Weather Watch

Longest day of the year marks first day of summer

The sun is seen setting in Morro Bay on a recent evening. Today is the summer solstice, making it the longest day of the year.
The sun is seen setting in Morro Bay on a recent evening. Today is the summer solstice, making it the longest day of the year.

Summer solstice arrived Sunday at 9:39 a.m. Pacific Daylight Time on the West Coast, when the Earth’s orbit brings the North Pole to its greatest exposure to the sun.

At this period, if you happen to be north of the Arctic Circle, the sun never sets but remains above the horizon. Farther south in Fairbanks, Alaska, the sun drops below the horizon near midnight and comes back up about 3 a.m.

This condition produces only a few hours of twilight. In fact, each year on the summer solstice, the Alaska Goldpanners of Fairbanks celebrates their status as the baseball team farthest north with a game that starts about 10 p.m. and goes into the following morning without lights.

At our latitude in San Luis Obispo County, the sun rose at 5:49 a.m. and will set at 8:21 p.m. That gives us about 14 hours and 21 minutes of daylight. It is the longest day of the year and the first day of summer.

In the Southern Hemisphere on this same date, the situation is reversed — there are 24 hours of darkness south of the Antarctic Circle, and this marks the first day of winter there.

The word solstice means “the sun stands still” in Latin. The sun has been moving north each day leading up to the summer solstice. On Sunday, the sun has reached as far north as it will go. On Monday, it begins its journey south until the first day of winter for the Northern Hemisphere in late December.

You might think that because the solstice occurs in summer that it means the Earth is closest to the sun.

Earth’s orbit around the sun is really an ellipse, a shape that can be thought of as a stretched-out circle, or an oval. Earth is farthest from the sun, which is called aphelion, on July 6, and it is at perihelion, or closest to the sun, around Jan. 4.

So, perihelion occurs in winter in the Northern Hemisphere and during summer in the Southern Hemisphere.

The summer outlook from the Climate Prediction Center indicates we will have above-normal temperatures — just in time for the California Mid-State Fair.

As far as the ocean is concerned, Jan Null, a former National Weather Service lead forecaster and PG&E meteorologist (and an expert on El Niños and their relationship to California’s weather) wrote:

“The just released International Research Institute for Climate and Society/CPC mid-June El Niño-Southern Oscillation Prediction Plume forecasts an even stronger El Niño event than the previous two months. And this forecast is important in that it is past the Spring Predictability Barrier.”

This is significant news. As I’ve written before, El Niño does not guarantee above-normal rainfall, but historically, the stronger the El Niño event, the higher the probability of greater amounts of average precipitation in California.

Did you know that PG&E delivers to its customers some of the nation’s cleanest electricity? More than 50 percent of the power comes from sources that emit no greenhouse gases, including Diablo Canyon nuclear power plant.