30-year climate normals

Franklin County Climate and Weather Averages

Hottest month — July

88.4°

average daily high. The coldest month is January, averaging a low of 24.8°F.

Franklin County gets 44.01" of precipitation a year, and 33% of it falls in Mar, Apr, May.

Temperature through the year

Each bar spans the average daily low to the average daily high for that month.

Month	Avg high	Avg low	Precip
January	41.7°	24.8°	2.79"
February	47.2°	27.8°	2.61"
March	57.1°	35.9°	4.14"
April	68.1°	45.2°	5.34"
May	77.0°	55.4°	4.98"
June	85.7°	64.2°	4.11"
July	88.4°	67.5°	3.61"
August	87.2°	64.8°	3.05"
September	80.8°	55.7°	2.85"
October	70.1°	44.7°	3.54"
November	56.2°	35.0°	3.87"
December	45.7°	28.2°	3.12"

Rainfall by month

Precipitation is spread fairly evenly through the year here, with 33% falling in the wettest three months (Mar, Apr, May).

January 2.79"

February 2.61"

March 4.14"

April 5.34"

May 4.98"

June 4.11"

July 3.61"

August 3.05"

September 2.85"

October 3.54"

November 3.87"

December 3.12"

Annual total 44.01"

What this climate costs you

Degree days measure how hard a building has to work to stay comfortable. They are the reason two identical houses have very different power bills, and they are the link between the weather here and what you pay every month.

Cooling degree days How much air conditioning the climate demands 1,370

Heating degree days How much heating the climate demands 4,460

Approximate annual cooling cost At 23.85¢/kWh, Illinois average $327

Approximate annual electric heating cost Lower where heating is gas rather than electric $372

These are rough planning figures from degree days and the state electricity price, not a bill estimate. House size, insulation and fuel type move them a lot. See the full cost of owning a home in Franklin County, where electricity is one line of eight.

Common questions

What is the weather like in Franklin County?

Franklin County averages a high of 88.4°F in July and a low of 24.8°F in January. Annual precipitation is 44.01 inches, with essentially no snow.

When is the rainy season in Franklin County?

The wettest stretch is Mar, Apr, May, which accounts for 33% of the year's precipitation. Precipitation is relatively evenly distributed across the year.

How hot does it get in Franklin County?

The average daily high in July, the hottest month, is 88.4°F. That drives 1,370 cooling degree days a year, which is what your air conditioning has to work against.

Does it snow in Franklin County?

Effectively no. Measurable snowfall is rare in Franklin County.

Sources

Temperature, precipitation and snowfall normals — NOAA National Centers for Environmental Information, 1991–2020 Monthly Climate Normals, station CARBONDALE SOUTHERN IL AP, IL US (USW00093810), 22.9 miles from the county centroid.
Heating and cooling degree days — NOAA, same station and period.
Electricity price — US Energy Information Administration, Electric Power Monthly Table 5.6.A, Illinois residential average.
Wet-season share is the wettest three consecutive months as a percentage of annual precipitation, calculated from the monthly normals.