Traders assign near-certainty to a 17°C high in Warsaw on September 11, 2026, because official meteorological observations from the Warszawa station recorded a daily maximum of 16.9°C under persistent overcast skies and light winds. This outcome aligns with a cool northeasterly flow suppressing daytime heating well below seasonal norms of 18–20°C. Model consensus from regional forecasts had projected modest afternoon peaks near 18–21°C earlier in the week, but actual surface readings remained capped by cloud cover and stable boundary-layer conditions. Only an unexpected late-day clearing or station-specific measurement revision reaching 20°C would shift the outcome, scenarios considered highly improbable given the completed observational record.