Marek Kučera 
🌎 South America: From a Cold Autumn to a Warm Start to Winter
June 2025 Weather Highlights
As the Southern Hemisphere moved from autumn into winter, South America has experienced a dramatic temperature reversal. After a notably cold end to autumn, winter began with anomalously warm temperatures—from the windswept plains of Patagonia to the tropical Amazon basin.
🔥 Tropical Heat Surges in Bolivia
- On June 10, 2025, the Bolivian town of Riberalta recorded a scorching 35.6°C.
- This reading was just 0.1°C below the all-time national June record for the location, making it one of the hottest June days in Bolivian history.
- Located in the northern lowlands near the Amazon, Riberalta is prone to heat surges, but this level of warmth is exceptional for the start of winter.
🌡️ 30–36°C Across Tropical South America
- Temperatures soared above 30°C across large swathes of Brazil, Paraguay, Bolivia, and Peru.
- Isolated stations even measured 36°C, more typical of summer months.
- These temperatures are 5–10°C above seasonal norms, indicating a strong warm anomaly.
🧊 Contrasting Patagonia: Warm, Not Cold
- Southern regions like Patagonia, which typically plunge into freezing temperatures by early June, are also experiencing milder than usual winter starts.
- Daytime highs in parts of southern Argentina and Chile have exceeded 20°C, highly unusual for this latitude and season.
🌍 Meteorological Explanation
- The warmth is linked to upper-level ridging, a pattern of high pressure that brings:
- Sinking air, which compresses and heats.
- Clear skies and strong solar radiation during the day.
- Reduced cold air advection from the Antarctic region.
- The situation may be influenced by climate variability (e.g. ENSO, jet stream anomalies), and possibly delayed onset of typical winter fronts.
⚠️ Implications
- Early warmth may disrupt seasonal agriculture, especially for crops that depend on cooler temperatures.
- Fire risks in dry tropical zones could increase due to heat and dryness.
- Continued monitoring is needed to determine if this warmth is temporary or part of a broader winter pattern shift.
Illustration picture: https://carta.guide/i/riberalta/-66.07515,-10.997337,13?r
Marek Sadowski