How we did it (the TL;DR version)
The data comes from the Swedish Meteorological and Hydrological Institute. They’ve done some pretty snazzy climate modelling on things like number of days with snow on the ground, which is broken down at a very granular level.
These are a bit of a treasure trove for data journalists interested in climate data, check it out here.
Using SMHI's modelled data you can see the number of snow days an area typically has per winter today, and what it can expect to have 50 years from now. The models for future data are based on two scenarios: RCP 4.5 and RCP 8.5.
All data analysis and charts done in R (as you may know, we’re Team Python, but we do have one lonely R fan here in the office).
Check out the full methodology on our website (only in Swedish, sorry!).