A heat wave is coming.
Most of the country will be gripped by dangerously high temperatures this weekend. According to the National Weather Service, some places will see temperatures as much as 10 to 15 degrees Fahrenheit above average for this time of year.
The reason that the temperatures are expected to be so much higher than normal is because of a meteorological event called a "heat dome." That's when a dome of high pressure in the upper atmosphere traps warm air beneath it. Under the dome, the air sinks towards the ground, becomes more compressed, and heats up even more - often to dangerous levels, as are expected this weekend.
The heat dome - which is expected to be especially large this time- will envelop the Midwest first, then move eastwards over the weekend. This is why eastern Missouri and southern Illinois are expected to see a high of 100 degrees on Friday. New York is expected to see a high of 97 degrees Fahrenheit on Saturday, according to Weather.com.
This heat dome formed largely because of the jet stream, reports LiveScience. This time of year, the jet stream is further north, passing roughly over the border between the US and extending into Canada. It effectively prevents cooler air from pushing southward into the country.
But that's not all. Not only is the heat expected be unbearable in parts of the country, but the humidity is going to make it "feel" worse - in other words, the heat index (which factors in humidity and raw temperature to give a better idea of how hot it will make you feel) will increase. For example, the heat index in eastern Missouri is forecasted to be between 105 - 112 this weekend.
The heat dome is a high-pressure mass, and in high pressure systems in the northern hemisphere, the air flows clockwise around its center. As the heat dome moves eastwards, it will suck up humid air behind it from the Gulf of Mexico.
The Midwest #heat advisories originate via air from the warm & humid Gulf of Mexico combining w/crop moisture- yuck! pic.twitter.com/no5J2sGtqb
In other parts of the country, such as the Midwest, the heat dome is going to be compounded by another weather phenomenon known as "corn sweat," reports NBC news. This is when evapotranspiration occurs, a phenomenon where water is released from crop plant leaves - such as corn - into the atmosphere, making it extra-muggy.
While eastern cities, like New York, will likely be spared the effects of corn sweat, the city is still likely to be hotter than the surrounding areas because of the "urban heat island effect." In these urban heat islands, heat is absorbed by concrete and asphalt and is trapped between tall buildings. The heat is also enhanced by vehicles, factories, air conditioners, and pollution. As a result, cities are generally 1.8 - 5.4 degrees Fahrenheit warmer than their surroundings, according to the US Environmental Protection Agency.
A lot of things are coming together to make it really hot this weekend, so be sure to take precautions to be safe and follow the advice from the National Weather Service: Stay indoors, limit strenuous activities outside, drink lots of water, don't leave anyone alone in a car, and find a local cooling center if you don't have access to air conditioning.