Weather in Oswego, Illinois
Roses open along the stoops. Day 59 of spring. Read this microseason across nine climate regions →
- TodayMay 16Light Rain49%82°61°
- SundayMay 17Light Drizzle16%86°64°
- MondayMay 18Rain70%82°68°
- TuesdayMay 19Showers61%76°55°
- WednesdayMay 20Overcast17%62°46°
- ThursdayMay 21Overcast—65°45°
- FridayMay 22Overcast11%59°51°
- PM 2.5
- 7.8 μg/m³
- PM 10
- 8.7 μg/m³
- NO₂
- 11.0 μg/m³
- Ozone
- 74.0 μg/m³
- UV Index
- 0.0 Low
When the dew is on the grass, rain will never come to pass.
- Moonrise
- 10:36 AM
- Moonset
- 1:38 AM
- In sign
- ♊︎ Gemini
Roses open along the stoops
Oswego at a glance
- Today vs. normal: 68°F — typical for the season
- Last frost: April 26 (climatological average for this latitude)
- Microseason: 28 of 72, May 16–20
- Planting window: Direct sow okra, melons, and southern peas. Thin carrot rows.
Right now in the garden
Warm-season window is open
As of May 17, the last spring frost has passed for most years. Transplant tomatoes, peppers, eggplants, basil, and cucurbits (cucumbers, squash, melons) now. Direct-sow beans and corn into warm soil.
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
Oswego's warmest month is July (~74°F mean) and its coldest is January (~23°F). Rainfall peaks in May (4.9 inches) and bottoms out in February (1.8 inches).
| Month | Mean temp | Precip | Rainy days |
|---|---|---|---|
| January | 23° | 1.9″ | 5 |
| February | 27° | 1.8″ | 4 |
| March | 38° | 2.4″ | 6 |
| April | 50° | 4.0″ | 8 |
| May | 61° | 4.9″ | 8 |
| June | 70° | 4.5″ | 8 |
| July | 74° | 4.2″ | 7 |
| August | 73° | 3.9″ | 7 |
| September | 66° | 3.4″ | 6 |
| October | 53° | 3.7″ | 6 |
| November | 40° | 2.7″ | 5 |
| December | 29° | 2.2″ | 5 |
Regional context
Oswego 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 Oswego?
- Oswego's last spring frost typically falls around mid-April, and the first fall frost arrives around mid-November.
- What is the rainy season in Oswego?
- May is the wettest month with about 4.9 inches of rain on average; the city receives roughly 39 inches annually.
- What is the warmest month in Oswego?
- July is typically warmest, averaging about 74°F.
- What is the coldest month in Oswego?
- January is typically coldest, averaging about 23°F.
- When can I start a vegetable garden in Oswego?
- 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 Oswego get?
- Oswego averages about 74 rainy days per year.
- What hardiness zone is Oswego?
- Oswego'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
Oswego, Illinois sits in a warm-summer humid continental climate zone. January means hover near 23°F while July averages 74°F — a 51°F seasonal swing.
Across the year, Oswego receives about 39 inches of precipitation spread over roughly 74 rainy days.
The rhythm of the year is set by latitude (41.7°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.