Even with September well underway on the calendar, conditions across vast stretches of the United States remain stubbornly locked in summer mode. The typical early autumn cooldown has been delayed as forecasters with the US Climate Prediction Center continue to project elevated odds for hotter-than-normal conditions across much of the nation through at least the end of September. Computer forecasting models indicate a pronounced ridge pattern aloft, a sprawling atmospheric configuration that traps persistent warm air over the continent. Within this setup, the greatest likelihood of above-normal temperatures is centered over the Upper Midwest and the Deep South, where some guidance suggests readings could climb 5 to 10 degrees Fahrenheit above historical averages for the second half of the month.
Tens of Thousands of Heat Milestones Fall in 2026
This late-season wave of heat follows on the heels of the hottest summer ever documented in US history. Weather stations situated nationwide have tracked tens of thousands of broken milestones since the start of 2026. The counts include nearly 44,000 record daytime highs alongside more than 53,000 record-high overnight minimums. In addition to daily marks, thousands of monthly and all-time heat records have tumbled over the course of the year. In stark contrast, only about 21,500 record lows were logged during the identical timeframe, reflecting a lopsided ratio of roughly one cold record for every four heat records.
Milestones Dating Back to the 1870s Surpassed
Many of the temperatures eclipsed during this prolonged hot cycle had stood untouched for more than a hundred years. On July 12, Salt Lake City reached a searing 109 degrees Fahrenheit, which stands as its hottest observation since record-keeping began in 1874. Meanwhile, on July 3, the overnight low in Washington, DC, only dropped to 84 degrees Fahrenheit, tying the warmest overnight minimum ever recorded in the nation's capital since daily meteorological tracking started there in 1871.
Excessive Heat and Humidity Push into Southern California
The oppressive conditions have pushed deep into areas that frequently steer clear of broader national heatwaves. During the second week of September, extensive portions of Southern California fell under excessive heat warnings as uncharacteristic humidity and high temperatures took over the region. The thick, muggy atmosphere transformed the environment to the point where strolling down Rodeo Drive felt more akin to walking along Bourbon Street in the humid South.
Climate Change and Persistent Heat Domes Amplify Danger
Climate change stands out as the primary force driving this extreme heat across the American landscape. Increasing baseline temperatures elevate the floor for hot weather, causing modern extreme heat days to be noticeably warmer than identical setups would have been several decades ago. This shift is particularly striking during nighttime hours, as communities experience sharply higher overnight minimums coupled with rising humidity. The absence of nighttime cooling removes the crucial window when the human body recovers from heat stress, significantly increasing health hazards. Furthermore, global warming alters upper-atmosphere dynamics, strengthening high-pressure centers aloft that force air downward. As this air compresses, it warms substantially, combining with intense solar radiation and dry ground conditions to generate massive heat domes.
El Niño Prepares to Shape Autumn and Winter Weather
While daytime peaks for the rest of September are not expected to reach the extreme thresholds seen in July, summer-like conditions are projected to linger. Compounding these dynamics is the steady influence of El Niño, characterized by warmer-than-normal ocean waters across the equatorial Pacific that reverberate through global atmospheric patterns. The primary impacts of El Niño typically emerge during the colder months, when heated ocean waters disrupt the path of the jet stream that dictates storm tracks and seasonal temperatures throughout autumn and winter. The current event is shaping up to challenge historic benchmarks, and patterns observed during prior strong episodes indicate that large portions of the country face warmer-than-average conditions straight through the upcoming fall and winter seasons.
