Photo: Denise Krebs · CC BY 2.0Alton has some of the coldest winter nights among U.S. towns
The warmest part of a July day comes in at 84° on average. Seasons differ by 77°, from the coldest nights to the warmest afternoons. It is a dry place: less rain and snow fall here than on 86% of U.S. towns. For walks and days out, May, June, August and September bring highs of 71–82°.
A year in Alton at a glance
Each month’s typical high and low, and what it brings.
What stands out about Alton’s climate
Compared with towns across the U.S., with Alton’s place in Iowa beside it.
What a year in Alton feels like
Typical highs and lows by season and by month, from NOAA’s 30-year normals.
About 154 frost-free days a year
In half of years the last 32° night comes by April 30 and the first by October 3. Frost and day counts come from NOAA’s station at Sioux Ctr 2 Se, IA, 9 miles from the town’s center, at about the same height.
The 2023 USDA map puts Alton’s center in zone 5a: the coldest night of a typical winter, averaged over 1991–2020, reaches about −17°. 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 27 inches of snow a winter
Snow, measured at Alton, IA, falls mostly in January. Precipitation (rain plus melted snow) adds up to 29 inches a year; June is the wettest month and January the driest. Rain or snow falls on about 81 days a year.
Rain + melted snow by month
Inches of water
Snowfall by month
Inches of snow
Heating and cooling a home in Alton
89% 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 Sioux Ctr 2 Se, IA.
Living with Alton’s climate
What the numbers mean for a garden, a free afternoon and a bad-weather day.
154 frost-free days in zone 5a. The last frost comes by Apr 30 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 3.
Months with highs of 62–84° and lows of 40° or more: May, June, August and September. 0.0 miles of trails are waiting.
Parks & trails →Of the yearly building losses FEMA expects in Alton from natural hazards, river flooding is the largest share (34%); heat waves, cold waves, winter storms and ice storms together are 12%. Normals are averages; the hazards page covers the extremes.
Natural hazards →Alton and similar climates
TownRatings has no climate map of the towns around Alton yet.
Climates most like Alton’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 |
|---|---|---|---|---|
| Alton, IA | 8° | 84° | 29" | 27" |
| Lake City, MN | 6° | 83° | 35" | 34" |
| Berlin, WI | 9° | 82° | 33" | 38" |
| Grand Island, NE | 15° | 87° | 27" | 28" |
| Marengo, IL | 14° | 83° | 37" | 31" |
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 Alton averaged 0.8° warmer than the 1900s. The biggest change is in December (+2.1°).
A smaller shift than in 90% 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 Alton compares
Against 12,954 U.S. towns of 2,500 or more (one per 5 km climate cell), with Alton’s place among Iowa’s.
Alton weather by month
Highs, lows and precipitation from NOAA’s grid at Alton’s center; snow, wet days and snow on the ground from Alton, IA. 1991–2020 normals.
| Month | High | Low | Rain + melt | Snow | Wet days | 30-yr range |
|---|---|---|---|---|---|---|
| January | 26° | 8° | 0.7" | 6.4" | 5 | 6° – 31° |
| February | 32° | 12° | 0.8" | 4.8" | 5 | 11° – 33° |
| March | 45° | 24° | 1.6" | 5.2" | 6 | 26° – 50° |
| April | 59° | 35° | 3.0" | 1.2" | 8 | 37° – 54° |
| May | 71° | 47° | 4.2" | 0.0" | 10 | 54° – 65° |
| June | 81° | 58° | 4.5" | 0.0" | 10 | 65° – 75° |
| July | 84° | 62° | 3.5" | 0.0" | 8 | 66° – 79° |
| August | 82° | 59° | 3.4" | 0.0" | 7 | 65° – 75° |
| September | 75° | 50° | 3.2" | 0.0" | 7 | 56° – 67° |
| October | 62° | 37° | 2.3" | 0.3" | 6 | 42° – 54° |
| November | 45° | 24° | 1.4" | 3.1" | 5 | 24° – 45° |
| December | 31° | 13° | 0.9" | 5.6" | 5 | 8° – 28° |
| Year | 58° | 36° | 29.4" | 26.6" | 81 |
How much a month can swing
A normal is an average. January swings the most: from 1991 to 2020 its average ranged from 6° to 31°. June is the most reliable, staying within 9°.
Where Alton’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 Alton’s center.
- Snow: Alton, IA (NOAA station in town).
- Frost, freezing nights, 90° and 100° days, heating and cooling: Sioux Ctr 2 Se, IA, 9 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 Alton’s climate
What is the weather like in Alton?
A typical July afternoon reaches 84°, a January night drops to 8°, and about 27 inches of snow falls in a normal winter. Colder January nights than 96% of U.S. towns; cooler July afternoons than 58% of U.S. towns.
How cold does it get in Alton in winter?
January nights average 8°. About 154 nights a year reach 32° or below and 20 reach 0° or below. In the coldest January of the last 30 years the month averaged 6°.
How much snow does Alton get?
About 27 inches in a normal winter at Alton, IA, most of it in January.
How hot does it get in Alton?
July, with a typical high of 84° and a low of 62°. About 23 days a year reach 90° (Sioux Ctr 2 Se, IA).
When is the first and last frost in Alton?
In half of years the last spring frost (32°) comes by April 30 and the first fall frost by October 3, about 154 frost-free days, at Sioux Ctr 2 Se, IA.
What growing zone is Alton in?
Zone 5a on the 2023 USDA Plant Hardiness Zone Map: the coldest night of a typical winter reaches about −17°.
What is the best time of year to visit Alton?
By one simple rule (highs of 62–84° and lows of 40° or more), May, June, August and September. The rule is ours, not NOAA’s; the month table has the numbers to judge by.
Is Alton getting warmer?
Yes: 1991–2020 averaged 0.8° warmer than 1901–2000 on NOAA’s grid. A smaller shift than 90% of U.S. towns.
Neighbors talk weather
Gardens, snow, and the best days of the year in Alton.
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.