Southwest US Heat Wave June 2017
The fingerprint of global warming has been firmly identified in the increasing intensity, duration and frequency of extreme heat events.[1] The trend in warming has contributed to the probability and magnitude of 82 percent of record-hot days observed globally.[1]
It is within this context that mid-June temperatures soared 15 to 30°F above normal across the Southwestern US,[2] from California's Central Valley, to Las Vegas, and down to Phoenix. High temperatures are typical before the Southwest monsoon season; however, the extreme — record-breaking — nature of the event is a classic signal of climate change. This is the second of two back-to-back years of extreme heat in the Southwest during the pre-monsoon season.
Heat waves have generally become more frequent across the US in recent decades, with western regions setting records for numbers of these events in the 2000s.[3]