today i decided last minute to stay home from the barn because with the wind chill it is about -26 (-20 without). the temps you are describing (even with wind factored in) are downright balmy compared to here! lol. i'd be overjoyed to get just one day 'warm' like that so i could have a decent time at the barn instead of a quick 'here's a carrot, now lets make sure you don't have ice balls in your feet, ok, bye, see you tomorrow' visit.
i would ride if i were you, but i wouldn't ride too hard or get my horse past a light sweat if they aren't used to being worked in cooler weather. remember to cool them out well and ensure they are fully dry before putting them back in stall or pasture after.
as for jumping, i would hold off until the weather is nicer. not sure if the ground freezes in the winter where you are (BC is a big province, you don't say what area you are in), but i know i wouldn't want to jump my horse on frozen ground, even if it was good footing and dry.