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The forecast of the European model ECMWF indicates that Brazil will face a week of simultaneous extreme thermal events: in the South, temperatures may drop to 12°C below average with minimums close to 0°C and risk of frost, while São Paulo, Rio de Janeiro, Goiás, and Mato Grosso may register maximums of 38°C with anomalies of up to 9°C above normal. Tuesday (28) will be the coldest day in the South, and the contrast is expected to last until mid-May.
The forecast for this week paints a Brazil literally split in half by the climate. A mass of cold air moving over the South since Sunday (26) will drop the temperatures to 12°C below the average in Rio Grande do Sul, while a bubble of warm air parked over the central-eastern part of the country pushes thermometers close to 40°C in São Paulo, Rio de Janeiro, Goiás, and Mato Grosso. The extreme forecast index from the ECMWF model confirms that both the cold and the heat this week are unusual events for the period.
The thermal contrast is so intense that Brazil can have negative temperatures and close to 40°C on the same day. On Tuesday (28), while the dawn in Rio Grande do Sul records minimums between 0°C and 4°C with risk of frost, the afternoon in Goiás and the interior of São Paulo may exceed 36°C. The difference of almost 40 degrees between the coldest and hottest regions of the country constitutes an episode of continental thermal amplitude that requires distinct alerts for each part of the territory.
The extreme cold that brings temperatures 12°C below average in the South
According to information released by the Meteored portal, Tuesday (28) will be the coldest day of the week in the South region. The minimums in Rio Grande do Sul are expected to be between 3°C and 4°C according to the ECMWF model, but clear sky conditions and calm winds may lead surface temperatures to 0°C or negative values. The absence of clouds favors the loss of heat by radiation, a phenomenon that can reduce soil temperature by up to 5°C compared to the air, increasing the risk of frost formation.
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In Santa Catarina, the minimums will be up to 10°C below the average, with nights below 10°C in much of the state. The maximums on Tuesday will also be cold: between 15°C and 17°C in the southern half of Rio Grande do Sul and in the eastern regions of Santa Catarina and Paraná, values that normally only appear at the height of winter. The intense cold is expected to keep minimums below 10°C in the South region until at least Friday (1st), although starting Wednesday, the lower temperatures will be restricted to Rio Grande do Sul and the Serra Catarinense.
The heat of up to 38°C that bakes the Midwest and Southeast at the same time
While the South freezes, the center of Brazil experiences the opposite scenario. In the lead of the cold front, a phenomenon called warm advection occurs that favors the rise in temperatures before the arrival of cold air, pushing thermometers to extreme levels. On Wednesday (29), the interior of São Paulo may register maximums of 36°C, a value that represents 6°C above the average for the period.
In the state of Rio de Janeiro, the anomalies expected for Wednesday reach impressive 9°C above the average during the afternoon, which means maximums that may approach or exceed 35°C. On Friday (1st), the heat intensifies even more: Mato Grosso, Mato Grosso do Sul, Goiás, Tocantins, and Piauí may hit 38°C or more, configuring an extreme heat event that coincides with the persistence of cold in the South of the country.
What explains two climatic extremes happening at the same time
The mechanism is meteorological, not coincidental. The same cold front that transports icy air to the South generates, in its lead, a flow of warm winds that heats the center of Brazil before its passage. It’s like an atmospheric sandwich: behind the front, polar air drops the temperatures; ahead of it, northern winds pull warm and dry air that raises the thermometers well above normal.
The hot air bubble acting over central-eastern Brazil intensifies precisely because the frontal system compresses the warm air against the central region. The result is a week where temperature anomalies are extreme in both directions: 12°C below the average in the South and up to 9°C above in the Southeast. The pattern, according to ECMWF, should remain until the week between May 11 and 18, with a forecast of weekly anomalies of up to 6°C in both directions.
What to expect day by day in the South, Southeast, and Central-West
On Monday (27), the cold begins to advance through Rio Grande do Sul with a significant drop in temperatures at night. On Tuesday (28), the most extreme day, minimums reach 0°C to 4°C in the South while maximums already exceed 33°C in São Paulo and Goiás. On Wednesday (29), the cold remains in the South with minimums of 5°C to 8°C, but maximums already begin to rise above 20°C in most cities in Rio Grande do Sul.
In the Southeast and Central-West, the heat progressively intensifies. On Thursday (30), Mato Grosso and Goiás already record maximums close to 37°C, and on Friday (1st) thermometers may reach or exceed 38°C in Mato Grosso, Mato Grosso do Sul, Goiás, Tocantins, and Piauí. In Paraná, the cold front causes a drop in temperatures between Wednesday and Thursday, with minimums of 13°C on Thursday morning.
How to prepare for a week of extremes in each region
For those in the South, the recommendation is the same as for a winter cold wave: adequate warm clothing, attention to the elderly and homeless people, protection of agricultural crops against frost, and care for hypothermia on Tuesday and Wednesday mornings. Rural producers in Rio Grande do Sul should monitor the forecast hour by hour because the difference between frost and just intense cold can be determined by local wind conditions and cloud cover.
In the Southeast and Central-West, extreme heat requires constant hydration, avoiding sun exposure between 10 AM and 4 PM, and attention to relative humidity, which can drop below 30% in inland areas. The forecast indicates that the thermal contrast pattern may extend for at least two more weeks, meaning Brazil will not have quick relief from either the southern cold or the heat in the center of the country.
Are you in the cold South or the hot Southeast this week? Tell us in the comments what the temperature is in your city and if you prefer to face the risk of frost or the 38 degrees in central Brazil.
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