Westby, Montana climate: Normal weather by month, frost dates and records
Westby's normal year runs from −2°F January nights to 80°F July afternoons, with 14.9 inches of precipitation a year. (NOAA 1991-2020 normals)
In metric: a yearly mean of 3.9°C, January lows of −19°C, July highs of 27°C, 379 mm of precipitation a year.
- NOAA stationWestby
- Station IDUSC00248777
- Location48.87°N 104.05°W
- Elevation2,103 ft (641 m)
- Population162
On October 23, the normal high in Westby is 49°F and the normal low 25°F.
Normals describe a typical year at the station, not a forecast. The National Weather Service forecast for Westby.
- Jan 20° -2°
- Feb 24° 2°
- Mar 36° 14°
- Apr 53° 27°
- May 65° 40°
- Jun 73° 50°
- Jul 80° 55°
- Aug 80° 52°
- Sep 70° 41°
- Oct 54° 29°
- Nov 36° 15°
- Dec 24° 4°
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 Westby each month?
July is the warmest month, with normal highs of 80°F; January the coldest, with normal lows of −2°F. The most precipitation falls in June (3.14 in), the least in February (0.34 in).
| Month | High | Low | Mean | Precip. | Wet days | 90°F days | Freezing nights | Daylight |
|---|---|---|---|---|---|---|---|---|
| January | 20°F | −2°F | 8.7°F | 0.37 | – | <1 | 31 | 8 h 40 min |
| February | 24°F | 2°F | 12.8°F | 0.34 | – | <1 | 28 | 10 h 10 min |
| March | 36°F | 14°F | 25.0°F | 0.55 | – | <1 | 30 | 11 h 50 min |
| April | 53°F | 27°F | 39.9°F | 0.98 | – | <1 | 22 | 13 h 40 min |
| May | 65°F | 40°F | 52.4°F | 2.17 | – | <1 | 7 | 15 h 10 min |
| June | 73°F | 50°F | 61.5°F | 3.14 | – | 1 | <1 | 16 h 10 min |
| July | 80°F | 55°F | 67.3°F | 2.49 | – | 3 | <1 | 15 h 50 min |
| August | 80°F | 52°F | 65.9°F | 1.64 | – | 4 | <1 | 14 h 30 min |
| September | 70°F | 41°F | 55.4°F | 1.26 | – | 1 | 4 | 12 h 40 min |
| October | 54°F | 29°F | 41.0°F | 0.97 | – | <1 | 21 | 10 h 50 min |
| November | 36°F | 15°F | 25.4°F | 0.52 | – | <1 | 29 | 9 h 10 min |
| December | 24°F | 4°F | 13.7°F | 0.48 | – | <1 | 31 | 8 h 20 min |
| Year (annual) | 51°F | 27°F | 39.1°F | 14.91 | – | 10 | 202 |
The same normals in °C and millimetres
| Month | High | Low | Mean | Precip. |
|---|---|---|---|---|
| January | −7°C | −19°C | −12.9°C | 9 mm |
| February | −5°C | −17°C | −10.7°C | 9 mm |
| March | 2°C | −10°C | −3.9°C | 14 mm |
| April | 11°C | −3°C | 4.4°C | 25 mm |
| May | 19°C | 4°C | 11.3°C | 55 mm |
| June | 23°C | 10°C | 16.4°C | 80 mm |
| July | 27°C | 13°C | 19.6°C | 63 mm |
| August | 27°C | 11°C | 18.8°C | 42 mm |
| September | 21°C | 5°C | 13.0°C | 32 mm |
| October | 12°C | −2°C | 5.0°C | 25 mm |
| November | 2°C | −10°C | −3.7°C | 13 mm |
| December | −5°C | −16°C | −10.2°C | 12 mm |
NOAA publishes no 1991-2020 snowfall normal for this station. The nearest record that keeps one, Fortuna (11 miles away), gets 37 inches of snow in a normal year; elevation and distance can change that.
Source: NOAA NCEI 1991-2020 monthly normals, station USC00248777; 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 Westby?
Normal highs sit between 65°F and 85°F in May, June, July, August and September.
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 USC00248777.
When is the last frost in Westby?
In Westby, the last spring frost (32°F) comes after May 18 in half of years and after May 30 in one year in ten; the first autumn frost comes before September 21 in half of years and before September 7 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 181 year in 10 after May 30; 9 in 10 after May 6
- First autumn frost, half of years before
- September 211 year in 10 before September 7; 9 in 10 before October 1
NOAA puts the median frost-free season at 125 days, and the season without a hard freeze (28°F) at 141 days.
A hard freeze (28°F) comes after May 8 in half of springs and before September 28 in half of autumns.
The USDA's 2023 Plant Hardiness Zone Map puts Westby in zone 3b in ZIP code 59275, the nearest ZIP area. By the map's own method, the average of each year's coldest night over 1991-2020, Westby's NOAA station is in zone 3b: the coldest night of a typical year reaches −31°F (16 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 USC00248777; 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 Westby?
In a normal year in Westby, 10 days a year reach 90°F and 202 nights fall to 32°F or colder.
- Days at 90°F or more
- 10a normal year
- Days at 100°F or more
- fewer than 1a normal year
- Nights at 32°F or colder
- 202a normal year
- Days that stay below freezing
- 92high of 32°F or less
The highest temperature in this station's record (since 1937) is 112°F, on July 5, 1937; the lowest is −45°F, on January 25, 1943.
The wettest calendar year on that record is 1953, with 25.31 in; the snowiest season is 1998–99, with 61.4 inches.
Source: NOAA NCEI 1991-2020 annual normals, station USC00248777; records: ACIS (NOAA Regional Climate Centers), station USC00248777. Records use complete months only; a month missing more than three days is left out.
How sunny is Westby?
Over a year 78% of the sunlight that would reach the ground under clear skies gets through the clouds in the area around Westby, 4.0 kWh per square metre a day. July is the sunniest month (86%) and December the cloudiest (70%).
| Month | Share of clear-sky sunshine | Sunshine, kWh/m² a day |
|---|---|---|
| January | 80% | 1.6 |
| February | 83% | 2.8 |
| March | 77% | 3.9 |
| April | 73% | 4.9 |
| May | 74% | 5.9 |
| June | 77% | 6.5 |
| July | 86% | 6.8 |
| August | 83% | 5.6 |
| September | 78% | 4.1 |
| October | 73% | 2.6 |
| November | 72% | 1.6 |
| December | 70% | 1.2 |
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 Westby need?
A normal year in Westby brings 9,695 heating degree days, 80% more than the median U.S. place (5,373), and 286 cooling degree days, 69% 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 1,797 growing degree days a year above 50°F.
| Month | Heating | Cooling |
|---|---|---|
| January | 1,747 | 0 |
| February | 1,462 | 0 |
| March | 1,242 | 0 |
| April | 752 | 0 |
| May | 397 | 7 |
| June | 145 | 40 |
| July | 46 | 116 |
| August | 77 | 104 |
| September | 308 | 18 |
| October | 743 | 1 |
| November | 1,189 | 0 |
| December | 1,589 | 0 |
| Year (annual) | 9,695 | 286 |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00248777. 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 Westby been warmer than normal lately?
2025 averaged 40.0°F, 0.9°F above the 1991-2020 normal of 39.1°F. 3 of the 3 complete years since 2021 ran warmer than the normal.
| Year | Mean | Against normal | Precip. |
|---|---|---|---|
| 2021 | 41.3°F | +2.2°F | 8.23 |
| 2024 | 41.8°F | +2.7°F | 13.37 |
| 2025 | 40.0°F | +0.9°F | 17.04 |
Over 44 complete years from 1937 to 2025, the station's annual mean temperature rose at a fitted 3.6°F per century (+0.20°C per decade). A fitted rate summarizes the whole record; single years swing well above and below it.
Source: observed years: ACIS, station USC00248777; trend: NOAA GHCN-Monthly v4. A year counts only with all twelve months complete.
How does Westby's climate compare?
Westby is warmer than 8 of the other 140 places with their own NOAA record in Montana, and wetter than 68. Across the 7,247 U.S. stations with normals, its annual mean of 39.1°F is warmer than 4%.
In the Köppen classification computed from these normals, Westby 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 Westby share this climate record?
Grenora 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.
- Grenora, ND220 people · 18 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 Westby's climate
What is the coldest month in Westby?
January, with a normal high of 20°F and a normal low of −2°F. The warmest is July (80°F by day, 55°F at night).
Does it snow in Westby?
Yes. NOAA publishes no 1991-2020 snowfall normal for Westby's NOAA station; the nearest record that keeps one, Fortuna (11 miles away), records 37 inches of snow in a normal year.
What is the rainiest month in Westby?
June, with 3.14 in of precipitation in a normal year; the driest is February with 0.34 in.
What plant hardiness zone is Westby in?
The USDA's 2023 map puts Westby in zone 3b in ZIP code 59275, the nearest ZIP area. By the same method at Westby's NOAA station, the coldest night of a typical year reaches −31°F (16 years, 1991-2020): zone 3b.
How late can frost come in Westby?
In half of years the last 32°F night comes after May 18; in one year in ten it comes after May 30. Waiting until May 30 leaves about a one-in-ten chance of a later frost.
Nearby and next
- Montana climateThe statewide normals and every place in the state
- Fortuna, ND11 miles from this station, 38.3°F a year
- Plentywood, MT24 miles from this station, 39.4°F a year
- Raymond Border Station, MT25 miles from this station, 40.6°F a year
- Medicine Lake, MT33 miles from this station, 41.0°F a year
- Compare two placesMonth by month, side by side
Download these normals (CSV) · JSON · How these figures are made