Highest temperature in Seoul on May 21?

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Market context

Seoul has warmed noticeably over the past 24-48 hours, with the city moving into its late-spring regime: typical highs rise quickly through May, from the high 20s °C at the start of the month towards the mid-20s °C by the end, and AccuWeather’s May range for Seoul points to highs around 19-32°C. For Incheon, the relevant airport site is usually a touch cooler than central Seoul because of its coastal position, but it still sits in a period where a midday high in the low-to-mid 20s °C is ordinary and the first mid- to high-20s °C readings are plausible on a sunnier day. The crowd-implied 0% YES looks anchored to that broad seasonal expectation rather than any sign of a cold outbreak.

The best historical guide is that late May around Seoul and the north-western coast often produces moderate warmth rather than extremes. Seoul’s climate normals show May as the transition into the hot season, with temperatures climbing steadily and only a gradual increase in humidity until summer sets in. Nearby airport readings can differ from city-centre values, but the pattern is similar: a narrow band of outcomes, with most days landing comfortably below heatwave territory and occasional spikes when skies clear and winds ease. That makes the upper temperature range especially sensitive to whether conditions briefly tip sunny and dry in the early afternoon.

For the remainder of the day, the key watchpoints are cloud cover, onshore flow, and any short shower line crossing the north-west of the peninsula. If the Korean Meteorological Administration has a stronger sea-breeze signal or more cloud than expected, the airport maximum can be capped well below Seoul’s headline temperature. If instead the afternoon stays bright and winds remain light, Incheon can still catch a warmer inland push. By settlement time, the market will hinge on the highest reading posted at Incheon International Airport in the Wunderground history entry once finalised.

Sources: 1 · 2 · 3 · 4 · 5

Methodology

This page reviews Highest temperature in Seoul on May 21? across five venues. We show live odds for Polymarket-based markets (sourced from the Polygon order book); for other venues we list platform attributes, since the comparable contracts are not exposed via a public API on every venue. Every CTA points at PolyGram — the application we operate, where you trade directly against the Polymarket order book at 0% fees.

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