This report describes the typical weather at the Ottawa Macdonald-Cartier International Airport (Ottawa, Ontario, Canada) weather station over the course of an average year. It is based on the historical records from 1977 to 2012. Earlier records are either unavailable or unreliable.
Ottawa, Ontario has a humid continental climate with warm summers and no dry season. The area within 25 mi of this station is covered by forests (73%), croplands (18%), lakes and rivers (3%), and built-up areas (3%).
Over the course of a year, the temperature typically varies from 5°F to 79°F and is rarely below -12°F or above 87°F.
The warm season lasts from May 21 to September 17 with an average daily high temperature above 68°F. The hottest day of the year is July 25, with an average high of 79°F and low of 62°F.
The cold season lasts from December 3 to March 10 with an average daily high temperature below 32°F. The coldest day of the year is January 19, with an average low of 5°F and high of 21°F.
The length of the day varies significantly over the course of the year. The shortest day is December 21 with 8:43 hours of daylight; the longest day is June 20 with 15:40 hours of daylight.
The earliest sunrise is at 5:14am on June 15 and the latest sunset is at 8:55pm on June 26. The latest sunrise is at 7:45am on November 3 and the earliest sunset is at 4:19pm on December 11.
Daylight savings time (DST) is observed in this location during 2012, starting in the spring on March 11 and ending in the fall on November 4.
The median cloud cover ranges from 67% (partly cloudy) to 95% (overcast). The sky is cloudiest on December 14 and clearest on August 13. The clearer part of the year begins around June 2. The cloudier part of the year begins around October 5.
On August 13, the clearest day of the year, the sky is clear, mostly clear, or partly cloudy 49% of the time, and overcast or mostly cloudy 50% of the time.
On December 14, the cloudiest day of the year, the sky is overcast, mostly cloudy, or partly cloudy 72% of the time, and clear or mostly clear 25% of the time.
The probability that precipitation will be observed at this location varies throughout the year. Precipitation is most likely around December 20, occurring in 78% of days. Precipitation is least likely around August 12, occurring in 46% of days.
Over the entire year, the most common forms of precipitation are light snow, light rain, moderate rain, and moderate snow.
Light snow is the most severe precipitation observed during 29% of those days with precipitation. It is most likely around January 4, when it is observed during 47% of all days.
Light rain is the most severe precipitation observed during 25% of those days with precipitation. It is most likely around May 20, when it is observed during 24% of all days.
Moderate rain is the most severe precipitation observed during 20% of those days with precipitation. It is most likely around September 27, when it is observed during 20% of all days.
Moderate snow is the most severe precipitation observed during 11% of those days with precipitation. It is most likely around December 20, when it is observed during 18% of all days.
During the warm season, which lasts from May 21 to September 17, there is a 50% average chance that precipitation will be observed at some point during a given day. When precipitation does occur it is most often in the form of light rain (39% of days with precipitation have at worst light rain), moderate rain (30%), and thunderstorms (27%).
During the cold season, which lasts from December 3 to March 10, there is a 70% average chance that precipitation will be observed at some point during a given day. When precipitation does occur it is most often in the form of light snow (59% of days with precipitation have at worst light snow), moderate snow (22%), heavy snow (7%), and light rain (6%).
The likelihood of snow falling is highest around January 3, occurring in 69% of days. The season in which it is relatively likely for snow to fall spans from October 31 to April 9.
During peak snow season, accumulation at this location on a given day is just more likely than not. The chances of there being snow on the ground are highest around January 8, occurring 65% of the time. The season in which snow is relatively likely to be on the ground spans from November 21 to April 7.
The snow is typically at its deepest on February 9, with a median depth of 11.0"; the depth exceeds 25.0" only one year out of ten.
The relative humidity typically ranges from 40% (comfortable) to 94% (very humid) over the course of the year, rarely dropping below 22% (dry) and reaching as high as 100% (very humid).
The air is driest around April 28, at which time the relative humidity drops below 49% (comfortable) three days out of four; it is most humid around September 23, exceeding 91% (very humid) three days out of four.
Dew point is often a better measure of how comfortable a person will find the weather than relative humidity because it more directly relates to whether perspiration will evaporate from the skin, thereby cooling the body. Lower dew points feel drier and higher dew points feel more humid.
Over the course of a year, the dew point typically varies from -2°F (dry) to 64°F (mildy humid) and is rarely below -22°F (dry) or above 71°F (muggy).
The time of the year between May 20 and October 2 is the most comfortable, with dew points that are neither too dry nor too muggy.
Over the course of the year typical wind speeds vary from 0 mph to 16 mph (calm to moderate breeze), rarely exceeding 23 mph (fresh breeze).
The highest average wind speed of 10 mph (gentle breeze) occurs around April 14, at which time the average daily maximum wind speed is 16 mph (moderate breeze).
The lowest average wind speed of 6 mph (light breeze) occurs around August 3, at which time the average daily maximum wind speed is 12 mph (gentle breeze).