I’ve long wanted to capture a photo of “green flash,” an optical phenomenon that can be seen near the upper limb of the sun during sunset or sunrise, when a green flash of light is visible for a second or two.
However, it’s rare to have just the right atmospheric conditions to get a photo of the flash. The seemingly ever present northwesterly (onshore) winds often produce haze near the ocean’s surface that blocks out the faint light of the flash. During the summer months, coastal stratus and fog often shroud the coastline along Montaña de Oro State Park northward toward Morro Bay, making it difficult to even see the sunset.
Whenever we had a clear night in Los Osos, Sean, my 7-year-old son, and I would drive to the entrance of Montaña de Oro State Park with a camera and tripod in tow. Pointing the camera toward the Pacific, we quickly released the shutter button as the sun slowly passed below the horizon, hoping to get a photograph of the elusive green flash.
One evening last week we finally got one. The winds were calm and a strong temperature inversion layer had developed without the usual marine low clouds and fog. From my experience, this condition often produces the best chance of seeing the flash.
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A long time ago, I was incorrectly told that the green flash was the sun shining through the ocean waves. Green flashes are really byproducts of mirages appearing slightly above the horizon and not in the sea.
The cause of this green-colored mirage is mostly due to atmospheric dispersion. The shorter wavelengths of blue and violet light are scattered to a much greater extent than the red and yellow hues by the air we breathe — that’s why the sky is blue. As the sun sets, the longer wavelengths of the reds and yellows disappear first, leaving behind the greens. In other words, the red image of the sun sets or disappears first, followed by yellow and then finally the green.
I’ve seen green flashes from different altitudes, even from naval aircraft patrolling over the vast expanses of the ocean. One evening during sunset while driving westward on Los Osos Valley Road towards the ocean, I saw the green flash for nearly 10 seconds. As you drive westward along LOVR, the road gently ascends a little past Foothill Boulevard. The gain in altitude as I travel westward slowed the apparent sunset from my perspective, allowing me to see a much longer flash.
The green flash can last much longer above the Arctic Circle or below the Antarctic circle. Here, the sun transitions from the perpetual darkness of winter to the everlasting light of summer. During the equinox, the sun moves along the horizon for an extended period of time. Adm. Byrd reported seeing the green flash off and on for over half an hour during his expedition to the South Pole during the September equinox.
A 1,035-millibar Eastern Pacific High will remain nearly stationary about 1,700 miles to the westnorthwest of San Luis Obispo, while a thermal trough will persist over the Central Valley of California.
Low clouds will blanket the coast and coastal valleys this morning, producing some mist or light drizzle along the immediate coastline.
The low clouds will retreat to the northwesterly facing (Montaña de Oro, Los Osos and Morro Bay) beaches later this morning, leaving behind clear and sunny skies in the coastal valleys and along the southwesterly (Cayucos and Avila Beach) facing beaches.
The northwesterly facing beaches will range between low to mid 60s, while the southwesterly facing beaches will range between the mid to high-70s.
The coastal valleys (San Luis Obispo) will range between the low to mid 70s while the North County will reach the low to mid 90s.
Low clouds and fog will surge inland tonight.
Beginning Monday, an upper-level ridge of high pressure will slowly build over the Central Coast allowing temperatures to gradually warm to near normal levels through midweek, especially across the North County. However, low clouds and fog are expected to return nightly to the coastal areas, with daytime temperatures only warming a couple degrees.
As the upper-level ridge persists through late next week, fair and dry weather with near normal to slightly above-normal temperatures will develop.
Fresh to strong (19- to 31-mph) northwesterly winds will generate a 3- to 5-foot northwesterly (320-degree deepwater) sea and swell (with a 5- to 8-second period) through Tuesday.
The Wind fields will shift northward off the Sonoma and Mendocino coastlines, leaving behind a 3- to 4-foot northwesterly (300-degree deepwater) swell (with an 8- to 14-second period) Wednesday through Friday morning.
Increasing northwesterly winds will generate 3- to 5-foot northwesterly (320-degree deepwater) sea and swell (with a 5- to 8-second period) Friday afternoon through Saturday.
Arriving from the Southern Hemisphere:
Today’s 1- to 3-foot Southern Hemisphere (210-degree deepwater) swell (with a 14- to 16-second period) will remain at this height and period through Saturday.
Medium period swell from former hurricane Eugene will arrive from an incoming direction of between 155 and 175 degrees, far too southeasterly for our coastline.
Typhoon Herbok, currently 700 miles off the coastline of Japan, is forecast to move toward the Aleutian Islands and become extra tropical. If this condition develops as advertised, a longer-period west-northwesterly swell could arrive on our coastline next Sunday. Seawater temperatures will range between 55 and 57 degrees through Friday.
Intake seawater temperatures are expected to remain at a 55- to 57-degree level through most of next week.
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John Lindsey, media relations representative for PG&E and local weather expert, has lived along the Central Coast for more than 25 years. To subscribe to his daily weather forecast or ask him a question, email him at firstname.lastname@example.org.