Photo: Gogerr · CC BY-SA 4.0Frosty mornings in St. Marys are scarcer than in 75% of Canadian towns
The warmest part of a July day comes in at 26.6°C on average. In July, afternoons here are warmer than in 70% of Canadian towns. Rain or snow is most frequent in September and least in February. Long walks are most pleasant from June to September, when afternoons reach 22–27°C.
ECCC publishes no normals for St. Marys itself; the figures are those of London, 25 km south.
A year in St. Marys at a glance
Each month’s typical high and low, in °C.
What stands out about St. Marys’s climate
Compared with Canadian towns, with its place among towns of 2,500+ in Ontario beside it.
What a year in St. Marys feels like
Seasons and months as ECCC’s 1991–2020 normals give them: a typical day’s high and low.
139 frost days and 128 days above 20°C a year
The frost season runs October to May, and January freezes nearly every night. About 11 days a year top 30°C.
Frost days by month
Average days at 0°C or below
Days above 20°C by month
Average days
About 962 mm of rain and snow a year
Some 128 days a year see 1 mm of rain or snow or more.
Rain and snow by month
Millimetres
152 cm of snow in a typical year
From October to April snow is likely; January is the peak, at about 43 cm.
Snowfall by month
Centimetres
Snow on the ground by month
Centimetres at month’s end
Snowfall: Strathroy-Mullifarry, 54 km away (London records no complete year of it).
Heating a home in St. Marys
92% of a year’s heating need falls between October and April. Months averaging under 10°C: October to April.
Measured against 18°C: each day’s shortfall in mean temperature, added over twelve months. That means homes here need less heating than 79% of Canadian towns.
Living with St. Marys’s climate
Gardening, time outside, winter cold and summer heat, from the 1991–2020 normals.
Frost usually lets go around 3 May and returns near 16 October, about 165 days apart.
Plan time outside for Jun, Jul, Aug and Sep: highs of 17–27°C and nights no colder than 8°C.
Parks & trails →About 18 days a year bring a wind chill under −20, when bare skin chills fast.
Humid summer days, the humidex above 30, number about 55 a year.
For the weather that does damage, from ice storms to floods, see St. Marys’s hazards page.
Flood & hazards →ECCC’s normals location: London
London is a composite: ECCC joins 3 stations’ readings to make its 1991–2020 normals.
| Distance from the town | 25 km south |
| Station altitude | 278 m |
| Completeness | meets the WMO “3 and 5” rule |
| WMO standard normals | No |
| Snowfall from | Strathroy-Mullifarry, 54 km |
| Coldest reading, 1991–2020 | −29.1°C |
| Hottest reading, 1991–2020 | 37.0°C |
| Average wind | 14.0 km/h on average, most often from the west |
| Next-nearest location | Strathroy-Mullifarry, 54 km |
How St. Marys compares
Against the 2,611 Canadian towns and neighbourhoods of 2,500 or more, each read from its own normals location; the dots are the other locations those towns use in Ontario.
Nearby towns’ climate
The nearest places on a normals location of their own: those that share St. Marys’s would only repeat its figures. No closer places have figures: these lie 31–42 km from St. Marys.
| Town | July high | January low | Rain & snow |
|---|---|---|---|
| St. Marys London | 26.6°C | −9.1°C | 962 mm |
| Exeter 31 km · Strathroy-Mullifarry | 27.3°C 0.7°C warmer | −8.5°C 0.6°C milder | 966 mm |
| Perth East 32 km · Elora | 25.4°C 1.2°C cooler | −10.7°C 1.6°C colder | 851 mm |
| Woodstock 34 km · Delhi | 27.5°C 0.9°C warmer | −8.9°C about the same | 965 mm |
| New Hamburg 42 km · Kitchener/Waterloo | 26.6°C about the same | −10.3°C 1.2°C colder | 851 mm |
St. Marys weather by month
Average daily high and low, mean temperature, rain and snow (as water) and snowfall by month, 1991–2020.
| Month | High | Low | Mean | Rain & snow | Snow |
|---|---|---|---|---|---|
| January | −1.6°C | −9.1°C | −5.4°C | 79 mm | 43 cm |
| February | −0.6°C | −9.0°C | −4.8°C | 63 mm | 32 cm |
| March | 4.6°C | −4.5°C | 0.1°C | 67 mm | 20 cm |
| April | 12.2°C | 1.4°C | 6.8°C | 89 mm | 5 cm |
| May | 19.3°C | 7.7°C | 13.5°C | 89 mm | under 1 cm |
| June | 24.4°C | 13.2°C | 18.8°C | 86 mm | 0 cm |
| July | 26.6°C | 15.3°C | 21.0°C | 81 mm | 0 cm |
| August | 25.7°C | 14.4°C | 20.1°C | 67 mm | 0 cm |
| September | 22.1°C | 10.5°C | 16.3°C | 93 mm | 0 cm |
| October | 14.7°C | 5.0°C | 9.9°C | 83 mm | 2 cm |
| November | 7.5°C | −0.3°C | 3.6°C | 88 mm | 13 cm |
| December | 1.4°C | −5.2°C | −2.0°C | 79 mm | 37 cm |
| Year | 13.0°C | 3.3°C | 8.2°C | 962 mm | 152 cm |
In March, anything from −25.6°C to 27.2°C
Bars run from each month’s record low to its record high over 1991–2020; February is the month whose average wanders most from year to year (±3.0°C around −4.8°C), June the one that wanders least (±1.1°C).
Where St. Marys’s numbers come from
Averages over 30 years, not a forecast.
- Normals: 1991–2020 normals for London from ECCC’s climate data site, the nearest location with every month of temperature.
- Other locations: ECCC blanks a month that fails its completeness rule, so the precipitation or snowfall here comes from the next location with all twelve months.
- Comparisons: all Canadian places of 2,500 or more except city totals and reserves, each read the same way.
- Not on this page: sunshine (no 1991–2020 normals exist for it) and any altitude adjustment, since there is no elevation for the town itself.
Canadian Climate Normals 1991–2020 · ECCC Data Services End-use Licence. Data Source: Environment and Climate Change Canada
Questions about St. Marys’s climate
How warm does St. Marys get in summer?
The warmest month is July, when afternoons average 26.6°C.
How cold does St. Marys get in winter?
At its coldest, in January, the normal low is −9.1°C.
How much rain and snow does St. Marys get?
Count on roughly 962 mm a year, heaviest in September (93 mm) and lightest in February (63 mm).
Are these figures for St. Marys itself?
No, they come from London; ECCC keeps no 1991–2020 normals in St. Marys itself.
Data Source: Environment and Climate Change Canada · ECCC Data Services End-use Licence Today’s forecast for St. Marys →
Adapted from Statistics Canada (Census of Population 2021, population estimates 2025, 2021 census boundaries) under the Statistics Canada Open Licence; this does not constitute an endorsement by Statistics Canada. Neighbourhood names in some cities © OpenStreetMap contributors (ODbL).