A cold air mass of polar origin enters Rio Grande do Sul tomorrow and will bring a streak of frigid mornings and frost formation to the state through the middle of next week. The cold air will be driven by a cyclone in the South Atlantic, away from the continent, which will intensify sharply between this Friday and Saturday, pushing cold air across the interior of the continent with an anticyclone of 1,030 hPa in northeastern Argentina.
This is not a very intense polar air mass, but the very dry atmosphere with clear weather and calm winds will promote very strong overnight cooling over the next few days, bringing significantly low lows. . Low cloud cover and a calm to light wind with a dry atmosphere profile are the main conditions for a very strong cooling.
The temperature will see a sharp drop tomorrow with lows occurring later in the day, overnight, and not at dawn as usual. The sixth will end with 3ºC to 5ºC in Campanha, 5ºC in Centro Gaucho, 7ºC to 8ºC in Grande Porto Alegre, 3ºC to 5ºC in Serra, 1ºC to 3ºC in Aparados and 5ºC to 7ºC in the Middle Plateau. The thermal sensation at the end of the day on Friday will however be lower than the temperature indicated by the thermometers.
The cold air will arrive with a moderate wind and sometimes with gusts, especially in the south and east of Rio Grande do Sul. The wind tomorrow and the weekend will bring very weak wind chill. Gusts will be between 60 km/h and 80 km/h on the coast, in particular on the south coast, and, on average, between 40 km/h and 60 km/h in Porto Alegre, due to the extratropical cyclone of Atlantic Ocean and strong cold advection.
Lows below zero in many cities in Rio Grande do Sul
If it is cold enough tomorrow, a much more intense cold is expected in the early hours of Saturday, Sunday and Monday. A large number of municipalities in Rio Grande do Sul will record minimum temperatures around 0 ° C or negative over the three days and several cities are expected to have their lowest temperatures so far this year.
Lows of 4ºC to 5ºC are expected in Porto Alegre, 1ºC to 3ºC in the metropolitan area, -2ºC to 0ºC in Campanha and the Uruguayan border, down to -5ºC in Serra do Sudeste, 0ºC to 2ºC in the West and the Center, -4ºC to – 2 ºC in the Northwest Lowlands with marks around 0 ºC in most towns, -1 ºC to 1 ºC in Planalto and Serra with -4 ºC to -2 ºC in the lowlands, and negative marks in the Aparados with up to -6 ºC or -5 ºC in the lowlands of São José dos Ausentes.
On weekends, not only will the nights be freezing but the afternoons will be cold with low highs even with sunshine. Saturday and Sunday, but especially Saturday, expect low temperatures on thermometers in the afternoon, which tend to be between 11°C and 13°C in most municipalities of Rio Grande do Sul.
Although the minimums increase from Tuesday, Tuesday and Wednesday mornings will still be very cold, with frost in several cities and the possibility of negative ratings in the state. Porto Alegre can have 7ºC to 8ºC on both days while inland most towns will record lows around or below 5ºC on both days. There will still be a lot of fog early next week due to the thermal inversion.
Cold in Santa Catarina and Paraná
The cold should also be felt strongly in Santa Catarina and Paraná, where the mass of cold air begins to penetrate this Friday afternoon at night. Weekend and early week mornings are expected to be freezing in both states with negative marks in higher elevation areas and between 0°C and 5°C in many municipalities. It can drop to -6°C or -7°C at points in the Planalto Sul Catarinense and between -2°C and -3°C in the Planalto de Palmas. Marks below 10ºC are expected for Florianópolis and up to 1ºC to 3ºC in the Curitiba region, especially at dawn on Sunday, which will be the coldest.
Cools down in part of the Midwest and Southeast
The temperature will drop in the Southeast and Center-West of Brazil as the cold air advances across the interior of the continent, to the point of cooling in northern states such as Acre and Rondônia, but this will not will not be an event like May, which brought cold weather to 17 states and the Federal District, snow to the three southern states, lowest lows in May since 1977 to three capitals and frost even to the south of the Amazon and Brasilia. It was an intense and enormous mass of polar air, which was advancing through the interior of the continent and there was still a cyclone (Yakecan) on the coast of southern Brazil to push the freezing air further north than d ‘habit. This time it is cooler in south-central Mato Grosso do Sul, São Paulo and southern Minas Gerais.
The cold air mass will bring several days in a row with the formation of frost in the Center-South of Brazil. The main frost days are expected to be Saturday, Sunday and Monday with the most widespread frost in southern Brazil, mainly on Sunday and reaching more southeastern cities between Monday and Tuesday, when cloudiness will be lower. It can still freeze in parts of Mato Grosso do Sul, especially further south in the state.
The maps above show the Canadian weather model’s frost projections for south-central Brazil on Saturday, Sunday, Monday and Tuesday of next week, although some areas are still expected to freeze, especially at higher elevations in the South and Southeast, still on Wednesday and Thursday of next week.
There will be widespread frost in the early hours of the weekend and the start of the week in Rio Grande do Sul. In many places the frost is expected to be moderate to severe and in the lowlands of the highlands of southern Brazil the frost is expected to be severe to severe with frost. It can freeze in parts of Porto Alegre in the south and east areas, and in parts of Greater Porto Alegre there is a moderate to sometimes severe risk of frost, especially in rural areas.
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