Clarifying the drivers of winter precipitation increases in the southwestern U.S. during Heinrich stadials

David McGee, Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, Cambridge, United States, Eduardo Moreno-Chamarro, Massachusetts Institute of Technology, Earth, Atmospheric and Planetary Sciences, Cambridge, MA, United States and Eric D Galbraith, ICREA Catalan Institution for Research and Advanced Studies, Barcelona, Spain