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A blast of hot air is forecast to raise temperatures across much of the continental United States in the coming week, adding another stretch of sweltering days to what has already been a punishing summer for many.

The Great Plains and Midwest — along with parts of the East — can expect highs that are 10 to 15 degrees above average, according to the National Weather Service. And in places where residents must also cope with high humidity, those temperatures could feel like they have reached triple digits.

That extreme heat will be the product of a “heat dome,” much like the one that oppressed the Pacific Northwest this summer.

Here is what you need to know about the heat waves:

In most parts of the country, temperatures must be above the historical average in an area for two or more days before the label “heat wave” is applied to a hot spell, according to the National Weather Service. But the definition can vary by region; in the Northeast, it is defined as three straight days in the 90s or above.

Heat waves begin when high pressure in the atmosphere moves in and pushes warm air toward the ground. That air warms up further as it is compressed, and we begin to feel a lot hotter.

The high-pressure system pressing down on the ground expands vertically, forcing other weather systems to change course. It even minimizes wind and cloud cover, making the air more stifling. This is also why a heat wave parks itself over an area for several days or longer.

As the ground warms, it loses moisture, which makes it easier to heat even more. And in the drought-ridden West, there is plenty of heat for the high-pressure system to trap.

As that trapped heat continues to warm, the system acts like a lid on a pot — earning the name “heat dome.” In the drought-ridden West, there was plenty of heat for the high-pressure system to trap, leading to triple-digit temperatures in late June and early July that killed hundreds of people in Oregon, Washington and British Columbia.

The deadly weather event would have been all but impossible without climate change, according to a team of researchers.

We have long known that the world has warmed by more than 1 degree Celsius (about 1.8 degrees Fahrenheit) since 1900, and that the pace of warming has accelerated in recent decades. The warmer baseline contributes to extreme-weather events and helps make periods of extreme heat more frequent, longer and more intense.

Last year was the warmest on record, and the past seven years have been the warmest in recorded history, making extreme summer heat more frequent.

To help reduce demand, consider raising the thermostat by a few degrees and closing window shades and blinds. Avoid using large appliances like ovens, washing machines and dryers during the hottest part of the day, and turn off all lights and electronic devices not in use. With water heating accounting for about 18 percent of the energy consumed in your home, consider shorter or colder showers, the Energy Department suggests.

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