Longmont weather in September: Longmont, Colorado: normal highs, lows, rain and records for September
Longmont in September has a normal high of 80°F and a normal low of 46°F, a daily mean of 63°F, falling from 85°F on the 1st to 74°F by the 30th. Measurable precipitation falls on 6 days in a normal September, 1.26 inches in all. (NOAA 1991-2020 normals)
In metric: a normal high of 27°C and low of 8°C, 32 mm of precipitation in September.
- 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
- 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.
How warm is Longmont in September?
The normal high is 80°F and the normal low 46°F, for a daily mean of 63.0°F. September is 7.8°F cooler than August and 13.5°F warmer than October. September is the 4th warmest month of the year in Longmont and the 6th wettest. Across the month the normal high falls 11°F, from 85°F on September 1 to 74°F on September 30. From one year to the next September's mean temperature typically moves about 3.0°F either way (NOAA's standard deviation), so roughly two Septembers in three average between 60°F and 66°F.
Bars above: each day's normal high to low. Columns below: the chance of 0.01 inch or more of precipitation that day, on a scale of 0 to 100% (highest 21%).
| Day | High | Low | Chance of 0.01 in | Chance of 0.10 in |
|---|---|---|---|---|
| September 1 | 85°F | 51°F | 21% | 11% |
| September 8 | 83°F | 49°F | 21% | 12% |
| September 15 | 81°F | 46°F | 21% | 12% |
| September 22 | 78°F | 43°F | 21% | 13% |
| September 30 | 74°F | 39°F | 20% | 12% |
Every day of September: normal high, low and chance of precipitation (warmest afternoon September 1, coldest night September 30)
| Day | High | Low | Chance of 0.01 in | Chance of 0.10 in | Daylight |
|---|---|---|---|---|---|
| September 1 | 85°F | 51°F | 21% | 11% | 13 h 10 min |
| September 2 | 85°F | 51°F | 21% | 11% | 13 h |
| September 3 | 85°F | 51°F | 21% | 11% | 13 h |
| September 4 | 84°F | 50°F | 21% | 11% | 13 h |
| September 5 | 84°F | 50°F | 21% | 11% | 13 h |
| September 6 | 84°F | 50°F | 21% | 12% | 12 h 50 min |
| September 7 | 84°F | 49°F | 21% | 12% | 12 h 50 min |
| September 8 | 83°F | 49°F | 21% | 12% | 12 h 50 min |
| September 9 | 83°F | 49°F | 21% | 12% | 12 h 50 min |
| September 10 | 83°F | 48°F | 21% | 12% | 12 h 40 min |
| September 11 | 82°F | 48°F | 21% | 12% | 12 h 40 min |
| September 12 | 82°F | 48°F | 21% | 12% | 12 h 40 min |
| September 13 | 82°F | 47°F | 21% | 12% | 12 h 40 min |
| September 14 | 81°F | 47°F | 21% | 12% | 12 h 30 min |
| September 15 | 81°F | 46°F | 21% | 12% | 12 h 30 min |
| September 16 | 81°F | 46°F | 21% | 12% | 12 h 30 min |
| September 17 | 80°F | 46°F | 21% | 12% | 12 h 30 min |
| September 18 | 80°F | 45°F | 21% | 12% | 12 h 20 min |
| September 19 | 79°F | 45°F | 21% | 13% | 12 h 20 min |
| September 20 | 79°F | 44°F | 21% | 13% | 12 h 20 min |
| September 21 | 78°F | 44°F | 21% | 13% | 12 h 20 min |
| September 22 | 78°F | 43°F | 21% | 13% | 12 h 10 min |
| September 23 | 78°F | 43°F | 21% | 12% | 12 h 10 min |
| September 24 | 77°F | 42°F | 21% | 12% | 12 h 10 min |
| September 25 | 77°F | 42°F | 20% | 12% | 12 h 10 min |
| September 26 | 76°F | 41°F | 20% | 12% | 12 h |
| September 27 | 76°F | 41°F | 20% | 12% | 12 h |
| September 28 | 75°F | 40°F | 20% | 12% | 12 h |
| September 29 | 75°F | 40°F | 20% | 12% | 11 h 50 min |
| September 30 | 74°F | 39°F | 20% | 12% | 11 h 50 min |
- Normal high
- 80°FSeptember average
- Normal low
- 46°FSeptember average
- Precipitation
- 1.26 inmonth total
- Days with precipitation
- 60.01 inch or more
- Days at 90°F or more
- 6
- Nights at 32°F or colder
- 2
- Daylight
- 13 h 10 min to 11 h 50 minSeptember 1 to September 30
- Days at 70°F or more
- 25
- Days at 80°F or more
- 19
- Sunshine
- 80%of clear-sky sunlight (NASA)
Source: NOAA NCEI 1991-2020 daily normals, station USC00055116; monthly normals. Daylight is computed from the place's latitude with NOAA's solar equations.
Does it rain in Longmont in September?
On a given September day the chance of 0.01 inch or more is 21% on average, highest around September 10 (21%). In all, 1.26 in falls on 6 days of a normal September.
In a normal September in Longmont, 6 days reach 90°F and 2 nights fall to freezing.
Source: NOAA NCEI 1991-2020 daily and monthly normals, station USC00055116.
What are the records for September in Longmont?
The warmest September temperature on this station's record (since 1893) is 101°F, on September 6, 2020; the coldest is 18°F, on September 30, 1985. The wettest September brought 6.06 in (1938); the snowiest, 10.0 inches (1971).
The September mean against the 1991-2020 normal of 63.0°F: 2021 66.5°F (+3.5), 2022 65.9°F (+2.9), 2023 65.0°F (+2.0), 2024 67.2°F (+4.2), 2025 64.5°F (+1.5), 2026 68.3°F (+5.3). 6 of 6 ran warmer than normal.
| September | Mean | Against normal | Precip. |
|---|---|---|---|
| 2021 | 66.5°F | +3.5°F | 0.33 in |
| 2022 | 65.9°F | +2.9°F | 1.19 in |
| 2023 | 65.0°F | +2.0°F | 1.06 in |
| 2024 | 67.2°F | +4.2°F | 0.99 in |
| 2025 | 64.5°F | +1.5°F | 1.70 in |
| 2026 | 68.3°F | +5.3°F | 0.32 in |
Source: records: ACIS, station USC00055116; recent months: ACIS, station USC00055116. Records and recent months use complete months only.
How does September in Longmont compare across Colorado?
Across the 125 places PlainClimate covers in Colorado, September normal highs run from 62°F in Leadville to 86°F in Lamar; Longmont's is 80°F.
Source: NOAA NCEI 1991-2020 monthly normals for every station in the state.