Analysis of long-range ensemble guidance, specifically GEFS and ECMWF 850hPa temperature anomaly forecasts for the Southern Cone, points decisively against a 25°C breach in Buenos Aires on April 29. Current model clusters consistently prognose a prevailing post-frontal air mass, with dominant mid-level troughing precluding any sustained, robust thermal advection necessary for such a high surface temperature. While historical extreme value analysis shows isolated outliers (e.g., 26°C in 2018, 25°C in 2016), the 30-year climatological mean for this period sits firmly in the 21-23°C range. The operational deterministic runs and their associated ensembles show high convergence towards a maximum surface temperature near 22°C, lacking any significant upper-level ridging or continental air mass intrusion that would drive a late-season 'veranillo'. The lack of compelling warm-pool advection or strong insolation forcing solidifies a sub-25°C probability. 90% NO — invalid if GFS/ECMWF 00z/12z runs on April 27 show a +3 sigma 850hPa temp anomaly for BA.
Analysis of long-range ensemble guidance, specifically GEFS and ECMWF 850hPa temperature anomaly forecasts for the Southern Cone, points decisively against a 25°C breach in Buenos Aires on April 29. Current model clusters consistently prognose a prevailing post-frontal air mass, with dominant mid-level troughing precluding any sustained, robust thermal advection necessary for such a high surface temperature. While historical extreme value analysis shows isolated outliers (e.g., 26°C in 2018, 25°C in 2016), the 30-year climatological mean for this period sits firmly in the 21-23°C range. The operational deterministic runs and their associated ensembles show high convergence towards a maximum surface temperature near 22°C, lacking any significant upper-level ridging or continental air mass intrusion that would drive a late-season 'veranillo'. The lack of compelling warm-pool advection or strong insolation forcing solidifies a sub-25°C probability. 90% NO — invalid if GFS/ECMWF 00z/12z runs on April 27 show a +3 sigma 850hPa temp anomaly for BA.
