The climate in Harristown sits close to the middle of U.S. towns
On a normal January night the air cools to about 19°. The gap between a January night and a July afternoon is 67°. Its January nights bite harder than in 67% of U.S. towns. Keep the boiler serviced for the months from November to March, which average under 50°.
A year in Harristown at a glance
Each month’s typical high and low, and what it brings.
What stands out about Harristown’s climate
Compared with towns across the U.S., with Harristown’s place in Illinois beside it.
What a year in Harristown feels like
Typical highs and lows by season and by month, from NOAA’s 30-year normals.
About 192 frost-free days a year
In half of years the last 32° night comes by April 14 and the first by October 24. Frost and day counts come from NOAA’s station at Decatur Wtp, IL, 6 miles from the town’s center, at about the same height.
The 2023 USDA map puts Harristown’s center in zone 6a: the coldest night of a typical winter, averaged over 1991–2020, reaches about −6°. Plant labels use the zone; frost dates tell you when to plant.
Freezing nights by month
Average nights at or below 32°
90° days by month
Average days at 90° or more
About 14 inches of snow a winter
Snow, measured at Decatur Wtp, IL, falls mostly in January. Precipitation (rain plus melted snow) adds up to 39 inches a year; May is the wettest month and February the driest. Rain or snow falls on about 116 days a year.
Rain + melted snow by month
Inches of water
Snowfall by month
Inches of snow
Heating and cooling a home in Harristown
83% of the work is heating. Months averaging under 55° run from November through April.
Degree days add up how far each day’s average falls below (heating) or rises above (cooling) 65° over a year. NOAA normals at Decatur Wtp, IL.
Living with Harristown’s climate
What the numbers mean for a garden, a free afternoon and a bad-weather day.
192 frost-free days in zone 6a. The last frost comes by Apr 14 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 24.
Months with highs of 62–84° and lows of 40° or more: April, May, June, September and October.
Parks & trails →Of the yearly building losses FEMA expects in Harristown from natural hazards, river flooding is the largest share (35%); heat waves, cold waves, winter storms and ice storms together are 19%. Normals are averages; the hazards page covers the extremes.
Natural hazards →Harristown and its neighbors
Every town next door is within a degree of Harristown in January and July, closer than the 5 km grid can tell apart. Tap a town to see its climate.
Climates most like Harristown’s, farther away
TownRatings’ own comparison of NOAA 1991–2020 normals, not a NOAA product: places of 5,000+ at least 150 miles away, one per state, closest on January low, July high, precipitation and snow.
| Town | Jan. low | July high | Precip. | Snow |
|---|---|---|---|---|
| Harristown, IL | 19° | 86° | 39" | 14" |
| Van Wert, OH | 19° | 84° | 39" | 17" |
| Macon, MO | 18° | 87° | 42" | 15" |
| Wabash, IN | 19° | 84° | 40" | 20" |
| Ambridge, PA | 21° | 85° | 39" | 20" |
Temperatures and rain come from NOAA’s 5 km grid, so each town gets its own value. Snow and frost-free days come from the nearest weather station, so neighbors often share them.
Warmer than it used to be
The last 30 years in Harristown averaged 1.0° warmer than the 1900s. The biggest change is in December (+2.1°).
A smaller shift than in 77% of U.S. towns.
Change by month
The two periods overlap (1991–2000 is in both), which makes the gap a little smaller than it would be between separate periods.
How Harristown compares
Against 12,954 U.S. towns of 2,500 or more (one per 5 km climate cell), with Harristown’s place among Illinois’.
Harristown weather by month
Highs, lows and precipitation from NOAA’s grid at Harristown’s center; snow, wet days and snow on the ground from Decatur Wtp, IL. 1991–2020 normals.
| Month | High | Low | Rain + melt | Snow | Wet days | 30-yr range |
|---|---|---|---|---|---|---|
| January | 35° | 19° | 2.2" | 5.9" | 9 | 20° – 38° |
| February | 40° | 22° | 2.0" | 2.5" | 8 | 19° – 41° |
| March | 51° | 32° | 2.7" | 0.9" | 10 | 35° – 56° |
| April | 64° | 42° | 4.1" | 0.4" | 11 | 46° – 58° |
| May | 74° | 53° | 4.6" | 0.0" | 13 | 58° – 72° |
| June | 83° | 62° | 4.5" | 0.0" | 11 | 68° – 76° |
| July | 86° | 65° | 4.0" | 0.0" | 10 | 70° – 82° |
| August | 84° | 63° | 3.3" | 0.0" | 7 | 69° – 79° |
| September | 79° | 55° | 3.1" | 0.0" | 8 | 61° – 72° |
| October | 66° | 44° | 3.3" | 0.0" | 10 | 50° – 61° |
| November | 52° | 33° | 3.1" | 0.4" | 9 | 35° – 50° |
| December | 39° | 24° | 2.3" | 3.5" | 9 | 17° – 41° |
| Year | 63° | 43° | 39.2" | 13.6" | 116 |
How much a month can swing
A normal is an average. December swings the most: from 1991 to 2020 its average ranged from 17° to 41°. June is the most reliable, staying within 8°.
Where Harristown’s numbers come from
Normals are 30-year averages, not a forecast. How TownRatings reads climate data →
- Temperatures and precipitation: NOAA’s gridded 1991–2020 normals for the 5 km cell at Harristown’s center.
- Snow: Decatur Wtp, IL.
- Frost, freezing nights, 90° and 100° days, heating and cooling: Decatur Wtp, IL, 6 miles from the town’s center, at about the same height; the nearest station that passes our checks for distance, height and agreement with the grid.
- Growing zone: USDA Plant Hardiness Zone Map, 2023. USDA Agricultural Research Service and PRISM Group, Oregon State University, prism.oregonstate.edu/phzm, accessed 8 Oct 2026.
- Then and now: NOAA’s gridded normals for 1901–2000 at the same cell.
- Storms and extremes: FEMA National Risk Index (expected annual losses to buildings).
Common questions about Harristown’s climate
What is the weather like in Harristown?
A typical July afternoon reaches 86°, a January night drops to 19°, and about 14 inches of snow falls in a normal winter. Colder January nights than 67% of U.S. towns; hotter July afternoons than 53% of U.S. towns.
How cold does it get in Harristown in winter?
January nights average 19°. About 110 nights a year reach 32° or below and 4 reach 0° or below. In the coldest January of the last 30 years the month averaged 20°.
How much snow does Harristown get?
About 14 inches in a normal winter at Decatur Wtp, IL, most of it in January.
How hot does it get in Harristown?
July, with a typical high of 86° and a low of 65°. About 26 days a year reach 90° (Decatur Wtp, IL).
When is the first and last frost in Harristown?
In half of years the last spring frost (32°) comes by April 14 and the first fall frost by October 24, about 192 frost-free days, at Decatur Wtp, IL.
What growing zone is Harristown in?
Zone 6a on the 2023 USDA Plant Hardiness Zone Map: the coldest night of a typical winter reaches about −6°.
What is the best time of year to visit Harristown?
By one simple rule (highs of 62–84° and lows of 40° or more), April, May, June, September and October. The rule is ours, not NOAA’s; the month table has the numbers to judge by.
Is Harristown getting warmer?
Yes: 1991–2020 averaged 1.0° warmer than 1901–2000 on NOAA’s grid. A smaller shift than 77% of U.S. towns.
Neighbors talk weather
Gardens, snow, and the best days of the year in Harristown.
Source: NOAA NCEI U.S. Climate Normals, 1991–2020 and 1901–2000; USDA/PRISM 2023 hardiness zones; FEMA National Risk Index. Today’s forecast: National Weather Service.