Nights turn raw in Seneca Township each January, colder than in 88% of U.S. towns
Midsummer highs settle at about 83°. Precipitation is light here, less than falls on 71% of U.S. towns. December has warmed most since 1901–2000, part of a 1.1° rise. The heating season runs November to April: each of those months averages under 50°.
A year in Seneca Township at a glance
Each month’s typical high and low, and what it brings.
What stands out about Seneca Township’s climate
Compared with towns across the U.S., with Seneca Township’s place in Illinois beside it.
What a year in Seneca Township feels like
Typical highs and lows by season and by month, from NOAA’s 30-year normals.
About 166 frost-free days a year
In half of years the last 32° night comes by April 28 and the first by October 12. Frost and day counts come from NOAA’s station at Marengo, IL, 5 miles from the town’s center, at about the same height.
The 2023 USDA map puts Seneca Township’s center in zone 5b: the coldest night of a typical winter, averaged over 1991–2020, reaches about −13°. 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 31 inches of snow a winter
Snow, measured at Marengo, IL, falls mostly in February and December. Precipitation (rain plus melted snow) adds up to 37 inches a year; June is the wettest month and February the driest. Rain or snow falls on about 101 days a year.
Rain + melted snow by month
Inches of water
Snowfall by month
Inches of snow
Heating and cooling a home in Seneca Township
90% 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 Marengo, IL.
Living with Seneca Township’s climate
What the numbers mean for a garden, a free afternoon and a bad-weather day.
166 frost-free days in zone 5b. 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 12.
Months with highs of 62–84° and lows of 40° or more: May, June, July, August and September. 5.7 miles of trails are waiting.
Parks & trails →Of the yearly building losses FEMA expects in Seneca Township from natural hazards, river flooding is the largest share (63%); heat waves, cold waves, winter storms and ice storms together are 15%. Normals are averages; the hazards page covers the extremes.
Natural hazards →Seneca Township and its neighbors
Every town next door is within a degree of Seneca Township in January and July, closer than the 5 km grid can tell apart. Tap a town to see its climate.
Climates most like Seneca Township’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 |
|---|---|---|---|---|
| Seneca Township, IL | 14° | 83° | 37" | 31" |
| Grinnell, IA | 12° | 84° | 38" | 31" |
| Garrett, IN | 17° | 83° | 38" | 30" |
| Sayre, PA | 17° | 84° | 37" | 35" |
| Bryan, OH | 18° | 84° | 37" | 29" |
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 Seneca Township averaged 1.1° warmer than the 1900s. The biggest change is in December (+2.4°).
A smaller shift than in 73% 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 Seneca Township compares
Against 12,954 U.S. towns of 2,500 or more (one per 5 km climate cell), with Seneca Township’s place among Illinois’.
Seneca Township weather by month
Highs, lows and precipitation from NOAA’s grid at Seneca Township’s center; snow, wet days and snow on the ground from Marengo, IL. 1991–2020 normals.
| Month | High | Low | Rain + melt | Snow | Wet days | 30-yr range |
|---|---|---|---|---|---|---|
| January | 29° | 14° | 1.8" | 8.0" | 7 | 11° – 33° |
| February | 34° | 17° | 1.7" | 9.1" | 6 | 12° – 37° |
| March | 46° | 26° | 2.2" | 2.4" | 8 | 26° – 51° |
| April | 59° | 36° | 3.8" | 0.4" | 11 | 39° – 54° |
| May | 70° | 47° | 4.5" | 0.0" | 12 | 53° – 65° |
| June | 80° | 57° | 4.7" | 0.0" | 10 | 65° – 73° |
| July | 83° | 62° | 4.0" | 0.0" | 9 | 66° – 79° |
| August | 81° | 60° | 3.9" | 0.0" | 9 | 65° – 77° |
| September | 75° | 52° | 3.4" | 0.0" | 7 | 58° – 68° |
| October | 62° | 40° | 3.0" | 0.0" | 8 | 47° – 57° |
| November | 47° | 30° | 2.4" | 1.6" | 7 | 30° – 47° |
| December | 34° | 19° | 1.9" | 9.3" | 7 | 14° – 38° |
| Year | 58° | 38° | 37.3" | 30.8" | 101 |
How much a month can swing
A normal is an average. February swings the most: from 1991 to 2020 its average ranged from 12° to 37°. June is the most reliable, staying within 9°.
Where Seneca Township’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 Seneca Township’s center.
- Snow: Marengo, IL.
- Frost, freezing nights, 90° and 100° days, heating and cooling: Marengo, IL, 5 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 Seneca Township’s climate
What is the weather like in Seneca Township?
A typical July afternoon reaches 83°, a January night drops to 14°, and about 31 inches of snow falls in a normal winter. Colder January nights than 88% of U.S. towns; cooler July afternoons than 66% of U.S. towns.
How cold does it get in Seneca Township in winter?
January nights average 14°. About 147 nights a year reach 32° or below and 15 reach 0° or below. In the coldest January of the last 30 years the month averaged 11°.
How much snow does Seneca Township get?
About 31 inches in a normal winter at Marengo, IL, most of it in February and December.
How hot does it get in Seneca Township?
July, with a typical high of 83° and a low of 62°. About 15 days a year reach 90° (Marengo, IL).
When is the first and last frost in Seneca Township?
In half of years the last spring frost (32°) comes by April 28 and the first fall frost by October 12, about 166 frost-free days, at Marengo, IL.
What growing zone is Seneca Township in?
Zone 5b on the 2023 USDA Plant Hardiness Zone Map: the coldest night of a typical winter reaches about −13°.
What is the best time of year to visit Seneca Township?
By one simple rule (highs of 62–84° and lows of 40° or more), May, June, July, August and September. The rule is ours, not NOAA’s; the month table has the numbers to judge by.
Is Seneca Township getting warmer?
Yes: 1991–2020 averaged 1.1° warmer than 1901–2000 on NOAA’s grid. A smaller shift than 73% of U.S. towns.
Neighbors talk weather
Gardens, snow, and the best days of the year in Seneca Township.
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.