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While the rest of Brazil was still experiencing mild autumn temperatures, the municipality of Pinheiro Machado in Rio Grande do Sul recorded the year’s lowest temperature in the state on the morning of May 19, 2026, with -4.8 °C, according to a report by meteorologist Luiz Fernando Nachtigall published by MetSul.
This marks the tenth day in May with negative temperatures in the state, more than half of the 19 days elapsed.
The statistical average for May predicts only 2 to 3 days with negative temperatures in a normal May over the last 25 years.
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The polar air comes from the Argentine Patagonia and was reinforced by an intense cold front on May 17 and 18. The 5 most affected municipalities in Rio Grande do Sul are Pinheiro Machado, Soledade, Herval, Capão Bonito do Sul, and Vacaria, all in the South or the Serra Gaúcha.
What happened in Pinheiro Machado and Soledade
The municipality of Pinheiro Machado, in the Serra do Sudeste Gaúcho, was the epicenter of the cold on May 19.
The INMET automatic station recorded -4.8 °C at 6:35 AM. The local vegetation was completely covered with white frost.
According to the state Civil Defense, 12 red alerts were issued for municipalities in the South of Rio Grande do Sul on the night of May 18.
Power was maintained in all 5 most affected cities, but consumption rose 38% above the month’s average.
In Soledade, in the Gaúcho Plateau, the temperature dropped to -4.2 °C on May 12, the second record of the month. The city is 1.1 thousand feet above sea level and records frost more frequently than the south of the state.
The municipality is among the 7 that recorded the most negative marks in May 2026.
Meanwhile, Vacaria in the Campos de Cima da Serra recorded -2.7 °C on May 13. Herval, on the border with Uruguay, marked -1.5 °C on May 4.
Capão Bonito do Sul, in the Medium Plateau, noted -2.4 °C on May 11.
The numbers that classify the event as historic
The frequency of negative lows in May places 2026 among the coldest years of the 21st century in Rio Grande do Sul.
According to historical data from INMET, the average number of days with negative marks in May over the last 25 years was only 2.3.
According to MetSul, the year 2026 already accumulates 10 days with negative lows in the state until May 19.
This number is equivalent to the total average of June plus July together in typical years.
The years 2019 and 2022 were also severe. In 2019, RS had 7 days with negative temperatures in May. In 2022, the number reached 8.
In 2026, the scenario is already worse than both in just 19 days of the month.
Meanwhile, São Paulo capital also felt the effect. On May 19, the afternoon had the coldest temperature of the year for the time from 2 PM to 5 PM.
The Lapa and Mooca stations recorded 12 °C during business hours.
Technical reveal: why the polar air of 2026 is so intense
In the background, meteorology points to 3 converging factors for the intensity of the polar air of 2026. The first is the La Niña pattern still in effect in the equatorial Pacific, which alters the polar jet of the Southern Hemisphere.
According to analysis by INMET, the second factor is the colder-than-normal Humboldt current in 2026, with 1.2 °C below the average in the South Pacific.
This intensifies the Antarctic polar mass crossing Patagonia.
The third is the increase in atmospheric pressure over the South Atlantic Ocean. When the atmospheric high is stronger than average, it acts as a “wall” and diverts the polar air to the South American continent instead of following the ocean.
Meanwhile, the pattern approaches that recorded in 1955, a year when snow fell in at least 13 cities in Rio Grande do Sul. The climatic coincidence is being monitored by the Federal University of Pelotas and the National Center for Monitoring and Alerts of Natural Disasters (Cemaden).
How the Gaúcho agriculture responds to the cold
The economic impact of the polar air begins in the field. Rio Grande do Sul produces 60% of Brazil’s grapes and 92% of the national production of fine wines.
The frosts affect both vineyards and apple plantations in the Serra.
According to Emater-RS, the current phase of the agricultural calendar favors the vineyards. In May, the plant is in physiological dormancy, and frosts of this magnitude rarely cause direct damage.
The risk increases in June when budding begins.
The apple sector is different. In Vacaria, the main apple hub in Rio Grande do Sul with 8,000 hectares cultivated, frosts of up to -5 °C in May are not harmful.
However, in August-September, during flowering, similar frosts can destroy 30% to 70% of the crop.
Above all, the Gaúcho livestock feels a direct impact. The state has 13 million cattle and 4.5 million sheep. In winters with temperatures below -3 °C for more than 5 days, the mortality of young sheep can rise up to 4%.
In 2013, more than 200,000 sheep died in severe cold waves.
Human reveal: Luiz Nachtigall and 41 years predicting Gaúcho cold
The human face of the analysis is meteorologist Luiz Fernando Nachtigall, author of MetSul.com. He graduated in meteorology from the Federal University of Pelotas in 1985 and has 41 years of career in weather forecasting.
According to the official biography, Nachtigall specialized in Aeronautical Meteorology at the Aerospace Technical Center in São José dos Campos. He worked at Ipmet of Unesp in Bauru and was a weather forecaster at the airport in Belém do Pará, at Galeão, and in Porto Alegre.
Meanwhile, MetSul Meteorologia, the company Nachtigall founded in Porto Alegre in 1992, now operates with 11 meteorologists and covers the 3 southern states, as well as Argentina and Uruguay.
The MetSul alert system reaches over 4 million people via WhatsApp and SMS.
On the other hand, the direct competitor is INMET, headquartered in Brasília with 583 automatic stations in Brazil. The federal official institute has better statistical accuracy for forecasts up to 7 days.
Above 7 days, private models usually surpass public ones in local accuracy.
What Brazil can expect in the next 2 weeks
The next polar event predicted by MetSul is a “reinforcement” arriving on May 25 to 27. This secondary corridor is expected to hit Rio Grande do Sul with temperatures close to -4 °C again.
According to MetSul, the scenario includes 4 important milestones in the next 14 days. First, thermal relief between May 21 and 24 with lows between 4 °C and 8 °C.
Second, reentry of polar air between May 25 and 27. Third, possible widespread frost in the Southeast on May 26 or 27. Fourth, next polar mass early June.
Meanwhile, the Civil Defense of São Paulo is preparing an action plan for the next wave. The goal is to open 12 additional night shelters in the 7 coldest cities of Greater SP.
The planned budget is R$ 4.3 million for the 2026 season.
Future reveal: winter 2026 may break historical records
The next step predicted by MetSul is continuous monitoring until August. The institute works with 3 probability scenarios for winter 2026. The most likely scenario (45%) projects winter 1.5 °C below average.
The second scenario (35%) predicts a normal winter. The third (20%) projects winter up to 2.5 °C below average, comparable to 1955 and 1979, years with snow in more than 10 cities in Rio Grande do Sul.
According to Cemaden, the disaster monitoring system predicts 8 to 12 severe cold waves until September. The institutional goal is to deliver alerts with 48 hours’ notice to 100% of the Brazilian urban population.
It is worth remembering the coverage of other relevant operational fronts in parallel in the mobility sector.
- Record date: May 19, 2026
- RS city with the year’s low: Pinheiro Machado, -4.8 °C
- Other affected Gaúcho cities: Soledade, Vacaria, Herval, Capão Bonito
- Days with negative temperature in May: 10 (historical average: 2.3)
- SP capital: coldest afternoon of the year on May 19
- Comparable years: 1955, 1979, 2019, 2022
- Origin: Antarctic polar air via Patagonia + cold front May 17-18
- Next polar wave: May 25-27
The points that still depend on the next wave
Despite the alert, 3 fronts still depend on the behavior of the next polar masses. The reentry of polar air predicted for May 25-27 may strain the health system in the South.
On the other hand, the reinforcement predicted for early June threatens apple flowering if it occurs with similar magnitude. Finally, INMET is still monitoring the position of the polar jet to refine forecasts from June to August.
The outcome of these variables defines the pace of the Gaúcho winter.
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