So I started looking into it a little.
Suunto app doesn’t enrich activities after upload, but Strava and Garmin does. Worth knowing before. So I don’t know how to do it in a place without a cell phone signal. That’s really bad.
I tried ran with a Suunto Vertical and a Garmin Enduro 3 at the same time from no phone signal location. The Garmin activity came out with weather conditions and a place name attached; the Suunto one had neither. My first assumption was that the Vertical hadn’t got a GPS fix at the start.
But it looks the difference is entirely server-side, after upload:
Weather. Garmin Connect and Strava both take the activity’s coordinates and start time and pull historical conditions from a weather API. Suunto doesn’t do this. The only weather-ish data in my FIT is the watch’s own temperature sensor, which mostly measures your wrist.
Place name. Same story - Garmin reverse-geocodes the start coordinates and names the activity after the location. Suunto leaves it as the sport type.
One separate thing that caught me out: the forecast widget in the Suunto app takes its location from your phone, not the watch.