Meteorological Piracicaba/October 11, 2024 Bow Echo
On the evening of October 11, 2024, the city of Piracicaba was impacted by an arc-shaped storm, characterized as a bow echo. The event, which occurred in the midst of a severe weather wave that affected the state of São Paulo, had wind gusts of up to 84.2 km/h recorded by the Brazilian National Institute of Meteorology (INMET), heavy rain and small, localized hail. This study analyzes the meteorological factors that led to the formation of the storm, its chronology and characteristics.
Formation of the Storm
The sequence of events that culminated in the storm of October 11, 2024 began on October 9, when Piracicaba began to experience a combination of meteorological factors. The entry of a cold front, an area of low pressure coming from Paraguay, the persistence of heat, most humid air and the formation of an atmospheric trough contributed to an environment conducive to atmospheric instability. The rains that occurred on October 10 raised the humidity of the air, setting the stage for convective development.
On the 11th, the entry of a cold front associated with an extratropical cyclone met with the heat air mass, whose temperature reached 31°C, and the accumulated humidity in the region. In the afternoon, several convective cells began to form in the state of São Paulo due to thermodynamic instability, driven by a jet stream at low levels of the atmosphere and the entry of an atmospheric trough.
Chronology and Characteristics of the Storm
The storm began to intensify as the cold front's squall line advanced, reinforcing convective cells and forming mesoscale convective complexes (CCM). Around 6 pm, an arc-shaped storm formed west of Piracicaba, moving towards the city.
At 7:10 pm. The storm began to affect Piracicaba, bringing intense winds and heavy rain. At 7:15 pm, the city was under the influence of the gust front, with the intensification of precipitation. At 7:22 pm, small hail began to be reported in parts of the city, lasting approximately three minutes. The hailstones fell irregularly and in sequence, coinciding with the intensity of the rain, while the storm's downdrafts pushed the hail toward the ground.
At 7:30 pm, the storm ended, with wind gusts reaching 84.2 km/h and total precipitation of 6 mm, according to data from the INMET station. The hail was an isolated phenomenon, as Piracicaba was the only city in the state of São Paulo to register the occurrence at that time.
Features of a bow echo
The storm exhibited typical bow echo features, including the curved echo, strong and sudden winds, hail, and radar behavior. Although the storm line was initially nearly straight, it curved as it moved.