US Fall Temperatures Rise Nearly 3F Since 1970s as El Nino Heats Halloween

Q: Is Halloween becoming a second summer in America, and which cities are seeing the fastest shift toward hotter October nights?

Yes. The data suggests Halloween is increasingly feeling like an extension of summer in much of the United States, especially in the South and parts of the West. Climate Central found average fall temperatures have risen about 2.9°F since 1970 across 241 of 245 major U.S. cities, and October nights have warmed in 93% of 246 cities by an average of 3.4°F. That shift is changing Halloween conditions in practical ways. In Houston, for example, the last 90-degree day used to arrive around Oct. 5 on average; now it tends to come around Oct. 19 or 20. Climate Central also says Dallas, San Antonio and Austin have each warmed by about 4°F in fall since the 1970s. Families there are already adapting with lighter costumes and fewer layers. The fastest warming in October nights has been concentrated in a handful of cities. Climate Central’s top five are Reno, Nevada, with October nighttime temperatures up 11.9°F since 1970; El Paso, Texas, up 10.1°F; Las Vegas, Nevada, up 9.5°F; Tyler, Texas, up 8.3°F; and New Orleans, Louisiana, up 8.1°F. More broadly, the Northeast has seen the largest average regional increase in October nighttime temperatures, about 4.1°F. Experts say the long-term driver is mainly human-caused climate change, with this year’s heat amplified by a strong El Niño. The result is not just warmer trick-or-treating weather, but a longer season for heat risk, wildfire danger, allergies, mosquitoes and higher cooling demand.

Q: Why is Houston’s last 90-degree day arriving weeks later than it used to, and what does that reveal about changing U.S. fall weather?

Houston’s last 90-degree day is arriving weeks later mainly because fall is warming, especially in the South, and the long-term driver is human-caused climate change. Climate Central found that in Houston the average last 90-degree day used to fall around Oct. 5, but now it tends to come around Oct. 19 or 20. This year’s strong El Niño has likely added extra short-term warmth on top of that longer trend. The Houston shift reflects a broader national pattern: summer-like heat is lasting deeper into autumn across much of the United States. Climate Central’s analysis found fall temperatures have risen by about 2.9 degrees Fahrenheit on average since 1970 across 241 of 245 major U.S. cities, and October nights have warmed in 93% of cities by about 3.4 degrees on average. Researchers tracked this by measuring how late cities continue to hit warm-weather thresholds, such as 90 degrees in Houston. What it reveals is that U.S. fall weather is becoming less traditionally seasonal. In many places, especially in the South and parts of the West, warm days and mild nights are extending later into October and around Halloween. Scientists say that does more than change costume choices or delay sweater weather: it can prolong heat stress, boost cooling demand, extend allergy and mosquito seasons, and keep wildfire risks elevated later in the year.

3 articles · Updated · NPR · Oct 30

Climate Central found U.S. autumn temperatures have climbed nearly 3 degrees Fahrenheit since the 1970s, extending summer-like heat deeper into the Halloween season.
Human-caused climate change is driving the long-term warming, while a strong, record-breaking El Nino is adding extra heat in some regions this year, meteorologists said.
Regional effects differ: in the North, summer warmth is lingering through September, while in the South it can stretch into October, forcing families to avoid heavier costumes.
The trend is showing up in everyday fall rituals too — one Texas meteorologist said pumpkins carved the weekend before Halloween rotted before the holiday because of the heat.