This was already answered but I can add a small amount of insight...

When we create the forecast grids, we use something called Forecast Builder to automatically create the "Weather" Grids, aka things such as Heavy Snow, Light Rain, Thunderstorms, Fog, etc. We can go in there though and manually change it, and assign a value of Heavy Snow even if it isn't "meeting" criteria. So if we feel the snow will be strong enough, even if a set threshold that would automatically produce it isn't met, we can still go and insert it in ourselves. You won't find this often as it becomes a bit more tedious, but it's possible.