As the novel coronavirus SARS-CoV-2 continues to proliferate across the globe, it is a struggle to predict and prevent its spread. The successes of mobility interventions demonstrate how policies can help limit the person-to-person interactions that are essential to infection. With significant community spread, experts predict this virus will continue to be a threat until a safe and effective vaccine has been developed and widely deployed.3 We aim to understand mobility changes during the first major quarantine period in the United States, measured via mobile device tracking, by assessing how people changed their behavior in response to policies and to weather. Here we show that consistent national messaging was associated with consistent national behavioral change, regardless of local policy. Furthermore, while behavior changed with weather conditions, generally the changes did not increase encounters between people. The independence of encounters and temperatures suggests that behavioral changes may have at most a limited impact relative to any direct physical modulation of transmission by weather. Both of these results are encouraging for the potential of clear national messaging to help contain any future pandemics, and possibly to help contain COVID-19.