Heat waves are periods of time where the weather is significantly warmer than is usual for the season and usual climate. In spite of differences in opinion of what exactly constitutes this type of weather condition, many locations around the world routinely report experiencing a heat wave at some point during the calendar year. In some places, the heat wave is a common phenomenon that takes place during the summer months, although a weather condition of this type of not limited to a particular season.
While qualifying a hot weather condition as a heat wave varies from one location to another, there are a few basic facts on heat waves that seem to apply just about everywhere. First, the weather is noticeably warmer than is considered normal for the time of year and the climate. Second, the unusual weather continues for a period of time considered sufficient to be considered a specific phase. Last, the weather is likely to bring about some type of increased risk to people, animals, and may place additional strain on power supplies.
In general, the main cause of heat waves has to do with the positioning of the jet stream in an area where a significant amount of high pressure is present in the atmosphere. The air found on one side of the jet stream is likely to be much warmer than on the opposing side. At the same time, if the higher pressure in the region is characterized by almost no cloud cover or precipitation, the air and top level of ground are heated to temperatures above the normal range for that time of year. As long as the cloud cover remains thin and there is not sufficient precipitation to cool the air and ground, a heat wave is likely to develop.
Different places around the world define a heat wave as lasting for specific periods of time. In some locations, the weather conditions must persist for a minimum of three calendar days before the phenomenon is classified as a wave. In other areas, a period as short as twenty-four consecutive hours of unusually warm weather is sufficient.
There are dangers related to the occurrence of a heat wave. Dehydration may also occur if care is not taken to drink sufficient quantities of liquid during a prolonged wave of heat. The condition can lead to the incidence of heat exhaustion or heat stroke. Additional stress on power supplies as people attempt to remain comfortable with air conditioning can lead to power failures at different points along a power grid. During a heat wave, it is important to check on elderly relatives and neighbors, provide shade and plenty of water for pets, and in general find ways to keep the body properly hydrated.
What is considered a heat wave in one location during a given season may not be considered to be an unusual phenomenon in another part of the world. For example, high temperatures with excessive humidity during the month of July may be considered unusual in the New England area of the United States, but would be normal in the Deep South during the same time frame.