# Meteorological Piracicaba/December 7, 2023 Downdraft Outbreak
## Summary

On December 7, 2023, the city of Piracicaba, in southeastern Brazil, experienced a sudden and intense meteorological event characterized by a downdraft outbreak, which led to the formation of at least one significant microburst. This microburst struck the Industrial Village with wind gusts exceeding 100 km/h. This study provides a detailed analysis of this microburst, examining its formation, impact, and the resultant damage within the affected areas. By reviewing meteorological data and field observations, the study aims to contribute to a better understanding of microburst dynamics and their implications for urban areas.

## Introduction

At midday of December 7, 2023, Piracicaba was abruptly thrust into the spotlight of a severe weather phenomena. The city was struck by a sudden and vigorous downdraft outbreak, an atmospheric disturbance that ignited the formation of at least one notable microburst. This localized wind event was distinguished by its intense and destructive nature, with the Industrial Village, Rezende Village, Algodoal and Monumento Garden neighborhoods bearing the brunt of this weather phenomena, which unleashed wind gusts that surpassed 100 km/h.
Microbursts, though brief in duration, can have devastating effects on local environments due to their concentrated, high-speed winds. This study delves into the specifics of the microburst observed in Piracicaba, aiming to dissect the underlying meteorological conditions that facilitated their occurrence, assess the impact on the affected regions, and draw conclusions that could aid in forecasting.

## Causes

In 2023, Piracicaba experienced the influence of a strong El Niño event, which was a significant driver of the year's weather patterns. This climatic phenomenon contributed to an unusually high number of notable storms throughout the year, particularly in October. On September 27, 2023, the city had already witnessed a powerful microburst in its East Region, characterized by wind gusts reaching 100 km/h. This early event foreshadowed the intensity of subsequent weather disturbances.
By early December, Piracicaba was enveloped by a persistent heat and humid air mass. This, combined with the intermittent arrival of cold fronts, created conditions conducive to convective rainfall, a hallmark of summer weather in the region. These conditions persisted throughout the month, setting the stage for a heightened level of atmospheric instability. On December 7, the atmospheric instability peaked, surpassing that of any other day in the month. This pronounced instability, coupled with the pre-existing warm and humid conditions, culminated in the development of many cumulonimbi through the state of São Paulo. One caused a severe downdraft outbreak that triggered the formation of the microbursts affecting the city.

## Formation

The formation of the microbursts on December 7, 2023, was triggered by the interaction between a cold front's instability area and the persistent hot air mass that had settled over Piracicaba. As the cold front approached, it clashed with the warmer, more humid air in the region, creating an environment ripe for severe atmospheric instability.
The day began with clear skies, giving no immediate indication of the impending storm. However, by 9:50 A.M., significant vertical cloud development was observed as the warm air was rapidly lifted into the cooler upper atmosphere. This marked the initial stages of convection, with towering cumulonimbus clouds quickly forming. By 11:00 A.M., the storm system responsible for the downdrafts was fully developed, with the massive cumulonimbus clouds already advancing toward the city. The intense vertical development within these clouds set the stage for the powerful downdrafts that would soon produce the destructive microburst in the Industrial Village of Piracicaba.

## Impact

The microburst event on December 7, 2023, caused significant but localized damage in Piracicaba. The most severe impacts were observed in the Industrial Village and the Algodoal neighborhood, where wind gusts in excess of 100 km/h were recorded. At least 16 trees were uprooted, with three of them falling directly onto parked cars, causing substantial damage. The high winds ripped off the ceiling of a local gas station, which was subsequently carried away by the wind. Additionally, numerous residential buildings in the area sustained damage, with some homes having the roofs of their front torn off.
The total economic damage from the event was estimated to exceed 10,000 BRL, though this figure is likely a conservative estimate given the localized nature of the destruction. The widespread disruption caused by the storm included power outages and blocked roads. Although the damage was not catastrophic on a city-wide scale, its impact on the immediate area was nonetheless noteworthy.

## Discussion

The microburst event in Piracicaba on December 7, 2023, exemplifies the unique risks posed by these localized severe weather phenomena. Despite their brevity, microbursts can produce winds strong enough to cause significant damage, particularly in urban environments where structures and trees are vulnerable to the sudden force of downdrafts.
The damage observed in the Industrial Village highlights the importance of preparedness and resilience in urban planning. In particular, the vulnerability of buildings with flat roofs or poorly secured structures must be addressed in building codes. Additionally, the ability of trees to pose a hazard when uprooted suggests that urban forestry practices should also consider the risk of microburst events.

## Conclusion

This study of the December 7, 2023, microburst in Piracicaba provides valuable insights into the dynamics of these powerful but localized weather phenomena. While the impact of this particular event was not as severe as some larger-scale storms, the damage it caused to infrastructure and the disruption it brought to the community serves as a reminder of the destructive potential of microbursts.