UPDATE: June 20, 2017, 5:26 p.m. EDT Phoenix has reached 119 degrees Fahrenheit, which is its fourth-highest temperature on record. The temperature is climbing further, with a forecast high around 120 degrees, which would flirt with the city's hottest temperature on record of 122 degrees. Numerous other records are being set across the Southwest.

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The heat in the Southwest United States is building to a peak on Tuesday and Wednesday, with everything from power disruptions to flight cancellations expected as humans and machinery fall apart in this extreme weather.

Phoenix, Arizona will make a run at its all-time highest temperature of 122 degrees Fahrenheit, with a forecast high of around 120 degrees. If the high reaches at least 120 degrees, it would be the hottest temperature seen in that city since 1995.

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Out of 11,059 days since summer records began in Phoenix in 1896, the city has only seen 15 days with a high temperature of 118 degrees Fahrenheit or higher. Notably, all but one of these days have been since 1989, according to the National Weather Service (NWS).

While the city is known for its dry heat and summertime monsoon thunderstorms, the current heat wave is, for lack of a technical meteorological term, bonkers.

Forecast high temperatures, with records indicated in circles, on June 20, 2017.Credit: weatherbell analytics/nws

Excessive heat warnings and heat advisories have been posted across six western states, including all of Arizona and much of California. Many of these warnings will remain in effect through Friday, illustrating the long duration of this event.

The NWS is forecasting record highs for Phoenix, Las Vegas, and Death Valley, California, among other locations. In Death Valley, which is typically the hottest place in the U.S. during the summer, the high temperature may reach or eclipse 125 degrees Fahrenheit on Tuesday.

This heat wave comes after another major heat wave in June 2016, which also set numerous records. The record high temperature forecast in Phoenix Tuesday, for example, will smash the existing daily high temperature record of 116 degrees Fahrenheit, which was set just last year.

The NWS is also warning of the possibility for dust storms to occur in and around Phoenix on Tuesday afternoon.

While the epicenter of the heat wave is in Arizona, southern Nevada, and California's low-lying desert region, even areas in the Central Valley of California, outside of San Francisco, will see temperatures in the lower 100s Fahrenheit on Tuesday and Wednesday.

Heat is grounding flights

The extreme heat is causing flight cancellations in the Southwest, including Arizona, Nevada and California.

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When the air is this hot, it's harder for aircraft to generate the lift they need to become airborne.

An American Eagle jet is seen through heat ripples as it lands at Sky Harbor International Airport,in Phoenix.Credit: AP/REX/Shutterstock

This is because hotter air is thinner, which means planes need longer distances to take off, especially when you combine the heat with the relatively high altitudes at many Southwestern airports (air is also thinner at higher altitudes).

While airports like Phoenix Sky Harbor International have runways that are long enough to handle such impacts, smaller regional jets are particularly affected.

Of the about 50 flights reportedly canceled by American Airlines on Sunday, for example, most, if not all, of them were regional.

According to American Airlines' media relations department, the airlines' Airbus and Boeing aircraft have operating limits of 127 and 126 degrees Fahrenheit, respectively. That means they're likely to continue flying throughout the day on Tuesday, unless temperatures spike even higher than anticipated in Phoenix.

However, the Bombardier regional jets operated by American Eagle have a lower limit, forcing the airline to delay or cancel flights if temperatures hit 118 degrees Fahrenheit, as they are predicted to on Tuesday. On average, American Eagle has 90 departures and 90 arrivals daily from Phoenix, the airline said in an email. Only flights taking place during the hottest temperatures of the day are likely to be affected.

Credit: CLimate central

While it may not be the first impact that comes to mind, the possibility that heat waves can cause air travel disruptions has been apparent to experts in the climate and transportation industries for years.

The 2014 National Climate Assessment, for example, found that heat waves -- which are already becoming more frequent, severe, and longer-lasting due to human-caused global warming -- will cause more flight delays and cancellations in the future.

"High air temperatures can affect aircraft performance; lift-off limits at hot-weather and high-altitude airports will reduce aircraft operations," the report found.

Climate change moves into the foreground

Heat waves are one of the most certain impacts of human-caused global warming, since as average temperatures increase, the likelihood of heat extremes jumps even more. Studies have shown a sharply increased risk of these events  as ocean and surface temperatures climb.

In April, researchers reported that in addition to making extreme weather events more likely throughout the world, climate change is also making such events more severe. By midcentury, what is considered extreme heat now will be more common in many places across the U.S.

Credit: Climate CentralCredit: climate central

Using weather observations and a group of  climate models known as an ensemble, the researchers from Stanford University and the University of California at Los Angeles found that the warming-to-date has already caused the severity and probability of the hottest month and hottest day of the year to increase at more than 80 percent of weather observing sites. 

"The world isn’t at the point where every extreme hot event has a human component, but it’s getting close,” said Noah Diffenbaugh, a climate scientist at Stanford University and lead author of the study.

As global warming continues, it's becoming easier for locations to set all-time records, particularly temperature records, because the baseline climate is shifting so significantly and quickly. 

This is similar to a basketball game in which the floor is steadily rising, making it easier for players to dunk the ball. 

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