National Weather Service
Grand Junction Office
Every thunderstorm produces lightning. Lightning is simply a giant spark that moves within the cloud, between the clouds, or between the cloud and the ground.
As lightning passes through the air, it heats the air rapidly to a temperature of about 50,000 degrees Fahrenheit. This causes a rapid expansion of the air along the lightning channel. This rapid expansion causes a shock wave that we hear as thunder.
Thunderstorms will form if there is sufficient moisture and instability in the atmosphere. As the sun warms the air near the ground, pockets of warmer air begin to rise and cool. Condensation of water vapor causes cumulus clouds to form. Continued heating can cause these cumulus clouds to continue to grow upward into the atmosphere. Towering cumulus clouds may be one of the first indications of a developing thunderstorm. The mature thunderstorm has both an updraft of rising warm air and a downdraft of sinking cool air accompanied by rain and sometimes hail.
Thunderstorms grow tens of thousands of feet into the atmosphere. Within the thunderstorm, precipitation forms as ice crystals, graupel, and rain. Collisions between these particles causes electrical charges to separate, with the positively charged ice crystals carried up into the updraft, while the negatively charged heavier graupel are carried downward in the downdraft. With time, the top of the thunderstorm becomes positively charged and the lower part of the thunderstorm becomes negatively charged.
The best advice in order to minimize your risk of becoming a lightning strike victim is to get indoors into a substantial shelter the second you hear thunder, and to remain there for at least 30 minutes after the last rumble of thunder. In general, When Thunder Roars, Go Indoors!
An enclosed hard-topped automobile is also a very safe place to be during thunderstorms.
NOAA's lightning website which contains abundant information on lightning safety can be found at www.lightningsafety.noaa.gov
Lightning information specific for the State of Colorado can be found at www.weather.gov/pub/lightning.