Three Forks, Montana · field elev 4,089 ft
Density Altitude at Three Forks (9S5)
From a field elevation of 4,089 ft, a typical July afternoon at Three Forks (85 °F) raises density altitude to about 6,637 ft — solidly into the range where performance charts deserve a close read.
Typical density altitude by month
| Month | Avg temp °F | DA at avg temp | Afternoon high °F | DA on a typical afternoon |
|---|---|---|---|---|
| January | 24.4 | 2,756 ft | 33.4 | 3,372 ft |
| February | 27.4 | 2,963 ft | 37.1 | 3,622 ft |
| March | 36.9 | 3,608 ft | 47.8 | 4,330 ft |
| April | 44.5 | 4,113 ft | 56.2 | 4,873 ft |
| May | 53.6 | 4,706 ft | 65.7 | 5,474 ft ▲ |
| June | 61.2 | 5,191 ft | 73.9 | 5,982 ft ▲ |
| July | 69.2 | 5,692 ft | 84.7 | 6,637 ft ▲ |
| August | 67.3 | 5,574 ft | 83.7 | 6,577 ft ▲ |
| September | 58.3 | 5,007 ft | 73.3 | 5,945 ft ▲ |
| October | 45.8 | 4,199 ft | 58.2 | 5,000 ft ▲ |
| November | 32.7 | 3,325 ft | 42.4 | 3,975 ft |
| December | 24.0 | 2,729 ft | 32.9 | 3,339 ft |
▲ above 5,000 ft · ⚠ above 8,000 ft. These are planning references at standard pressure and dry air — afternoon humidity and low pressure both push the real number higher. Run today's values below.
Run today’s numbers for 9S5
DENSITY ALTITUDE caution
Field elevation 4,089 ft — the air behaves like 6,655 ft.
- PRESSURE ALT
- 4,091 ft
- ISA DEVIATION
- —
- RULE-OF-THUMB DA
- —
- AIR DENSITY INDEX
- —
- AIR DENSITY
- —
- WATER · GRAINS/LB
- —
For training and reference · verify with official sources and your POH before flight · no tool on this site renders a go / no-go judgment
Nearby Montana fields
- KBZN — Bozeman Yellowstone International
Bozeman · elev 4,473 ft
- 8U8 — Townsend
Townsend · elev 3,897 ft
- 3U9 — Boulder
Boulder · elev 4,968 ft
- 8U9 — Canyon Ferry
Townsend · elev 3,840 ft
- KEKS — Ennis Big Sky
Ennis · elev 5,433 ft
- KRVF — Ruby Valley Field
Twin Bridges · elev 4,789 ft
- 9U1 — Wilsall
Wilsall · elev 5,140 ft
- KBTM — Bert Mooney
Butte · elev 5,551 ft
Frequently asked questions
How high does density altitude get at 9S5 in summer?
On a typical July afternoon — around 85 °F at the nearest NOAA normals station — density altitude at Three Forks reaches roughly 6,637 ft at standard pressure. Hotter-than-normal days, low pressure, and humidity all push it higher, so run the day's actual numbers before flying.
What is the density altitude at 9S5 on an average day?
It swings with the seasons: from roughly 2,729 ft at the coldest month's average temperature to about 5,692 ft at the warmest month's — all from a constant field elevation of 4,089 ft. The month-by-month table above carries the full year.
What is the field elevation of Three Forks?
4,089 ft MSL, from the FAA NASR airport record (28-day cycle effective 2026-08-06). The identifier is 9S5 (FAA), in Three Forks, Montana.