Chasers may operate whenever significant thunderstorm activity is occurring, whatever the date. This most commonly includes more sporadic activity occurring in warmer months of the year bounding the spring maximum, such as the active month of April and to a lesser extent March. The focus in the summer months is the Central or Northern Plains states and the Prairie Provinces, the Upper Midwest, or on to just east of the Colorado Front Range. An annually inconsistent and substantially smaller peak of severe thunderstorm and tornado activity also arises in the transitional months of autumn, particularly October and November. This follows a pattern somewhat the reverse of the spring pattern with the focus beginning in the north then dropping south and with an overall eastward shift. In the area with the most consistent significant tornado activity, the Southern Plains, the tornado season is intense but is relatively brief whereas central to northern and eastern areas experience less intense and consistent activity that is diffused over a longer span of the year.