The Aliso Canyon (Porter Ranch), California, natural gas blowout lasted 112 days, from October 23, 2015 to February 11, 2016, releasing 97 100 metric tonnes of methane, 7300 tonnes of ethane, and a host of other hydrocarbons into the Southern California air. This study estimates the impacts of the leak on transient weather, climate, air quality, and health in California and the Los Angeles Basin using a nested global-through-local weather-climate-air quality computer model. Results suggest that the Aliso Canyon leak may have increased the mixing ratios of multiple emitted hydrocarbon gases throughout California. Subsequent gas-phase photochemistry increased the mixing ratios of additional byproducts, including carbon monoxide, formaldehyde, acetaldehyde, peroxyacetyl nitrate, and ozone. Increases in air temperatures aloft and lesser increases at the surface due to thermal-infrared radiation absorption by methane stabilized the air over much of California, slightly reducing clouds, precipitation, and near-surface wind speed with greater reductions in Los Angeles than in California. The reduction in precipitation, in particular, increased PM2.5 concentration, with a greater increase in Los Angeles than in California. The higher PM2.5 increased estimated premature mortality in California by +32 (9-54) to +43 (15-66), depending on the set of relative risks used. Despite higher PM2.5 in Los Angeles due to the leak, premature mortalities there were more ambiguous, ranging from a mean decrease of -7 to a mean increase of +15, for 2 simulations with different resolution and boundary conditions. The remaining mortalities occurred in the Central Valley and San Francisco Bay Area. Ozone premature mortalities away from the leak increased by <1. The study did not evaluate potential health impacts, including cancers, immediately near the leak. As such, the Aliso Canyon leak affected temperatures, pollution, and health throughout California. Future leaks will also likely have impacts.