Fort Simpson and Yellowknife face a severe thunderstorm watch, Environment and Climate Change Canada said Wednesday afternoon.
Conditions could develop into heavy rains this afternoon and evening, it said, adding a downpour can cause flash floods and water pooling on roads.
"Lightning kills and injures Canadians every year. Remember, when thunder roars, go indoors!" the department said in its Fort Simpson release.
The warnings are typically issued when atmospheric conditions could develop into a thunderstorm with hail, strong winds and heavy rainfall.