Storms of heavy rain and hail advance and bring damage

Hail fell in large quantities in Ijuí and caused damage in the municipality | Karin Franco

Storms wreak havoc in Rio Grande do Sul as a result of the formation of a hot front over the state of Rio Grande do Sul. The storms, as it was warned since the end of last week by MetSul, bring hail that in some points can be of medium to large size. There is also a record of heavy to intense rain in part of the state, which is accompanied by many rays.

The atmospheric dynamics that lead to storms in Rio Grande do Sul involve a very hot air mass that advances through the Northeast of Argentina and Paraguay to the South of Brazil with a low thermal pressure center in the North of Argentina. Asunción, capital of Paraguay, registered heat of 28ºC at six o’clock this Tuesday morning.

Warm front, which occurs when a hot air mass advances over a cold one, which makes it a common phenomenon in winter, usually brings heavy rain, lots of lightning and hail. This is the scenario expected for this Tuesday. Rio Grande do Sul will have huge lightning frequency today and many cloud-to-ground with intense thunderstorms, which makes it very dangerous to be outdoors. The warm air that enters at altitude is the energy for the formation of thunderstorms and, with the atmosphere very heated, there will be many storms and singly strong to severe.

Medium to large hail in Ijuí | Carlos Kist

With the formation of the hot front in recent hours, storms hit several areas of the state. The first occurrences of hail took place during the afternoon of Monday in São Borja, on the West Frontier. Residents described it as the largest hailstorm in the city in years.

At night, on Monday, strong storms of hail with larger diameter ice rocks hit municipalities in the Northwest and Alto Jacuí. Hundreds of houses ended up unroofed by the hailstorm that hit the municipality of Ijuí, which led the Civil Defense to distribute tarpaulins to the affected population.

At dawn this Tuesday, intense rain accompanied by a lot of hail hit the area of ​​Livramento and Rivera, in the border region with Uruguay. The local authorities of firefighters and Civil Defense attended to floods, localized floods and some roofing due to the strong storm that hit the cities at two in the morning.

Late in the morning and early this Tuesday morning, the most intense instability was concentrated over the west of Rio Grande do Sul. Satellite images of the temperature of the tops of the clouds showed tops as low as -70ºC, which means the presence of clouds extremely loaded with huge vertical development of the Cumulonimbus type. These clouds are capable of pouring huge amounts of rain in a short period, bringing many rays and even causing hail and strong winds.

Satellite image at 6 am this Tuesday with very intense instability in the west of Rio Grande do Sul | NOAA

The tendency is for the strongest instability in the West to move during the morning and afternoon of this Thursday towards the Center, South and East of Rio Grande do Sul with heavy to torrential rain, many rays and even strong gusts locally to intense winds with hailstorms of varying sizes. These regions can register accumulations in some cities of 30mm to 50mm per hour and totals today of up to 100mm to 200mm at some points. As a result, the risk of flooding, flooding and overflowing rivers and streams is high.

The areas at greatest risk of severe weather this Tuesday in Rio Grande do Sul are part of the West, the Campanha, the Center of the State, the South of Rio Grande do Sul, the valleys, and the East of the State which includes Greater Porto Alegre, the Coast and the Serra Gaúcha.

The Capital and the metropolitan region are thus included in the zone of greatest meteorological risk with the possibility of heavy rain and storms of wind and hail with a lot of lightning. The light rain at dawn in Porto Alegre tends to intensify throughout the day with many thunderstorms.

In the Northwest and North of Rio Grande do Sul, on the contrary, which will be under the influence of very hot air north of the hot front, the sun will appear with clouds during part of this holiday and the day will be very hot with excessive sweltering, which does not allow for ward off isolated rain or hail with some clouds located more heavily, but in the overwhelming majority of municipalities in these regions rain only arrives on the fourth with a cold front.

Since the hot front retreats to the South with the deepening of a low pressure center in Buenos Aires that will give rise to a cyclone, between the afternoon and evening there may be moments of improvement in points in the West, Center and Northeast of the State. In some municipalities that started this Tuesday with rain, it is not ruled out that the sun appears in the middle or late afternoon with a lot of suffocation and excessive humidity on surfaces such as floors, walls and tiles.

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Tomorrow, an extratropical cyclone forms in the Buenos Aires region and will give rise to a cold front. The hot front between Uruguay and Rio Grande do Sul becomes cold as it starts to be driven no longer by hot air but by cold air and crosses the state of Rio Grande do Sul during the day with rain and storms, with the risk strong wind the biggest concern. In the West and South, rain can be heavy at the beginning of Wednesday.