Weather Watch

Want to avoid sunburn this summer? Learn the UV Index

The sun over Morro Bay, as seen from Baywood Park.
The sun over Morro Bay, as seen from Baywood Park.

With the days growing longer as we move toward summer, the risk of sunburn from an overexposure to ultraviolet electromagnetic radiation increases.

To help people make informed decisions about the amount of time they spend in the sun, the UV Index was created. The UV Index is a forecast of the amount of UV radiation that’s expected to reach Earth’s surface when the sun is at its highest point in the sky (solar noon).

Each day the National Weather Service predicts the UV index forecast; it can be found in in the back of The Tribune’s sports section under weather. An index of 1 indicates very weak ultraviolet rays, while an index of 11 indicates extremely powerful rays.

Sunlight is part of the electromagnetic spectrum, with radio waves at the low-frequency part of the spectrum and gamma rays at the higher end. Within this spectrum, infrared, visible and ultraviolet light fall in the upper half.

Infrared light has a longer wavelength and is too red for our eyes to see, but you can certainly feel it as heat on your skin.

Ultraviolet light is on the opposite end of the rainbow and has a shorter wavelength. It’s too blue for our eyes to detect, but unlike infrared, you can’t feel it as heat. However, near-UV light is visible to some insects and birds.

The higher your elevation, the greater amount of UV you will receive. A deep marine layer (coastal low clouds and fog) can reduce the amount of UV by 67 percent.

On the other hand, water, sand and snow can all reflect ultraviolet rays. Fresh snow reflects as much as 80 percent of UV. One of the worst sunburns I have ever received was while skiing at Heavenly Valley despite it being partly cloudy that day.

A small amount of exposure to sunlight can be helpful; however, overexposure to UV is responsible for major health problems: skin cancers, including melanoma (a very dangerous form of cancer), and cataracts.

The UV Index is not based upon surface observations. Rather, it is computed using the forecasted ozone data from instruments on board polar-orbiting satellites, a radioactive transfer model, forecasted cloud cover and the elevation of the forecast cities.

The UV Index is made available daily to 58 cities throughout the United States. At least one city in each state has a UV Index forecast.

California has two — Los Angeles and San Francisco. The actual UV exposure is usually not the same at the coast, coastal valleys and North County. However, because the data from The Tribune weather page is derived from the Los Angeles index, they are reported as such.

That’s why our interior, coastal valleys and beaches have the same forecast index, despite the differences in altitude and cloud cover.

Here are some tips to reduce your exposure to UV radiation:

▪ Seek shade when the sun’s UV rays are strongest, between 10 a.m. and 4 p.m. Remember the shadow rule when in the sun: No Shadow, Seek Shade.

▪ Generously apply sunscreen using a sun protection factor (SPF) of at least 15 that provides broad-spectrum protection (UV-A, B and C). Reapply every two hours, even on cloudy days and after swimming or sweating.

▪ Wear protective clothing, such as a long-sleeved shirt, pants, a wide-brimmed hat and sunglasses.

Robyn O’Leary of Los Osos told me, “In Australia, where the incidence rate of melanoma is quite high, they have a great UV awareness program called ‘Slip, Slap, Slop and Wrap’ — slip on a shirt, slap on a hat, slop on some sunblock and wrap on some shades.”

California and PG&E continue to set the pace as national leaders in clean energy and greenhouse gas reductions. State goals called for an average of 23.3 percent Renewables Portfolio Standard between 2014 and 2016. PG&E far surpassed that target, serving 29.5 percent of its retail electricity sales with renewable power in 2015. Additionally, PG&E is well ahead of schedule in meeting the state’s 33 percent target by 2020.