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Weather & Climate in St. Marys, ON
Temperature, precipitation, air quality, natural hazards, and monthly weather data.
St. Marys experiences four distinct seasons with an average annual temperature of 48°F (9°C). Winters average 30°F in January while summers reach 69°F in July. The area gets 224 sunny days per year, above the national average. Annual precipitation totals 40.6 inches. The area receives 48.4 inches of snow annually, making winter weather a significant factor for residents. The city sits at an elevation of 1,070 feet.
Temperature
30°F Jan (-1°C)
69°F Jul (20°C)
| Annual Average | 48.1°F |
| 11% below US avg | |
| January Average | 30°F (-1°C) |
| July Average | 69°F (20°C) |
| Sunny Days | 224 days/yr |
Geography
| Elevation | 1,070 ft (326 m) |
| Area | 4.8 sq mi (12.4 km²) |
| Population Density | 1,538/sq mi |
| Coordinates | 43.2501°N, 81.1330°W |
| Timezone | America/Toronto |
Precipitation & Snow
Air Quality
Earthquake History
5 earthquakes (M2.5+) recorded within 150 km since 1990. Strongest on record: M3.9.
| Jan 26, 2001 | 8 km NNW of Edgewood, Ohio | M3.9 | 148 km | 5 km |
| Mar 15, 1992 | 15 km NW of North Perry, Ohio | M3.5 | 149 km | 5 km |
| Mar 28, 2005 | 16 km NW of Virgil, Canada | M2.8 | 150 km | 7 km |
| Sep 20, 2009 | 20 km ESE of Oakville, Canada | M2.6 | 138 km | 4 km |
| May 23, 2022 | 2 km NNW of Corunna, Canada | M2.5 | 114 km | 5 km |
Source: USGS Earthquake Catalog (M2.5+, 1990-2025). Sorted by magnitude.
Tsunami History
2 tsunamis recorded within 500 km. Highest wave on record: 2.7 m (9 ft).
| Year | Location | Cause | Max Wave | Deaths | Distance |
| 1823 | LAKE ERIE | Unknown | 2.7 m | - | 107 km |
| 1952 | LAKE HURON, MI | Avalanche | 1.5 m | - | 104 km |
Source: NOAA/NCEI Historical Tsunami Database.
Monthly Weather
| Month | Avg Temperature | Precipitation | Summary |
|---|---|---|---|
| January | 30°F (-1°C) | 3.2 in | |
| February | 21°F (-6°C) | 2.6 in | Coldest, Driest |
| March | 30°F (-1°C) | 2.9 in | |
| April | 42°F (6°C) | 3.2 in | |
| May | 55°F (13°C) | 3.4 in | |
| June | 64°F (18°C) | 3.2 in | |
| July | 69°F (20°C) | 3.5 in | Warmest |
| August | 67°F (19°C) | 3.5 in | |
| September | 60°F (15°C) | 4.1 in | Wettest |
| October | 48°F (9°C) | 3.5 in | |
| November | 37°F (3°C) | 4.1 in | |
| December | 26°F (-3°C) | 3.7 in |
St. Marys has a seasonal temperature swing of 48°F / from 21°F in February to 69°F in July. Total annual precipitation is 40.8 inches, with September being the wettest month (4.1") and February the driest (2.6").