Jefferson County, IL Climate

The climate in Jefferson County, IL is generally moderate and comfortable. Summers are hot and humid with temperatures reaching into the high 80s Fahrenheit. Winters are cold and snowy with temperatures averaging between the mid-teens to low 30s. Spring and Fall are warm but can experience mild fluctuations between cool and warm weather. Precipitation is spread throughout the year, mostly in the form of rain, but snow does occur during winter months. Generally, the area experiences four distinct seasons which provides for a unique landscape throughout the year.

Jefferson County, Illinois gets 44 inches of rain, on average, per year. The US average is 38 inches of rain per year.

Jefferson County averages 9 inches of snow per year. The US average is 28 inches of snow per year.

On average, there are 205 sunny days per year in Jefferson County. The US average is 205 sunny days.

Jefferson County gets some kind of precipitation, on average, 99 days per year. Precipitation is rain, snow, sleet, or hail that falls to the ground. In order for precipitation to be counted you have to get at least .01 inches on the ground to measure.

Weather Highlights

Summer High: the July high is around 88 degrees
Winter Low: the January low is 22
Rain: averages 44 inches of rain a year
Snow: averages 9 inches of snow a year

Bestplaces Comfort Index

The annual BestPlaces Comfort Index for Jefferson County is 7.2 (10=best), which means it is one of the most pleasant places in Illinois.

7.8 Summer - 5.6 Winter

September, May and June are the most pleasant months in Jefferson County, while January and December are the least comfortable months.

Climate	Jefferson, Illinois	United States
	44.0 in.	38.1 in.
	9.3 in.	27.8 in.
	99.2 days	106.2 days
	205 days	205 days
	87.6°	85.8°
	21.8°	21.7°
	7.2	7
	4.3	4.3
	487 ft.	2443 ft.

Climate

YOU SHOULD KNOW

Many people confuse weather and climate but they are different. Weather is the conditions of the atmosphere over a short period of time, and climate is how the atmosphere is over long periods of time.

Weather is how the atmosphere is behaving and its effects upon life and human activities. Weather can change from minute-to-minute. Most people think of weather in terms of temperature, humidity, precipitation, cloudiness, brightness, visibility, wind, and atmospheric pressure.

Climate is the description of the long-term pattern of weather in a place. Climate can mean the average weather for a particular region and time period taken over 30 years. Climate is the average of weather over time.

July is the hottest month for Jefferson County with an average high temperature of 87.6°, which ranks it as warmer than most places in Illinois. In Jefferson County, there are 3 comfortable months with high temperatures in the range of 70-85°. The most pleasant months of the year for Jefferson County are September, May and June.

In Jefferson County, there are 29.4 days annually when the high temperature is over 90°, which is hotter than most places in Illinois.

January has the coldest nighttime temperatures for Jefferson County with an average of 21.8°. This is warmer than most places in Illinois.

In Jefferson County, there are 101.1 days annually when the nighttime low temperature falls below freezing, which is warmer than most places in Illinois.

In Jefferson County, there are 2.4 days annually when the nighttime low temperature falls below zero°, which is warmer than most places in Illinois.

The humidity can be uncomfortably heavy or close in Jefferson County during the summer months. July is the most humid month, though humidity is low for most of the year. July, August and June are the three most humid months in Jefferson County.

May is the wettest month in Jefferson County with 5.2 inches of rain, and the driest month is January with 2.6 inches. The wettest season is Summer with 30% of yearly precipitation and 20% occurs in Spring, which is the driest season. The annual rainfall of 44.0 inches in Jefferson County means that it is wetter than most places in Illinois.

May is the rainiest month in Jefferson County with 10.7 days of rain, and September is the driest month with only 6.3 rainy days. There are 99.2 rainy days annually in Jefferson County, which is less rainy than most places in Illinois. The rainiest season is Summer when it rains 30% of the time and the driest is Winter with only a 23% chance of a rainy day.

An annual snowfall of 9.3 inches in Jefferson County means that it is one of the least snowy places in Illinois. January is the snowiest month in Jefferson County with 2.8 inches of snow, and 4 months of the year have significant snowfall.

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