Cold front brings September’s first major weather change

A cold front will change the weather in the south of Brazil between today and tomorrow with rain in most of the region and that should reach the south and east of São Paulo on Saturday. The frontal system precedes a new mass of cold air, the second to reach the south of the country, which will bring a drop in temperature later this week.

The sun appeared throughout Rio Grande do Sul during the morning of this Thursday, but the clouds increase throughout the day in the state. Areas of instability begin to enter the region of Uruguaiana and bring rain from afternoon to night in cities in the West, Center and South of Rio Grande do Sul.

There will be thunderstorms and isolated points may have strong blows, not ruling out very localized hail. In the other regions, firm weather marks this Thursday and the rain won’t arrive until tomorrow, as in Porto Alegre, da Serra, Aparados da Serra and the North Coast, in the northeast sector of the state’s territory.

The cold front advances through Rio Grande do Sul throughout this Friday and brings rain to all regions in the first half of the day. Between afternoon and night, instability persists in the North Half while in the West and South of Rio Grande do Sul the weather improves with the return of the sun in several locations. In isolated points there may be passing heavy rain with lightning and thunderstorms, with isolated hail not moving away.

The frontal system, then, should advance through Santa Catarina and Paraná throughout this Friday and even part of Saturday with increased cloudiness and rain, but it will be irregular and, for example, should not reach all municipalities in Paraná.

The cold front arrives in the state of São Paulo, where it should influence the weather more in the south and east of São Paulo at the end of the week. Therefore, the weather becomes unstable with rain in the city of São Paulo on Saturday with increased cloud cover and a chance of precipitation later in the evening.

Volumes of rain and storms

The volumes of rain in the passage of this cold front through southern Brazil should not be high in most locations. Data from meteorological models indicate that in most municipalities in Rio Grande do Sul, the accumulated precipitation should be between 15 mm and 30 mm with marks from 30 mm to 50 mm, occasionally higher, more localized.

The map above shows the projection of accumulated rainfall up to 9 pm on Saturday from MetSul’s high resolution WRF weather model. There is a tendency to rain more in Rio Grande do Sul and Santa Catarina with low accumulated in most of Paraná, where in many cities further north of Paraná it would not rain.

Similar rainfall distribution scenario, albeit with different volumes, is designed by the German weather model Icon, in the map above. The German model also concentrates the highest volumes of rain in the states of Rio Grande do Sul and Paraná, with little rainfall further north in the state of Paraná. Both do not indicate much rain until the end of Saturday in the south and east of São Paulo.

The data do not suggest a more generalized risk of severe weather in the passage of this front, which is always a concern when dealing with frontal systems in the climatic spring, a period of the year with high incidence of severe weather. Thunderstorms can occur, but if they do, they will be too isolated and more with hail, especially small ones.

Rain precedes incursion of cold air

A cold air mass advances in the rear of the cold front, but it will not be as intense as the one that arrived last Sunday. The drop in temperature will already be felt in many cities in Rio Grande do Sul at the end of Friday, when the minimum of the day occurs and the feeling will be cold. It will be on Saturday, however, that the cooling will be more generalized in the Gaucho territory and tends to accentuate.

With the arrival of cold air, the weather improves in much of Rio Grande do Sul on Saturday, but there will still be more cloudiness with light rain or drizzle in the south and east of the state, especially in the first half of the day, with improvement later. Sunday should have more open weather in Rio Grande do Sul, with a high pressure center associated with the cold air mass positioned over Rio Grande do Sul.

How to consult the maps

All the rain maps in this bulletin, and others of temperature, hail risk, wind, humidity, atmospheric pressure, frost and snow, among other variables, can be consulted at any time by our subscriber at maps section. Model projections update two to four times a day, according to each simulation. In the maps section, it is also possible to consult MetSul’s very high resolution WRF model.

The article is in Portuguese

Tags: Cold front brings Septembers major weather change

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