In Pics | What is a 'Heat Dome'? Everything you need to know

Here is what you need to know about these heat dome that is melting US and Canada:

The National Weather Service issued another excessive-heat warning for much of Washington state and Oregon that will remain in effect until June 27. Here is what you need to know about these heat waves: Credit: Getty Images

What is a heat dome? 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.” Credit: AFP Photo

Why is it hotter than normal in North America? 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. Credit: Getty Images

When will the heat wave end? - Forecasters say that temperatures will remain unseasonably hot into next week in the Pacific Northwest. Temperatures will remain 10 to 20 degrees above average at least until the first week of July. Credit: Getty Images