Fort Thompson has some of the coldest winter nights among U.S. towns
The warmest part of a July day comes in at 88° on average. Temperatures cover 80° across the year, low to high. By precipitation alone, it ranks drier than 89% of U.S. towns. Plan time outside for May, June and September, when highs sit at 71–81°.
A year in Fort Thompson at a glance
Each month’s typical high and low, and what it brings.
What stands out about Fort Thompson’s climate
Compared with towns across the U.S., with Fort Thompson’s place in South Dakota beside it.
What a year in Fort Thompson feels like
Typical highs and lows by season and by month, from NOAA’s 30-year normals.
About 152 frost-free days a year
In half of years the last 32° night comes by May 6 and the first by October 5. Frost and day counts come from NOAA’s station at Lake Sharpe Prj, SD, 3 miles from the town’s center, at about the same height.
The 2023 USDA map puts Fort Thompson’s center in zone 4b: the coldest night of a typical winter, averaged over 1991–2020, reaches about −20°. 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 19 inches of snow a winter
Snow, measured at Lake Sharpe Prj, SD, falls mostly in February. Precipitation (rain plus melted snow) adds up to 21 inches a year; June is the wettest month and January the driest. Rain or snow falls on about 71 days a year.
Rain + melted snow by month
Inches of water
Snowfall by month
Inches of snow
Heating and cooling a home in Fort Thompson
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 Lake Sharpe Prj, SD.
Living with Fort Thompson’s climate
What the numbers mean for a garden, a free afternoon and a bad-weather day.
152 frost-free days in zone 4b. 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 5.
Months with highs of 62–84° and lows of 40° or more: May, June and September. 1.0 miles of trails are waiting.
Parks & trails →Cold waves are 55% of the yearly building losses FEMA expects in Fort Thompson from natural hazards, the largest share. Normals are averages; the hazards page covers the extremes.
Natural hazards →Fort Thompson and similar climates
TownRatings has no climate map of the towns around Fort Thompson yet.
Climates most like Fort Thompson’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 |
|---|---|---|---|---|
| Fort Thompson, SD | 8° | 88° | 21" | 19" |
| Lexington, NE | 14° | 88° | 23" | 20" |
| Sheridan, WY | 11° | 89° | 15" | 33" |
| Sidney, MT | 4° | 85° | 15" | 30" |
| Fort Morgan, CO | 14° | 91° | 14" | 23" |
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 Fort Thompson averaged 1.1° warmer than the 1900s. The biggest change is in January (+3.6°).
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 Fort Thompson compares
Against 12,954 U.S. towns of 2,500 or more (one per 5 km climate cell), with Fort Thompson’s place among South Dakota’s.
Fort Thompson weather by month
Highs, lows and precipitation from NOAA’s grid at Fort Thompson’s center; snow, wet days and snow on the ground from Lake Sharpe Prj, SD. 1991–2020 normals.
| Month | High | Low | Rain + melt | Snow | Wet days | 30-yr range |
|---|---|---|---|---|---|---|
| January | 29° | 8° | 0.4" | 2.7" | 3 | 9° – 34° |
| February | 34° | 12° | 0.7" | 5.4" | 3 | 7° – 34° |
| March | 46° | 22° | 0.9" | 3.0" | 4 | 24° – 48° |
| April | 59° | 33° | 2.2" | 2.6" | 6 | 37° – 52° |
| May | 71° | 45° | 3.3" | 0.0" | 11 | 52° – 64° |
| June | 81° | 56° | 3.7" | 0.0" | 10 | 64° – 73° |
| July | 88° | 61° | 2.8" | 0.0" | 9 | 66° – 81° |
| August | 86° | 59° | 2.5" | 0.0" | 9 | 67° – 76° |
| September | 78° | 49° | 2.0" | 0.0" | 6 | 58° – 69° |
| October | 62° | 36° | 1.7" | 0.1" | 6 | 41° – 54° |
| November | 46° | 23° | 0.6" | 1.2" | 3 | 23° – 43° |
| December | 33° | 12° | 0.5" | 3.9" | 2 | 10° – 30° |
| Year | 59° | 35° | 21.3" | 18.9" | 71 |
How much a month can swing
A normal is an average. February swings the most: from 1991 to 2020 its average ranged from 7° to 34°. August is the most reliable, staying within 9°.
Where Fort Thompson’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 Fort Thompson’s center.
- Snow: Lake Sharpe Prj, SD.
- Frost, freezing nights, 90° and 100° days, heating and cooling: Lake Sharpe Prj, SD, 3 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 Fort Thompson’s climate
What is the weather like in Fort Thompson?
A typical July afternoon reaches 88°, a January night drops to 8°, and about 19 inches of snow falls in a normal winter. Colder January nights than 96% of U.S. towns; hotter July afternoons than 68% of U.S. towns.
How cold does it get in Fort Thompson in winter?
January nights average 8°. About 171 nights a year reach 32° or below and 26 reach 0° or below. In the coldest January of the last 30 years the month averaged 9°.
How much snow does Fort Thompson get?
About 19 inches in a normal winter at Lake Sharpe Prj, SD, most of it in February.
How hot does it get in Fort Thompson?
July, with a typical high of 88° and a low of 61°. About 31 days a year reach 90° and 4 reach 100° (Lake Sharpe Prj, SD).
When is the first and last frost in Fort Thompson?
In half of years the last spring frost (32°) comes by May 6 and the first fall frost by October 5, about 152 frost-free days, at Lake Sharpe Prj, SD.
What growing zone is Fort Thompson in?
Zone 4b on the 2023 USDA Plant Hardiness Zone Map: the coldest night of a typical winter reaches about −20°.
What is the best time of year to visit Fort Thompson?
By one simple rule (highs of 62–84° and lows of 40° or more), May, June and September. The rule is ours, not NOAA’s; the month table has the numbers to judge by.
Is Fort Thompson 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 Fort Thompson.
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.