Kalkstein had developed a system called spatial synoptic classification, which identifies eight different types of air masses: dry tropical, moist tropical, etc. He looks at cities and sees how these different air masses correlate with data from all causes of mortality for the region. He can see that in, say, Albuquerque, when a dry tropical air mass moves in, the mortality rate spikes by 15 percent. If he does this correlation enough times with air masses in any given city, he can get a pretty good estimate for how many people that air mass will kill whenever it arrives.
