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Climate in Cornwall · ECCC 1991–2020 normals

Cornwall has warmer summer afternoons than 91% of Canadian towns

The coldest hours of a January night bottom out at −11.8°C on average. Seasons differ by 39°C, from the coldest nights to the warmest afternoons. By frosts alone, it ranks gentler than 72% of Canadian towns. Windshields need scraping on about 140 mornings a year, the days the air reaches 0°C or below.

July afternoons: warmer than 91% of Canadian towns

January nights: milder than 61% of Canadian towns

Rain and snow a year: wetter than 68% of Canadian towns

Measured at Cornwall, 1.7 km south-west: ECCC’s normals for 1991–2020.

July high

27.3°C

Typical Canadian town 25.5°C

January low

−11.8°C

Typical Canadian town −13.5°C

Rain & snow a year

1,006 mm

Typical Canadian town 883 mm

Snowfall a year

198 cm

Typical Canadian town 141 cm

Frost days

140

a year at 0°C or below

A year in Cornwall at a glance

Each month’s typical high and low, in °C.

Jan−4°C−12°CColdest nightsSnowiest

Feb−2°C−11°C

Mar4°C−5°C

Apr12°C2°C

May20°C9°C

Jun25°C14°C

Jul27°C17°CWarmest

Aug26°C16°C

Sep22°C12°C

Oct14°C6°CWettest

Nov now7°C0°C

Dec0°C−7°C

What stands out about Cornwall’s climate

Compared with Canadian towns, with its place among towns of 2,500+ in Ontario beside it.

Warmer than 91% of Canadian townsJuly afternoons average 27.3°C, the warmest of the year.Snowier than 70% of Canadian townsAbout 198 cm of snow falls in a year, most of it in January.

A normal year

What a year in Cornwall feels like

Seasons and months as ECCC’s 1991–2020 normals give them: a typical day’s high and low.

Winter

−2°C / −10°C

219 mm, with 135 cm of snow

Spring

12°C / 2°C

233 mm, with 46 cm of snow

Summer

26°C / 16°C

275 mm of rain and snow

Autumn

14°C / 6°C

280 mm, with 16 cm of snow: the wettest season

−20°

−10°

0°

10°

20°

30°

40°

−4°C−12°C

−2°C−11°C

4°C−5°C

12°C2°C

20°C9°C

25°C14°C

27°C17°C

26°C16°C

22°C12°C

14°C6°C

7°C0°C

0°C−7°C

JanFebMarAprMayJunJulAugSepOctNovDec

Best months to be outsideMayJunAugSepHighs of 17–27°C and nights of 8°C or more

Frost & warm days

About 140 frosts and 125 warm days a year

The frost season runs October to April, and January freezes nearly every night. On about 8 nights a year the air falls below −20°C.

140

Frost days a year (0°C or below)

Fewer frosts than 72% of Canadian towns

Days that stay below 0°C

Nights a year below −20°C

125

Days a year above 20°C

Days a year above 30°C

Frost days by month

Average days at 0°C or below

JFMAMJJASOND

Days above 20°C by month

Average days

JFMAMJJASOND

Rain & snow

1,006 mm of precipitation in a typical year

The most falls in October, the least in February. About 134 days a year bring 1 mm or more.

1,006 mm

Rain and snow a year

Wetter than 68% of Canadian towns

809 mm

Of it as rain alone (80%)

100 mm

October, the wettest month

63 mm

February, the driest month

Rain and snow by month

Millimetres

100 mm

JFMAMJJASOND

Rain alone by month

Millimetres

99 mm

JFMAMJJASOND

Snow

198 cm of snow in a typical year

From November to April snow is likely; January is the peak, at about 51 cm.

198 cm

Snowfall a year

Snowier than 70% of Canadian towns

Days a year with 0.2 cm of snow or more

20 cm

Snow on the ground at the end of February, the deepest month

Snowfall by month

Centimetres

51 cm

JFMAMJJASOND

Snow on the ground by month

Centimetres at month’s end

20 cm

JFMAMJJASOND

Heating

Heating a home in Cornwall

94% of a year’s heating need falls between October and April. Months averaging under 10°C: October to April.

4,003 heating degree days (below 18°C)a year, 1991–2020

2,408 growing degree days (above 5°C)a year, 1991–2020

The count adds up, day by day, how far the mean temperature falls short of 18°C. A house here needs less heating than 71% of Canadian towns.

Living here

Living with Cornwall’s climate

Gardening, time outside, winter cold and summer heat, from the 1991–2020 normals.

Get outside

Mild days and mild nights together (17–27°C by day, 8°C or more at night) belong to May, Jun, Aug and Sep.

Parks & trails →

Storms and extremes

Storms, floods and heat waves sit outside these normals; Cornwall’s hazards page covers them.

Flood & hazards →

Weather station

ECCC’s normals location: Cornwall

The page’s figures are ECCC’s 1991–2020 normals for Cornwall, one of its 450 normals locations.

Distance from the town	1.7 km south-west
Station altitude	64 m
Completeness	meets the WMO “3 and 5” rule
WMO standard normals	No
Coldest reading, 1991–2020	−32.0°C
Hottest reading, 1991–2020	37.5°C
Next-nearest location	St-Anicet, 32 km

Compared with other towns

How Cornwall compares

Placed among 2,611 Canadian towns and neighbourhoods of 2,500+, each on its nearest normals location; each dot is another location used in Ontario.

July afternoons27.3°C

CornwallMedian Canadian town

20°C22°C24°C26°C28°C30°C

Warmer than 91% of Canadian towns

January nights−11.8°C

CornwallMedian Canadian town

−25°C−20°C−15°C−10°C−5°C

Milder than 61% of Canadian towns

Rain and snow a year1,006 mm

CornwallMedian Canadian town

05001,0001,5002,000

Wetter than 68% of Canadian towns

Snowfall a year198 cm

CornwallMedian Canadian town

0100200300400

Snowier than 70% of Canadian towns

Next door

Nearby towns’ climate

Places around Cornwall whose figures come from another normals location. No closer places have figures: these lie 30–44 km from Cornwall.

Town	July high	January low	Rain & snow
Cornwall	27.3°C	−11.8°C	1,006 mm
Saint-Anicet 30 km · St-Anicet	26.7°C 0.6°C cooler	−13.0°C 1.2°C colder	1,047 mm
Morrisburg 44 km · Kemptville	26.8°C 0.5°C cooler	−14.0°C 2.2°C colder	925 mm

Month by month

Cornwall weather by month

Each month’s normals, 1991–2020: high, low, mean, precipitation and snowfall.

Month	High	Low	Mean	Rain & snow	Snow
January	−3.8°C	−11.8°C	−7.8°C	80 mm	51 cm
February	−2.1°C	−10.6°C	−6.4°C	63 mm	48 cm
March	3.5°C	−5.3°C	−0.9°C	64 mm	35 cm
April	11.8°C	2.0°C	6.9°C	83 mm	11 cm
May	19.8°C	8.8°C	14.3°C	85 mm	0 cm
June	24.6°C	14.1°C	19.3°C	95 mm	0 cm
July	27.3°C	17.0°C	22.2°C	97 mm	0 cm
August	26.3°C	16.2°C	21.2°C	83 mm	0 cm
September	22.0°C	11.8°C	16.9°C	99 mm	0 cm
October	14.1°C	5.7°C	9.7°C	100 mm	1 cm
November	6.9°C	−0.3°C	3.3°C	82 mm	16 cm
December	0.0°C	−6.7°C	−3.3°C	75 mm	37 cm
Year	12.5°C	3.4°C	8.0°C	1,006 mm	198 cm

Year to year

A March here can run from −27.0°C to 26.0°C

Two years in three, January’s average falls within 3.0°C of its normal of −7.8°C; June keeps to within 1.1°C.

−40°

−30°

−20°

−10°

0°

10°

20°

30°

40°

JanFebMarAprMayJunJulAugSepOctNovDec

Record low to record high, 1991–2020Normal

Sources

Where Cornwall’s numbers come from

Averages over 30 years, not a forecast.

Normals: ECCC’s normals for Cornwall, 1991–2020, chosen as the nearest location with a full temperature record.
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 Cornwall’s climate

How warm does Cornwall get in summer?

A normal July afternoon tops out at about 27.3°C, the year’s high point.

How cold does Cornwall get in winter?

Expect nights around −11.8°C in January; no month is colder.

How much rain and snow does Cornwall get?

Count on roughly 1,006 mm a year, heaviest in October (100 mm) and lightest in February (63 mm).

Are these figures for Cornwall itself?

Yes: ECCC’s normals station is inside Cornwall itself.

Data Source: Environment and Climate Change Canada · ECCC Data Services End-use Licence Today’s forecast for Cornwall →

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).