In Brittany, what is the historic record for rain falling in a single day?

The Breton record, and even for the entire west of France according to Météo France, for rain falling in a single day, dates back to September 17, 1929 and an exceptional storm which swept across the entire north of Brittany, on a line going from from Saint-Brieuc (Côtes-d’Armor) to Cancale (Ille-et-Vilaine).

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For a long time, they believed it was an error as the volumes of precipitation recorded seemed out of the norm. 246 mm of rain, or 246 liters of water per m² in 24 hours. This absolute record in the known weather history of Brittany dates back to September 17, 1929, in Saint-Malo (Ille-et-Vilaine). In reality, it is the entire north of Brittany, on a line going from Saint-Brieuc (Côtes-d’Armor) to Cancale (Ille-et-Vilaine), which was swept away by these torrential rains. The event is so exceptional…