Did give rise to a slightly morbid thought though.. Much like one has a limited number of birthdays, one also has a limited number of instances of realising "ah, summer is coming again". Pretty much the same number of each.
So much in the way that a birthday reminds you that you're a year nearer to death, so too can a nice day outside. If you're predisposed to thinking odd things.
At least each year has effectively two significant seasonal transitions, so I guess you have two instances of "ah, new type of prevailing weather coming up" for every birthday.. Still, it's odd to think that the number of times you realise "summer is coming" is actually very easily countable.