Multi cells are a combination of at least two single cells. Such multi cells have diameters of 20 to 30 kilometres. The entire complex of multi cells reachs lifetimes of several hours.
Essentially, the same process which forms a single cell thunderstorm creates the multicell storm with one exception. As the initial thunderstorm cell dies, a new secondary cell develops somewhere along the flanks of the original cell due to low level convergence along the gust front (the gust front is the microscale leading edge of the rain cooled air). As the second cell begins to decay, a third cell might form along the gust front as long as supply of warm moist air continues (see figure).
While the radar reflectance resolve the internal structures it is not easy to detect the single cells by satellite data. Only highly resolved images or advanced composits delivers useful information about that.