Warm front advances to the south with heavy rain and large hail

A hot front formed between Rio Grande do Sul and Uruguay this Friday with the advance of very hot air from the Northeast of Argentina to the West, Northwest and North of the state of Rio Grande do Sul. The hot front generates instability in the south and east of the state and also in Uruguay, where the heaviest clouds operate.

The advance of hot air with very heavy clouds brought rain in the last few hours to a large part of Uruguayan territory, including heavy intensity in some places. The capital Montevideo also had rain, accompanied by thunderstorms and wind.

The strongest instability due to the hot front is concentrated in the Uruguayan interior departments, where storms have been recorded since the morning with heavy rain, lots of lightning and hail in different parts this Friday.

This morning, hail storms affected several departments in Uruguay. The stones were of large size in localities in the departments of Canelones and Lavelleja. In Las Piedras, in Canelones, hail caused damage to roofs.

One of the main characteristics of warm fronts is precisely the cause of hail and hail events in a large number of cities during the winter months in Rio Grande do Sul usually occur during the action of warm frontal systems.

In the next few hours and part of Saturday, Uruguay will continue with rain and storms with a front that is hot today and will become cold tomorrow. Some storms can be locally strong to severe with intense rain, lots of lightning, hail and localized gales.

Warm front generates huge contrast in Rio Grande do Sul

The satellite image at 1pm today showed many clouds, some quite heavy, following the hot front, over the South and East of Rio Grande do Sul. In these regions it was raining in several places and even locally heavily with thunderstorms. In the West, Northwest and North of the state, the sun appeared in very clear weather.

O warm, drier air it enters from the West and Northwest, which means that these areas with open weather were recording temperatures between 31ºC and 34ºC in several cities. In contrast, in the South and East of Rio Grande do Sul, under clouds and instability, it was between 21ºC and 24ºC in most locations in the early afternoon, or 10ºC less.

Tomorrow, Saturday, the front will be over Uruguay and the extreme south of Rio Grande do Sul at the beginning of the day causing rain, locally heavy, and isolated thunderstorms. It turns out that it will no longer be moved by hot air and will start being driven by colder air that will advance through Argentina.

As a result, the warm front will stop being hot and become cold, moving north. It rains first with thunderstorms in the West and South and then in most regions of Rio Grande do Sul, where part of Saturday will be sunny and very hot before the arrival of the cold front with rain and the risk of isolated thunderstorms.

Hail is a sign of warm fronts

Unlike a cold front, which is driven by cold air, a warm front has its movement dictated by the advance of warm air. Therefore, its movement in the state is from North to South, unlike cold frontal systems that advance from South to North. This is also why after the passage of the warm front it heats up a lot, unlike the cold front which brings a drop in temperature.

Warm fronts traditionally occur in autumn and winter, especially in June, and usually bring locally heavy to intense rain, lots of lightning and hail. Although isolated thunderstorms with wind may occur, heavy rain, lightning and hail are more common than wind on warm fronts.

MetSul Meteorologia is on WhatsApp channels. Subscribe here to access the channel in the messaging app and receive forecasts, alerts and information about the most important events in the weather and climate in Brazil and around the world, with exclusive data and information from our team of meteorologists.