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A cold air mass driven by an extratropical cyclone in the Atlantic brings the first typical winter conditions to Southern Brazil starting Sunday (26), with winds of 50 to 70 km/h and a sharp drop in temperature. MetSul Meteorologia predicts lows of 0°C to 2°C in the Serra region and frost in several regions of Rio Grande do Sul and Santa Catarina between Tuesday and Wednesday.
The first cold spell with a taste of winter in 2026 is scheduled to arrive in Southern Brazil. Starting late Sunday (26), a cold air mass will begin to enter through the West and South of Rio Grande do Sul, advancing to the other regions of the state and to Santa Catarina on Monday (27). The arrival of the cold air will be accompanied by moderate winds with gusts of 50 to 70 km/h, especially in the South and East of Rio Grande do Sul, intensifying the feeling of cold and marking a shift in the climate pattern that had been maintaining higher-than-expected temperatures.
The mechanism behind this change is a large extratropical cyclone that forms in Eastern Argentina and pushes cold air towards Brazilian territory. According to MetSul Meteorologia, this is not an intense cold air mass, as temperatures at the 850 hPa level are expected to be between 2°C and 3°C, below the threshold for more potent incursions. Still, the event will be enough to drop minimums below 5°C in several cities and cause frost in higher altitude locations, marking the first typical winter event of the season.
When the cold arrives and which days will be the coldest
The cold air mass begins to be felt late Sunday, mainly in the municipalities of Western, Central, and Southern Rio Grande do Sul. On Monday (27), the cold spreads throughout the state and reaches Santa Catarina, with winds that intensify the thermal sensation and make the day uncomfortable even under the sun. The coldest mornings are expected on Tuesday (28) and Wednesday (29), when minimums drop generally.
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The forecast indicates that Tuesday will be the coldest day of the week. Most of Rio Grande do Sul is expected to record minimums of 5°C to 10°C, with several cities marking values below 5°C, especially in higher altitude locations. The Serra do Sudeste and Campos de Cima da Serra regions may have minimums of 0°C to 2°C, and negative temperatures in isolated spots are not ruled out. In Santa Catarina, the Southern Plateau is expected to record temperatures around 0°C and even negative on Tuesday and Wednesday.
How much the temperature can drop in Porto Alegre and the metropolitan region
For Porto Alegre, the minimums on Tuesday and Wednesday are expected to be between 10°C and 11°C at the reference point of the Jardim Botânico neighborhood station. In the southernmost and easternmost neighborhoods of the capital, temperatures could drop to 8°C to 9°C, with possibly lower values in some points more exposed to the wind. The metropolitan region is expected to record minimums between 7°C and 10°C on Tuesday and Wednesday mornings.
The values may seem moderate to those accustomed to winter peaks, but the contrast with the warmth of previous days makes the perception more intense. The abrupt drop in temperature between the warm weekend and the cold Monday will require quick adaptation, especially for the elderly, children, and homeless people. The combination of strong winds on Monday with cold temperatures on subsequent mornings creates a period of thermal discomfort that deserves attention.
Where frost is expected to form in Rio Grande do Sul and Santa Catarina
Frost has the potential to affect several regions during the three coldest days of the week. Monday, Tuesday, and Wednesday present conditions for frost formation, with greater coverage on Tuesday, when the lowest minimums are expected to be more widespread. Areas with the highest probability include the Serra do Sudeste, Campos de Cima da Serra, Northern Rio Grande do Sul, and areas of the Santa Catarina Plateau.
The Greater Porto Alegre and the Northern Coast of Rio Grande do Sul are the regions with the lowest probability of frost, due to their proximity to the ocean and the influence of maritime humidity that prevents temperatures from dropping enough for the formation of ice crystals. In the Midwestern region of Santa Catarina, isolated frost cannot be ruled out, expanding the impact area of the event beyond the higher altitude locations. For rural producers, the alert is relevant: crops sensitive to cold may suffer damage if there is no adequate protection.
Why the afternoons will not be cold and how long the cold will last
Despite the cold mornings, the afternoons are expected to be mild. The maximum temperatures on Monday and Tuesday should range between 15°C and 20°C in many cities, which means that the cold is concentrated in the nighttime and early morning periods. If it were a more intense cold air mass, low temperatures would persist even during the day, but that is not the case in this episode.
The cold will also not be prolonged. The forecast indicates that starting from the afternoon of Wednesday (29), temperatures will begin to rise, and on Thursday (30), the minimums should be higher than in the previous days, although the dawn will still hold remnants of cold. The episode will last approximately three to four days, configuring a typical autumn transition that gives the South a taste of winter without the persistence that characterizes the cold waves of June and July.
What to expect in the Southeast: Will São Paulo and Rio de Janeiro feel the cold?
The short answer is no. The cold front associated with the system is expected to pass along the coast of São Paulo on Monday, but without bringing winter cold to the capital. What is expected is a drop in maximum temperatures and an increase in cloudiness and rain in the afternoons of the first half of the week, a relief from the intense heat of the weekend, but nothing compared to what the South will face.
In Rio de Janeiro, temperatures are expected to be even higher than in São Paulo, with no significant impact from the cold air mass. The episode confirms that the onset of winter in 2026 will be felt primarily in Rio Grande do Sul and Santa Catarina, with no significant advance to regions further north. For those living in the Southeast, the cold next week will be news to follow, not a reason to wear a coat.
Are you ready for the first cold of winter or are you still in shorts and flip-flops? Tell us in the comments how the weather is in your city and if you have already taken the blankets out of the closet to face next week.
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