I think its more to do with your wireless router than the weather.
I used to have a Linksys one that would basically overheat and for months I thought it was a problem with my phoneline. It would overheat, drop the connection for a very short time and then reconnect as if nothing was wrong!!!
The best thing you can do is find the make and model of your wireless modem and search for it on google adding the word "forum" to the search too.
You will be amazed how many people waste their lives talking about modems but they know their onions and your answer may be there.
I personally think its overheating though!!!!