You have to do some arithmetic to really understand the effect of "light" wind on a micro. In the case of a Cub, the full scale version has a 35 foot wingspan, while the UM Cub is 18 inches. That's 1/23 scale for size. It's not a perfect comparison, but calculating the wind means that a 4 mph breeze in the UM feels like a 92 mph breeze for the full scale version. No sane pilot would fly in that. An even more practical comparison is to compare with other things that the wind tosses around. A big maple leaf has close to the same area to weight ratio, as does a sheet of cardboard. Look how much effect a light wind has on those items to get an idea of what you're fighting to fly in it with a UM model.
My flying is mostly 40-60 size nitro planes, but I've come up with a rule of thumb that seems to serve me well for figuring wind. I try to stay below 1/3 of my plane's top speed in wind speed for planes that are good in the wind, and below 1/4 in planes that are not. My Stick is good in the wind and can go about 60 mph. So I find that 20mph wind is flyable weather, although the workload does increase near the ground where the turbulence is worse. For my Cub, it doesn't go over 50, so about 12 mph is all I fly it in. I'm thinking the UM Cub or Champ will top out around 7-8 mph, so over 2mph wind is the limit. It take 4-5 to make leaves move on the trees, so even "dead calm" may still be too much air movement for comfortable flight.