Hi,
I live in Halkidiki and February can be a bit of mixed bag! It can be warm towards the end of the month but nothing will be open, most beach bars and hotels etc open the first week of May.
I have a new site which I'm just in the process of finishing and should be fully online next week, its a complete travel guide to Halkidiki and it also has quite an extensive guide to the weather.
You're quite welcome to join the forum where I'll be adding up to date forecast thoughout the summer season.
Like I say, it's not fully operational yet but the forum and flights pages work for now....keep checking back as it's almost finished.
If you need to know any more about Halkidiki I'd be happy to try and help.