Vertical moisture profile characteristics of severe surface drought and surface wetness in the western United States: 1973-2002

Drought can be viewed as a three-dimensional phenomenon rather than simply a surface feature. We characterize drought across the western United States from 1973 to 2002 in a three-dimensional context by examining its vertical moisture extent using NCEP/NCAR Reanalysis data derived from rawinsonde moisture profiles. We then apply a discriminant analysis to establish the degree of difference between the vertical moisture profiles of extreme drought and extreme wetness conditions. The mean vertical moisture profiles of dry cases are measurably drier than those of wet regions, particularly at the lower levels of the profile. The discriminant analysis of the 9254 cases indicates that moisture in the lowest (850 hPa) level of the profile is most important in identifying dry versus wet regions, and, consequently, implies a strong influence of convective precipitation in defining surface drought and wet conditions in the study region.