Monticello, Illinois Weather
Fireflies pulse through the magnolias. Day 77 of spring. Read this microseason across nine climate regions →
Monticello weather forecast — hour by hour, 7-day outlook, NOAA radar
- TodayJun 4Overcast——83°58°—
- FridayJun 5Drizzle28%0.03″83°65°0°
- SaturdayJun 6Light Showers50%—85°67°+2°
- SundayJun 7Light Showers32%—85°69°0°
- MondayJun 8Light Showers47%—81°69°-4°
- TuesdayJun 9Light Drizzle30%—85°68°+4°
- WednesdayJun 10Light Showers23%—89°73°+4°
Ozone at AQI 36 now. AQI down 22 over the last 6 hours — air quality is improving sharply. With UV 3.3 peaking around 1 PM under partly cloudy skies, surface ozone likely climbs to AQI 11 by mid-afternoon.
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 36 now. With UV 3.3 peaking around 1 PM under partly cloudy skies, surface ozone likely climbs to AQI 11 by mid-afternoon.
- Present
- AQI 36
- UV peak
- 3.3 at 1 PM
- Sky at peak
- partly cloudy
- Projected peak
- AQI 11
PM × Wind × Precip
PM2.5 at 4.8 µg/m³, PM10 at 5.1 µg/m³ — typical background levels with no transport signature.
- PM2.5/PM10
- 0.94
- Wind
- light
- Recent rain
- 0h in last 6h
- Pattern
- background
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).
A summer fog for fair, a winter fog for rain.
- Moonrise
- 4:23 AM
- Moonset
- 1:56 PM
- In sign
- ♑︎ Capricorn
Fireflies pulse through the magnolias
Monticello at a glance
- Today vs. normal: 15°F below the seasonal normal for this latitude
- Last frost: April 16 (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 4, 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 — Monticello
SPC has placed Monticello in the General Thunderstorms category for severe thunderstorms tomorrow.
- TODAYNONENo severe risk
- TOMORROWTSTMGeneral Thunderstorms
- 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
Monticello's warmest month is July (~73°F mean) and its coldest is January (~25°F). Rainfall peaks in June (4.9 inches) and bottoms out in February (2.0 inches).
| Month | Mean temp | Precip | Rainy days |
|---|---|---|---|
| January | 25° | 2.3″ | 6 |
| February | 30° | 2.0″ | 5 |
| March | 40° | 2.9″ | 6 |
| April | 52° | 3.7″ | 7 |
| May | 62° | 4.6″ | 8 |
| June | 71° | 4.9″ | 7 |
| July | 73° | 4.3″ | 6 |
| August | 71° | 3.3″ | 5 |
| September | 65° | 3.1″ | 5 |
| October | 53° | 3.1″ | 6 |
| November | 41° | 3.1″ | 5 |
| December | 31° | 2.3″ | 6 |
Regional context
Monticello's baseline climate, derived from NOAA NCEI 1991-2020 normals at the nearest reporting station, swings from a January mean of 25°F to a July mean of 73°F — a 48°F seasonal arc typical of the mid-latitude bands. Annual precipitation runs about 39.6 inches spread across roughly 72 days with measurable rain or snow each year.
Precipitation runs summer-dominant here: June averages 4.9 inches across 7.2 days with measurable rain, driven mostly by warm-season storms and thunderstorm activity, while February drops to just 2.0 inches across 4.9 rainy days under drier cool-season air. That summer-storm-driven distribution puts Monticello in a cohort with places like White Heath, IL, De Land, IL and Bement, IL, all of which depend on warm-season convective activity for the bulk of their annual moisture.
The frost-sensitive growing window opens around mid-April, when overnight lows reliably clear freezing for cool-season crops like kale, peas, spinach, and parsnips. Warm-soil crops — tomatoes, peppers, eggplant — wait until soil temperatures reach the mid-50s°F, usually two weeks past the last-frost date. The window closes around mid-November, when overnight lows resume dipping below freezing and frost-tender plants need protection or harvest. These are 30-year central tendencies; year-to-year frost dates can move by up to two weeks. Local features matter: a south-facing slope inside Monticello typically runs 3-5 days ahead of the regional last-frost date, while a low-lying lot along a creek or drainage can lag the same date by a week or more on calm clear nights.
Similar climates: White Heath, IL, De Land, IL, Bement, IL, Cisco, IL, Ivesdale, IL.
Frequently asked
- When does it freeze in Monticello?
- Monticello's last spring frost typically falls around mid-April, and the first fall frost arrives around mid-November.
- What is the rainy season in Monticello?
- June is the wettest month with about 4.9 inches of rain on average; the city receives roughly 40 inches annually.
- What is the warmest month in Monticello?
- July is typically warmest, averaging about 73°F.
- What is the coldest month in Monticello?
- January is typically coldest, averaging about 25°F.
- When can I start a vegetable garden in Monticello?
- 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 Monticello get?
- Monticello averages about 72 rainy days per year.
- What hardiness zone is Monticello?
- Monticello'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
Monticello, Illinois sits in a humid subtropical climate zone. January means hover near 25°F while July averages 73°F — a 48°F seasonal swing.
Across the year, Monticello receives about 40 inches of precipitation spread over roughly 72 rainy days.
The rhythm of the year is set by latitude (40.0°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.