Storm chasers are most active in the spring and early summer, particularly May and June, across the Great Plains of the United States (extending into Canada) in an area colloquially known as Tornado Alley, with many hundred individuals active on some days during this period. This coincides with the most consistent tornado days in the most desirable topography of the Great Plains. Not only are the most intense supercells common here, but due to the moisture profile of the atmosphere the storms tend to be more visible than locations farther east where there are also frequent severe thunderstorms. There is a tendency for chases earlier in the year to be farther south, shifting farther north with the jet stream as the season progresses. Storms occurring later in the year tend to be more isolated and slower moving, both of which are also desirable to chasers.