Photo: Dima Sergiyenko; Please attribute this image as the work of "DiscoverWithDima." · CC BY-SA 4.0Midwinter lows in Oak Brook sink below those of 79% of U.S. towns
On a normal July day the thermometer tops out near 84°. Precipitation is light here, less than falls on 66% of U.S. towns. Decade by decade the climate has edged up, 1.4° above 1901–2000. Tender plants can go out after about April 28; in half of years the first frost comes by October 16.
A year in Oak Brook at a glance
Each month’s typical high and low, and what it brings.
What stands out about Oak Brook’s climate
Compared with towns across the U.S., with Oak Brook’s place in Illinois beside it.
What a year in Oak Brook feels like
Typical highs and lows by season and by month, from NOAA’s 30-year normals.
About 169 frost-free days a year
In half of years the last 32° night comes by April 28 and the first by October 16. Frost and day counts come from NOAA’s station at Lisle-morton Arboretum, IL, 6 miles from the town’s center, at about the same height.
The 2023 USDA map puts Oak Brook’s center in zone 6a: the coldest night of a typical winter, averaged over 1991–2020, reaches about −9°. 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 42 inches of snow a winter
Snow, measured at Oak Brook 2w, IL, falls mostly in February. Precipitation (rain plus melted snow) adds up to 38 inches a year; May is the wettest month and February the driest. Rain or snow falls on about 133 days a year.
Rain + melted snow by month
Inches of water
Snowfall by month
Inches of snow
Heating and cooling a home in Oak Brook
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 Lisle-morton Arboretum, IL.
Living with Oak Brook’s climate
What the numbers mean for a garden, a free afternoon and a bad-weather day.
169 frost-free days in zone 6a. 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 16.
Months with highs of 62–84° and lows of 40° or more: May, June, August, September and October. 8.1 miles of trails are waiting.
Parks & trails →Of the yearly building losses FEMA expects in Oak Brook from natural hazards, river flooding is the largest share (63%); heat waves, cold waves, winter storms and ice storms together are 14%. Normals are averages; the hazards page covers the extremes.
Natural hazards →Oak Brook and its neighbors
Every town next door is within a degree of Oak Brook in January and July, closer than the 5 km grid can tell apart. Tap a town to see its climate.
Climates most like Oak Brook’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 |
|---|---|---|---|---|
| Oak Brook, IL | 16° | 84° | 38" | 42" |
| Duryea, PA | 18° | 84° | 40" | 45" |
| Fort Wayne, IN | 18° | 84° | 39" | 34" |
| Southport, NY | 16° | 83° | 36" | 42" |
| Marshall, MI | 17° | 83° | 37" | 40" |
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 Oak Brook averaged 1.4° warmer than the 1900s. The biggest change is in December (+2.7°).
A bigger shift than in 56% 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 Oak Brook compares
Against 12,954 U.S. towns of 2,500 or more (one per 5 km climate cell), with Oak Brook’s place among Illinois’.
Oak Brook weather by month
Highs, lows and precipitation from NOAA’s grid at Oak Brook’s center; snow, wet days and snow on the ground from Oak Brook 2w, IL. 1991–2020 normals.
| Month | High | Low | Rain + melt | Snow | Wet days | Snow on ground | 30-yr range |
|---|---|---|---|---|---|---|---|
| January | 31° | 16° | 2.0" | 12.6" | 11 | 17 | 15° – 35° |
| February | 36° | 20° | 1.8" | 14.5" | 10 | 18 | 15° – 38° |
| March | 47° | 29° | 2.4" | 4.1" | 12 | 6 | 30° – 53° |
| April | 60° | 38° | 3.9" | 0.8" | 12 | 1 | 41° – 55° |
| May | 71° | 49° | 4.7" | 0.0" | 13 | 0 | 54° – 66° |
| June | 81° | 59° | 4.4" | 0.0" | 13 | 0 | 66° – 74° |
| July | 84° | 64° | 3.8" | 0.0" | 10 | 0 | 69° – 80° |
| August | 82° | 62° | 4.0" | 0.0" | 10 | 0 | 67° – 79° |
| September | 76° | 55° | 3.3" | 0.0" | 9 | 0 | 59° – 69° |
| October | 63° | 43° | 3.5" | 0.0" | 11 | 0 | 48° – 59° |
| November | 48° | 32° | 2.5" | 0.6" | 9 | 0 | 32° – 48° |
| December | 36° | 22° | 2.1" | 9.7" | 13 | 14 | 16° – 39° |
| Year | 60° | 41° | 38.3" | 42.3" | 133 | 55 |
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 Oak Brook’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 Oak Brook’s center.
- Snow: Oak Brook 2w, IL (NOAA station in town).
- Frost, freezing nights, 90° and 100° days, heating and cooling: Lisle-morton Arboretum, 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 Oak Brook’s climate
What is the weather like in Oak Brook?
A typical July afternoon reaches 84°, a January night drops to 16°, and about 42 inches of snow falls in a normal winter. Colder January nights than 79% of U.S. towns; cooler July afternoons than 59% of U.S. towns.
How cold does it get in Oak Brook in winter?
January nights average 16°. About 144 nights a year reach 32° or below and 12 reach 0° or below. In the coldest January of the last 30 years the month averaged 15°.
How much snow does Oak Brook get?
About 42 inches in a normal winter at Oak Brook 2w, IL, most of it in February, with snow on the ground about 55 days a year.
How hot does it get in Oak Brook?
July, with a typical high of 84° and a low of 64°. About 17 days a year reach 90° (Lisle-morton Arboretum, IL).
When is the first and last frost in Oak Brook?
In half of years the last spring frost (32°) comes by April 28 and the first fall frost by October 16, about 169 frost-free days, at Lisle-morton Arboretum, IL.
What growing zone is Oak Brook in?
Zone 6a on the 2023 USDA Plant Hardiness Zone Map: the coldest night of a typical winter reaches about −9°.
What is the best time of year to visit Oak Brook?
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 Oak Brook getting warmer?
Yes: 1991–2020 averaged 1.4° warmer than 1901–2000 on NOAA’s grid. A bigger shift than 56% of U.S. towns.
Neighbors talk weather
Gardens, snow, and the best days of the year in Oak Brook.
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.