In southern California and northern Baja California, “blanket clouds”, or low coastal clouds that extend horizontally across the sky, are critical for cooling summer daytime temperatures and for providing dry ecosystems with water and nutrients when the clouds intercept the ground as fog. In a new study, published in Geophysical Research Letters, Southwest CASC researchers sought to understand how coastal low clouds in southern coastal California were impacted by another regional climate event – the North American Monsoon (NAM). NAM develops each summer and provides temperature relief and rain to the desert southwest. Though coastal southern California does not receive much rain from NAM, the region is on the edge of NAM’s influence. In their study, the Southwest CASC researchers showed that southern California and northern Baja California experience a reduction in coastal low clouds when NAM transports higher altitude moisture to the region in late summer. The link between coastal low clouds and NAM outlined in this study can help improve predictions of future coastal cloudiness, weather patterns, and climate in the region.  

This work is supported by the Southwest CASC Project, "Actionable Science to Understand the Effects of Recent Temperature Increases to Inform Natural Resources Management in the Southwestern United States."