Recent forecasts from models and INMET guidance indicate an extratropical cold front advecting polar maritime air into southeastern Brazil, driving the leading 4°C-or-below outcome at 47% implied probability. Clear skies expected overnight on August 21–22 will enhance radiative cooling, with minimum temperatures in São Paulo sensitive to boundary-layer mixing and local urban effects. Recent model runs have trended slightly cooler than climatological August lows near 11–13°C, though ensemble spread remains notable around the 4–6°C threshold. Updated official briefings and satellite observations of the frontal passage on August 21 represent the next key data points that could shift trader positioning before resolution.