The mature stage of a storm may be marked on the ground by a sudden reversal of wind direction, a noticeable rise in wind speed, and a sharp drop in temperature. Heavy rain, hail and lightning occur only in the mature stage of a thunderstorm.

During a thunderstorm:

• Do not use radios or telephones.
• Put down all tools.
• Do not carry objects "up" such as a pike pole.
• Sit or lie down, if in open.
• Avoid grouping together.
• Do not handle flammable materials in open containers.
• Stay in your vehicle.
• Take shelter in a vehicle, if possible.
• Turn off machinery, electric motors, computers, etc.
• Take shelter in a building , if possible.
• Do not seek shelter under trees.
• When there is no shelter, avoid high objects such as lone trees, extension ladders, or radio antennae.
• If only isolated trees are nearby, the best protection is to crouch in the open, keeping the distance of twice the height of the object away.
• Keep away from wire fences, telephone lines, and electrically conductive elevated objects.
• Avoid high places, wide-open spaces and exposed shelters.
• Advise crew that if they feel an electrical charge--if their hair stands on end or their skin tingles--lightning may be about to strike them.
• They must drop to the ground immediately.

Remember that down drafts and strong winds are associated with these storms. They can blow wildfires out of containment, change the fire's direction and/or cause a significant change in the wildfire's intensity and behavior.

Thunderstorms have been a direct factor in the death and serious injury to many firefighters.