The national meteorological institute DMI has issued weather warnings for torrential rain and thunderstorms that will affect Jutland and Funen today.
Some places could see between 15 to 25 mm of rain in 30 minutes, including hail.
DMI warns against the risk of flooding in low-lying areas and on roadways.
Cold front from the west will hit Denmark full on on Tuesday, pushing temperatures down to 17-23 degrees.
Overcast conditions, rain showers and temperatures below 25 degrees will prevail for most of the week.