A low pressure trough is expected to cross Southern Ontario early Wednesday. Scattered thunderstorms are expected to develop ahead of the trough overnight.
There is the risk that a few of these storms could be locally severe with torrential downpours and damaging winds.
Environment Canada will monitor this situation closely.
Meanwhile a severe thunderstorm watch is in effect for areas near the Michigan border with the main threat being torrential downpours.
This special weather statement is in effect for: London, Middlesex, Simcoe, Delhi, Norfolk, Dunnville, Caledonia, Haldimand, Oxford, Brant, Niagara, Hamilton, Waterloo, Kitchener, Cambridge, Paris, Tillsonburg, Port Dover, Woodstock, Ingersoll, Norwich, Six Nations.