Dillon, Montana climate: Normal weather by month, frost dates and records
Dillon's normal year runs from 12°F December nights to 82°F July afternoons, with 9.8 inches of precipitation a year. (NOAA 1991-2020 normals)
In metric: a yearly mean of 5.4°C, December lows of −11°C, July highs of 28°C, 250 mm of precipitation a year.
- NOAA stationDillon Airport
- Station IDUSW00024138
- Location45.26°N 112.55°W
- Elevation5,200 ft (1,585 m)
- Population4,242
Normals describe a typical year at the station, not a forecast. The National Weather Service forecast for Dillon.
- Jan 32° 13°
- Feb 35° 14°
- Mar 45° 21°
- Apr 53° 28°
- May 62° 36°
- Jun 71° 42°
- Jul 82° 48°
- Aug 81° 46°
- Sep 70° 39°
- Oct 55° 29°
- Nov 41° 19°
- Dec 31° 12°
Each month: normal high (large) and low, °F. Fill: the month's normal mean, colder blue to hotter red.
What is the weather like in Dillon each month?
July is the warmest month, with normal highs of 82°F; December the coldest, with normal lows of 12°F. The most precipitation falls in June (1.91 in), the least in January (0.20 in).
| Month | High | Low | Mean | Precip. | Wet days | 90°F days | Freezing nights | Daylight |
|---|---|---|---|---|---|---|---|---|
| January | 32°F | 13°F | 22.3°F | 0.20 | 3 | <1 | 30 | 9 h 10 min |
| February | 35°F | 14°F | 24.5°F | 0.24 | 5 | <1 | 27 | 10 h 20 min |
| March | 45°F | 21°F | 33.2°F | 0.52 | 7 | <1 | 28 | 11 h 50 min |
| April | 53°F | 28°F | 40.1°F | 1.18 | 9 | <1 | 22 | 13 h 30 min |
| May | 62°F | 36°F | 49.0°F | 1.76 | 11 | <1 | 8 | 14 h 50 min |
| June | 71°F | 42°F | 56.6°F | 1.91 | 11 | 1 | 1 | 15 h 40 min |
| July | 82°F | 48°F | 64.9°F | 0.89 | 6 | 6 | <1 | 15 h 20 min |
| August | 81°F | 46°F | 63.4°F | 0.87 | 7 | 5 | <1 | 14 h 10 min |
| September | 70°F | 39°F | 54.7°F | 0.91 | 6 | <1 | 3 | 12 h 40 min |
| October | 55°F | 29°F | 42.2°F | 0.72 | 6 | <1 | 18 | 11 h |
| November | 41°F | 19°F | 29.9°F | 0.37 | 5 | <1 | 26 | 9 h 30 min |
| December | 31°F | 12°F | 21.1°F | 0.26 | 5 | <1 | 30 | 8 h 50 min |
| Year (annual) | 55°F | 29°F | 41.8°F | 9.83 | 80 | 12 | 193 |
The same normals in °C and millimetres
| Month | High | Low | Mean | Precip. |
|---|---|---|---|---|
| January | 0°C | −11°C | −5.4°C | 5 mm |
| February | 2°C | −10°C | −4.2°C | 6 mm |
| March | 7°C | −6°C | 0.7°C | 13 mm |
| April | 11°C | −2°C | 4.5°C | 30 mm |
| May | 17°C | 2°C | 9.4°C | 45 mm |
| June | 22°C | 6°C | 13.7°C | 49 mm |
| July | 28°C | 9°C | 18.3°C | 23 mm |
| August | 27°C | 8°C | 17.4°C | 22 mm |
| September | 21°C | 4°C | 12.6°C | 23 mm |
| October | 13°C | −2°C | 5.7°C | 18 mm |
| November | 5°C | −7°C | −1.2°C | 9 mm |
| December | −1°C | −11°C | −6.1°C | 7 mm |
NOAA publishes no 1991-2020 snowfall normal for this station. Dillon's own co-op station Dillon U Of Montana Western does: 11 inches of snow in a normal year (see the other stations below).
Source: NOAA NCEI 1991-2020 monthly normals, station USW00024138; annual normals. Wet days: 0.01 inch or more; 90°F days and freezing nights: NOAA's day counts. Daylight: sunrise to sunset on the 15th, computed from the latitude.
When is the best weather to visit Dillon?
Normal highs sit between 65°F and 85°F in June, July, August and September. Of those, September has the fewest days with rain (6).
That is a measurement, not a recommendation: it counts the months whose normal afternoon high sits between 65°F and 85°F, where a light layer is enough by day.
Source: NOAA NCEI 1991-2020 monthly normals, station USW00024138.
When is the last frost in Dillon?
In Dillon, the last spring frost (32°F) comes after June 2 in half of years and after June 21 in one year in ten; the first autumn frost comes before September 13 in half of years and before August 30 in one year in ten.
Frost-free in half of yearsFrost in 1 to 9 years out of 10Frost most years
- Last spring frost, half of years after
- June 21 year in 10 after June 21; 9 in 10 after May 17
- First autumn frost, half of years before
- September 131 year in 10 before August 30; 9 in 10 before September 28
NOAA puts the median frost-free season at 101 days, and the season without a hard freeze (28°F) at 132 days.
A hard freeze (28°F) comes after May 14 in half of springs and before September 27 in half of autumns.
The USDA's 2023 Plant Hardiness Zone Map puts Dillon in zone 5a in ZIP code 59725, the nearest ZIP area.
Frost dates for every NOAA station in Montana · Frost dates by ZIP code
Source: NOAA NCEI 1991-2020 annual normals (frost probabilities), station USW00024138; USDA 2023 Plant Hardiness Zone Map, ZIP listings: PRISM Group, Oregon State University, https://prism.oregonstate.edu, accessed October 8, 2026. A 10% date means one year in ten has a frost after it in spring or before it in autumn.
How hot and how cold does it get in Dillon?
In a normal year in Dillon, 12 days a year reach 90°F, 193 nights fall to 32°F or colder and 80 days bring measurable precipitation.
- Days at 90°F or more
- 12a normal year
- Days at 100°F or more
- fewer than 1a normal year
- Nights at 32°F or colder
- 193a normal year
- Days that stay below freezing
- 45high of 32°F or less
- Days with 0.01 inch of precipitation
- 80a normal year
The highest temperature in this station's record (since 1940) is 102°F, on July 12, 2002; the lowest is −41°F, on January 13, 2024.
The wettest calendar year on that record is 1987, with 14.60 in; the snowiest season is 1968–69, with 67.1 inches.
Source: NOAA NCEI 1991-2020 annual normals, station USW00024138; records: ACIS (NOAA Regional Climate Centers), station USW00024138. Records use complete months only; a month missing more than three days is left out.
How sunny is Dillon?
Over a year 76% of the sunlight that would reach the ground under clear skies gets through the clouds in the area around Dillon, 4.2 kWh per square metre a day. July is the sunniest month (85%) and December the cloudiest (65%).
| Month | Share of clear-sky sunshine | Sunshine, kWh/m² a day |
|---|---|---|
| January | 70% | 1.7 |
| February | 73% | 2.8 |
| March | 73% | 4.0 |
| April | 70% | 5.1 |
| May | 70% | 5.9 |
| June | 76% | 6.8 |
| July | 85% | 7.3 |
| August | 84% | 6.2 |
| September | 80% | 4.7 |
| October | 73% | 3.0 |
| November | 68% | 1.9 |
| December | 65% | 1.4 |
Source: NASA POWER solar climatology, 2001-2020 (CERES SYN1deg). Satellite-based, for the 1-degree cell (about 100 km across) around the station, so it describes the area rather than the airport.
How much heating and cooling does Dillon need?
A normal year in Dillon brings 8,544 heating degree days, 59% more than the median U.S. place (5,373), and 117 cooling degree days, 87% fewer than the median (908). Nine months need 300 or more heating degree days, a monthly mean of about 55°F or colder. For gardens and crops, NOAA counts 1,406 growing degree days a year above 50°F.
| Month | Heating | Cooling |
|---|---|---|
| January | 1,324 | 0 |
| February | 1,134 | 0 |
| March | 986 | 0 |
| April | 747 | 0 |
| May | 497 | 1 |
| June | 262 | 8 |
| July | 63 | 60 |
| August | 92 | 43 |
| September | 316 | 6 |
| October | 707 | 0 |
| November | 1,055 | 0 |
| December | 1,362 | 0 |
| Year (annual) | 8,544 | 117 |
Source: NOAA NCEI 1991-2020 monthly normals, station USW00024138. A degree day is one degree of a day's mean temperature below 65°F (heating) or above it (cooling); utilities use them to estimate energy use.
Has Dillon been warmer than normal lately?
2025 averaged 44.6°F, 2.8°F above the 1991-2020 normal of 41.8°F. 3 of the 4 complete years since 2021 ran warmer than the normal.
| Year | Mean | Against normal | Precip. |
|---|---|---|---|
| 2021 | 43.9°F | +2.1°F | 3.11 |
| 2022 | 41.3°F | −0.5°F | 4.63 |
| 2024 | 44.0°F | +2.2°F | 3.60 |
| 2025 | 44.6°F | +2.8°F | – |
Source: observed years: ACIS, station USW00024138. A year counts only with all twelve months complete.
How does Dillon's climate compare?
Dillon is warmer than 28 of the other 140 places with their own NOAA record in Montana, and wetter than 2. Across the 7,247 U.S. stations with normals, its annual mean of 41.8°F is warmer than 9%.
In the Köppen classification computed from these normals, Dillon is BSk: cold semi-arid steppe. What the classes mean.
Places with the most similar year elsewhere
Measured month by month on the normal high, low and precipitation, among places of 20,000 or more people in other states:
Source: NOAA NCEI 1991-2020 normals for every station PlainClimate covers. Similarity: the root-mean-square difference of the 36 monthly figures, precipitation weighted so an inch counts like 6°F.
Which places near Dillon share this climate record?
Argenta has no NOAA station with 1991-2020 normals of its own, and this station is the nearest full record. A place's own climate can differ from these figures, by several degrees where it sits much higher or lower than the station, nearer the coast, or inside a large city's heat; for the larger places the next nearest records are named with their yearly mean, so the spread around them is visible, and places of 50,000 or more have their own page with NOAA's gridded normals.
- Argenta, MT98 people · 15 mi W
Source: Census Bureau 2024 Gazetteer (place centers) and Vintage 2024 population estimates. Distance and direction from the station to each place's center.
What do Dillon's other NOAA stations record?
2 more NOAA stations keep 1991-2020 normals in or near Dillon. This page uses Dillon Airport; the others differ by site and elevation:
| Station | From this station | Elevation | Year | Jan low | Jul high | Precip. | Snow | Last frost |
|---|---|---|---|---|---|---|---|---|
| Dillon (18 mi WSW) USW00004137 | 23 mi W | 5,971 ft | 38.7°F | 8°F | 81°F | 10.1 | – | – |
| Dillon U Of Montana Western USC00242409 | 5 mi SW | 5,129 ft | 42.8°F | 15°F | 83°F | 11.3 | 11 | June 5 |
Source: NOAA NCEI 1991-2020 normals for each station. Last frost: the median last spring date of 32°F.
Questions about Dillon's climate
What is the coldest month in Dillon?
December, with a normal high of 31°F and a normal low of 12°F. The warmest is July (82°F by day, 48°F at night).
Does it snow in Dillon?
Yes. NOAA publishes no 1991-2020 snowfall normal for Dillon's NOAA station; Dillon's own co-op station Dillon U Of Montana Western records 11 inches of snow in a normal year.
What is the rainiest month in Dillon?
June, with 1.91 in of precipitation in a normal year; the driest is January with 0.20 in.
What plant hardiness zone is Dillon in?
The USDA's 2023 map puts Dillon in zone 5a in ZIP code 59725, the nearest ZIP area.
How late can frost come in Dillon?
In half of years the last 32°F night comes after June 2; in one year in ten it comes after June 21. Waiting until June 21 leaves about a one-in-ten chance of a later frost.
Nearby and next
- Montana climateThe statewide normals and every place in the state
- Glen, MT20 miles from this station, 42.5°F a year
- Twin Bridges, MT23 miles from this station, 43.5°F a year
- Laurin (2 mi NE), MT24 miles from this station, 43.0°F a year
- Alder (19 mi S), MT25 miles from this station, 40.8°F a year
- Compare two placesMonth by month, side by side
Download these normals (CSV) · JSON · How these figures are made