Hamilton, Montana climate: Normal weather by month, frost dates and records
Hamilton's normal year runs from 18°F December nights to 84°F July afternoons, with 13.6 inches of precipitation a year. (NOAA 1991-2020 normals)
In metric: a yearly mean of 7.1°C, December lows of −8°C, July highs of 29°C, 345 mm of precipitation a year.
- NOAA stationHamilton
- Station IDUSC00243885
- Location46.25°N 114.17°W
- Elevation3,585 ft (1,093 m)
- Population5,383
On October 23, the normal high in Hamilton is 53°F and the normal low 29°F, and the chance of measurable rain or snow is 30%.
Normals describe a typical year at the station, not a forecast. The National Weather Service forecast for Hamilton.
- Jan 35° 19°
- Feb 39° 20°
- Mar 49° 25°
- Apr 56° 31°
- May 66° 38°
- Jun 73° 45°
- Jul 84° 50°
- Aug 82° 48°
- Sep 72° 40°
- Oct 57° 31°
- Nov 43° 23°
- Dec 34° 18°
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 Hamilton each month?
July is the warmest month, with normal highs of 84°F; December the coldest, with normal lows of 18°F. The most precipitation falls in June (1.65 in), the least in August (0.80 in).
| Month | High | Low | Mean | Precip. | Wet days | 90°F days | Freezing nights | Daylight |
|---|---|---|---|---|---|---|---|---|
| January | 35°F | 19°F | 27.0°F | 0.96 | 9 | <1 | 28 | 9 h |
| February | 39°F | 20°F | 29.3°F | 1.18 | 9 | <1 | 26 | 10 h 20 min |
| March | 49°F | 25°F | 36.7°F | 0.98 | 10 | <1 | 26 | 11 h 50 min |
| April | 56°F | 31°F | 43.4°F | 1.12 | 9 | <1 | 16 | 13 h 30 min |
| May | 66°F | 38°F | 51.9°F | 1.53 | 11 | <1 | 5 | 15 h |
| June | 73°F | 45°F | 58.9°F | 1.65 | 10 | 2 | <1 | 15 h 50 min |
| July | 84°F | 50°F | 66.8°F | 0.85 | 7 | 11 | <1 | 15 h 30 min |
| August | 82°F | 48°F | 65.0°F | 0.80 | 7 | 9 | <1 | 14 h 10 min |
| September | 72°F | 40°F | 56.2°F | 0.81 | 6 | 1 | 2 | 12 h 40 min |
| October | 57°F | 31°F | 43.9°F | 0.94 | 9 | <1 | 17 | 11 h |
| November | 43°F | 23°F | 32.9°F | 1.45 | 10 | <1 | 25 | 9 h 30 min |
| December | 34°F | 18°F | 25.7°F | 1.33 | 10 | <1 | 28 | 8 h 40 min |
| Year (annual) | 57°F | 32°F | 44.8°F | 13.60 | 107 | 22 | 173 |
The same normals in °C and millimetres
| Month | High | Low | Mean | Precip. |
|---|---|---|---|---|
| January | 2°C | −7°C | −2.8°C | 24 mm |
| February | 4°C | −7°C | −1.5°C | 30 mm |
| March | 9°C | −4°C | 2.6°C | 25 mm |
| April | 13°C | −1°C | 6.3°C | 28 mm |
| May | 19°C | 3°C | 11.1°C | 39 mm |
| June | 23°C | 7°C | 14.9°C | 42 mm |
| July | 29°C | 10°C | 19.3°C | 22 mm |
| August | 28°C | 9°C | 18.3°C | 20 mm |
| September | 22°C | 5°C | 13.4°C | 21 mm |
| October | 14°C | −1°C | 6.6°C | 24 mm |
| November | 6°C | −5°C | 0.5°C | 37 mm |
| December | 1°C | −8°C | −3.5°C | 34 mm |
NOAA publishes no 1991-2020 snowfall normal for this station. The nearest record that keeps one, Stevensville (19 miles away), gets 17 inches of snow in a normal year; elevation and distance can change that.
Source: NOAA NCEI 1991-2020 monthly normals, station USC00243885; 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 Hamilton?
Normal highs sit between 65°F and 85°F in May, 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 USC00243885.
When is the last frost in Hamilton?
In Hamilton, the last spring frost (32°F) comes after May 21 in half of years and after June 6 in one year in ten; the first autumn frost comes before September 22 in half of years and before September 6 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 211 year in 10 after June 6; 9 in 10 after May 7
- First autumn frost, half of years before
- September 221 year in 10 before September 6; 9 in 10 before October 5
NOAA puts the median frost-free season at 122 days, and the season without a hard freeze (28°F) at 149 days.
A hard freeze (28°F) comes after May 5 in half of springs and before October 2 in half of autumns.
The USDA's 2023 Plant Hardiness Zone Map puts Hamilton in zone 5b in ZIP code 59840, the nearest ZIP area. By the map's own method, the average of each year's coldest night over 1991-2020, Hamilton's NOAA station is in zone 6a: the coldest night of a typical year reaches −9°F (24 complete years); the map interpolates between stations and terrain, so the station and the ZIP area can differ by half a zone.
Frost dates for every NOAA station in Montana · Frost dates by ZIP code
Source: NOAA NCEI 1991-2020 annual normals (frost probabilities), station USC00243885; 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 Hamilton?
In a normal year in Hamilton, 22 days a year reach 90°F (1 of them 100°F or more), 173 nights fall to 32°F or colder and 107 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
- 173a normal year
- Days that stay below freezing
- 29high of 32°F or less
- Days with 0.01 inch of precipitation
- 107a normal year
The highest temperature in this station's record (since 1895) is 105°F, on July 23, 1895; the lowest is −39°F, on February 4, 1899.
The wettest calendar year on that record is 1980, with 20.11 in; the snowiest season is 1955–56, with 65.9 inches.
Source: NOAA NCEI 1991-2020 annual normals, station USC00243885; records: ACIS (NOAA Regional Climate Centers), station USC00243885. Records use complete months only; a month missing more than three days is left out.
How sunny is Hamilton?
Over a year 71% of the sunlight that would reach the ground under clear skies gets through the clouds in the area around Hamilton, 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 Hamilton need?
A normal year in Hamilton brings 7,551 heating degree days, 41% more than the median U.S. place (5,373), and 216 cooling degree days, 76% 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 1,654 growing degree days a year above 50°F.
| Month | Heating | Cooling |
|---|---|---|
| January | 1,178 | 0 |
| February | 998 | 0 |
| March | 876 | 0 |
| April | 648 | 0 |
| May | 410 | 2 |
| June | 205 | 21 |
| July | 52 | 110 |
| August | 74 | 75 |
| September | 274 | 8 |
| October | 656 | 0 |
| November | 963 | 0 |
| December | 1,218 | 0 |
| Year (annual) | 7,551 | 216 |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00243885. 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 Hamilton been warmer than normal lately?
2021 averaged 46.5°F, 1.7°F above the 1991-2020 normal of 44.8°F.
| Year | Mean | Against normal | Precip. |
|---|---|---|---|
| 2021 | 46.5°F | +1.7°F | 11.11 |
Over 77 complete years from 1904 to 2021, the station's annual mean temperature rose at a fitted 0.0°F per century (+0.00°C per decade). A fitted rate summarizes the whole record; single years swing well above and below it.
Source: observed years: ACIS, station USC00243885; trend: NOAA GHCN-Monthly v4. A year counts only with all twelve months complete.
How does Hamilton's climate compare?
Hamilton is warmer than 87 of the other 140 places with their own NOAA record in Montana, and wetter than 46. Across the 7,247 U.S. stations with normals, its annual mean of 44.8°F is warmer than 18%.
In the Köppen classification computed from these normals, Hamilton 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.
Questions about Hamilton's climate
What is the coldest month in Hamilton?
December, with a normal high of 34°F and a normal low of 18°F. The warmest is July (84°F by day, 50°F at night).
Does it snow in Hamilton?
Yes. NOAA publishes no 1991-2020 snowfall normal for Hamilton's NOAA station; the nearest record that keeps one, Stevensville (19 miles away), records 17 inches of snow in a normal year.
What is the rainiest month in Hamilton?
June, with 1.65 in of precipitation in a normal year; the driest is August with 0.80 in.
What plant hardiness zone is Hamilton in?
The USDA's 2023 map puts Hamilton in zone 5b in ZIP code 59840, the nearest ZIP area. By the same method at Hamilton's NOAA station, the coldest night of a typical year reaches −9°F (24 years, 1991-2020): zone 6a.
How late can frost come in Hamilton?
In half of years the last 32°F night comes after May 21; in one year in ten it comes after June 6. Waiting until June 6 leaves about a one-in-ten chance of a later frost.
Nearby and next
- Montana climateThe statewide normals and every place in the state
- Western Agricultural Research Center, MT7 miles from this station, 45.7°F a year
- Darby, MT15 miles from this station, 44.6°F a year
- Stevensville, MT19 miles from this station, 45.6°F a year
- Sula, MT30 miles from this station, 42.0°F a year
- Compare two placesMonth by month, side by side
Download these normals (CSV) · JSON · How these figures are made