Darby, Montana climate: Normal weather by month, frost dates and records
Darby's normal year runs from 19°F December nights to 82°F July afternoons, with 15.1 inches of precipitation a year. (NOAA 1991-2020 normals)
In metric: a yearly mean of 7.0°C, December lows of −7°C, July highs of 28°C, 384 mm of precipitation a year.
- NOAA stationDarby
- Station IDUSC00242221
- Location46.03°N 114.18°W
- Elevation3,880 ft (1,183 m)
- Population873
On October 23, the normal high in Darby is 53°F and the normal low 30°F, and the chance of measurable rain or snow is 27%.
Normals describe a typical year at the station, not a forecast. The National Weather Service forecast for Darby.
- Jan 34° 19°
- Feb 38° 21°
- Mar 47° 27°
- Apr 54° 31°
- May 64° 39°
- Jun 72° 45°
- Jul 82° 50°
- Aug 81° 48°
- Sep 71° 42°
- Oct 57° 33°
- Nov 42° 25°
- Dec 32° 19°
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 Darby each month?
July is the warmest month, with normal highs of 82°F; December the coldest, with normal lows of 19°F. The most precipitation falls in June (2.09 in), the least in March (0.85 in).
| Month | High | Low | Mean | Precip. | Wet days | 90°F days | Freezing nights | Daylight |
|---|---|---|---|---|---|---|---|---|
| January | 34°F | 19°F | 26.5°F | 1.08 | 8 | <1 | 28 | 9 h |
| February | 38°F | 21°F | 29.5°F | 0.87 | 6 | <1 | 25 | 10 h 20 min |
| March | 47°F | 27°F | 37.1°F | 0.85 | 6 | <1 | 24 | 11 h 50 min |
| April | 54°F | 31°F | 42.5°F | 1.04 | 7 | <1 | 16 | 13 h 30 min |
| May | 64°F | 39°F | 51.5°F | 1.60 | 9 | <1 | 5 | 14 h 50 min |
| June | 72°F | 45°F | 58.0°F | 2.09 | 10 | 2 | <1 | 15 h 40 min |
| July | 82°F | 50°F | 65.7°F | 1.14 | 6 | 10 | <1 | 15 h 30 min |
| August | 81°F | 48°F | 64.1°F | 0.90 | 6 | 8 | <1 | 14 h 10 min |
| September | 71°F | 42°F | 56.4°F | 1.23 | 6 | 1 | 3 | 12 h 40 min |
| October | 57°F | 33°F | 44.8°F | 1.50 | 8 | <1 | 14 | 11 h |
| November | 42°F | 25°F | 33.2°F | 1.55 | 8 | <1 | 24 | 9 h 30 min |
| December | 32°F | 19°F | 25.7°F | 1.26 | 8 | <1 | 28 | 8 h 40 min |
| Year (annual) | 56°F | 33°F | 44.6°F | 15.11 | 87 | 22 | 167 |
The same normals in °C and millimetres
| Month | High | Low | Mean | Precip. |
|---|---|---|---|---|
| January | 1°C | −7°C | −3.1°C | 27 mm |
| February | 3°C | −6°C | −1.4°C | 22 mm |
| March | 8°C | −3°C | 2.8°C | 22 mm |
| April | 12°C | 0°C | 5.8°C | 26 mm |
| May | 18°C | 4°C | 10.8°C | 41 mm |
| June | 22°C | 7°C | 14.4°C | 53 mm |
| July | 28°C | 10°C | 18.7°C | 29 mm |
| August | 27°C | 9°C | 17.8°C | 23 mm |
| September | 22°C | 5°C | 13.6°C | 31 mm |
| October | 14°C | 0°C | 7.1°C | 38 mm |
| November | 5°C | −4°C | 0.7°C | 39 mm |
| December | 0°C | −7°C | −3.5°C | 32 mm |
NOAA publishes no 1991-2020 snowfall normal for this station. The nearest record that keeps one, Sula (14 mi NE) (22 miles away), gets 88 inches of snow in a normal year; elevation and distance can change that.
Source: NOAA NCEI 1991-2020 monthly normals, station USC00242221; 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 Darby?
Normal highs sit between 65°F and 85°F in June, July, August and September. Of those, July 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 USC00242221.
When is the last frost in Darby?
In Darby, the last spring frost (32°F) comes after May 24 in half of years and after June 14 in one year in ten; the first autumn frost comes before September 23 in half of years and before September 4 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
- May 241 year in 10 after June 14; 9 in 10 after May 6
- First autumn frost, half of years before
- September 231 year in 10 before September 4; 9 in 10 before October 8
NOAA puts the median frost-free season at 118 days, and the season without a hard freeze (28°F) at 150 days.
A hard freeze (28°F) comes after May 5 in half of springs and before October 4 in half of autumns.
The USDA's 2023 Plant Hardiness Zone Map puts Darby in zone 5b in ZIP code 59827, the nearest ZIP area. By the map's own method, the average of each year's coldest night over 1991-2020, Darby's NOAA station is in zone 5b: the coldest night of a typical year reaches −11°F (19 complete years).
Frost dates for every NOAA station in Montana · Frost dates by ZIP code
Source: NOAA NCEI 1991-2020 annual normals (frost probabilities), station USC00242221; USDA 2023 Plant Hardiness Zone Map, ZIP listings: PRISM Group, Oregon State University, https://prism.oregonstate.edu, accessed October 8, 2026; the station zone: ACIS daily lows, 1991-2020. 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 Darby?
In a normal year in Darby, 22 days a year reach 90°F (1 of them 100°F or more), 167 nights fall to 32°F or colder and 87 days bring measurable precipitation.
- Days at 90°F or more
- 22a normal year
- Days at 100°F or more
- 1a normal year
- Nights at 32°F or colder
- 167a normal year
- Days that stay below freezing
- 28high of 32°F or less
- Days with 0.01 inch of precipitation
- 87a normal year
The highest temperature in this station's record (since 1898) is 105°F, on July 13, 2002; the lowest is −36°F, on January 7, 1937.
The wettest calendar year on that record is 1975, with 24.60 in; the snowiest season is 1955–56, with 117.3 inches.
Source: NOAA NCEI 1991-2020 annual normals, station USC00242221; records: ACIS (NOAA Regional Climate Centers), station USC00242221. Records use complete months only; a month missing more than three days is left out.
How sunny is Darby?
Over a year 71% of the sunlight that would reach the ground under clear skies gets through the clouds in the area around Darby, 3.8 kWh per square metre a day. July is the sunniest month (89%) and December the cloudiest (52%).
| Month | Share of clear-sky sunshine | Sunshine, kWh/m² a day |
|---|---|---|
| January | 56% | 1.3 |
| February | 58% | 2.0 |
| March | 59% | 3.1 |
| April | 64% | 4.4 |
| May | 68% | 5.6 |
| June | 73% | 6.4 |
| July | 89% | 7.4 |
| August | 86% | 6.2 |
| September | 79% | 4.4 |
| October | 67% | 2.6 |
| November | 56% | 1.4 |
| December | 52% | 1.0 |
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 Darby need?
A normal year in Darby brings 7,589 heating degree days, 41% more than the median U.S. place (5,373), and 178 cooling degree days, 80% fewer than the median (908). Eight months need 300 or more heating degree days, a monthly mean of about 55°F or colder. For gardens and crops, NOAA counts 1,583 growing degree days a year above 50°F.
| Month | Heating | Cooling |
|---|---|---|
| January | 1,192 | 0 |
| February | 993 | 0 |
| March | 864 | 0 |
| April | 675 | 0 |
| May | 421 | 2 |
| June | 223 | 14 |
| July | 69 | 91 |
| August | 89 | 61 |
| September | 266 | 9 |
| October | 627 | 0 |
| November | 954 | 0 |
| December | 1,218 | 0 |
| Year (annual) | 7,589 | 178 |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00242221. 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.
How does Darby's climate compare?
Darby is warmer than 83 of the other 140 places with their own NOAA record in Montana, and wetter than 75. Across the 7,247 U.S. stations with normals, its annual mean of 44.6°F is warmer than 18%.
In the Köppen classification computed from these normals, Darby is Dfb: continental, no dry season, warm summer. 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 Darby share this climate record?
2 places have no NOAA station with 1991-2020 normals of their 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.
- Charlos Heights, MT213 people · 8 mi N
- Conner, MT102 people · 7 mi S
Source: Census Bureau 2024 Gazetteer (place centers) and Vintage 2024 population estimates. Distance and direction from the station to each place's center.
Questions about Darby's climate
What is the coldest month in Darby?
December, with a normal high of 32°F and a normal low of 19°F. The warmest is July (82°F by day, 50°F at night).
Does it snow in Darby?
Yes. NOAA publishes no 1991-2020 snowfall normal for Darby's NOAA station; the nearest record that keeps one, Sula (14 mi NE) (22 miles away), records 88 inches of snow in a normal year.
What is the rainiest month in Darby?
June, with 2.09 in of precipitation in a normal year; the driest is March with 0.85 in.
What plant hardiness zone is Darby in?
The USDA's 2023 map puts Darby in zone 5b in ZIP code 59827, the nearest ZIP area. By the same method at Darby's NOAA station, the coldest night of a typical year reaches −11°F (19 years, 1991-2020): zone 5b.
How late can frost come in Darby?
In half of years the last 32°F night comes after May 24; in one year in ten it comes after June 14. Waiting until June 14 leaves about a one-in-ten chance of a later frost.
Nearby and next
- Montana climateThe statewide normals and every place in the state
- Hamilton, MT15 miles from this station, 44.8°F a year
- Sula, MT17 miles from this station, 42.0°F a year
- Western Agricultural Research Center, MT21 miles from this station, 45.7°F a year
- Stevensville, MT34 miles from this station, 45.6°F a year
- Compare two placesMonth by month, side by side
Download these normals (CSV) · JSON · How these figures are made