Fogbows and Drop Size
Fogbows (and cloudbows) are formed similarly to rainbows, but since the water droplets in clouds and fog are much smaller than the raindrops in rainbows, the appearance of the bow is different. Note that fogbows and cloudbows are the same phenomenon, since fog is just clouds low to the ground.
The bigger the raindrops, the thinner the rainbow. Likewise, the smaller the drops, the wider the rainbow. Cloud and fogbows feature waterdrops from 1 micron to 100 microns, usually 10 to 20 microns. Bows made from larger droplets will not only be relatively narrower, but more colorful than bows made from smaller droplets (which will be wider and paler). Fogbow Droplet Size - AtOpt
Like with supernumerary rainbows, fogbows are a result of the wave nature of light, which is noticeable when the the droplets are smaller than 1mm in diameter. In fact, the wave nature of light is the whole reason rainbows look different when made by different drop sizes. Rainbow Drop Size - AtOpt Readers should read the supernumerary page before continuing, for information about interference.
Both simulations show how the primary and supernumerary bands change in appearance and drop size decreases, notice how as the drops get smaller, the width of the bands increase.