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Live forecasts update automatically; written guidance last reviewed 16 June 2026 by the Civic Maple Weather Desk. Data from Environment and Climate Change Canada and other national met services via Open-Meteo.
Live data from Open-Meteo · updates automatically ·
For a 21-day outlook on Montreal weather, the live forecast above provides the most current trend. Expect typical spring variability: cool mornings, mild afternoons, and a mix of sun and showers as the season progresses.
What does a 21-day forecast for Montreal actually tell you?
Beyond 10 days, forecast accuracy drops significantly. A 21-day outlook shows general patterns—temperature averages, precipitation chances, and storm tracks—not exact daily highs or lows. Use it for trip planning, not packing details. For hourly details in that window, check our 10-day forecast closer to the date.
How does Montreal’s spring weather behave over three weeks?
Montreal’s spring is unpredictable. Early in the 21-day period, lingering winter chill often brings frost and occasional snow flurries. By week two or three, daytime highs climb into the low to mid-teens Celsius. Rain becomes more frequent, and the risk of a late-winter storm fades slowly. This pattern matches what you’d see in a 30-day outlook but with slightly sharper day-to-day shifts.
Frequently asked questions about Montreal 21-day weather
Is a 21-day forecast accurate enough to plan an outdoor event?
For outdoor events, rely on the 7-day window. The 21-day forecast gives a general sense of temperature and rain trends, but day-to-day accuracy falls sharply after day 10.
Where can I see hourly data for Montreal over 21 days?
Most services, including the live forecast above, only provide hourly details for the first 48 hours. For 21-day hourly estimates, check specialized tools like The Weather Network – but treat hour-by-hour predictions beyond day 3 with caution.
How does AccuWeather’s 21-day forecast for Montreal compare?
AccuWeather and other private providers often use proprietary models, but their 21-day outlooks share the same limits as government forecasts. For official Canadian data, Environment Canada remains the most reliable source.
Sources
For broader Canadian forecasts, visit our Canada weather hub or get a closer look at Toronto weather and Ottawa weather. If you need more lead time, try our 30-day forecast.