A passing cold front from the southwest is the primary driver keeping the highest temperature in Buenos Aires on August 18 centered on 13–14°C, as reflected in the market's 57% implied probability for 14°C and 27% for 13°C. Official Servicio Meteorológico Nacional guidance and supporting model consensus indicate a daily maximum in this narrow range under persistent cloud cover, light southerly winds, and limited boundary-layer mixing that suppresses afternoon warming. This aligns with typical late-winter conditions in the region, where August highs average near 15–17°C but frontal passages frequently produce 2–4°C cooler outcomes. Modest forecast spread in peak timing and cloud thickness accounts for the remaining probability mass on 12°C and 15°C, with newer model runs or observational updates expected to refine these odds before resolution.