Brazilian authorities have issued alerts for heavy rain and intense cold across the South, Southeast, and Central-West regions through Thursday, May 21, 2026 [3].
This weather system poses significant risks to public safety and agriculture, as the combination of a polar air mass and a cold front increases the likelihood of hail and frost.
Defesa Civil de Belo Horizonte warned of potential rainfall between 20 and 40 millimeters [1]. These showers may be accompanied by lightning and wind gusts reaching up to 50 km/h [1]. The agency said the alerts remain active until Thursday [3].
Meteorological services, including Climatempo and INMET, identified an intense polar air mass as the primary driver of the temperature drop. The system is moving through the South and maintaining low temperatures while a cold front over the ocean sustains the risk of heavy rain [2].
While some reports indicate the weather shift began as early as May 15, the most acute alerts are concentrated on the current window ending May 21 [3]. The impact is widespread, affecting major urban centers such as São Paulo and Belo Horizonte, as well as states including Paraná and Santa Catarina [4, 5].
Officials said that the system also brings low humidity and the possibility of frost in certain areas [6]. The geographic scope of the event varies by report, with some focusing on the South and São Paulo, while others include the broader Center-South region [4, 5].
"A new polar air mass advances through the South and keeps temperatures low, while the passage of a cold front through the ocean sustains the alert for heavy rain," Climatempo said [2].
“Rainfall intensity expected between 20 and 40 millimeters”
The convergence of a polar air mass and a maritime cold front creates a volatile weather pattern that extends beyond simple temperature drops. By affecting the Center-South region—including agricultural hubs in the South and the industrial center of São Paulo—these conditions can disrupt logistics and threaten crop yields through unexpected frost and hail.
