This paper analyzes in detail the role of environmental and economic shocks in the migration of the 1930s. The 1940 US Census of Population asked every inhabitant where they lived five years earlier, a unique source for understanding migration flows and networks. Earlier research documented migrant origins and destinations, but we will show how short-term and annual weather conditions at sending locations in the 1930s explain those flows, and how they operated through agricultural success. Beyond demographic data, we use data about temperature and precipitation, plus data about agricultural production from the agricultural census. The widely known migration literature for the 1930s describes an era of relatively low migration, with much of the migration that did occur radiating outward from the Dust Bowl region and the cotton South. Our work about the complete United States will provide a fuller examination of migration in this socially and economically important era.