Autumn may officially begin on September 22 or 23 each year, but it often feels like the weather takes a few weeks to get the memo.
Here at TIME Labs, we were curious when it begins to actually feel like fall around the country. To do so, we looked at 21 years of data from the National Oceanic and Atmospheric Administration, defining autumn as the first five consecutive days in which the high was lower than 70 percent of a region’s yearly range in temperatures. (For example, a place with yearly lows of 10 and yearly highs of 90 would have a “fall line” of 66 degrees, which is 70 percent of the distance between those extremes.) Enter your city or county below to see when you can expect cooler weather in your neighborhood.
This sort of analysis is more Farmer’s Almanac than fine meteorology, but in most cases summer does overstay its welcome for at least a few days. In playing around with our own interactive, we found many instances of fake outs in which there would be a few fall-like days in August or early September followed by a resurgence of sweltering weather.
Weather data can be as finicky as the weather itself as measuring stations go on and offline. For this interactive, we looked at the five closest weather stations to the center of a city or county, limiting the search to stations that have been active since 1995. We then averaged the high temperature for each of those stations for each day from Jan. 1, 1995 to the present. In limited cases in rural areas, there were not five stations within a 50-miles radius.