According to the following rule
Ubivis: Each guess is only allowed once (only the first one will count) and editing the post will result in a disqualification
This would be the current list:
TheCheese33 - 10
saramakos - 16
olgar - 17
phenom_x8 - 18
kazmar - 19
Darling_Jimmy - 20
Fujek - 20.5
SLP2000 - 21
Smannesman - 21.5
Aningan - 22
Roman5 - 23
liquidsnakehpks - 26
I'll take a guess of 20.5°C as highest temperature on that day, hoping that you were talking of the maximum value and that you're going to measure exact (including decimals ;)).
Oh and a few clouds with some sporadic rain, but mostly sunshine.
And happy birthday to your wife, I hope you two are going to have a nice party.