Canada: Severe weather forecast across parts of far southeastern Ontario and southern Quebec Aug. 19

Thunderstorms and heavy rainfall are forecast across parts of southeastern Ontario and southern Quebec Aug. 19. Strong wind gusts, lightning, and hail may accompany storms. Heavy downpours have been ongoing in the area overnight Aug. 18-19 and are will probably taper off throughout the morning of Aug. 19, though they may linger in some areas. Additional rainfall totals of around 3 cm (1.2 inches) are likely early Aug. 19, bringing overnight totals to around 4-5 cm (1.6-2 inches). The downpours may trigger flooding in low-lying areas and ponding on road surfaces.

Environment Canada has issued red heavy rainfall warnings (the highest level on a three-tier scale) across the affected areas in Ontario and all areas west of the St. Lawrence River in the affected areas in Quebec, with the exception of Montreal. Grey special weather statements are in place for the rest of the affected areas in Montreal east of the St Lawrence River and for Montreal. 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 heavy rain has saturated the soil. Disruptions to electricity and telecommunications services are possible where significant flooding, landslides, or strong winds impact utility networks.

Floodwaters and debris flows could 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 regional airports, 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 with heavy rainfall and potential track inundation. Localized business disruptions may occur in low-lying areas.