Jefferson, IL climate
Jefferson has cold, snowy winters and pleasant summers. A typical July afternoon reaches 83°, a January night drops to 12°, and about 36 inches of snow falls in a normal winter.
NOAA 1991-2020 climate normals Updated once a decadeWhat a year in Jefferson feels like
Winter
Spring
Summer
Fall
Jefferson weather by month
Average highs, lows, rain and snow for every month, from NOAA’s 1991–2020 normals.
| Month | High | Low | Rain + melt | Snow | Wet days | Snow on ground | 30-yr range |
|---|---|---|---|---|---|---|---|
| January | 29° | 12° | 1.5" | 10.7" | 9 | 21 | 11° – 33° |
| February | 34° | 16° | 1.7" | 8.1" | 8 | 16 | 11° – 36° |
| March | 46° | 27° | 2.4" | 4.9" | 10 | 6 | 29° – 52° |
| April | 60° | 37° | 3.7" | 1.3" | 12 | 1 | 39° – 55° |
| May | 71° | 48° | 4.3" | 0.1" | 13 | 0 | 54° – 67° |
| June | 80° | 58° | 5.5" | 0 | 12 | 0 | 65° – 73° |
| July | 83° | 62° | 4.6" | 0 | 9 | 0 | 67° – 79° |
| August | 82° | 60° | 3.9" | 0 | 10 | 0 | 65° – 77° |
| September | 75° | 51° | 3.8" | 0 | 9 | 0 | 57° – 68° |
| October | 62° | 40° | 2.9" | 0.5" | 9 | 0 | 47° – 57° |
| November | 47° | 29° | 2.3" | 2.1" | 9 | 2 | 30° – 47° |
| December | 34° | 18° | 1.9" | 8.0" | 10 | 13 | 12° – 36° |
| Year | 59° | 38° | 38.4" | 35.7" | 118 | 58 |
“Wet days” have at least 0.01" of rain or melted snow. “Snow on ground” counts days with 1" or more. The 30-year range is the coldest and warmest that month’s average temperature got between 1991 and 2020.
Rain and snow in Jefferson
Jefferson gets 38 inches of rain and melted snow a year. June is the wettest month and January the driest. Rain or snow falls on about 118 days a year. Snow covers the ground about 58 days of the year.
About 165 frost-free days a year
In half of years the last 32° night comes by April 27 and the first one by October 9. That leaves about 165 frost-free days for gardens, shorter than 65% of U.S. towns.
Heating and cooling a home in Jefferson
Engineers use “degree days” to estimate how hard a furnace or air conditioner works. In Jefferson, 91% of that work is heating and 9% is cooling, so the furnace matters far more than the air conditioner.
Degree days measure how far each day’s average temperature falls below or rises above 65°, added up over a year. Source: NOAA station normals.
Jefferson and its neighbors
Jefferson borders 6 towns with climate data. January nights across them vary by 0.4°. Kent has the coldest January nights (12°) and Freedom the hottest July afternoons (83°). Jefferson’s January low is 12° and its July high 83°.
Temperatures and rain come from NOAA’s 5 km grid, so each town gets its own value.
How Jefferson compares
Compared with every U.S. town and city on TownTapestry, each counted once.
Warmer than it used to be
The last 30 years in Jefferson averaged 1.6° warmer than the 1900s. The biggest change is in December (+2.9°). The shift is larger than in 77% of U.S. towns.
Change by month1991–2020 average minus 1901–2000 average, at Jefferson’s spot on NOAA’s grid
How much a month can swing
A normal is an average, and real years wander around it. February swings the most: between 1991 and 2020 its average temperature ranged from 11° to 36°. June is the most reliable, staying within 8°.
Common questions about Jefferson’s climate
What is the coldest month in Jefferson?
January, with a typical high of 29° and a low of 12°.
What is the hottest month in Jefferson?
July, with a typical high of 83° and a low of 62°. About 8 days a year reach 90°.
How much snow does Jefferson get?
About 36 inches in a normal winter, most of it in January.
When is the first frost in Jefferson?
In half of years the first 32° night comes by October 9, and the last spring frost by April 27.
What is the rainiest month in Jefferson?
June, with 5.5 inches of rain and melted snow. The year totals 38 inches.
Temperatures and rainfall come from NOAA’s gridded climate normals for Jefferson itself (about a 3-mile square). Snow, frost dates and day counts come from NOAA’s weather station at Stockton 3 Nne, IL (12 mi) away. Normals are 30-year averages, not a forecast. Source: NOAA NCEI U.S. Climate Normals, 1991–2020 and 1901–2000.