Updated October 2026
Fort Union Trading Post National Historic Site Weather by Month
Fort Union Trading Post National Historic Site is warmest in August, when the nearest NOAA climate station averages a high of 85°F and a low of 55°F, and coldest in January, with an average high of 24°F and an average low of 4°F. June is the wettest month, with about 2.8 inches of precipitation. Snowfall is heaviest in December, at about 9 inches.
These figures are NOAA's 1991–2020 climate normals, the 30-year average for each calendar month, from the nearest long-record weather station, 16.8 miles from the park's reference point. A single station cannot describe a whole park: temperatures elsewhere in Fort Union Trading Post National Historic Site can differ from these, particularly with elevation.
Warmest month
Aug
85°F avg high
Coldest month
Jan
4°F avg low
Wettest month
Jun
2.8 in avg
Snowiest month
Dec
9.0 in avg
Longest days
Jun
15.8 h of daylight
Average weather at Fort Union Trading Post by month
| Month | Avg high | Avg low | Precipitation | Snowfall | Daylight |
|---|---|---|---|---|---|
| January | 24°F | 4°F | 0.4 in | 7.9 in | 8.6 h |
| February | 29°F | 8°F | 0.3 in | 6.3 in | 10.0 h |
| March | 42°F | 19°F | 0.5 in | 4.4 in | 11.6 h |
| April | 58°F | 31°F | 1.1 in | 2.9 in | 13.4 h |
| May | 69°F | 42°F | 2.1 in | 0.9 in | 15.0 h |
| June | 77°F | 51°F | 2.8 in | 0.0 in | 15.8 h |
| July | 85°F | 57°F | 2.5 in | 0.0 in | 15.5 h |
| August | 85°F | 55°F | 1.7 in | 0.0 in | 14.1 h |
| September | 75°F | 46°F | 1.4 in | 0.0 in | 12.3 h |
| October | 58°F | 33°F | 1.0 in | 2.6 in | 10.6 h |
| November | 40°F | 20°F | 0.5 in | 5.3 in | 9.0 h |
| December | 27°F | 9°F | 0.4 in | 9.0 in | 8.2 h |
| Year total | 14.7 in | 39.3 in |
NOAA 1991–2020 climate normals from station USC00329430, 16.8 miles from the park's reference point. Daylight is the monthly average, computed from the park's latitude. Each month links to how crowded Fort Union Trading Post is at that time of year.
Fort Union Trading Post weather by season
Winter: December to February
Average highs bottom out at 24°F in January, between 27°F in December and 29°F in February, with average lows between 4°F and 9°F. The average high stays at or below freezing in all three months. Together the three months average 1.1 inches of precipitation, about 7% of the yearly total and less than in any other season. Snowfall averages about 23 inches for the season. Daylight is at its shortest, about 8.2 hours in December.
Spring: March to May
Average highs climb from 42°F in March to 69°F in May, with average lows between 19°F and 42°F. The average low is at or below freezing in March and April. Together the three months average 3.7 inches of precipitation, about 25% of the yearly total. Snowfall averages about 8.2 inches for the season. Daylight lengthens from about 11.6 hours in March to 15.0 in May.
Summer: June to August
Average highs climb from 77°F in June to 85°F in August, with average lows between 51°F and 57°F. Together the three months average 7 inches of precipitation, about 48% of the yearly total and more than in any other season. Daylight is at its longest, about 15.8 hours in June.
Fall: September to November
Average highs fall from 75°F in September to 40°F in November, with average lows between 20°F and 46°F. The average low is at or below freezing in November. Together the three months average 2.9 inches of precipitation, about 20% of the yearly total. Snowfall averages about 7.9 inches for the season, most of it in November. Daylight shortens from about 12.3 hours in September to 9.0 in November.
What the National Park Service says about the weather
Weather in western North Dakota can be harsh, with extremes in temperature and sudden, violent storms. Be prepared for rapidly changing conditions. Summers are warm with average high temperatures in the 80s-90s May through September. Winters are cold with average lows in the single digits December through February. Wind is considerable year-round. Conditions can change quickly. Travelers should be aware of the potential for violent thunderstorms in the summer and the possibility of blizzards.
Weather description courtesy of the National Park Service — official park site.
Today's forecast for Fort Union Trading Post
Averages describe a typical month, not this week. For current conditions and the seven-day outlook, the National Weather Service issues a forecast for the park's reference point at 48.00°N, 104.04°W. It covers that one spot, so other elevations in the park can differ from it, as they do from the averages above.
National Weather Service forecast for Fort Union Trading Post National Historic Site →
Weather and crowds together
August, the warmest month, sees about 1.9× the visitors of the park's average month. June is the busiest month of the year and January the quietest. To see those crowds set against the weather for all twelve months, read the best time to visit Fort Union Trading Post National Historic Site. For hotels, cabins and rentals close to the park, see where to stay near Fort Union Trading Post.
Where to stay near Fort Union Trading Post
Picked a month for Fort Union Trading Post National Historic Site? Compare hotels, cabins and vacation rentals near the park with live availability and prices.
Top-rated places to stay near Fort Union Trading Post
Prices for Oct 16–18, 4 adults. Change dates on the map below.
Availability and prices from Stay22 partners (Booking.com, Vrbo, Expedia). We may earn a commission from bookings, at no extra cost to you.
Planning a trip to Fort Union Trading Post?
Get crowd forecasts and lodging deals for Fort Union Trading Post by email. No spam, unsubscribe anytime.
Frequently Asked Questions
August is the warmest month at Fort Union Trading Post National Historic Site, with an average high of 85°F and an average low of 55°F. That is the 1991–2020 average at the nearest long-record NOAA station, 16.8 miles from the park's reference point. Temperatures inside the park can differ, particularly with elevation.
January is the coldest month at Fort Union Trading Post National Historic Site, with an average low of 4°F and an average high of 24°F, based on NOAA 1991–2020 climate normals.
June is the wettest month, with about 2.8 inches of precipitation. February is the driest, at about 0.3 inches. The station records about 14.7 inches of precipitation in an average year.
Yes. The nearest long-record NOAA station, 16.8 miles from the park's reference point, averages about 39 inches of snow a year. December is the snowiest month, at about 9 inches. The station averages at least a tenth of an inch of snow in 8 of the 12 months.
Weather at nearby parks
Keep exploring
Sources: NOAA NCEI U.S. Climate Normals 1991–2020 (station USC00329430), daylight computed from latitude, weather description from the National Park Service, crowd levels from National Park Service Visitor Use Statistics (1979–2025). Updated 2026-10-11. Lodging results are provided by Stay22; WhenToVisitParks may earn a commission from bookings, at no extra cost to you.