Environment Canada says thunderstorms with heavy downpours are possible Sunday.
The national weather agency has issued a special weather statement for Sarnia-Lambton.
Showers at times heavy with embedded thunderstorms are likely to affect much of southwestern Ontario Sunday night as a strong disturbance approaches from the American Midwest. Showers and thunderstorms are expected to arrive over areas near the Michigan border by early evening then quickly spread east across remaining regions.
Current indications suggest that some areas may see rainfall amounts of 30 to 40 mm by Monday morning with local amounts of near 50 mm (2 in) quite possible for locales that receive two or three thunderstorms in a row.
The public is advised to monitor future forecasts and warnings as warnings may be required or extended.