded 5.1 inches or 94 percent of average.

Cal Poly (official home of climatology for San Luis Obispo) has seen about 7 inches of rain or about 75 percent of average. At the same time, SLOWeather.com in western San Luis Obispo reported 77 percent of average rainfall.

I mistakenly thought that with all the chilly air filtering in behind these cold fronts since late November, our air temperatures were well below normal through mid-January, at least that’s the way it seemed to me. I was surprised that San Luis Obispo was about half of a degree warmer than usual, while both Paso Robles and Santa Maria were nearly two degrees above average.

So, what will the rest of the winter and spring bring?

Since fall, 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 called the Pacific Decadal Oscillation (PDO) 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 average as the lack of ice caused more solar energy to get absorbed by the Arctic Ocean.

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.

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. Overall, the precipitation outlook for the Central Coast this winter is expected to range between 75 and 90 percent of normal.

According to NOAA and NASA’s global temperature data, 2019 was the second-hottest year on Earth since records began. Even more remarkable, 2019 wasn’t an El Nino year. The 2010s were the warmest decade on record.

I will be giving a presentation about climate change and what it means for our local weather at the Santa Maria Public Library, 421 S McClelland St., on Friday, Jan. 24, from 3 to 4 p.m. with time for questions afterward. All are welcome, including families. This talk is sponsored by the Santa Maria branch of the American Association of University Women.