Dairy operations in California's San Joaquin Valley emit more methane than previously thought. In June 2021, airborne measurements showed that these dairies release 39% more methane than estimated in current inventories. The emissions increase with temperature, and dairy farms are the main source of methane in the area, accounting for about 65% of total emissions. This study suggests that the VISTA-CA inventory is more accurate than the EPA GHG-I inventory for this region. The findings support the need for better understanding of how weather affects methane emissions from dairy operations.