For the Canadians!!
In Ontario, Canada (Canada in general),
Recreational weather balloons are generally okay. Here is an excerpt from the email discussion I had with Transport Canada:
The regulation relating to large unmanned balloon launches is Canadian Aviation Regulation (CAR) 602.42 and it states: "No person shall release an unoccupied free balloon having a gas-carrying capacity of more than 115 cubic feet (3.256 m3) except in accordance with an authorization issued by the Minister pursuant to section 602.44."
If the gas-carrying capacity of the proposed balloon is greater than 115 cubic feet, the request for an authorization should be sent to Chief of Airspace Standards and Procedures (Contact Transport Canada to get this person's email).
If the gas-carrying capacity of the proposed balloon is 115 cubic feet or less, an authorization issued by the Minister is not required. However, this office recommends that the proposed activity be coordinated with Transport Canada.
The information should include the following and if in Ontario Region, should be sent to firstname.lastname@example.org :
1) Type of balloon. (make, model, and gas-carrying capacity)
2) Proposed launch site, including date and time of launch.
3) Payload description (contents and weight).
4) Maximum height balloon is expected to reach.
5) Means of tracking the balloon.
In our case, our 600g weather balloon will expand to <70 cubic feet and should not exceed.