A recent polar cold front advancing from an extratropical cyclone has driven cooler air masses into São Paulo, producing the sharp overnight temperature drop expected on August 22. Official guidance and ensemble models indicate a minimum near 11–13 °C under mostly clear skies that favor strong radiative cooling after the front passes, with light southeasterly winds limiting mixing. This marks a departure from the seasonal average low of roughly 15 °C for the date. Market-implied probabilities cluster tightly around 11–13 °C because forecast spreads remain modest yet sensitive to small differences in boundary-layer moisture, cloud cover timing, and local urban heat effects. Updated model runs and INMET observations through the night will be the key data points for traders assessing whether the low settles at 12 °C or edges lower.