The risk of thunderstorms stretch from late Wednesday afternoon straight into Tuesday.
By 9:30 a.m., Environment and Climate Change Canada had issued yellow severe thunderstorm watches that barely skirted Montreal Island.
The South Shore, Laurentians and Lanaudière, plus areas to the north and west, are under alerts.
Meanwhile, the high will be 24 C with a humidex of 30 and UV index of 5, or moderate. Up to 33 mm of rain is expected.
Environment and Climate Change Canada has issued severe thunderstorm watches for most of southwestern Quebec.
The pattern repeats Thursday, with a slightly elevated UV index.