(CNN) - A rare, dangerous and potentially deadly heat wave is progressing into the workweek. If it's not already hot enough, the high temperatures in some areas haven't even reached their peaks.
The torrid heat is a fitting welcome to the official start of summer on Wednesday, when the US will get a luminous view of the solstice sky.
Sacramento, California, saw record high temperatures of 106 degrees on Sunday, heat last seen almost 75 years ago, when it reached 105 degrees Fahrenheit.
Wednesday looks to challenge that fresh record with a forecast temperature of 109 degrees.
San Jose melted records as well, at 103 degrees on Sunday, exceeding the 1945 record by 4 degrees.
The days will continue to be sweltering and the nights will prove to be no relief, as overnight low temperatures remain well above average.
Las Vegas also gets into the extreme heat game with peaks on Tuesday and Wednesday. The city could gamble with its highest temperature ever observed, which was 117 degrees Fahrenheit in 2013. It will be close, as the current forecast for Vegas is 116 Fahrenheit.
The heat wave was already affecting travel at one Arizona airport, where the temperature reached 118 degrees on Monday.
American Airlines canceled 50 flights to and from Phoenix Sky Harbor Airport due to "extreme heat," the airport said.
Is the end in sight?
Although temperatures will begin to drop into the weekend, we won't see a decline to normal until next week. Be prepared for several more days of sweltering above-average temperatures.
These values can be deadly if the proper precautions are not taken.
Heat: The deadliest type of weather
Heat kills more people in the United States than any other type of weather.
But it's not just the heat, it's the humidity. The heat index, a measure that combines the air's temperature and moisture content, essentially indicates what it will feel like when you step outside. The compounding effects of increasing temperature and humidity can be exceptionally dangerous.
Given the high temperature and humidity values forecast for this heat wave, it is important to watch for heat index values to get a better idea of the danger that awaits outside.
The National Weather Service is providing updates in the regional offices that are being affected by this heat wave.
Under a heat dome
High pressure is partly to blame for the prolonged expectancy of this heat wave. High pressure will dominate in the Southwest, creating what is known as a heat dome.
Sinking air, associated with an area of high pressure, essentially traps the heat near the surface. When heat is trapped, health officials become concerned about not only heat exhaustion but air quality.
"These (heat wave) conditions, coupled with what we call an atmospheric inversion, essentially trap pollution near the surface instead of it going up higher," said Patrick Chandler, a senior specialist for the South Coast Air Quality Management District.
He explained that this process will trap the pollutants closer to people and will last for several days. Also worrying Chandler is the fact that this danger will extend over a broader area than usual.
"If the pollution layer is trapped low to people, then there's a higher instance for respiratory issues or other lung diseases," Chandler said. "So that's why we are asking people to limit their outdoor activities, (such as) running and playing outside, when we have such unhealthy air quality."
How to beat the heat
With summer bringing outdoor activities such as barbecues and sporting events, it is important to know the dangers that extreme heat creates.
If you can't avoid being outside and staying close to air conditioning, here's some ways to beat the heat:
Never leave your car locked or unattended without checking for pets and children inside. Hydrate with water, avoiding sugary drinks and alcohol. Wear light-colored clothing, which can keep your body temperature down several degrees. Wear sunscreen SPF 15 or higher to protect your skin from harmful UV rays. Don't forget to check on neighbors, friends and family, especially the young or elderly, who are at more risk of heath damage from excessive heat.
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