Shanghai enters mid-April in spring transition, with typical high temperatures ranging from 20 to 22°C. This market asks whether the city's maximum temperature on April 18 will settle at exactly 18°C—a narrower outcome than most weather forecasts provide. An exact temperature match is inherently precise; meteorological forecasting typically operates in ranges of 2-3°C rather than single-degree accuracy. The 4% implied probability reflects what that specificity demands: Shanghai would need to cool slightly below seasonal norms while missing adjacent temperatures like 17°C or 19°C. Historically, daily temperature distributions show that hitting a single-degree target is statistically uncommon, especially when that target sits below the seasonal mean. As April 18 approaches, weather models will narrow their range of likely highs, and odds typically shift or tighten as forecasts converge toward specific outcomes. Traders pricing this at 4% suggest they view 18°C as an outlier outcome relative to expected spring patterns for this period.