http://shootingtracker.com/wiki/Mass_Shootings_in_2015

According to this list, the US has averaged about 1 mass shooting per day this year. I must say I had no idea the problem was that bad. I expect some of these were gang-related shootings involving people no-one cares about, but, even so, on the face of it it seems kinda insane. Does anyone know if this truly is an insane number of mass shootings? Is this year an outlier? What's going on in the US?