According to historical weather records, cool mornings with frost can occur well into June across the Northland. The graphic to the left shows average dates across Minnesota that is considered the last frost dates. After these dates, the probability of a morning frost decreases rapidly, but is still possible.
The lastest date that the Duluth National Weather Service Office recorded a freezing temperature was the morning of June 21st, 1992 with a temperature of 30 F. The International Falls Airport recrded a morning temperature of 29 F on June 23rd, 2004. However, in 1911 when unoffical weather observations were taken in International Falls, a morning low temperature of 32 F was reached on July 11th, 1911.
The charts below show two particulary cold Junes- 1972 and 1992. They contained record cold temperatures.