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(NEXSTAR) – As extreme cold and snowstorms slam of the U.S. Monday, some cities are experiencing widespread rolling blackouts.

But what is a rolling blackout and why is it necessary?

According to Direct Energy, an energy provider in the U.S. and Canada, rolling blackouts are “systemic, temporary power outages that help bring balance to the supply demand of electricity in the market.”

Generally, rolling blackouts occur as the “last step in a series of emergency procedures” when a power supply shortage is detected in a market. They help to prevent widespread blackouts across a region.

Rolling blackouts generally occur in one area at a time and last for a few hours, but the length of the blackout depends on the severity of the event.

Utility providers decide which parts of the city will be subject to rolling blackouts and try to avoid areas with hospitals, medical centers or downtown regions, for which electricity is vital.

Reliant Energy, a Texas utility provider, offered the following tips to Nexstar affiliate KIAH to help Houston-area residents prevent rolling blackouts:

  • Set your thermostat four degrees lower than usual.
  • Avoid the use of large electric appliances, including washer/dryers and dishwashers, during the early morning and late evening hours, when demand for electricity is highest.
  • Close heat escape routes in your home.
  • Set your ceiling fan to rotate clockwise, which helps force warm air down into the room.
  • Close blinds and shades to reduce the amount of heat seeping out of windows.