Traditionally and in terms agriculture and animal husbandry, the harvest season ('fall') starts in August with the grain harvest.
Very noticeable in parts of Scandinavia or Canada.
For the Celts, Summer - or the warmer half of the year - ends at Samhain (samh = Summer, fuin = end), which you know as Halloween, the blood harvest, when livestock who aren't going to make it through the winter are slaughtered and preserved.
I remember that in the 90s and early 00s, it only got cold here for about 3 weeks in January and after Valentine's day, it started to warm up quickly, snow storms were VERY rare and VERY quickly over, temps in the 30s were rare as well.
This is no longer the case, it can cool down fairly drastically as early as September, snow storms can last 3 days, temps can drop to -6F and it doesn't start to warm back up until mid May.
Someone needs to tell Greta Thunberg that her global warming isn't working.
I'll ride as long as the roads are not fully icy - driving a car on ice is already not the best idea you've ever had, riding a bicycle on ice is a potential suicide mission - the wind is below 30 mph and my fingers don't turn to icicles the minute I step out the door.