Somonauk’s winters are colder and snowier than most of the U.S.
A typical July afternoon reaches 84°, a January night drops to 15°, and about 30 inches of snow falls in a normal winter.
A year in Somonauk at a glance
Each month’s typical high and low, and what it brings.
What stands out about Somonauk’s climate
Compared with towns across the U.S., with Somonauk’s place in Illinois beside it.
What a year in Somonauk feels like
Typical highs and lows by season and by month, from NOAA’s 30-year normals.
About 166 frost-free days a year
In half of years the last 32° night comes by April 28 and the first by October 13. Frost and day counts come from NOAA’s station at Chicago Aurora Muni Airport, 14 miles from the town’s center, at about the same height.
The 2023 USDA map puts Somonauk’s center in zone 5b: the coldest night of a typical winter, averaged over 1991–2020, reaches about −12°. 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 30 inches of snow a winter
Snow, measured at Shabbona 3s, IL, falls mostly in January. Precipitation (rain plus melted snow) adds up to 37 inches a year; May is the wettest month and February the driest. Rain or snow falls on about 108 days a year.
Rain + melted snow by month
Inches of water
Snowfall by month
Inches of snow
Heating and cooling a home in Somonauk
89% 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 Chicago Aurora Muni Airport.
Living with Somonauk’s climate
What the numbers mean for a garden, a free afternoon and a bad-weather day.
166 frost-free days in zone 5b. The last frost comes by Apr 28 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 13.
Months with highs of 62–84° and lows of 40° or more: May, June, July, August, September and October. 1.2 miles of trails are waiting.
Parks & trails →Of the yearly building losses FEMA expects in Somonauk from natural hazards, river flooding is the largest share (52%); heat waves, cold waves, winter storms and ice storms together are 23%. Normals are averages; the hazards page covers the extremes.
Natural hazards →Somonauk and its neighbors
Every town next door is within a degree of Somonauk in January and July, closer than the 5 km grid can tell apart. Tap a town to see its climate.
Climates most like Somonauk’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 |
|---|---|---|---|---|
| Somonauk, IL | 15° | 84° | 37" | 30" |
| Auburn, IN | 17° | 84° | 38" | 30" |
| Sayre, PA | 17° | 84° | 37" | 35" |
| North Liberty, IA | 12° | 84° | 37" | 29" |
| Bryan, OH | 18° | 84° | 37" | 29" |
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 Somonauk averaged 1.2° warmer than the 1900s. The biggest change is in December (+2.4°).
A smaller shift than in 65% 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 Somonauk compares
Against 12,954 U.S. towns of 2,500 or more (one per 5 km climate cell), with Somonauk’s place among Illinois’.
Somonauk weather by month
Highs, lows and precipitation from NOAA’s grid at Somonauk’s center; snow, wet days and snow on the ground from Shabbona 3s, IL. 1991–2020 normals.
| Month | High | Low | Rain + melt | Snow | Wet days | 30-yr range |
|---|---|---|---|---|---|---|
| January | 30° | 15° | 1.7" | 10.2" | 8 | 14° – 34° |
| February | 35° | 19° | 1.6" | 7.1" | 7 | 14° – 38° |
| March | 47° | 28° | 2.3" | 3.4" | 8 | 29° – 53° |
| April | 61° | 38° | 3.7" | 0.3" | 10 | 40° – 56° |
| May | 72° | 49° | 4.7" | 0.0" | 12 | 54° – 67° |
| June | 81° | 59° | 4.6" | 0.0" | 11 | 66° – 74° |
| July | 84° | 63° | 3.9" | 0.0" | 9 | 68° – 80° |
| August | 82° | 61° | 3.8" | 0.0" | 8 | 66° – 78° |
| September | 76° | 53° | 3.4" | 0.0" | 8 | 60° – 69° |
| October | 64° | 42° | 3.2" | 0.0" | 9 | 48° – 58° |
| November | 48° | 31° | 2.4" | 0.5" | 7 | 32° – 49° |
| December | 36° | 20° | 2.0" | 8.3" | 9 | 14° – 39° |
| Year | 60° | 40° | 37.3" | 29.8" | 108 |
How much a month can swing
A normal is an average. December swings the most: from 1991 to 2020 its average ranged from 14° to 39°. June is the most reliable, staying within 8°.
Where Somonauk’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 Somonauk’s center.
- Snow: Shabbona 3s, IL.
- Frost, freezing nights, 90° and 100° days, heating and cooling: Chicago Aurora Muni Airport, 14 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 Somonauk’s climate
What is the weather like in Somonauk?
A typical July afternoon reaches 84°, a January night drops to 15°, and about 30 inches of snow falls in a normal winter. Colder January nights than 85% of U.S. towns; cooler July afternoons than 62% of U.S. towns.
How cold does it get in Somonauk in winter?
January nights average 15°. About 142 nights a year reach 32° or below and 14 reach 0° or below. In the coldest January of the last 30 years the month averaged 14°.
How much snow does Somonauk get?
About 30 inches in a normal winter at Shabbona 3s, IL, most of it in January.
How hot does it get in Somonauk?
July, with a typical high of 84° and a low of 63°. About 16 days a year reach 90° (Chicago Aurora Muni Airport).
When is the first and last frost in Somonauk?
In half of years the last spring frost (32°) comes by April 28 and the first fall frost by October 13, about 166 frost-free days, at Chicago Aurora Muni Airport.
What growing zone is Somonauk in?
Zone 5b on the 2023 USDA Plant Hardiness Zone Map: the coldest night of a typical winter reaches about −12°.
What is the best time of year to visit Somonauk?
By one simple rule (highs of 62–84° and lows of 40° or more), May, June, July, August, September and October. The rule is ours, not NOAA’s; the month table has the numbers to judge by.
Is Somonauk getting warmer?
Yes: 1991–2020 averaged 1.2° warmer than 1901–2000 on NOAA’s grid. A smaller shift than 65% of U.S. towns.
Neighbors talk weather
Gardens, snow, and the best days of the year in Somonauk.
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.