False autumn, a fleeting respite from the heat in late August or early September, frequently misleads individuals. Weakened late-summer warmth, dry conditions, and more potent cold fronts are responsible for these sudden temperature drops. True autumn, on the other hand, differs from place to place and is typically marked by sustained cooler temperatures or the conclusion of the moist season.
This phenomenon recurs nearly annually—following a sweltering summer, a spell of cooler weather arrives at the end of August or the start of September. As pumpkin spice lattes and Halloween decorations become prevalent, you might mistakenly believe that autumn has arrived.
Yet, it’s inevitable that summer temperatures often make a comeback as you retrieve your autumn sweaters from storage. This phenomenon is known as a false or false autumn, with the temperature drop being fleeting, followed by the remaining weeks of summer, sometimes referred to as “second summer.”
Here’s why you might be deceived by false autumn and why Mother Nature often plays a trick with temperatures during the shift between seasons.
If cooler temperatures arrive sooner than expected, it might signal an early autumn.
“What I consider false autumn is when we experience a cooldown around or just before the beginning of meteorological autumn (September 1st),” explains Paul Pastelok, senior meteorologist and lead long-range forecaster at AccuWeather. “If there are warm periods during September, then this late-August period can be misleading regarding the arrival of autumn.”
The term “false” or “fake” autumn is used because, after the cooldown, temperatures revert to typical summer conditions. Depending on your location, you might enjoy a few more weeks of summer warmth before temperatures consistently decline, signaling the onset of autumn.
However, “average” temperatures can vary greatly from one place to another; it might be normal to see cooler temperatures arrive earlier in the northern regions. Conversely, other states might experience warmer weather year-round.
Despite their deceptive nature at the end of summer, a brief spell of cooler temperatures isn’t uncommon.
“During the late summer, daytime heating is starting to wane across the United States, allowing occasional intrusions of cooler air from Canada,” says Jonathan Belles, senior digital meteorologist at The Weather Company. “These can last a day or two, and their frequency increases through autumn until only cool weather remains.”
A cold front can occur at any time during summer, but it’s more likely to occur during the seasonal transition, or around the time of “false” autumn.
“For autumn in the northern hemisphere, the ocean waters are reaching their peak temperatures, and daylight hours are beginning to shorten, more so near the poles,” Pastelok notes. “This combination can lead to decreasing temperature averages, more pronounced contrasts, and stronger cold fronts compared to mid-summer.”
A lack of rain in your area can also contribute to false autumn temperatures. This year, with various regions facing droughts, the likelihood of a false autumn might be heightened if your area is experiencing rainfall deficits.
“In regions that are experiencing drought at this time of year, or are entering extended dry periods, the nights tend to be cooler than anticipated,” Pastelok adds. “The dryness, low humidity, and longer nights allow temperatures to drop more quickly and for longer.”
False autumn is not confined to the cooler temperatures typically observed in August and September. You might feel misled by a false autumn if temperatures drop as expected, only to unexpectedly rise in October.
“You can definitely have warmer intrusions battling their way northward during October and November,” Belles points out.
Although autumn officially commences on September 22nd this year, meteorological autumn is based on an average of annual temperatures and spans from September 1st through November 30th. The definition of the true “start” of autumn can also vary based on where you live.
“Real autumn can be defined in several ways, often by feeling rather than strict rules,” Belles says. “Many would define the arrival of real autumn as the first significant cold front to sweep through your region. In the south, the feeling of autumn often begins when the last of the truly humid weather passes. In the north, it is the last day with temperatures in the 70s or 80s.”
Some regions are also witnessing a slight rise in average autumn temperatures, which can make pinpointing the official start of autumn more challenging.
“There is a trend toward milder autumns,” Pastelok observes. “Last autumn, 2024, was tied with 2016 for the warmest autumn on record.”
Coupled with drought conditions, this could mean your area is more prone to a false autumn this year. However, observing the changing leaves isn’t always a reliable sign of when autumn arrives. Instead of temperature, Belles suggests that shorter daylight hours and lower sun angles have the most significant impact on when leaves begin to change color.
While weather does play a role in leaf color change, drought and freezing temperatures also have a substantial effect on vegetation,” Belles notes. “A prolonged drought during the summer months can cause vegetation to turn brown and orange sooner, while a wet summer and autumn might keep leaves green longer.”
Following the leaf drop, you might still notice slightly warmer temperatures even once autumn has fully set in. “Observe when the leaves fall completely to the ground,” Pastelok advises. “There tends to be a warm-up in northern latitudes around that time as the absence of leaves removes the shading.”
