My prediction was more....lots of people within Canada are looking for affordable places to live and the overlap between affordable places and decent climates in Canada now is pretty narrow. Southern Alberta is sort of overlooked in that sense. It's possible that Medicine Hat doesn't grow much because most of the people in that category just pick Lethbridge but I also wouldn't be surprised if it did get get some traction.
Medicine Hat
Avg Annual Temp: 6.1C
Avg Annual Sunshine Hours: 2544
Avg Annual Snowfall: 88cm
If there are people moving for the weather, I don't think that they're moving for 30 minutes of sunshine a day or 20 cm less of snow to shovel a year.
I couldn't help notice some cities you didn't mention in terms of weather:
I can get moving from the cold places to the not-cold places if you can afford it; how big a difference is it really to move between the colder places?
I imagine someone has done a study on this before about "good weather attracts growth" - I know people always talk about the weather, and it's a big factor for vacation decisions, but is that actually a core driver of why people actually move/stay/leave a place? I'd assume for most people employment, family and access to services/amenities are the bigger factors, probably more so than even affordability - which is why some cities keep growing yet are wildly expensive.
Perhaps in wealthier, seniors in retirement demographics weather is a more important factor as they have the means to move and aren't looking for access to employment markets usually?
Not to say that some people don't move for the weather - people move for millions of reasons - just trying to think through how major of a factor it actual is.
Statistics Canada does the Canadian Housing Survey, which asks about over a dozen reasons for moving; weather isn't included amongst them. There is the option to pick "other reasons", which almost nobody chooses. (And it's not more commonly chosen for people who move to CMAs in BC, which would be the most obvious move-for-the-weather group.)
Here's the reasons given why people move, based on whether they move within a city or to a new city. This is the 2021 CHS; the reason of moving because of a fire/disaster wasn't in the microdata and is pretty uncommon, so far. Note that people can answer more than one thing, so it doesn't add up to 100%. Also note that "move to a different city" can mean someone moving to Calgary from Chestermere, or from Charlottetown, or from Chongqing.
The main reasons people move between cities (but not within) are for a new job or school, or to be closer to family. The main reasons people move within a city are for a bigger/better dwelling or because of a change in the household size (Forced to by the bank, landlord, previous tenants etc. are also more move-within-city reasons). Becoming a homeowner, reducing household costs and moving to a better neighbourhood are common in both groups.
I took households who moved in the last 10 years (to get more observations) and split them into households with a senior and households without a senior. Here's the reasons:
Here there's a few interesting gaps between the different groups; the households changing cities for jobs/school are mostly nonseniors, while those moving to family are mostly seniors. Nonseniors are also more likely to move (same city or different) to form households, reduce commuting time, and become homeowners, while seniors are likely to move (same city or another) to reduce housing costs or for personal health reasons.