Climate and Average Weather Year Round in Sarnia Canada

In Sarnia, the summers are warm; the winters are freezing, snowy, and windy; and it is partly cloudy year round. Over the course of the year, the temperature typically varies from 17°F to 80°F and is rarely below 1°F or above 89°F.

Based on the tourism score, the best time of year to visit Sarnia for warm-weather activities is from late June to early September.

The warm season lasts for 3.7 months, from May 27 to September 19, with an average daily high temperature above 70°F. The hottest month of the year in Sarnia is July, with an average high of 80°F and low of 61°F.

The cold season lasts for 3.3 months, from December 1 to March 11, with an average daily high temperature below 40°F. The coldest month of the year in Sarnia is January, with an average low of 19°F and high of 31°F.

In Sarnia, the average percentage of the sky covered by clouds experiences significant seasonal variation over the course of the year.

The clearer part of the year in Sarnia begins around May 27 and lasts for 5.2 months, ending around November 2.

The clearest month of the year in Sarnia is August, during which on average the sky is clear, mostly clear, or partly cloudy 66% of the time.

The cloudier part of the year begins around November 2 and lasts for 6.8 months, ending around May 27.

The cloudiest month of the year in Sarnia is January, during which on average the sky is overcast or mostly cloudy 66% of the time.

A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. The chance of wet days in Sarnia varies throughout the year.

The wetter season lasts 7.0 months, from March 30 to October 31, with a greater than 25% chance of a given day being a wet day. The month with the most wet days in Sarnia is June, with an average of 9.9 days with at least 0.04 inches of precipitation.

The drier season lasts 5.0 months, from October 31 to March 30. The month with the fewest wet days in Sarnia is February, with an average of 5.2 days with at least 0.04 inches of precipitation.

Among wet days, we distinguish between those that experience rain alone, snow alone, or a mixture of the two. Based on this categorization, the most common form of precipitation in Sarnia changes throughout the year.

Rain alone is the most common for 11 months, from February 17 to January 8. The month with the most days of rain alone in Sarnia is June, with an average of 9.9 days.

Snow alone is the most common for 1.3 months, from January 8 to February 17. The month with the most days of snow alone in Sarnia is January, with an average of 2.6 days.

Rainfall

To show variation within the months and not just the monthly totals, we show the rainfall accumulated over a sliding 31-day period centered around each day of the year. Sarnia experiences significant seasonal variation in monthly rainfall.

Rain falls throughout the year in Sarnia. The month with the most rain in Sarnia is September, with an average rainfall of 2.7 inches.

The month with the least rain in Sarnia is January, with an average rainfall of 0.7 inches.

Snowfall

As with rainfall, we consider the snowfall accumulated over a sliding 31-day period centered around each day of the year. Sarnia experiences significant seasonal variation in monthly snowfall.

The snowy period of the year lasts for 4.7 months, from November 17 to April 7, with a sliding 31-day snowfall of at least 1.0 inches. The month with the most snow in Sarnia is February, with an average snowfall of 5.1 inches.

The snowless period of the year lasts for 7.3 months, from April 7 to November 17. The least snow falls around July 27, with an average total accumulation of 0.0 inches.

The length of the day in Sarnia varies significantly over the course of the year. In 2024, the shortest day is December 21, with 9 hours, 0 minutes of daylight; the longest day is June 20, with 15 hours, 22 minutes of daylight.

The earliest sunrise is at 5:49 AM on June 14, and the latest sunrise is 2 hours, 16 minutes later at 8:06 AM on November 2. The earliest sunset is at 4:54 PM on December 7, and the latest sunset is 4 hours, 18 minutes later at 9:12 PM on June 26.

Daylight saving time (DST) is observed in Sarnia during 2024, starting in the spring on March 10, lasting 7.8 months, and ending in the fall on November 3.

The figure below presents a compact representation of key lunar data for 2024. The horizontal axis is the day, the vertical axis is the hour of the day, and the colored areas indicate when the moon is above the horizon. The vertical gray bars (new Moons) and blue bars (full Moons) indicate key Moon phases.

We base the humidity comfort level on the dew point, as it determines whether perspiration will evaporate from the skin, thereby cooling the body. Lower dew points feel drier and higher dew points feel more humid. Unlike temperature, which typically varies significantly between night and day, dew point tends to change more slowly, so while the temperature may drop at night, a muggy day is typically followed by a muggy night.

Sarnia experiences significant seasonal variation in the perceived humidity.

The muggier period of the year lasts for 3.5 months, from June 6 to September 21, during which time the comfort level is muggy, oppressive, or miserable at least 9% of the time. The month with the most muggy days in Sarnia is July, with 10.1 days that are muggy or worse.

The least muggy day of the year is February 14, when muggy conditions are essentially unheard of.

This section discusses the wide-area hourly average wind vector (speed and direction) at 10 meters above the ground. The wind experienced at any given location is highly dependent on local topography and other factors, and instantaneous wind speed and direction vary more widely than hourly averages.

The average hourly wind speed in Sarnia experiences significant seasonal variation over the course of the year.

The windier part of the year lasts for 7.0 months, from October 5 to May 6, with average wind speeds of more than 11.2 miles per hour. The windiest month of the year in Sarnia is January, with an average hourly wind speed of 13.8 miles per hour.

The calmer time of year lasts for 5.0 months, from May 6 to October 5. The calmest month of the year in Sarnia is August, with an average hourly wind speed of 8.6 miles per hour.

The predominant average hourly wind direction in Sarnia varies throughout the year.

The wind is most often from the north for 3.5 months, from March 5 to June 20 and for 1.9 weeks, from August 11 to August 24, with a peak percentage of 33% on March 30. The wind is most often from the west for 1.7 months, from June 20 to August 11 and for 5.1 months, from October 2 to March 5, with a peak percentage of 37% on July 19. The wind is most often from the south for 1.3 months, from August 24 to October 2, with a peak percentage of 32% on October 1.

Sarnia is located near a large body of water (e.g., ocean, sea, or large lake). This section reports on the wide-area average surface temperature of that water.

The average water temperature experiences significant seasonal variation over the course of the year.

The time of year with warmer water lasts for 2.9 months, from June 29 to September 26, with an average temperature above 63°F. The month of the year in Sarnia with the warmest water is August, with an average temperature of 71°F.

The time of year with cooler water lasts for 4.4 months, from December 16 to April 30, with an average temperature below 41°F. The month of the year in Sarnia with the coolest water is February, with an average temperature of 34°F.

To characterize how pleasant the weather is in Sarnia throughout the year, we compute two travel scores.

The tourism score favors clear, rainless days with perceived temperatures between 65°F and 80°F. Based on this score, the best time of year to visit Sarnia for general outdoor tourist activities is from late June to early September, with a peak score in the second week of August.

The beach/pool score favors clear, rainless days with perceived temperatures between 75°F and 90°F. Based on this score, the best time of year to visit Sarnia for hot-weather activities is from early July to mid August, with a peak score in the third week of July.

Methodology

For each hour between 8:00 AM and 9:00 PM of each day in the analysis period (1980 to 2016), independent scores are computed for perceived temperature, cloud cover, and total precipitation. Those scores are combined into a single hourly composite score, which is then aggregated into days, averaged over all the years in the analysis period, and smoothed.

Our cloud cover score is 10 for fully clear skies, falling linearly to 9 for mostly clear skies, and to 1 for fully overcast skies.

Our precipitation score, which is based on the three-hour precipitation centered on the hour in question, is 10 for no precipitation, falling linearly to 9 for trace precipitation, and to 0 for 0.04 inches of precipitation or more.

Our tourism temperature score is 0 for perceived temperatures below 50°F, rising linearly to 9 for 65°F, to 10 for 75°F, falling linearly to 9 for 80°F, and to 1 for 90°F or hotter.

Our beach/pool temperature score is 0 for perceived temperatures below 65°F, rising linearly to 9 for 75°F, to 10 for 82°F, falling linearly to 9 for 90°F, and to 1 for 100°F or hotter.

Definitions of the growing season vary throughout the world, but for the purposes of this report, we define it as the longest continuous period of non-freezing temperatures (≥ 32°F) in the year (the calendar year in the Northern Hemisphere, or from July 1 until June 30 in the Southern Hemisphere).

The growing season in Sarnia typically lasts for 5.7 months (173 days), from around April 30 to around October 19, rarely starting before April 11 or after May 20, and rarely ending before September 29 or after November 8.

Growing degree days are a measure of yearly heat accumulation used to predict plant and animal development, and defined as the integral of warmth above a base temperature, discarding any excess above a maximum temperature. In this report, we use a base of 50°F and a cap of 86°F.

Based on growing degree days alone, the first spring blooms in Sarnia should appear around April 26, only rarely appearing before April 12 or after May 9.

This section discusses the total daily incident shortwave solar energy reaching the surface of the ground over a wide area, taking full account of seasonal variations in the length of the day, the elevation of the Sun above the horizon, and absorption by clouds and other atmospheric constituents. Shortwave radiation includes visible light and ultraviolet radiation.

The average daily incident shortwave solar energy experiences extreme seasonal variation over the course of the year.

The brighter period of the year lasts for 3.5 months, from May 2 to August 19, with an average daily incident shortwave energy per square meter above 5.9 kWh. The brightest month of the year in Sarnia is June, with an average of 6.8 kWh.

The darker period of the year lasts for 3.5 months, from October 31 to February 13, with an average daily incident shortwave energy per square meter below 2.5 kWh. The darkest month of the year in Sarnia is December, with an average of 1.4 kWh.

For the purposes of this report, the geographical coordinates of Sarnia are 42.979 deg latitude, -82.404 deg longitude, and 600 ft elevation.

The topography within 2 miles of Sarnia is essentially flat, with a maximum elevation change of 46 feet and an average elevation above sea level of 593 feet. Within 10 miles is essentially flat (177 feet). Within 50 miles contains only modest variations in elevation (705 feet).

The area within 2 miles of Sarnia is covered by artificial surfaces (81%), within 10 miles by cropland (35%) and water (24%), and within 50 miles by cropland (48%) and water (25%).