OTTAWA -- The coldest September 18 in Ottawa in history is in the forecast, as a stretch of near freezing overnight lows begins in Ottawa.

Environment Canada's forecast calls a clear night with a low of plus 1C. 

The record for coldest Sept. 18 in Ottawa history is 1.1C, set back in 1943.

This would also be the coldest night in Ottawa since June, when the temperature dropped to 0.7C on June 1.

Environment Canada has issued a frost advisory for Ottawa and eastern Ontario.

"Patchy frost is expected tonight into Friday morning as temperatures drop to near or just below the freezing mark. Temperatures are expected to drop well below the freezing mark Friday night and widespread frost is expected."

Here is a look at the forecast for the final few days of summer.

Tonight: Clear. Low plus 1 with the risk of frost.

Friday: Sunny. High 13C

Friday night: Clear. Low 0C

Saturday: Sunny. High 13C

Sunday: Sunny: High 15C.

The Environment Canada forecast calls for overnight lows hovering around freezing until Monday.