Weather can vary a lot across South Korea, even on the same day. Before you add a location in sanCheck, here's a quick overview of what to expect in each major region.
A mix of inland and coastal terrain that's relatively exposed to fine dust. Summer tropical nights and a strong urban heat-island effect in winter are common. Spring often brings yellow dust and PM alerts.
The Taebaek mountain range splits inland Yeongseo from coastal Yeongdong, producing very different weather on each side. Yeongdong sees frequent heavy snow in late autumn and winter; Yeongseo has larger daily temperature swings and summer showers.
Inland basin terrain leads to large temperature swings between hot summers and cold winters. Frequently affected by heavy rain during the monsoon (jangma) season.
Proximity to the Yellow Sea and South Sea brings high summer humidity and frequent exposure to the monsoon and typhoons. Heavy winter snow can occur along the west coast.
A notable temperature gap exists between coastal areas along the East and South Seas and inland basins like Daegu, which sees intense summer heat waves. The south coast lies directly in the typical path of typhoons.
A maritime climate keeps winters relatively mild, but weather is known for strong winds and rapid changes. Temperature and rainfall can differ sharply between the highlands of Mt. Halla and the coast.