South Korea braces for vernal spring with big day-night swings, winds, and supply-chain risks.

South Korea is entering a steadier spring pattern with a clear-sky forecast and pronounced day-night temperature swings as the vernal equinox arrives on March 20.

Forecasters say daytime highs will range from 11°C to 17°C nationwide, while morning lows are expected between -4°C and 6°C. Inland areas may see frosts, and the diurnal temperature range could reach 15°C to 20°C.

March 20 marks the vernal equinox, when day and night are of equal length. The forecast calls for sunny conditions across the country, with a continued large day-night temperature gap, especially inland, through the weekend.

City-level forecasts show Seoul from 2°C overnight to 14°C by day; Incheon 4°C/11°C; Daejeon -1°C/15°C; Gwangju 2°C/16°C; Daegu 2°C/17°C; Ulsan 4°C/16°C; and Busan 6°C/16°C.

The weekend is expected to remain sunny, and the big diurnal swings are likely to persist into late March.

Along the east coast and inland, strong winds are forecast, with gusts around 55 km/h and higher, up to about 70 km/h in mountainous areas. In addition, swells are expected along the East Sea through March 21, bringing high waves that could affect rocks, breakwaters and coastal roads.

Coastal conditions could pose risks for fishermen, coastal travelers, and offshore operations. The weather pattern matters beyond Korea because such frost risk, wind, and wave conditions can affect manufacturing schedules, port operations, and logistics in a regional supply chain linked to the United States, including electronics, automotive components, and batteries produced in South Korea.

As a major exporter of advanced electronics, semiconductors, and batteries, South Korea’s spring weather can influence production timelines and shipping reliability for multinational supply chains, with potential ripple effects on U.S. manufacturers and markets that depend on Korean parts and machinery.