Posen, Illinois Weather
Fireflies rise from the lawn. Day 77 of spring. Read this microseason across nine climate regions →
Posen weather forecast — hour by hour, 7-day outlook, NOAA radar
- TodayJun 4Overcast——88°59°—
- FridayJun 5Rain78%0.10″83°69°-5°
- SaturdayJun 6Showers60%0.02″80°67°-3°
- SundayJun 7Light Drizzle16%—83°68°+3°
- MondayJun 8Light Showers34%—83°69°0°
- TuesdayJun 9Light Drizzle26%—87°70°+4°
- WednesdayJun 10Light Showers19%0.09″84°72°-3°
PM2.5 at 8.5 µg/m³ (AQI 47) with a 0.93 fine-to-coarse ratio and 4 mph wind — combustion smoke trapped in calm air, not road dust. AQI down 26 over the last 6 hours — air quality is improving sharply.
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 35. Overcast through the UV peak window (cloud cover ~60%) — afternoon ozone should stay flat.
- Present
- AQI 35
- UV peak
- 3.3 at 1 PM
- Sky at peak
- overcast
- Projected peak
- AQI 8
PM × Wind × Precip
PM2.5 at 8.5 µg/m³ (AQI 47) with a 0.93 fine-to-coarse ratio and 4 mph wind — combustion smoke trapped in calm air, not road dust.
- PM2.5/PM10
- 0.93
- Wind
- calm
- Recent rain
- 0h in last 6h
- Pattern
- stagnant smoke
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
- 4:25 AM
- Moonset
- 1:47 PM
- In sign
- ♑︎ Capricorn
Fireflies rise from the lawn
Posen at a glance
- Today vs. normal: 10°F below the seasonal normal for this latitude
- Last frost: April 26 (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 — Posen
SPC has placed Posen in the Marginal Risk category for severe thunderstorms tomorrow.
- TODAYNONENo severe risk
- TOMORROWMRGLMarginal Risk
- DAY 3MRGLMarginal Risk
Isolated severe storms possible. Limited threat for hail or damaging wind.
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
Posen's warmest month is July (~76°F mean) and its coldest is January (~26°F). Rainfall peaks in May (4.1 inches) and bottoms out in February (1.5 inches).
| Month | Mean temp | Precip | Rainy days |
|---|---|---|---|
| January | 26° | 1.5″ | 3 |
| February | 30° | 1.5″ | 3 |
| March | 40° | 1.9″ | 5 |
| April | 51° | 3.6″ | 7 |
| May | 62° | 4.1″ | 8 |
| June | 72° | 4.0″ | 8 |
| July | 76° | 3.5″ | 6 |
| August | 75° | 4.0″ | 6 |
| September | 68° | 2.8″ | 5 |
| October | 55° | 3.5″ | 6 |
| November | 42° | 2.4″ | 5 |
| December | 31° | 1.8″ | 4 |
Regional context
Posen sits within a warm-summer humid continental climate region — a cohort that shares similar temperature ranges, seasonal patterns, and growing conditions across nearby cities.
Similar climates: Chicago, IL, Rockford, IL, Round Lake Beach, IL, Aurora, IL, Naperville, IL.
Frequently asked
- When does it freeze in Posen?
- Posen's last spring frost typically falls around mid-April, and the first fall frost arrives around mid-November.
- What is the rainy season in Posen?
- May is the wettest month with about 4.1 inches of rain on average; the city receives roughly 34 inches annually.
- What is the warmest month in Posen?
- July is typically warmest, averaging about 76°F.
- What is the coldest month in Posen?
- January is typically coldest, averaging about 26°F.
- When can I start a vegetable garden in Posen?
- 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 Posen get?
- Posen averages about 68 rainy days per year.
- What hardiness zone is Posen?
- Posen'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
Posen, Illinois sits in a warm-summer humid continental climate zone. January means hover near 26°F while July averages 76°F — a 50°F seasonal swing.
Across the year, Posen receives about 34 inches of precipitation spread over roughly 68 rainy days.
The rhythm of the year is set by latitude (41.6°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.