An unprecedented March heat wave that unfolded across western North America this week broke hundreds of monthly records from Mexico to British Columbia. Friday saw the United States’ all-time March temperature record shattered by several degrees. Numerous heat records even fell across portions of Canada. An extremely powerful ridge of high pressure centred over the US Southwest built summerlike heat across the western half of the U.S. and much of northern Mexico, with unseasonably warm readings even eking across the border into Canada. The scope and severity of this heat wave is unprecedented in modern records for this time of year. It’s almost certainly the most extreme North American heat wave since the infamous heat dome event of 2021. Nearly 700 monthly high temperature records have fallen over the past seven days across the western and central United States.