Downslope windstorms are responsible for wildfires, wind gusts, and turbulence in the lee side of the Taebaek Mountains, called Yeongdong region (YD) in Korea. We classified the synoptic conditions of the windstorms in the YD using a Self-Organizing Map (SOM). For the windstorm events from 1979 to 2019, sea level pressure anomalies were used to train the SOM. It was found that the synoptic patterns could be classified into three representative types: 1) the south high and north low pattern in spring, 2) the west high and east low pattern in winter, and 3) the strong low-pressure system passing the northern part of Korea. At the 850 hPa level, prevailing southwesterly (nortwesterly) flow with warm (cold) advection was dominant in Type 1 (2), and Type 3 presented a well-developed baroclinic system of cyclone. Adiabatic warming by downslope windstorm is the strongest in Type 1, which is likely to have a huge impact on the spread of wildfires. Three mesoscale generation mechanisms were examined under different synoptic patterns. Hydraulic jump theory was dominant for the windstorms in Type 2 due to upstream flows with moderate Froude numbers and inversion layers. The partial reflection of mountain waves was found in all types but more frequent in Type 1 than others. Downslope windstorms with wave breaking at critical levels mostly occurred in Type 1. This objective classification of weather patterns responsible for downslope windstorm in the YD is useful for better prediction and future projection of this event with climate change.