Chatham, Illinois Weather
Fireflies pulse through the magnolias. Day 76 of spring. Read this microseason across nine climate regions →
Chatham weather forecast — hour by hour, 7-day outlook, NOAA radar
- TodayJun 3Partly Cloudy——80°52°—
- ThursdayJun 4Overcast——83°57°+3°
- FridayJun 5Light Drizzle31%—85°64°+2°
- SaturdayJun 6Showers50%—83°66°-2°
- SundayJun 7Showers22%—88°70°+5°
- MondayJun 8Light Showers46%—79°70°-9°
- TuesdayJun 9Drizzle25%0.06″78°70°-1°
Ozone at AQI 83 — peak already passed at 1 PM under clear skies. AQI up 16 in the last 6 hours — air quality is degrading. Levels should ease through evening.
OK No precautions needed for the general population; unusually sensitive individuals may consider limiting prolonged outdoor exertion.
What's driving it
Ozone × UV × Sky
Ozone at AQI 83 — peak already passed at 1 PM under clear skies. Levels should ease through evening.
- Present
- AQI 83
- UV peak
- 6.3 at earlier today
- Sky at peak
- clear
- Projected peak
- AQI 83
Trends
Seven days of AQI and PM2.5.
Hourly air-quality data from the Copernicus Atmosphere Monitoring Service, charted across the past and next several days. Dashed lines mark the AQI breakpoints at 50 (Good → Moderate) and 100 (Moderate → Unhealthy for Sensitive Groups).
The higher the clouds, the finer the weather.
- Moonrise
- 3:49 AM
- Moonset
- 12:59 PM
- In sign
- ♑︎ Capricorn
Fireflies pulse through the magnolias
Chatham at a glance
- Today vs. normal: 4°F above the seasonal normal for this latitude
- Last frost: April 14 (climatological average for this latitude)
- Microseason: Jun 1–5
- Planting window: Harvest spring lettuce before it bolts. Sow heat-tolerant greens.
Right now in the garden
Peak growing season
As of June 3, the growing season is at its peak — frost is months away. Continue succession-planting beans and summer squash. Start fall brassicas (broccoli, cabbage, kale) from seed indoors for transplanting in late summer.
SPC Convective Outlook
Storm Prediction Center — Chatham
SPC has placed Chatham in the General Thunderstorms category for severe thunderstorms day after tomorrow.
- TODAYNONENo severe risk
- TOMORROWNONENo severe risk
- DAY 3TSTMGeneral Thunderstorms
Thunderstorms possible. Not severe, but capable of producing lightning and brief heavy rain.
Source: NOAA / NWS Storm Prediction Center categorical convective outlook. Outlooks are re-issued multiple times per day; this page reflects the most recent SPC polygons covering the city’s coordinates.
Planting calendar
| Month | Plant | Harvest |
|---|---|---|
| January | — | — |
| February | — | — |
| March | — | — |
| April | lettuce, peas, spinach, radishes | — |
| May | lettuce, peas, spinach, radishes, tomatoes, peppers, beans, squash | lettuce, peas, radishes |
| June | tomatoes, peppers, beans, squash | lettuce, peas, radishes |
| July | tomatoes, peppers, beans, squash | tomatoes, beans, summer squash |
| August | — | tomatoes, beans, summer squash |
| September | fall brassicas, garlic (overwinter), carrots | tomatoes, beans, summer squash |
| October | fall brassicas, garlic (overwinter), carrots | winter squash, tomatoes (last) |
| November | — | — |
| December | — | — |
A year in weather
Chatham's warmest month is July (~76°F mean) and its coldest is January (~27°F). Rainfall peaks in May (5.1 inches) and bottoms out in January (2.2 inches).
| Month | Mean temp | Precip | Rainy days |
|---|---|---|---|
| January | 27° | 2.2″ | 5 |
| February | 31° | 2.2″ | 5 |
| March | 42° | 3.0″ | 7 |
| April | 53° | 4.1″ | 7 |
| May | 63° | 5.1″ | 9 |
| June | 73° | 5.0″ | 7 |
| July | 76° | 4.4″ | 7 |
| August | 74° | 2.9″ | 5 |
| September | 67° | 3.1″ | 5 |
| October | 55° | 3.1″ | 6 |
| November | 43° | 3.1″ | 6 |
| December | 33° | 2.3″ | 6 |
Regional context
Chatham sits within a humid subtropical climate region — a cohort that shares similar temperature ranges, seasonal patterns, and growing conditions across nearby cities.
Similar climates: Peoria, IL, Springfield, IL, Champaign, IL, Bloomington, IL, Alton, IL.
Frequently asked
- When does it freeze in Chatham?
- Chatham's last spring frost typically falls around mid-April, and the first fall frost arrives around mid-November.
- What is the rainy season in Chatham?
- May is the wettest month with about 5.1 inches of rain on average; the city receives roughly 40 inches annually.
- What is the warmest month in Chatham?
- July is typically warmest, averaging about 76°F.
- What is the coldest month in Chatham?
- January is typically coldest, averaging about 27°F.
- When can I start a vegetable garden in Chatham?
- Cool-season crops (peas, lettuce) can be sown around the last spring frost (mid-April); warm-season crops (tomatoes, peppers) wait until 1–2 weeks after.
- How many rainy days does Chatham get?
- Chatham averages about 75 rainy days per year.
- What hardiness zone is Chatham?
- Chatham's USDA hardiness zone is determined by its lowest average winter temperature; check the USDA's online lookup with the city ZIP for the current zone designation.
Climate
Chatham, Illinois sits in a humid subtropical climate zone. January means hover near 27°F while July averages 76°F — a 49°F seasonal swing.
Across the year, Chatham receives about 40 inches of precipitation spread over roughly 75 rainy days.
The rhythm of the year is set by latitude (39.7°N), proximity to large water bodies, and elevation — all of which shape what grows here, when frost is likely, and what the weather story looks like day to day.