WEATHER WATCH COLUMNS:  JULY 2002 ISSUE

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Weather Watch: Blue Sky and Red Sun

Why is the sky blue?  The air preferentially scatters blue hues from
the sun's rays away from the sun to the rest of the sky.  Since the
sun's rays are composed of all the colors of the rainbow, the loss of
blue leaves the sun yellow-orange.  During sunrise and sunset, the
sun's rays pass through the atmosphere obliquely, and so travel longer
through the atmosphere.  The longer path means that more blues and
yellows are scattered away, leaving the oranges and reds.  When the
atmosphere is relatively clean, such as after a rain, the sun near the
horizon will be bright yellow-orange, but suspended particles (dust,
volcanic ash and sea salt) will increase scattering, leaving only the
deepest red hues.  Paddlers looking to enjoy a beautiful sunset paddle
should seek out these conditions.

<-David Schultz, NOAA/National Severe Storms Laboratory>

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Weather Watch: The UV Index

In order to provide the public with information to assess their
vulnerability to overexposure to the sun's rays, the National Weather
Service and the Environmental Protection Agency developed the
Ultraviolet (UV) Index.  The UV Index predicts tomorrow's potential
exposure to solar radiation on a scale of 0-10+.  Although you should
always be concerned about overexposure, take special precautions when
the UV Index equals or exceeds 5.  These precautions may include
applying sunscreen, covering exposed skin with a hat or clothing,
wearing UV-filtering sunglasses, and seeking shade.  More information
and forecasts of the UV Index can be found at
http://www.cimms.ou.edu/~schultz/c-k/uv.

<-David Schultz, NOAA/National Severe Storms Laboratory>