Indian Summer

I have to say I am finding our weather very strange these days. There was a time when summer arrived in late May and hung around, more or less, until late August or early September. For the last couple of years we seem to have had most of our summer by early May, then we have a strange mix of Spring and Autumn (including leaf drop some years), then in late September we have another visit from the 'Summer Fairy'. Don't get me wrong, I would rather we had this than no summer at all.

Could someone please let me know what is going on. I am getting confused and have no idea what I am meant to be wearing from one say to the next.