Tomorrow is NOT the first day of summer.
Tomorrow is the middle of summer, which began 45 days ago, and will end 45 days from tomorrow (amounting to 91 days per season, and 4 seasons totalling 364 days, which is Good Enough For Government Work).
My rationale is simple: after tomorrow, The Longest Day of the Year, it will not be getting more summer-like, which you might reasonably expect if it were the First Day of Summer.
Which it is not.
Days will shorten for the next 180 days until December 21st , also known (in my universe) as Midwinter.
After which, it will proceed once more to get more summery, until June 21st rolls around once more, and I rant again.
This has been a public service announcement.