Environment and Climate Change Canada issued a weather warning for a large chunk of southern Ontario, warning that a rare mid-May hard freeze and potentially damaging frost could affect plants, trees and crops. The advisory told people to cover up plants, especially in frost-prone areas.
Temperatures from London to Guelph could fall to as low as -3 C or -4 C during early Tuesday morning. By Monday night, the centre of a high-pressure system with the lightest winds was expected to cross southern Ontario, and winds in the pre-dawn hours on Tuesday were forecast to be about 5 km/h.
Toronto and the GTA
Highs on Monday were expected to reach 10 C to 12 C in the Greater Toronto Area, while temperatures in the traditional snowbelts were expected to stay in the single digits. Pearson International Airport normally sees its last freezing temperature around April 27, and there have been about 27 instances on record of freezing or below after May 12.
The forecast puts this cold stretch late enough in the season to stand out at Pearson and in London. If London drops to -4 C, it would be one of the coldest temperatures on record that late in spring.
May 2020 Cold Snap
May 2020 brought a severe cold snap across the region, with temperatures falling close to -5 C at Pearson on May 9, 2020. In Timmins, temperatures fell below -10 C on May 5, 2020.
That past spell gives a reference point for the current forecast, but the advisory now focuses on a narrower risk: overnight frost and a hard freeze reaching parts of southern Ontario before sunrise Tuesday. People with gardens, trees and crops in exposed areas were told to protect them before the coldest hours arrive.
