Introduction: Increases in asthma attacks have been sporadically reported during periods of high pollen counts, particularly following thunderstorms. These phenomena are poorly documented in France. The aim of this article is to describe an episode that occurred in Nantes in June 2013. Methods: Asthma attacks are monitored in the Nantes metropolitan area based on calls to SOS Médecins. Two systems (the National Aerobiological Monitoring Network and Pollinarium Sentinelle) provide information on pollen release with local-level accuracy. Data from Météo-France and Air Pays de la Loire were used to describe the meteorological and environmental conditions in the city of Nantes. Results: On June 7, 2013, a sharp increase in calls to SOS Médecins Nantes for asthma attacks was observed starting at 9:00 p.m. From June 7 to 10, 152 calls for asthma attacks were recorded, compared to 27 over the previous four days. The Pollinarium Sentinelle in Nantes had reported the start of ryegrass pollination that same day. In the two hours preceding the surge in calls, a thunderstorm broke out, accompanied by an increase in average wind speed and two precipitation peaks. Discussion: This phenomenon is linked to a mechanism whereby pollen grains break down into pollen particles, with intense and rapid dispersal caused by gusts of wind. The micronization of pollen grains allows for deeper penetration into the respiratory tract. During similar episodes in London in 1994 and Melbourne in 2016, the majority of patients had a history of allergic rhinitis. Although this phenomenon remains rare in France, recommendations for people with pollen allergies should emphasize the need to stay indoors with windows closed as a storm approaches during periods of high pollen release.