Photo: JERRYE AND ROY KLOTZ MD · CC BY-SA 3.0Hardly any U.S. towns see harsher January nights than Castlewood
On a normal July day the thermometer tops out near 82°. Its yearly precipitation falls short of 87% of U.S. towns. The latest 30-year average runs 1.2° warmer than 1901–2000’s, with December up the most. The frost-free window for a garden runs roughly May 6 to October 1.
A year in Castlewood at a glance
Each month’s typical high and low, and what it brings.
What stands out about Castlewood’s climate
Compared with towns across the U.S., with Castlewood’s place in South Dakota beside it.
What a year in Castlewood feels like
Typical highs and lows by season and by month, from NOAA’s 30-year normals.
About 145 frost-free days a year
In half of years the last 32° night comes by May 6 and the first by October 1. Frost and day counts come from NOAA’s station at Castlewood #2, SD, 0.2 miles from the town’s center, at about the same height.
The 2023 USDA map puts Castlewood’s center in zone 4a: the coldest night of a typical winter, averaged over 1991–2020, reaches about −26°. 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 34 inches of snow a winter
Snow, measured at Hayti, SD, falls mostly in December. Precipitation (rain plus melted snow) adds up to 25 inches a year; June is the wettest month and January the driest. Rain or snow falls on about 83 days a year.
Rain + melted snow by month
Inches of water
Snowfall by month
Inches of snow
Heating and cooling a home in Castlewood
95% 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 Castlewood #2, SD.
Living with Castlewood’s climate
What the numbers mean for a garden, a free afternoon and a bad-weather day.
145 frost-free days in zone 4a. The last frost comes by May 6 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 1.
Months with highs of 62–84° and lows of 40° or more: May, June, July, August and September. 1.7 miles of trails are waiting.
Parks & trails →Of the yearly building losses FEMA expects in Castlewood from natural hazards, river flooding is the largest share (46%); heat waves, cold waves, winter storms and ice storms together are 23%. Normals are averages; the hazards page covers the extremes.
Natural hazards →Castlewood and its neighbors
Every town next door is within a degree of Castlewood in January and July, closer than the 5 km grid can tell apart. Tap a town to see its climate.
Climates most like Castlewood’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 |
|---|---|---|---|---|
| Castlewood, SD | 3° | 82° | 25" | 34" |
| Monticello, MN | 4° | 81° | 31" | 40" |
| Jamestown, ND | 1° | 82° | 21" | 46" |
| Menomonie, WI | 5° | 82° | 34" | 41" |
| Storm Lake, IA | 9° | 83° | 31" | 31" |
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 Castlewood averaged 1.2° warmer than the 1900s. The biggest change is in December (+3.3°).
A smaller shift than in 60% 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 Castlewood compares
Against 12,954 U.S. towns of 2,500 or more (one per 5 km climate cell), with Castlewood’s place among South Dakota’s.
Castlewood weather by month
Highs, lows and precipitation from NOAA’s grid at Castlewood’s center; snow, wet days and snow on the ground from Hayti, SD. 1991–2020 normals.
| Month | High | Low | Rain + melt | Snow | Wet days | Snow on ground | 30-yr range |
|---|---|---|---|---|---|---|---|
| January | 22° | 3° | 0.5" | 5.4" | 4 | 26 | 0° – 25° |
| February | 27° | 7° | 0.6" | 6.9" | 4 | 22 | 3° – 28° |
| March | 39° | 19° | 1.2" | 5.2" | 5 | 16 | 19° – 44° |
| April | 54° | 31° | 2.3" | 3.8" | 8 | 4 | 33° – 51° |
| May | 67° | 44° | 3.2" | 0.0" | 11 | 0 | 50° – 62° |
| June | 77° | 55° | 4.1" | 0.0" | 12 | 0 | 60° – 70° |
| July | 82° | 59° | 3.5" | 0.0" | 8 | 0 | 62° – 77° |
| August | 79° | 56° | 3.2" | 0.0" | 8 | 0 | 63° – 72° |
| September | 72° | 47° | 2.7" | 0.0" | 8 | 0 | 53° – 64° |
| October | 57° | 34° | 2.1" | 0.8" | 7 | 1 | 38° – 50° |
| November | 40° | 21° | 0.9" | 2.0" | 3 | 4 | 19° – 41° |
| December | 27° | 9° | 0.7" | 9.9" | 4 | 18 | 5° – 25° |
| Year | 53° | 32° | 25.1" | 34.0" | 83 | 91 |
How much a month can swing
A normal is an average. March swings the most: from 1991 to 2020 its average ranged from 19° to 44°. August is the most reliable, staying within 10°.
Where Castlewood’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 Castlewood’s center.
- Snow: Hayti, SD.
- Frost, freezing nights, 90° and 100° days, heating and cooling: Castlewood #2, SD, 0.2 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 Castlewood’s climate
What is the weather like in Castlewood?
A typical July afternoon reaches 82°, a January night drops to 3°, and about 34 inches of snow falls in a normal winter. Colder January nights than all but 99 U.S. towns; cooler July afternoons than 84% of U.S. towns.
How cold does it get in Castlewood in winter?
January nights average 3°. About 182 nights a year reach 32° or below and 42 reach 0° or below. In the coldest January of the last 30 years the month averaged 0°.
How much snow does Castlewood get?
About 34 inches in a normal winter at Hayti, SD, most of it in December, with snow on the ground about 91 days a year.
How hot does it get in Castlewood?
July, with a typical high of 82° and a low of 59°. About 13 days a year reach 90° (Castlewood #2, SD).
When is the first and last frost in Castlewood?
In half of years the last spring frost (32°) comes by May 6 and the first fall frost by October 1, about 145 frost-free days, at Castlewood #2, SD.
What growing zone is Castlewood in?
Zone 4a on the 2023 USDA Plant Hardiness Zone Map: the coldest night of a typical winter reaches about −26°.
What is the best time of year to visit Castlewood?
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 Castlewood getting warmer?
Yes: 1991–2020 averaged 1.2° warmer than 1901–2000 on NOAA’s grid. A smaller shift than 60% of U.S. towns.
Neighbors talk weather
Gardens, snow, and the best days of the year in Castlewood.
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.