The temperature drop is already happening across much of the United States as a wave of autumn-like weather moves in. The drop started with a cold front moving through the north-central U.S. on Friday, continuing south and east over the weekend and into early next week with cooler air from Canada. Cities like Bismarck, Minneapolis, Chicago, and areas of the South and Plains will see temperatures significantly cooler than usual, with highs dropping into the 60s and 70s, and nighttime lows in the 50s. This autumn-like cool down is expected to persist through at least midweek, with some areas experiencing the coolest temperatures of the season so far by Wednesday, followed by slightly warmer but still below-average temperatures later in the week. Another wave of cool air could arrive late next week, extending the cooler weather through the Labor Day weekend in the U.S..

In the Netherlands, autumn begins meteorologically on September 1 and temperatures typically start to drop in autumn, with an average of 10.6°C during the season. Temperatures gradually decrease from September through November, with the average maximum daytime temperature dropping from about 18°C in September to around 9°C in November. Winter temperatures average around 3.4°C, so the temperature drop in the Netherlands is already underway as September progresses.

In the UK, recent forecasts indicate a period of cooler and more changeable weather with the possibility of temperature dips below average in parts of the UK, especially Northern Ireland and Scotland. Temperatures might gradually rise again by mid to late week, but overall cooler spells are expected to continue intermittently leading into October.

Overall, in many parts of the Northern Hemisphere, the temperature drop associated with autumn is already happening or imminent, spanning from early to mid-late September with some variations by region.