Longmont, Colorado climate: Normal weather by month, frost dates and records
Longmont's normal year runs from 14°F January nights to 91°F July afternoons, with 15.2 inches of precipitation a year. (NOAA 1991-2020 normals)
In metric: a yearly mean of 10.0°C, January lows of −10°C, July highs of 33°C, 386 mm of precipitation a year.
- NOAA stationLongmont (2 mi ESE)
- Station IDUSC00055116
- Location40.17°N 105.08°W
- Elevation4,950 ft (1,509 m)
- From the center1 miles
- Population99,818
On October 22, the normal high in Longmont is 63°F and the normal low 31°F, and the chance of measurable rain or snow is 17%.
Normals describe a typical year at the station, not a forecast. The National Weather Service forecast for Longmont.
- Jan 45° 14°
- Feb 47° 17°
- Mar 57° 26°
- Apr 63° 32°
- May 73° 41°
- Jun 84° 51°
- Jul 91° 55°
- Aug 88° 54°
- Sep 80° 46°
- Oct 66° 33°
- Nov 54° 24°
- Dec 45° 15°
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 Longmont each month?
July is the warmest month, with normal highs of 91°F; January the coldest, with normal lows of 14°F. The most precipitation falls in April (2.04 in), the least in December (0.46 in).
Each month has its own page with the day-by-day normals, the month's records and its recent years:
| Month | High | Low | Mean | Precip. | Wet days | 90°F days | Freezing nights | Daylight |
|---|---|---|---|---|---|---|---|---|
| January | 45°F | 14°F | 29.4°F | 0.56 | 4 | <1 | 31 | 9 h 40 min |
| February | 47°F | 17°F | 32.0°F | 0.57 | 5 | <1 | 28 | 10 h 40 min |
| March | 57°F | 26°F | 41.5°F | 1.17 | 5 | <1 | 27 | 11 h 50 min |
| April | 63°F | 32°F | 47.8°F | 2.04 | 8 | <1 | 16 | 13 h 10 min |
| May | 73°F | 41°F | 57.1°F | 1.97 | 10 | 1 | 3 | 14 h 20 min |
| June | 84°F | 51°F | 67.2°F | 1.75 | 8 | 9 | <1 | 15 h |
| July | 91°F | 55°F | 73.1°F | 1.69 | 6 | 17 | <1 | 14 h 50 min |
| August | 88°F | 54°F | 70.8°F | 1.95 | 7 | 15 | <1 | 13 h 50 min |
| September | 80°F | 46°F | 63.0°F | 1.26 | 6 | 6 | 2 | 12 h 30 min |
| October | 66°F | 33°F | 49.5°F | 1.04 | 5 | <1 | 15 | 11 h 10 min |
| November | 54°F | 24°F | 38.5°F | 0.75 | 5 | <1 | 27 | 10 h |
| December | 45°F | 15°F | 29.6°F | 0.46 | 3 | <1 | 31 | 9 h 20 min |
| Year (annual) | 66°F | 34°F | 50.0°F | 15.21 | 72 | 49 | 178 |
The same normals in °C and millimetres
| Month | High | Low | Mean | Precip. |
|---|---|---|---|---|
| January | 7°C | −10°C | −1.4°C | 14 mm |
| February | 8°C | −8°C | 0.0°C | 14 mm |
| March | 14°C | −3°C | 5.3°C | 30 mm |
| April | 17°C | 0°C | 8.8°C | 52 mm |
| May | 23°C | 5°C | 13.9°C | 50 mm |
| June | 29°C | 10°C | 19.6°C | 44 mm |
| July | 33°C | 13°C | 22.8°C | 43 mm |
| August | 31°C | 12°C | 21.6°C | 50 mm |
| September | 27°C | 8°C | 17.2°C | 32 mm |
| October | 19°C | 0°C | 9.7°C | 26 mm |
| November | 12°C | −5°C | 3.6°C | 19 mm |
| December | 7°C | −10°C | −1.3°C | 12 mm |
NOAA publishes no 1991-2020 snowfall normal for this station. The nearest record that keeps one, Boulder (16 miles away), gets 93 inches of snow in a normal year; elevation and distance can change that.
Source: NOAA NCEI 1991-2020 monthly normals, station USC00055116; 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 Longmont?
Normal highs sit between 65°F and 85°F in May, June, September and October. Of those, October has the fewest days with rain (5).
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 USC00055116.
When is the last frost in Longmont?
In Longmont, the last spring frost (32°F) comes after May 7 in half of years and after May 22 in one year in ten; the first autumn frost comes before October 5 in half of years and before September 23 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 71 year in 10 after May 22; 9 in 10 after April 24
- First autumn frost, half of years before
- October 51 year in 10 before September 23; 9 in 10 before October 16
NOAA puts the median frost-free season at 151 days, and the season without a hard freeze (28°F) at 169 days.
A hard freeze (28°F) comes after April 28 in half of springs and before October 12 in half of autumns.
The USDA's 2023 Plant Hardiness Zone Map puts Longmont in zone 5b across its 2 ZIP code areas (5b in 80501, the largest).
Frost dates for every NOAA station in Colorado · Frost dates by ZIP code
Source: NOAA NCEI 1991-2020 annual normals (frost probabilities), station USC00055116; 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.
What hardiness zone is each Longmont ZIP code in?
The USDA's 2023 map gives each ZIP code area one zone. Longmont's 2 ZIP code areas are all in zone 5b. Each ZIP's frost dates are in the frost tool.
Source: USDA 2023 Plant Hardiness Zone Map, ZIP listings: PRISM Group, Oregon State University, https://prism.oregonstate.edu, accessed October 8, 2026; ZIP areas in the place: Census Bureau 2020 ZCTA-to-place relationship file. A ZIP area counts when at least a tenth of its land (and 0.5 km²) lies in the place.
How hot and how cold does it get in Longmont?
In a normal year in Longmont, 49 days a year reach 90°F (4 of them 100°F or more), 178 nights fall to 32°F or colder and 72 days bring measurable precipitation.
- Days at 90°F or more
- 49a normal year
- Days at 100°F or more
- 4a normal year
- Nights at 32°F or colder
- 178a normal year
- Days that stay below freezing
- 19high of 32°F or less
- Days with 0.01 inch of precipitation
- 72a normal year
The highest temperature in this station's record (since 1893) is 106°F, on June 27, 1994; the lowest is −38°F, on January 16, 1930.
The wettest calendar year on that record is 1923, with 21.70 in; the snowiest season is 2019–20, with 75.8 inches.
Source: NOAA NCEI 1991-2020 annual normals, station USC00055116; records: ACIS (NOAA Regional Climate Centers), station USC00055116. Records use complete months only; a month missing more than three days is left out.
How sunny is Longmont?
Over a year 76% of the sunlight that would reach the ground under clear skies gets through the clouds in the area around Longmont, 4.6 kWh per square metre a day. September is the sunniest month (80%) and May the cloudiest (69%). Among the 459 U.S. places of 50,000 or more, that ranks tied 276th (with 27 others) in sunshine.
| Month | Share of clear-sky sunshine | Sunshine, kWh/m² a day |
|---|---|---|
| January | 79% | 2.5 |
| February | 79% | 3.5 |
| March | 77% | 4.7 |
| April | 71% | 5.4 |
| May | 69% | 6.0 |
| June | 78% | 7.0 |
| July | 77% | 6.6 |
| August | 76% | 5.8 |
| September | 80% | 5.0 |
| October | 77% | 3.7 |
| November | 76% | 2.6 |
| December | 76% | 2.1 |
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 Longmont need?
A normal year in Longmont brings 6,111 heating degree days, 14% more than the median U.S. place (5,373), and 657 cooling degree days, 28% fewer than the median (908). Seven months need 300 or more heating degree days, a monthly mean of about 55°F or colder. For gardens and crops, NOAA counts 2,765 growing degree days a year above 50°F.
| Month | Heating | Cooling |
|---|---|---|
| January | 1,102 | 0 |
| February | 925 | 0 |
| March | 730 | 0 |
| April | 518 | 1 |
| May | 265 | 19 |
| June | 58 | 124 |
| July | 7 | 257 |
| August | 11 | 189 |
| September | 124 | 66 |
| October | 480 | 1 |
| November | 795 | 0 |
| December | 1,096 | 0 |
| Year (annual) | 6,111 | 657 |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00055116. 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 Longmont been warmer than normal lately?
2025 averaged 52.4°F, 2.4°F above the 1991-2020 normal of 50.0°F. 5 of the 5 complete years since 2021 ran warmer than the normal.
| Year | Mean | Against normal | Precip. |
|---|---|---|---|
| 2021 | 51.6°F | +1.6°F | 15.78 |
| 2022 | 50.3°F | +0.3°F | 15.22 |
| 2023 | 50.4°F | +0.4°F | 21.10 |
| 2024 | 52.9°F | +2.9°F | 12.98 |
| 2025 | 52.4°F | +2.4°F | 12.47 |
Over 88 complete years from 1895 to 2025, the station's annual mean temperature rose at a fitted 1.7°F per century (+0.09°C per decade). A fitted rate summarizes the whole record; single years swing well above and below it.
Source: observed years: ACIS, station USC00055116; trend: NOAA GHCN-Monthly v4. A year counts only with all twelve months complete.
How does Longmont's climate compare?
Longmont is warmer than 75 of the other 124 places with their own NOAA record in Colorado, and wetter than 55. Across the 7,247 U.S. stations with normals, its annual mean of 50.0°F is warmer than 40%.
In the Köppen classification computed from these normals, Longmont 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 Longmont share this climate record?
10 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.
- Erie, CO38,594 people · 9 mi S
- Firestone, CO19,396 people · 7 mi E
- Frederick, CO17,937 people · 7 mi SE
- Berthoud, CO13,648 people · 10 mi NE
- Dacono, CO6,748 people · 10 mi SE
- Mead, CO6,735 people · 6 mi NE
- Niwot, CO3,773 people · 7 mi SW
- Platteville, CO2,904 people · 13 mi E
- Lyons, CO2,155 people · 11 mi W
- Leyner, CO0 people · 8 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 Longmont's climate
What is the coldest month in Longmont?
January, with a normal high of 45°F and a normal low of 14°F. The warmest is July (91°F by day, 55°F at night).
Does it snow in Longmont?
Yes. NOAA publishes no 1991-2020 snowfall normal for Longmont's NOAA station; the nearest record that keeps one, Boulder (16 miles away), records 93 inches of snow in a normal year.
What is the rainiest month in Longmont?
April, with 2.04 in of precipitation in a normal year; the driest is December with 0.46 in.
What plant hardiness zone is Longmont in?
The USDA's 2023 map puts Longmont in zone 5b across its 2 ZIP code areas (5b in 80501, the largest).
How late can frost come in Longmont?
In half of years the last 32°F night comes after May 7; in one year in ten it comes after May 22. Waiting until May 22 leaves about a one-in-ten chance of a later frost.
Nearby and next
- Longmont in OctoberThis month day by day, its records and recent years
- Colorado climateThe statewide normals and every place in the state
- Boulder, CO16 miles from this station, 51.5°F a year
- Loveland, CO19 miles from this station, 48.7°F a year
- Northglenn, CO19 miles from this station, 52.4°F a year
- Waterdale, CO19 miles from this station, 48.2°F a year
- Compare two placesMonth by month, side by side
Download these normals (CSV) · JSON · How these figures are made