noun, feminine/a.va.las/plural: avalasses
downpour, deluge, heavy rain; avalanche
“Il a mouillé une avalasse le soir.” — It rained a deluge in the evening.
Synonyms: averse, bourrasque, déluge, grosse pluie, ratatouille, rincée, saucée, avalanche
From avaler (“to swallow”) + -asse (nominal suffix), with avaler itself being from aval (“downstream area”) + -er (verbal suffix). So avalasse might literally be translated as a "movement downstream".