The western United States (U.S.) has been experiencing more severe wildfires due to climate warming, but the underlying synoptic patterns driving fire weather remain unclear. Here we investigated the relationship between weather regimes and fire weather indices, specifically vapor pressure deficit (VPD) and fire weather index (FWI). By identifying five historic weather regimes using k-means clustering, we found that one particular regime, characterized by a distinct tripolar wave train pattern over the continental U.S., exhibited an increasing frequency from 1980 to 2018; this regime was responsible for the rising trends in the fire weather indices. The increasing frequency of the weather regime, which can be attributed to anthropogenic forcing, was found to be associated with sea surface temperature anomalies over the subtropical eastern Pacific. Therefore, human-caused climate warming has contributed to the exacerbation of wildfire risk in the western U.S. through modulating weather regimes and resulting impacts on fire weather.