WATCH: Frost advisory issued across southern Ontario as overnight temperatures dip below freezing

Julie Atchison has the latest forecast for southern Ontario

Temperatures are on the cold side across southern Ontario this afternoon, according to meteorologist Julie Atchison. Single-digit highs are expected in Perth, Grey and Bruce counties, while London will reach about 10 C and other areas closer to 12 C, with cool conditions persisting through the day.

Atchison says a high-pressure system will hold tonight, bringing clear skies and light winds. A frost advisory is in effect from Chatham-Kent and Sarnia through London and east toward the GTA. Lakeshore areas should remain above freezing, but inland regions could see temperatures drop enough to produce widespread frost. The overnight low in London is expected to dip to about –2 C, near the record of –3 C.

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Tuesday will begin with sunshine before clouds build in during the afternoon, Atchison says. Rain is expected to arrive later in the day and into the evening, with the potential for a few thunderstorms as a cold front moves through.

Overcast conditions are expected Wednesday, with the bulk of the rain falling from Tuesday afternoon into Wednesday. Highs will remain below seasonal averages, reaching about 13 C Tuesday and Wednesday, and 14 C Thursday. Typical highs for this time of year range from 17 to 18 C.

Atchison says frosty conditions are expected overnight, with a brief period of sunshine early Tuesday before rain moves in later in the day.