Harmon has cold winters and warm summers
A typical July afternoon reaches 84°, a January night drops to 14°, and about 29 inches of snow falls in a normal winter.
A year in Harmon at a glance
Each month’s typical high and low, and what it brings.
What stands out about Harmon’s climate
Read from where Harmon sits among Illinois’s towns. The page puts what stands out first.
About 180 frost-free days a year
In half of years the last 32° night comes by April 21 and the first by October 19.
Freezing nights by month
Average nights at or below 32°
90° days by month
Average days at 90° or more
What a year in Harmon feels like
Typical highs and lows by season and by month, from NOAA’s 30-year normals.
29 inches of snow, 38 of rain and melt
June is the wettest month and January the driest. Rain or snow falls on about 109 days a year.
Rain + melted snow by month
Inches of water
Snowfall by month
Inches of snow
Living with Harmon’s climate
What the numbers mean for a garden, a driveway, a furnace and a free afternoon.
180 frost-free days. The last frost comes by Apr 21 in half of years, so many gardeners wait a week or two past that to set out tomatoes. The first fall frost comes by Oct 19.
About 29" a winter over 9 days with an inch or more, most in January. Snow covers the ground about 38 days a year.
Months averaging under 55° run from October through April. Heating is 88% of the year’s heating-and-cooling load.
About 11 days a year reach 90°, and July afternoons average 84°.
The nicest months are May, June, August, September and October.
Parks & trails →Normals are averages. Ice storms, nor’easters, floods and heat waves are on the natural hazards page.
Natural hazards →Warmer than it used to be
The last 30 years in Harmon averaged 1.2° warmer than the 1900s. The biggest change is in December (+2.6°).
A bigger shift than in 51% of U.S. towns.
Change by month
How Harmon compares
Against every U.S. town on TownTapestry, each counted once, with its place in Illinois.
Harmon 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 | 30° | 14° | 1.7" | 9.0" | 8 | 15 | 13° – 34° |
| February | 35° | 18° | 1.8" | 6.4" | 7 | 10 | 13° – 38° |
| March | 48° | 28° | 2.5" | 3.0" | 8 | 4 | 29° – 53° |
| April | 61° | 38° | 3.7" | 0.6" | 12 | 0 | 41° – 57° |
| May | 72° | 50° | 4.7" | 0 | 13 | 0 | 55° – 68° |
| June | 81° | 59° | 5.2" | 0 | 12 | 0 | 67° – 75° |
| July | 84° | 63° | 4.0" | 0 | 9 | 0 | 68° – 80° |
| August | 82° | 61° | 4.0" | 0 | 9 | 0 | 65° – 78° |
| September | 76° | 53° | 3.5" | 0 | 8 | 0 | 59° – 70° |
| October | 64° | 41° | 2.9" | 0.1" | 9 | 0 | 47° – 58° |
| November | 48° | 30° | 2.4" | 1.8" | 8 | 1 | 31° – 48° |
| December | 35° | 20° | 2.1" | 7.9" | 8 | 7 | 13° – 38° |
| Year | 60° | 39° | 38.4" | 28.8" | 109 | 38 |
Heating and cooling a home in Harmon
88% of the work is heating, so the furnace matters far more than the air conditioner.
Degree days add up how far each day’s average falls below (heating) or rises above (cooling) 65° over a year. Source: NOAA station normals.
How much a month can swing
A normal is an average. December swings the most: from 1991 to 2020 its average ranged from 13° to 38°. June is the most reliable, staying within 8°.
Common questions about Harmon’s climate
What is the coldest month in Harmon?
January, with a typical high of 30° and a low of 14°.
What is the hottest month in Harmon?
July, with a typical high of 84° and a low of 63°. About 11 days a year reach 90°.
How much snow does Harmon get?
About 29 inches in a normal winter, most of it in January.
When is the first frost in Harmon?
In half of years the first 32° night comes by October 19, and the last spring frost by April 21.
What is the rainiest month in Harmon?
June, with 5.2 inches of rain and melted snow. The year totals 38 inches.
Neighbors talk weather
Gardens, snow, and the best days of the year in Harmon.
Your answer becomes a post in Town Square.
Temperatures and rainfall come from NOAA’s gridded climate normals for Harmon itself (about a 3-mile square). Snow, frost dates and day counts come from NOAA’s weather station at Rock Falls 3 Ne, IL (7 mi, snow) and Dixon 1w, IL (8 mi, frost, heat and degree days). Normals are 30-year averages, not a forecast. Source: NOAA NCEI U.S. Climate Normals, 1991–2020 and 1901–2000. Today’s forecast: National Weather Service.