What is a heat dome? There’s one roasting Texas and the Midwest

Extreme-heat warnings are in effect for about 143 million Americans this week, due to a heat dome that is hovering over the Midwest, South and Southwest. This dangerous heat is already smashing temperature records dating back to at least 1950, according to weather trackers.

The “searing August heat wave,” as the National Weather Service (NWS) put it, is expected to persist in at least 22 states until the end of the week, and “numerous” temperature and heat-index records are likely to be set.

The…