Trader consensus on Polymarket closely splits between 19°C (34.5% implied probability) and 18°C (32.5%), reflecting genuine uncertainty in forecast models amid Japan Meteorological Agency (JMA) guidance for mostly cloudy skies and occasional scattered showers on April 17. Today's April 16 high reached around 23°C under mostly sunny conditions, boosting solar heating earlier in the week, but an incoming cloud deck is expected to limit insolation and cap peaks near mid-spring norms of 18–19°C at Tokyo's Haneda Airport station. Ensemble outputs from ECMWF and GFS converge tightly in this range, with differentiators including shower timing—earlier onset favors 18°C, delayed clearing tilts to 19°C—and boundary layer mixing. JMA's evening update may sharpen this ahead of resolution.