Recent forecasts from multiple models indicate a likely overnight low in Buenos Aires on September 18 near 13–15 °C, driven by northeasterly flow and elevated surface pressure that limits nocturnal cooling while advecting milder maritime air. September marks the Southern Hemisphere spring transition, when synoptic variability from passing ridges and weak fronts can produce 4–6 °C swings in minimum temperature; current runs show limited cold-air advection and cloud cover that moderates radiative losses. Persistent model agreement on these conditions underpins the clustered probabilities around 13–14 °C, while residual spread in boundary-layer mixing and exact wind timing sustains roughly equal market-implied odds for outcomes below 9 °C or above 17 °C. Updated model runs and official Servicio Meteorológico Nacional guidance expected overnight will further refine resolution thresholds.