Climate and monthly weather forecast
Decatur, IL

Weather in January

January, like December, in Decatur, Illinois, is another cold winter month, with average temperature varying between 21.2°F (-6°C) and 32.9°F (0.5°C). The coldest month is January, with an average high-temperature of 32.9°F (0.5°C) and an average low-temperature of 21.2°F (-6°C). Weather in January »

Weather in February

The last month of the winter, February, is also a wintry month in Decatur, Illinois, with average temperature ranging between max 37.8°F (3.2°C) and min 25.2°F (-3.8°C). In Decatur, Illinois, the average high-temperature is practically the same as in January - a still wintry 37.8°F (3.2°C). Weather in February »

Weather in March

The first month of the spring, March, is a cool month in Decatur, Illinois, with temperature in the range of an average high of 50.5°F (10.3°C) and an average low of 35.6°F (2°C). In March, the average high-temperature rises, from a cold 37.8°F (3.2°C) in February, to a fresh 50.5°F (10.3°C). Weather in March »

Weather in April

April is an enjoyable spring month in Decatur, Illinois, with average temperature fluctuating between 46°F (7.8°C) and 61.9°F (16.6°C). In April, the average high-temperature increases, from a cool 50.5°F (10.3°C) in March, to a comfortable 61.9°F (16.6°C). Weather in April »

Weather in May

May, the last month of the spring, in Decatur, is a pleasant month, with average temperature varying between 56.7°F (13.7°C) and 72.9°F (22.7°C). In Decatur, the average high-temperature in May rises, from a comfortable 61.9°F (16.6°C) in April, to a pleasant 72.9°F (22.7°C). Weather in May »

Weather in June

The first month of the summer, June, is a warm month in Decatur, Illinois, with average temperature fluctuating between 64°F (17.8°C) and 80.6°F (27°C). In Decatur, Illinois, the average high-temperature slightly increases, from an agreeable 72.9°F (22.7°C) in May, to a warm 80.6°F (27°C). Weather in June »

Weather in July

July, the same as June, is another warm summer month in Decatur, Illinois, with average temperature ranging between min 65.7°F (18.7°C) and max 82°F (27.8°C). With an average high-temperature of 82°F (27.8°C) and an average low-temperature of 65.7°F (18.7°C), July is the warmest month. In July, the average heat index is evaluated at a tropical 90°F (32.2°C). Weather in July »

Weather in August

The last month of the summer, August, is also a moderately hot month in Decatur, Illinois, with temperature in the range of an average high of 81.1°F (27.3°C) and an average low of 63.9°F (17.7°C). In Decatur, the average high-temperature in August is relatively the same as in July - a still moderately hot 81.1°F (27.3°C). Weather in August »

Weather in September

September, the first month of the autumn, in Decatur, is also a moderately hot month, with average temperature ranging between min 58.5°F (14.7°C) and max 77°F (25°C). In Decatur, the average high-temperature in September is practically the same as in August - a still moderately hot 77°F (25°C). Weather in September »

Weather in October

October, like September, in Decatur, Illinois, is another comfortable autumn month, with average temperature fluctuating between 48°F (8.9°C) and 64°F (17.8°C). In Decatur, the average high-temperature decreases, from a warm 77°F (25°C) in September, to an enjoyable 64°F (17.8°C). Weather in October »

Weather in November

November, the last month of the autumn, in Decatur, is another chilly month, with average temperature varying between 49.8°F (9.9°C) and 36.1°F (2.3°C). In Decatur, Illinois, the average high-temperature drops, from an enjoyable 64°F (17.8°C) in October, to a chilly 49.8°F (9.9°C). Weather in November »

Weather in December

The first month of the winter, December, is also a wintry month in Decatur, Illinois, with temperature in the range of an average low of 27.9°F (-2.3°C) and an average high of 38.5°F (3.6°C). In Decatur, Illinois, the average high-temperature drops, from a chilly 49.8°F (9.9°C) in November, to a cold 38.5°F (3.6°C). Weather in December »
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FAQ

What is the coldest month in Decatur?

The coldest month in Decatur is January, with an average high-temperature of 32.9°F (0.5°C) and an average low-temperature of 21.2°F (-6°C).

How much does it rain in Decatur?

Throughout the year, there are 130.2 rainfall days, and 16.34" (415mm) of precipitation is accumulated.

When does it snow in Decatur?

January through April, November and December are months with snowfall in Decatur.

What is the snowiest month in Decatur?

The month with the most snowfall in Decatur, Illinois, is January when snow falls for 7.2 days and typically aggregates up to 1.85" (47mm) of snow.

How much does it snow in Decatur?

In Decatur, during the entire year, snow falls for 23.1 days, and aggregates up to 5.67" (144mm) of snow.

What is the month with the least sunshine in Decatur?

With an average of 4.1h of sunshine, January has the least sunshine of the year in Decatur, Illinois.

What are the months with the lowest UV index in Decatur?

January, February, November and December, with an average maximum UV index of 2, are months with the lowest UV index.

What is the driest month in Decatur?

February and December are months with the least rain in Decatur when the rain falls for 5.8 days and typically aggregates up to 0.87" (22mm) of rain.

What is the wettest month in Decatur?

May is the month with the most rainfall. Rain falls for 17 days and accumulates 2.01" (51mm) of precipitation.

When it does not snow in Decatur?

In Decatur snow does not fall in May through October.

When are the longest days in Decatur?

The month with the longest days in Decatur, Illinois, is June, with an average of 15h of daylight.

What month has the most sunshine in Decatur?

With an average of 10.4h of sunshine, June has the most sunshine of the year in Decatur, Illinois.

When is the highest UV index in Decatur?

Months with the highest UV index are June through August, with an average maximum UV index of 6.

What is the warmest month in Decatur?

With an average high-temperature of 82°F (27.8°C) and an average low-temperature of 65.7°F (18.7°C), July is the warmest month in Decatur, Illinois.

What is the most humid month in Decatur?

With an average relative humidity of 84%, July is the most humid month.

What is the least humid month in Decatur?

With an average relative humidity of 70%, October is the least humid month in Decatur.

What is the month with the shortest days in Decatur?

December has the shortest days of the year, with an average of 9.4h of daylight.

Average pressure
Decatur, IL

Average pressure - Decatur, IL

The month with the highest atmospheric pressure is January (30.15").
The month with the lowest atmospheric pressure is June (29.92").

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Average wind speed
Decatur, IL

Average wind speed - Decatur, IL

The windiest month (with the highest average wind speed) is January (10.7mph).
The calmest months (with the lowest average wind speed) are July and August (6.3mph).

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Average rainfall
Decatur, IL

Average rainfall - Decatur, IL

The wettest month (with the highest rainfall) is May (2.01").
The driest months (with the least rainfall) are February and December (0.87").

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Average rainfall days
Decatur, IL

Average rainfall days - Decatur, IL

The month with the highest number of rainy days is May (17 days).
The month with the least rainy days is February (5.8 days).

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Average snowfall
Decatur, IL

Average snowfall - Decatur, IL

The month with the highest snowfall is January (1.85").
Months with the least snowfall are May, June, July, August, September and October (0").

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Average snowfall days
Decatur, IL

Average snowfall days - Decatur, IL

The month with the highest number of snowfall days is January (7.2 days).
Months with the least snowfall days are May, June, July, August, September and October (0 days).

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Average daylight / Average sunshine
Decatur, IL

Average daylight / Average sunshine - Decatur, IL

The month with the longest days is June (Average daylight: 15h).
The month with the shortest days is December (Average daylight: 9.4h).

The month with the most sunshine is June (Average sunshine: 10.4h).
The month with the least sunshine is January (Average sunshine: 4.1h).

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Average sunshine days
Decatur, IL

Average sunshine days - Decatur, IL

The month with the most sunshine days is October (19.8 days).
The month with the least sunshine days is May (11.5 days).

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Average UV index
Decatur, IL

Average UV index - Decatur, IL

Months with the highest UV index are June, July and August (UV index 6).
Months with the lowest UV index are January, February, November and December (UV index 2).

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Average visibility
Decatur, IL

Average visibility - Decatur, IL

Months with the highest visibility are January, February, March, April, May, June, September, October, November and December (6mi).
Months with the lowest visibility are July and August (5mi).

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