Educational - UV
From WunderWiki
Back to: Weather Q & A
NOAA AND EPA LAUNCH EXPERIMENTAL ULTRAVIOLET EXPOSURE INDEX
An experimental program designed to provide the public with an important new addition to the daily weather forecast --prediction of solar ultraviolet radiation levels -- premiered in July 1994 for 58 cities throughout the United States.
The program, announced jointly by the National Oceanic and Atmospheric Administration (NOAA) and the Environmental Protection Agency (EPA), will offer citizens a look at the next day's level of ultraviolet (UV) radiation and should help them guard against over exposure.
Prolonged exposure to ultraviolet radiation has been associated with an increased incidence of skin cancer and cataracts, and inhibits the immune system.
"With the UV Index forecast, the public should be better informed to take simple actions to reduce over exposure to UV radiation,"said EPA assistant administrator Mary Nichols. "Because scientists have estimated that people receive about 80 percent of their lifetime exposure to the sun by the age of 18, we think this is particularly important information for children and their parents."
The potential for a daily ultraviolet forecast to result in dollar savings is evidenced by Medicare's biggest cost line item in 1993 for 1.2 million cataract surgical procedures.
As the NWS continues to refine the science behind the daily UV forecasts, UV forecasts for 58 cities will be distributed during the experiment. EPA will work with the Centers for Disease Control and a coalition of health, medical and environmental groups to provide information to the public about the UV Index and risks of over exposure to UV radiation.
"The NWS will make UV forecasts approximately 30 hours in advance using satellites, ground-based weather observations and computer models," said Elbert W. Friday, Jr., director of the NWS. "We'll use this existing technology at no additional cost to taxpayers."
The ultraviolet forecasts will account for observed and predicted changes in stratospheric ozone data for all 58 cities and include the effects of computer-generated cloudiness for 56 of them. Clouds generally decrease the amount of ultraviolet radiation reaching the earth's surface. Forecasts for Honolulu and San Juan, Puerto Rico, will not include the effects of cloudiness because the required computer-generated cloud forecasts are not yet available for these locations.
Forecasts will be centrally-issued by the NWS's National Meteorological Center in Camp Springs, MD., and sent to NWS forecast offices around the country. NWS personnel at local forecast offices will voice the daily index over the NOAA Weather Radio network. Forecasts will also be distributed to public and private meteorologists over the NOAA Weather Wire Service, the Family of Services, and other weather service information dissemination channels.
The daily forecast value in the ultraviolet index will be for approximately 12:30 to 1:30 p.m. Daylight Savings Time in each U.S. time zone. The index value is on a scale from 0 to 10, or higher in some areas, with corresponding exposure levels categorized by EPA extending from minimal to very high.
Daily predictions of UV exposure are determined for the noon hour. Everybody needs to know about effects of UV exposure,which include the potential for sunburn, skin cancers, aging and wrinkling of the skin, ocular damage, cataracts and immune suppression.
Exposure levels are presented below:
Index Value Exposure Level
0 to 2 Minimal
3 to 4 Low
5 to 6 Moderate
7 to 9 High
10+ Very High
Frequently Asked Questions
Q: How do clouds affect predicted levels of UV radiation?
A: The effect of clouds on UV levels depends on the degree of cloudiness. Although thick overcast will reduce ultraviolet,thin overcast scattered clouds may not reduce UV levels. As with any forecast, local variability may change actual levels experienced. For this reason, a useful rule of thumb to offer your audience/user is that, whatever the day's prediction, they should protect themselves against over exposure to sunlight whenever they can see their shadow when outdoors.
Q: How does the forecast account for altitude?
A: UV levels increase with altitude because there's less atmosphere to attenuate the radiation. This factor is considered in the forecast for specific cities. In general, UV levels rise 2% for every 1,000 foot rise in altitude or 1 index unit for every 4 thousand feet in summer.
Q: How do reflective surfaces affect the predicted index level?
A: Snow, sand and water are all reflective surfaces and will intensify UV exposure to varying degrees. Grass reflects from 2.5-3%, sand 20-30%, snow and ice 80-90%. Depending on the angle of reflection, water can reflect up to 100% of rays striking the surface. Seasonally appropriate messages may help people be aware that, for example, sand and water at beaches can increase the reported level considerably.
Q: How much do UV levels vary by season?
A: Seasonal variability can be quite high. Late spring to summer typically produces the highest UV levels, while in the early winter, levels are lower.
Q: If I go on vacation in the Bahamas, how much more UV can I expect to be exposed to?
A: Generally speaking, the closer you are to the equator, the higher the level of UV you will be exposed to. Because you may not be used to such high levels, it makes particularly good sense to cover exposed areas and wear sunglasses. Even during the winter, you can be badly sunburned at lower latitudes.
Q: What affect does the ozone layer have on reported UV levels?
A: It is well known that atmospheric ozone decreases the amount of incident UV. The exact impact of ozone depletion, or other local effects, including haze, aerosols, et cetera, are not yet fully understood.
