A different red-blue split in the U.S.

"This map produced by NOAA shows the land-surface temperature anomaly: how the temperature deviated from normal, on average, over the month. The darkest red areas were 12 degrees Celsius (22 degrees Fahrenheit) above average, while the darkest blue areas were 12 degrees Celsius below average."

The thermal anomalies are the result of a deeper jet stream curvature, the genesis of which is explained as follows:

The jet stream is generated by a combination of Earth’s rotation and the flow of air down atmospheric gradients between high-pressure, mid-latitude warmth and low-pressure Arctic cold. Over the last several decades, the Arctic has warmed faster than any other region; during periods of especially heightened warming, as occurs when melting sea ice exposes dark, sunlight-absorbing waters, the north-to-south temperature difference shrinks. The pressure differences flatten.

This decreased gradient slows down the jet stream—and as it slows, it also seems to become wavier, plunging south or veering north when encountering atmospheric obstacles it would once have coursed straight through. “The best analogy is to think of a river. When it’s flowing down a steep mountainside, it flows fast and straight,” says Francis. “When it gets to the coastal plain where there’s little slope to the land, it flows slowly and is easily deflected from its path.”