Heavy thunderstorms, flood watch in Waterloo Region

Waterloo Region is stepping into the new week with a burst of spring warmth, but the mild spell comes packaged with a messy mix of rain, thunderstorms and a mid‑week temperature crash that will briefly pull the city back toward winter.

A yellow level severe thunderstorm warning was briefly issued around 3:30 a.m. Tuesday.

Environment Canada warned of heavy rain, frequent rain, and storms with the potential to bring nickel sized hail.

“Clusters of thunderstorms are tracking east from Michigan and Lake Huron across the region. Local rainfall amounts of 50 to 75 mm are possible in areas that receive several thunderstorms in a row.”

Forecasters say the next several days will feature dramatic swings — from near 20 C warmth to freezing rain risks — as southern Ontario rides the rollercoaster of early spring.

It prompted the Grand River Conservation Authority to issue a flood watch for the entire Grand River watershed. It blames the warmer weather and the risk of heavy rain in the next few days.

“Current forecasts indicate moderate to heavy precipitation throughout the week, with the majority expected (Tuesday), including a risk of thunderstorms,” the message reads. “While projected totals vary, most forecasts call for 50 to 60 mm of rain over the next few days.”

Low areas in the municipality could face flooding, the authority warns.

Conditions are expected to deteriorate Monday night as scattered showers develop, accompanied by a risk of thunderstorms. The low drops to 9 C, keeping the air warm enough for a soaking rain rather than anything wintry.

Tuesday is shaping up to be the most active day of the week. A surge of warm, unstable air will push temperatures to 18 C, with winds strengthening out of the southwest at 30–60 km/h. Forecasters expect 20+ mm of rain, and the risk of thunderstorms continues through the day.

This system taps into a broad plume of moisture, meaning rainfall could be locally higher in heavier downpours. The mild air hangs on into the evening before temperatures fall to 5 C overnight.

Wednesday: A transition day with a wintry twist

Wednesday brings a brief break in the action, with sunny breaks and a high near 8 C. But the calm won’t last. As colder air pushes in from the north, the region faces the risk of freezing rain or ice pellets on Wednesday evening and overnight.

This transition zone — warm air aloft, cold air at the surface — is classic early‑spring volatility. Even a short period of freezing rain could create slick conditions late Wednesday and early Thursday.

Thursday turns fully wet again, but this time with a colder, more persistent rain. Temperatures hold near 3 C, and 15–30 mm of rainfall is possible through the day. Winds shift easterly at 20–50 km/h, adding a raw, chilly feel.

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