A sprawling heat dome is bringing temperatures of up to 110°F, or possibly higher, to a broad swath of the U.S. on Wednesday, with more than 100 million people under heat warnings and advisories.

Driving the news: The extreme heat will be most intense in the southern Plains and lower Mississippi Valley, but the big cities of the Northeast will swelter as well.

Why it matters: Extreme heat is a public health threat and human emissions of greenhouse gases from burning fossil fuels are worsening such heat waves, studies show.

Oklahoma, Texas heat wave

The big picture: For a second day in a row, much of Oklahoma and a huge swath of Texas are under an excessive heat warning.

• On Tuesday, in an unprecedented event, every weather observing location in the state recorded temperatures of 102°F or higher, with Oklahoma City peaking at a high of 110°F. This tied the city's all-time high for July.
• The National Weather Service is calling the heat "dangerous," as heat is on average the number one weather-related killer annually in the U.S. The elderly and those without access to air conditioning are especially vulnerable to heat-related illnesses.
• Daily high temperature records are likely to be broken Wednesday in Texas, Louisiana and Arkansas.
• The heat in Texas has gone on for weeks and is tied to the extreme drought there, since dry soils allow for the air to heat up faster.
• According to Climate Central's Climate Shift Index, parts of Texas and Oklahoma will see high temperatures that climate change has made three to four times as likely to occur compared to a world without human-caused global warming.

Axios Local dispatch, via Asher Price: Today Austin is notching its fortieth triple-digit day of the year. It's not a bearable dry heat — more like sweltering-wet-blanket weather.

• Buses here now act as mobile chilling stations, ferrying people, for free, to the city's cooling centers — libraries and parks and recreation facilities.
• We're basically staying indoors from 10am to 6pm, venturing out only to make our way to our local public pool before closing time.

Excessive heat warnings

Threat level: At the same time as the Plains roasts under relentless, withering heat that is worsening drought in that region, the Mid-Atlantic and Northeast are also experiencing torrid heat as temperatures climb toward the century mark in Richmond and Washington, D.C., this weekend, with the heat extending northeastward to Boston.

The intrigue: Computer model projections show the heat in the U.S. is likely to migrate westward over time, with the potential for a significant heat wave to envelop much of the West, including California, Oregon and Washington, toward the end of July and into August.

• This carries considerable risks, since the ongoing severe drought has turned the region's forests into a tinderbox, and many areas are limiting water use in the midst of a multi-year megadrought.

Excessive Heat Warnings and Heat Advisories are in effect this morning throughout 28 states, stretching from California to New Hampshire. High temperatures into the 90s and 100s will increase the risk of heat related illnesses. For heat safety tips, visit: https://t.co/L4FyvSS6lj pic.twitter.com/rFmVCKxDSV

— NWS Weather Prediction Center (@NWSWPC) July 20, 2022

Global heat waves

Of note: The heat in the U.S. is connected to the deadly extreme weather event that continues in Europe, since the same wavy jet stream pattern (technically known as "wavenumber five" for its five major ridges, or heat domes, of high pressure).

• This pattern has led to heat waves in Asia, the U.S., Europe and the Middle East.

• Some studies have shown that human-caused climate change is making such patterns more durable during the summer and increasing the odds of them occurring.

Context: Studies have shown that climate change is making heat waves like this one hotter than they otherwise would have been, as well as more frequent and longer-lasting.

• European heat waves in particular have become more common compared to other parts of the globe, according to a recent study.