Canada: Rainfall warnings issued across parts of southern Ontario early Aug. 5 /update 1

Heavy rainfall is forecast across parts of southern Ontario early Aug. 5. Environment Canada has issued a red rainfall warning (the highest level on a three-tier scale) across Barrie-Collingwood-Hillsdale, Hanover-Dundalk-Southern Grey County, Innisfil-New Tecumseth-Aungus, Newmarket-Georgina-Northern York Region, Owen Sound-Blue Mountains-Northern Grey County, and Shelburne-Mansfield-Northern Dufferin County forecast districts. Rainfall totals in excess of 5 cm (2 inches) within the space of an hour or two are possible across the affected area during the morning Aug. 5. Heavy downpours could cause flash floods and water pooling on roads. Localized flooding in low-lying areas is possible. Authorities will likely issue new alerts or update/rescind existing advisories as weather conditions change over the coming hours.

Sustained heavy rainfall could trigger flooding in low-lying communities near rivers, streams, and creeks. Urban flooding is also possible in developed areas with easily overwhelmed stormwater drainage systems. Sites downstream from large reservoirs or rivers may be subject to flash flooding after relatively short periods of intense rainfall. Landslides are possible in hilly or mountainous areas, especially where the soil has become saturated by heavy rainfall. Disruptions to electricity and telecommunications services are possible where significant flooding, landslides, or strong winds impact utility networks.

Floodwaters and debris flows will likely render some bridges, rail networks, or roadways impassable, impacting overland travel around affected areas. Ponding on road surfaces could cause hazardous driving conditions on regional highways. Authorities could temporarily close some low-lying routes that become inundated by floodwaters.

Severe weather could also trigger intermittent flight delays and cancellations at airports in the region though these are unlikely to be severe or prolonged. Flooding could block regional rail lines; freight and passenger train delays and cancellations are possible in areas that see heavy rainfall and potential track inundation. Localized business disruptions may occur in low-lying areas.