When examining radar images, it is common to see storms grouping together into lines and/or clusters. One reason for this is due to a common forcing mechanism. Examples of forcing mechanisms include fronts, dry lines, a low level convergence axis, upper level divergence and warm air advection. Since forcing mechanisms commonly have an axis and/or area with the greatest uplift, naturally storms will form on these axes and/or within the region of greatest uplift. Another reason storms tend to form in bands and clusters is that the first storm(s) to develop will produce outflow boundaries. These outflow boundaries are like mini fronts that enhance lifting around them. Thus new storms will often develop in the vicinity of storms that have already developed.

It is common to see linear bands of strong storms since these storms are developing along a common low level convergence boundary. The storms within the band will move in a similar direction since the middle and upper level winds help steer the storms. The radar image below shows examples of lines and clusters of storms. Typically the heavier precipitation (darker oranges in sample) is along the leading edge of storm motion where convergence is maximized. Thus many times the heaviest precipitation will occur when the storm first moves through.