Photo: Busjack · CC BY-SA 3.0January in Riverwoods bites harder than in 77% of U.S. towns
Peak summer warmth arrives in July, with afternoons near 83°. June is the wettest month, February the driest. Its July afternoons stay fresher than in 73% of U.S. towns. Seedlings are safe outdoors from about April 26, with the first autumn frost due around October 21.
A year in Riverwoods at a glance
Each month’s typical high and low, and what it brings.
What stands out about Riverwoods’ climate
Compared with towns across the U.S., with Riverwoods’ place in Illinois beside it.
What a year in Riverwoods feels like
Typical highs and lows by season and by month, from NOAA’s 30-year normals.
About 176 frost-free days a year
In half of years the last 32° night comes by April 26 and the first by October 21. Frost and day counts come from NOAA’s station at Chicago Botanic Garden, IL, 6 miles from the town’s center, at about the same height.
The 2023 USDA map puts Riverwoods’ center in zone 6a: the coldest night of a typical winter, averaged over 1991–2020, reaches about −8°. 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 34 inches of snow a winter
Snow, measured at Chicago Botanic Garden, IL, falls mostly in January. Precipitation (rain plus melted snow) adds up to 37 inches a year; June is the wettest month and February the driest. Rain or snow falls on about 130 days a year.
Rain + melted snow by month
Inches of water
Snowfall by month
Inches of snow
Heating and cooling a home in Riverwoods
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 Botanic Garden, IL.
Living with Riverwoods’ climate
What the numbers mean for a garden, a free afternoon and a bad-weather day.
176 frost-free days in zone 6a. The last frost comes by Apr 26 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 21.
Months with highs of 62–84° and lows of 40° or more: May, June, July, August and September. 11 miles of trails are waiting.
Parks & trails →Of the yearly building losses FEMA expects in Riverwoods from natural hazards, river flooding is the largest share (76%); heat waves, cold waves, winter storms and ice storms together are 9%. Normals are averages; the hazards page covers the extremes.
Natural hazards →Riverwoods and its neighbors
Every town next door is within a degree of Riverwoods in January and July, closer than the 5 km grid can tell apart. Tap a town to see its climate.
Climates most like Riverwoods’, 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 |
|---|---|---|---|---|
| Riverwoods, IL | 17° | 83° | 37" | 34" |
| Sayre, PA | 17° | 84° | 37" | 35" |
| Garrett, IN | 17° | 83° | 38" | 30" |
| Charlotte, MI | 17° | 82° | 36" | 38" |
| Willard, OH | 18° | 83° | 39" | 33" |
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 Riverwoods averaged 1.3° warmer than the 1900s. The biggest change is in December (+2.6°).
A smaller shift than in 54% 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 Riverwoods compares
Against 12,954 U.S. towns of 2,500 or more (one per 5 km climate cell), with Riverwoods’ place among Illinois’.
Riverwoods weather by month
Highs, lows and precipitation from NOAA’s grid at Riverwoods’ center; snow, wet days and snow on the ground from Chicago Botanic Garden, IL. 1991–2020 normals.
| Month | High | Low | Rain + melt | Snow | Wet days | Snow on ground | 30-yr range |
|---|---|---|---|---|---|---|---|
| January | 31° | 17° | 1.9" | 11.3" | 11 | 20 | 14° – 35° |
| February | 35° | 20° | 1.8" | 7.7" | 9 | 14 | 15° – 38° |
| March | 46° | 29° | 2.2" | 5.6" | 10 | 7 | 29° – 52° |
| April | 57° | 38° | 3.8" | 1.1" | 13 | 1 | 39° – 54° |
| May | 69° | 48° | 4.4" | 0.0" | 13 | 0 | 52° – 65° |
| June | 78° | 58° | 4.5" | 0.0" | 12 | 0 | 64° – 73° |
| July | 83° | 64° | 3.8" | 0.0" | 10 | 0 | 68° – 80° |
| August | 81° | 62° | 3.8" | 0.0" | 10 | 0 | 66° – 77° |
| September | 74° | 55° | 3.4" | 0.0" | 10 | 0 | 59° – 69° |
| October | 62° | 43° | 3.2" | 0.1" | 11 | 0 | 48° – 58° |
| November | 48° | 32° | 2.5" | 1.9" | 10 | 2 | 32° – 48° |
| December | 36° | 23° | 2.1" | 5.9" | 11 | 10 | 17° – 39° |
| Year | 58° | 41° | 37.4" | 33.6" | 130 | 53 |
How much a month can swing
A normal is an average. February swings the most: from 1991 to 2020 its average ranged from 15° to 38°. June is the most reliable, staying within 9°.
Where Riverwoods’ 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 Riverwoods’ center.
- Snow: Chicago Botanic Garden, IL.
- Frost, freezing nights, 90° and 100° days, heating and cooling: Chicago Botanic Garden, 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 Riverwoods’ climate
What is the weather like in Riverwoods?
A typical July afternoon reaches 83°, a January night drops to 17°, and about 34 inches of snow falls in a normal winter. Colder January nights than 77% of U.S. towns; cooler July afternoons than 73% of U.S. towns.
How cold does it get in Riverwoods in winter?
January nights average 17°. About 128 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 14°.
How much snow does Riverwoods get?
About 34 inches in a normal winter at Chicago Botanic Garden, IL, most of it in January, with snow on the ground about 53 days a year.
How hot does it get in Riverwoods?
July, with a typical high of 83° and a low of 64°. About 17 days a year reach 90° (Chicago Botanic Garden, IL).
When is the first and last frost in Riverwoods?
In half of years the last spring frost (32°) comes by April 26 and the first fall frost by October 21, about 176 frost-free days, at Chicago Botanic Garden, IL.
What growing zone is Riverwoods in?
Zone 6a on the 2023 USDA Plant Hardiness Zone Map: the coldest night of a typical winter reaches about −8°.
What is the best time of year to visit Riverwoods?
By one simple rule (highs of 62–84° and lows of 40° or more), May, June, July, August and September. The rule is ours, not NOAA’s; the month table has the numbers to judge by.
Is Riverwoods getting warmer?
Yes: 1991–2020 averaged 1.3° warmer than 1901–2000 on NOAA’s grid. A smaller shift than 54% of U.S. towns.
Neighbors talk weather
Gardens, snow, and the best days of the year in Riverwoods.
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.