A severe thunderstorm watch issued Sunday afternoon has been upgraded to a warning for two southern Alberta areas by Environment Canada.

Brooks - Strathmore - Vulcan and Medicine Hat - Bow Island - Suffield are now under a severe thunderstorm warning.

"A warning means the storm is imminent," said CBC Calgary weather specialist Jodi Hughes. "A watch means it's possible."

The severe thunderstorm watch is still in effect for the areas of Cypress Hills Provincial Park - Foremost and Lethbridge - Taber - Milk River.

Environment Canada is warning the storms have the potential for large hail and damaging winds.

Residents in areas under a storm warning should take cover immediately.

Those in the areas still under a storm watch should monitor weather conditions and take immediate safety precautions if threatening weather approaches.