Flood Forecasting and Warning Program

Weather Situation

A series of low pressure systems and unsettled weather conditions are set to dominate the weather conditions in the province for Saturday, Sunday into Monday. Primary concerns are widespread scattered rainfall, heavy sometimes locally for northwest Ontario and southern Ontario in these coming days.

On Saturday there is a forecast of 10 to 20 mm of rainfall for southwest Ontario plus an additional risk of 10 to 25 mm of rain in the form of isolated thunderstorm for the region. Similarly in the northwest of the Province there is a risk of 20 to 30 mm of widespread rainfall plus an additional 10 to 25 mm in the form of thunderstorms.

For Sunday, the southern region could see an additional 10 to 20 mm of widespread rainfall with the higher values forecast for regions to the south of Georgian Bay and in the Ottawa River Region. There is a risk of additional rainfall due to thunderstorms for locations anywhere in the southern region. The exact track and timing of these rainfall events are still unclear at this time.

For Monday unsettled weather conditions will continue to dominate weather conditions in the south and in the northwest which could bring additional widespread rainfall accompanied with thunderstorms in the regions.

Cumulative 5 day rainfall totals for northwest not including thunderstorm could be 30+mm but the number could be higher locally due to thunderstorms in any or all of these coming days. Similarly in the southeast and southwest cumulative 5 day rainfall not including thunderstorms could be 45 and 35 mm respectively. Additional rainfall in the form of thunderstorms in any or all of these days could result in higher numbers locally.

Risks

NOTE: Lake Ontario and Lake Erie levels continue to be elevated and are forecast to remain so for all of the month of July. See our Special Lake Ontario Flood Watch for more information at www.ontario.ca/flooding.

Stream flow and levels are moderately high in northwest Ontario due to recent rainfall in the region. Similarly stream flow and reservoir levels are moderately elevated for this time of year due to recent rainfall in the Southern region. Recent rainfall and active weather in the region have reduced the capacity of soils to store additional water and thus can produce runoff more readily resulting in high water and flooding conditions locally in a short time. Short and intense storms, such as the one associated with this evolving weather system has the potential to cause increased runoff and result in localized flooding anywhere in the forecast region.

Close attention should be paid to local flood conditions reports from conservation authorities and municipalities, and as always, a close watch on meteorological conditions, including thunderstorm alerts, is recommended.

This message will be in effect until (or updated before) Monday July 24, 2017 at 5 PM.