August Weather in Ottawa, United States

Last updated: June 24, 2025

In Ottawa, United States, the average temperature in August is a warm 25°C (77°F). Expect a minimum temperature of 12°C (54°F) and a high of 36°C (97°F), making it a month of significant variability. During this time, precipitation averages around 120 mm (4.7 in) across 11 days, and the average humidity sits at a tropical 78%. Prepare for a dynamic climate that blends warmth with the occasional shower!

August Temperature in Ottawa

In August in Ottawa, the average temperature is 25°C (77°F). Maximum temperatures can reach 36°C (97°F), while minimums can drop to as low as 12°C (54°F). This makes it a perfect time for travelers to enjoy a variety of outdoor activities, but it's advisable to pack layers to stay comfortable throughout the day.

August Weather in Ottawa: Daily Temperature Highs, Lows, and Averages

The chart illustrates August temperature patterns in Ottawa, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In Ottawa, August typically has an average temperature of 25°C (77°F), with highs reaching up to 36°C (97°F) and lows dropping to around 12°C (54°F).

Data source: Temperature data for Ottawa generated using information from the Copernicus Climate Change Service.

August Precipitation in Ottawa

In Ottawa in August, the precipitation amount is 120 mm (4.7 in) during a span of 11 days.

August Precipitation Trends in Ottawa

The chart displays monthly precipitation patterns in Ottawa, with values for each month alongside August’s data, which is highlighted for easy comparison. It shows the amount of precipitation, providing insights into how August’s conditions compare to those of other months. In Ottawa, August typically receives around 120 mm (4.7 inches) of precipitation spread over approximately 11 days.

Data source: Precipitation data for August generated using information from the Copernicus Climate Change Service.

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Millimeters (mm) Inches (in)

August Humidity in Ottawa

In Ottawa in August, humidity is 78%. With an average temperature of 25°C (77°F), this humidity feels like walking through a warm, damp blanket, making travel feel a bit more exhausting and sticky as you navigate the sights.

August Average Humidity in Ottawa

This chart illustrates the average monthly humidity levels in Ottawa, with August’s data highlighted for easy comparison. It shows the fluctuation in humidity throughout the year, helping you understand how conditions vary by season. In August, average humidity in Ottawa is approximately 78%, offering insight into how humid the weather typically is during this month.

Data source: Humidity data for August generated using information from the Copernicus Climate Change Service.

August UV Index in Ottawa

In Ottawa in August, the maximum UV index reaches 10, which corresponds to a very high Exposure Category. With a time to burn of just 15 minutes, it's crucial to take precautions. For more detailed information, you can check the Hourly UV Index in Ottawa.

Maximum UV Index Levels in Ottawa for August

The chart shows the monthly maximum UV Index (UVI) for Ottawa in August, representing the highest UV radiation level. The UVI measures the intensity of ultraviolet radiation from the sun, indicating the potential risk of sunburn and UV-related health issues. In August, the maximum UV index in Ottawa typically reaches 10, which falls under the very high exposure category.

Data source: Ottawa August UVI data generated using information from the Copernicus Climate Change Service.

UV Risk Categories

Extreme (11+): Avoid the sun, stay in shade.
Very High (8-10): Limit sun exposure.
High (6-7): Use SPF 30+ and protective clothing.
Moderate (3-5): Midday shade recommended.
Low (0-2): No protection needed.

How August Weather in Ottawa Compares to Other Months

Weather in Ottawa varies notably across the year, with each month offering distinct climate conditions. This page compares August’s weather to other months in Ottawa, focusing on differences in temperature, rainfall, humidity, and UV levels.

This table compares monthly weather conditions in Ottawa, showing how August’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
	Temperature	Precipitation	Humidity	UV
January Weather	0°C (33°F)	56 mm (2.2 inches)	76%	moderate
February Weather	1°C (34°F)	36 mm (1.4 inches)	77%	high
March Weather	9°C (48°F)	98 mm (3.9 inches)	70%	high
April Weather	13°C (55°F)	96 mm (3.8 inches)	73%	very high
May Weather	19°C (66°F)	196 mm (7.7 inches)	82%	very high
June Weather	25°C (77°F)	109 mm (4.3 inches)	82%	extreme
July Weather	27°C (80°F)	112 mm (4.4 inches)	81%	extreme
August Weather	25°C (77°F)	120 mm (4.7 inches)	78%	very high
September Weather	22°C (73°F)	81 mm (3.2 inches)	71%	very high
October Weather	14°C (58°F)	115 mm (4.5 inches)	71%	high
November Weather	7°C (45°F)	41 mm (1.6 inches)	81%	moderate
December Weather	4°C (39°F)	33 mm (1.3 inches)	84%	moderate