The bill says the definition of 'extreme weather' will follow the definitions cities are using in their Extreme Weather Response Plans, but the provincial cabinet can make regulations to adjust the definition.
Criteria in Vancouver include temperatures near zero with rainfall making it 'difficult or impossible for homeless people to remain dry'. Sleet, freezing rain, snow, high winds or temperatures below negative two degrees Celsius also count as extreme weather.
In other words, the BC government can tweak the definition of 'extreme weather' to suit their own agenda-laden purposes, which is what I'd suggested likely in Part 1 of this post.
As the Bill itself suggests, when it comes to staying dry (or warm), 'difficult' isn't the same as 'impossible'. Street people are inventive; given how long many have been on the streets, it's safe to assume they know how to survive in all manner of weather.
Here's the short, and not so sweet, Bill 18 - Assistance to Shelter Act.
ETA: There's also this little inconsistency concerning the province's purported regard for street people's health and safety. (That David Eby! Formerly the driving force behind Pivot Housing and now, deservedly, the executive director of the BC Civil Liberties Association, he's a champion of the best sort.)
Recommend this post