Photo: AlphaBeta135 · CC BY 4.0Winter nights in Symerton are colder than in 78% of U.S. towns
In July the day’s top temperature is typically 84°. By precipitation alone, it ranks drier than 63% of U.S. towns. Decade by decade the climate has edged up, 1.3° above 1901–2000. The frost-free window for a garden runs roughly April 19 to October 25.
A year in Symerton at a glance
Each month’s typical high and low, and what it brings.
What stands out about Symerton’s climate
Compared with towns across the U.S., with Symerton’s place in Illinois beside it.
What a year in Symerton feels like
Typical highs and lows by season and by month, from NOAA’s 30-year normals.
About 188 frost-free days a year
In half of years the last 32° night comes by April 19 and the first by October 25. Frost and day counts come from NOAA’s station at Joliet Brandon Rd Dam, IL, 13 miles from the town’s center, 100 ft lower.
The 2023 USDA map puts Symerton’s center in zone 5b: the coldest night of a typical winter, averaged over 1991–2020, reaches about −10°. 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 27 inches of snow a winter
Snow, measured at Bourbonnais 3nw, 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 127 days a year.
Rain + melted snow by month
Inches of water
Snowfall by month
Inches of snow
Heating and cooling a home in Symerton
88% of the work is heating, so the furnace matters far more than the air conditioner. Months averaging under 55° run from October 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 Joliet Brandon Rd Dam, IL.
Living with Symerton’s climate
What the numbers mean for a garden, a free afternoon and a bad-weather day.
188 frost-free days in zone 5b. The last frost comes by Apr 19 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 25.
Months with highs of 62–84° and lows of 40° or more: May, June, August, September and October.
Parks & trails →Of the yearly building losses FEMA expects in Symerton from natural hazards, river flooding is the largest share (69%); heat waves, cold waves, winter storms and ice storms together are 16%. Normals are averages; the hazards page covers the extremes.
Natural hazards →Symerton and similar climates
TownRatings has no climate map of the towns around Symerton yet.
Climates most like Symerton’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 |
|---|---|---|---|---|
| Symerton, IL | 17° | 84° | 39" | 27" |
| Decatur, IN | 19° | 84° | 40" | 28" |
| Claverack, NY | 16° | 84° | 42" | 31" |
| Mount Pleasant, IA | 15° | 85° | 38" | 25" |
| Bryan, OH | 18° | 84° | 37" | 29" |
Temperatures and precipitation come from NOAA’s 5 km grid; snow and day counts from the stations named on this page.
Warmer than it used to be
The last 30 years in Symerton averaged 1.3° warmer than the 1900s. The biggest change is in December (+2.5°).
A smaller shift than in 52% 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 Symerton compares
Against 12,954 U.S. towns of 2,500 or more (one per 5 km climate cell), with Symerton’s place among Illinois’.
Symerton weather by month
Highs, lows and precipitation from NOAA’s grid at Symerton’s center; snow, wet days and snow on the ground from Bourbonnais 3nw, IL. 1991–2020 normals.
| Month | High | Low | Rain + melt | Snow | Wet days | Snow on ground | 30-yr range |
|---|---|---|---|---|---|---|---|
| January | 32° | 17° | 2.2" | 8.9" | 11 | 15 | 15° – 36° |
| February | 36° | 20° | 1.8" | 6.8" | 9 | 10 | 16° – 39° |
| March | 49° | 29° | 2.4" | 3.6" | 11 | 4 | 30° – 54° |
| April | 62° | 39° | 3.8" | 1.0" | 13 | 0 | 42° – 57° |
| May | 73° | 50° | 4.7" | 0.0" | 13 | 0 | 55° – 68° |
| June | 82° | 60° | 4.7" | 0.0" | 12 | 0 | 67° – 75° |
| July | 84° | 64° | 4.3" | 0.0" | 10 | 0 | 69° – 80° |
| August | 83° | 62° | 4.1" | 0.0" | 10 | 0 | 67° – 78° |
| September | 77° | 55° | 3.4" | 0.0" | 9 | 0 | 60° – 70° |
| October | 64° | 43° | 3.3" | 0.0" | 10 | 0 | 49° – 59° |
| November | 49° | 32° | 2.7" | 1.1" | 10 | 1 | 33° – 49° |
| December | 37° | 22° | 2.1" | 6.0" | 11 | 8 | 16° – 40° |
| Year | 61° | 41° | 39.4" | 27.4" | 127 | 39 |
How much a month can swing
A normal is an average. March swings the most: from 1991 to 2020 its average ranged from 30° to 54°. June is the most reliable, staying within 8°.
Where Symerton’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 Symerton’s center.
- Snow: Bourbonnais 3nw, IL.
- Frost, freezing nights, 90° and 100° days, heating and cooling: Joliet Brandon Rd Dam, IL, 13 miles from the town’s center, 100 ft lower; 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 Symerton’s climate
What is the weather like in Symerton?
A typical July afternoon reaches 84°, a January night drops to 17°, and about 27 inches of snow falls in a normal winter. Colder January nights than 78% of U.S. towns; cooler July afternoons than 56% of U.S. towns.
How cold does it get in Symerton in winter?
January nights average 17°. About 126 nights a year reach 32° or below and 8 reach 0° or below. In the coldest January of the last 30 years the month averaged 15°.
How much snow does Symerton get?
About 27 inches in a normal winter at Bourbonnais 3nw, IL, most of it in January, with snow on the ground about 39 days a year.
How hot does it get in Symerton?
July, with a typical high of 84° and a low of 64°. About 15 days a year reach 90° (Joliet Brandon Rd Dam, IL).
When is the first and last frost in Symerton?
In half of years the last spring frost (32°) comes by April 19 and the first fall frost by October 25, about 188 frost-free days, at Joliet Brandon Rd Dam, IL.
What growing zone is Symerton in?
Zone 5b on the 2023 USDA Plant Hardiness Zone Map: the coldest night of a typical winter reaches about −10°.
What is the best time of year to visit Symerton?
By one simple rule (highs of 62–84° and lows of 40° or more), May, June, August, September and October. The rule is ours, not NOAA’s; the month table has the numbers to judge by.
Is Symerton getting warmer?
Yes: 1991–2020 averaged 1.3° warmer than 1901–2000 on NOAA’s grid. A smaller shift than 52% of U.S. towns.
Neighbors talk weather
Gardens, snow, and the best days of the year in Symerton.
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.