Photo: User:Onemessedzebra · Public domainSummers, winters and rain in St. Joseph all run close to those of most U.S. towns
July afternoons average 85°. A year here swings 67° from midwinter lows to midsummer highs. By January nights alone, it runs colder than 70% of U.S. towns. Picnics, hikes and garden evenings come into their own from April to June and September to October, with highs of 64–83°.
A year in St. Joseph at a glance
Each month’s typical high and low, and what it brings.
What stands out about St. Joseph’s climate
Compared with towns across the U.S., with St. Joseph’s place in Illinois beside it.
What a year in St. Joseph feels like
Typical highs and lows by season and by month, from NOAA’s 30-year normals.
About 182 frost-free days a year
In half of years the last 32° night comes by April 20 and the first by October 21. Frost and day counts come from NOAA’s station at Ogden, IL, 4 miles from the town’s center, at about the same height.
The 2023 USDA map puts St. Joseph’s center in zone 6a: the coldest night of a typical winter, averaged over 1991–2020, reaches about −8°. 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 25 inches of snow a winter
Snow, measured at Ogden, IL, falls mostly in February. Precipitation (rain plus melted snow) adds up to 40 inches a year; June is the wettest month and February the driest. Rain or snow falls on about 134 days a year.
Rain + melted snow by month
Inches of water
Snowfall by month
Inches of snow
Heating and cooling a home in St. Joseph
85% 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 Ogden, IL.
Living with St. Joseph’s climate
What the numbers mean for a garden, a free afternoon and a bad-weather day.
182 frost-free days in zone 6a. The last frost comes by Apr 20 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 21.
Months with highs of 62–84° and lows of 40° or more: April, May, June, September and October. 0.4 miles of trails are waiting.
Parks & trails →Of the yearly building losses FEMA expects in St. Joseph from natural hazards, river flooding is the largest share (64%); heat waves, cold waves, winter storms and ice storms together are 20%. Normals are averages; the hazards page covers the extremes.
Natural hazards →St. Joseph and similar climates
TownRatings has no climate map of the towns around St. Joseph yet.
Climates most like St. Joseph’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 |
|---|---|---|---|---|
| St. Joseph, IL | 18° | 85° | 40" | 25" |
| Keokuk, IA | 18° | 86° | 40" | 23" |
| Lock Haven, PA | 19° | 86° | 41" | 30" |
| Delaware, OH | 20° | 85° | 41" | 24" |
| Decatur, IN | 19° | 84° | 40" | 28" |
Temperatures and precipitation come from NOAA’s 5 km grid; snow and day counts from the stations named on this page.
Warmer than it used to be
The last 30 years in St. Joseph averaged 1.2° warmer than the 1900s. The biggest change is in December (+2.2°).
A smaller shift than in 65% 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 St. Joseph compares
Against 12,954 U.S. towns of 2,500 or more (one per 5 km climate cell), with St. Joseph’s place among Illinois’.
St. Joseph weather by month
Highs, lows and precipitation from NOAA’s grid at St. Joseph’s center; snow, wet days and snow on the ground from Ogden, IL. 1991–2020 normals.
| Month | High | Low | Rain + melt | Snow | Wet days | Snow on ground | 30-yr range |
|---|---|---|---|---|---|---|---|
| January | 34° | 18° | 2.3" | 5.9" | 10 | 10 | 19° – 38° |
| February | 39° | 22° | 2.0" | 9.3" | 10 | 11 | 18° – 41° |
| March | 51° | 31° | 2.7" | 3.0" | 13 | 2 | 34° – 55° |
| April | 64° | 41° | 4.1" | 0.3" | 12 | 0 | 45° – 58° |
| May | 74° | 52° | 4.4" | 0.0" | 14 | 0 | 57° – 71° |
| June | 83° | 61° | 4.7" | 0.0" | 13 | 0 | 68° – 75° |
| July | 85° | 64° | 4.3" | 0.0" | 11 | 0 | 70° – 81° |
| August | 84° | 62° | 3.3" | 0.0" | 10 | 0 | 68° – 79° |
| September | 79° | 54° | 3.1" | 0.0" | 9 | 0 | 61° – 71° |
| October | 66° | 43° | 3.3" | 0.0" | 11 | 0 | 50° – 60° |
| November | 51° | 33° | 3.2" | 1.0" | 10 | 1 | 35° – 49° |
| December | 39° | 24° | 2.3" | 5.5" | 11 | 7 | 17° – 41° |
| Year | 63° | 42° | 39.7" | 25.0" | 134 | 31 |
How much a month can swing
A normal is an average. December swings the most: from 1991 to 2020 its average ranged from 17° to 41°. June is the most reliable, staying within 8°.
Where St. Joseph’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 St. Joseph’s center.
- Snow: Ogden, IL.
- Frost, freezing nights, 90° and 100° days, heating and cooling: Ogden, IL, 4 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 St. Joseph’s climate
What is the weather like in St. Joseph?
A typical July afternoon reaches 85°, a January night drops to 18°, and about 25 inches of snow falls in a normal winter. Colder January nights than 70% of U.S. towns; hotter July afternoons than 52% of U.S. towns.
How cold does it get in St. Joseph in winter?
January nights average 18°. About 118 nights a year reach 32° or below and 7 reach 0° or below. In the coldest January of the last 30 years the month averaged 19°.
How much snow does St. Joseph get?
About 25 inches in a normal winter at Ogden, IL, most of it in February, with snow on the ground about 31 days a year.
How hot does it get in St. Joseph?
July, with a typical high of 85° and a low of 64°. About 14 days a year reach 90° (Ogden, IL).
When is the first and last frost in St. Joseph?
In half of years the last spring frost (32°) comes by April 20 and the first fall frost by October 21, about 182 frost-free days, at Ogden, IL.
What growing zone is St. Joseph in?
Zone 6a on the 2023 USDA Plant Hardiness Zone Map: the coldest night of a typical winter reaches about −8°.
What is the best time of year to visit St. Joseph?
By one simple rule (highs of 62–84° and lows of 40° or more), April, May, June, September and October. The rule is ours, not NOAA’s; the month table has the numbers to judge by.
Is St. Joseph getting warmer?
Yes: 1991–2020 averaged 1.2° warmer than 1901–2000 on NOAA’s grid. A smaller shift than 65% of U.S. towns.
Neighbors talk weather
Gardens, snow, and the best days of the year in St. Joseph.
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.