Invitation wording... HELP !

Question- I ordered JA's photo invitations for his 1st Bday...
Its in early Oct., and we plan to have it in the backyard *weather permitting*

I didnt write 'backyard' or 'outdoor' or anything like that in the invitation, just a simple invitation with the necessary info.

Now im including a note with directions in the invite.
Im sure not everyone will assume that we are setting up a tent and tables in the backyard, so do I write something in the 'direction note' so that evryone that might be cold-blooded bring a light sweater, or do people KNOW this stuff...LOL
What would you do?
Id rather if its a little breezy, everyone feels comfy outside and I dont have everyone going 'im freezing '
for all we know it can be 85 degrees.
but I wanted to note the outdoor thing....

advice?

I know its sounds like a boring note, but I would write something like:

Please bring outerwear, as the celebration will be outside, weather permitting...