Boulder Weather in October: Temperatures, First Snow Odds, and What to Pack
Boulder Weather in October: A Month That Loses 14 Degrees
October takes 14 degrees off Boulder's afternoon high. The normal high falls from 72°F on October 1 to 58°F on October 31, and the normal low drops from 45°F to 33°F. The median first frost comes on October 6 and the median first measurable snow on October 20, so both median dates fall inside the month. Boulder's official station has stood near the NIST building on the western edge of town since 1990. For the other months, see Boulder weather by month.
How Warm and Cold Does October Get?
The first days of October still look like late summer, with normals of 72°F and 45°F on October 1. Normal highs stay between 68°F and 70°F from October 5 through October 11. They slip to 65°F by October 16, reach 62°F on October 25 and end at 58°F for the last three days of the month. Lows follow the same path: 42°F from October 6 to 10, 38°F from October 16 to 22, and 33°F on Halloween.
The records reach much further in both directions. Two dates hold a 90°F record high, October 1 (1953) and October 5 (1947). Recent years keep adding warm records: 89°F on October 2, 2024, 81°F on October 28, 2024, and records set or tied in 2023 on October 17 (85°F) and October 20 (87°F).
On the cold side, the lowest reading in the October records is -2°F on October 29, 1917, a date whose normals are 58°F and 34°F. That leaves 92 degrees between the month's warmest and coldest records. October 2019 ended with record lows of 3°F on both the 30th and the 31st.
Late October 2020 set three record lows in a row in Boulder: 10°F on October 25, 5°F on October 26 and 4°F on October 27. Denver set records in the same cold outbreak, a record cold high of 16°F, breaking 31°F from 1923, and a record low of 8°F, breaking 11°F from 1925.
Boulder's temperature records start in 1897 and its daily snow records in 1948. The record has one gap, 1989–1990, when Boulder had no official station.
October normals and records, day by day:
| Oct | Normal high (°F) | Normal low (°F) | Record high (°F, year) | Record low (°F, year) | Record daily snow (in, year) |
|---|---|---|---|---|---|
| 1 | 72 | 45 | 90 (1953) | 23 (1985) | 3.5 (1959) |
| 2 | 72 | 45 | 89 (2024) | 27 (1959) | 2.8 (1959) |
| 3 | 71 | 44 | 88 (1967) | 30 (1927, 2009) | 2.0 (1969) |
| 4 | 71 | 44 | 88 (1922) | 30 (1950) | 10.2 (1969) |
| 5 | 69 | 43 | 90 (1947) | 27 (1991) | 3.0 (1969) |
| 6 | 68 | 42 | 85 (1993, 2020) | 28 (1995) | 0.9 (2000) |
| 7 | 70 | 42 | 88 (1956) | 23 (1970) | 3.5 (1970) |
| 8 | 69 | 42 | 86 (1965) | 22 (1970) | 4.1 (1990) |
| 9 | 69 | 42 | 86 (1965) | 24 (1990) | 6.0 (1985) |
| 10 | 69 | 42 | 88 (1910) | 15 (2009) | 4.8 (2009) |
| 11 | 69 | 41 | 87 (1996) | 15 (2019) | 9.7 (1969) |
| 12 | 67 | 40 | 89 (1950) | 20 (1969) | 6.5 (1969) |
| 13 | 68 | 41 | 88 (1989) | 10 (1969) | 2.0 (1985) |
| 14 | 67 | 41 | 85 (1962) | 13 (1969) | 8.9 (2018) |
| 15 | 66 | 40 | 85 (1958) | 13 (2018) | 9.2 (1969) |
| 16 | 65 | 38 | 87 (1991) | 20 (1969) | 12.0 (1948) |
| 17 | 65 | 38 | 85 (2003, 2023) | 15 (1999) | 3.7 (2006) |
| 18 | 65 | 38 | 86 (1926) | 19 (1925) | 3.2 (2013) |
| 19 | 63 | 38 | 87 (2003) | 17 (1925) | 1.5 (1982) |
| 20 | 64 | 38 | 87 (1950, 2023) | 19 (1916) | 3.2 (1949) |
| 21 | 65 | 38 | 84 (1950) | 12 (1911) | 5.8 (2006) |
| 22 | 63 | 38 | 85 (2003) | 19 (1936) | 3.0 (1995) |
| 23 | 63 | 36 | 86 (2003) | 22 (1906) | 4.8 (1975) |
| 24 | 63 | 36 | 83 (2014) | 19 (1975) | 7.7 (1997) |
| 25 | 62 | 36 | 85 (2017) | 10 (2020) | 22.1 (1997) |
| 26 | 62 | 36 | 81 (1966) | 5 (2020) | 11.5 (2011) |
| 27 | 62 | 36 | 82 (2016) | 4 (2020) | 3.9 (2019) |
| 28 | 61 | 36 | 81 (2024) | 11 (1925) | 16.7 (2009) |
| 29 | 58 | 34 | 83 (1968) | -2 (1917) | 10.2 (1961) |
| 30 | 58 | 34 | 80 (1933) | 3 (2019) | 9.6 (1972) |
| 31 | 58 | 33 | 83 (1950) | 3 (2019) | 4.9 (1989)* |
*The 4.9-inch October 31 snow record from 1989 is not from the official dataset.
When Does Boulder's First Freeze Arrive?
In Boulder's climate record, frost means any night when the minimum temperature reaches 32°F or lower. Since 1948, the median and average dates for the first one are both October 6. The first quartile is September 27 and the third quartile is October 15, so half of all years get their first frost inside that 19-day window.
The extremes are September 8, 2020 and October 31, 1963. No year since 1948 has reached November without a frost. For spring and fall planting dates, see Boulder's first and last freeze dates.
The normal low never reaches freezing in October; its lowest point is 33°F on October 31. Even so, three years in four have their first frost by October 15, because single nights run far below normal. The 2019 and 2020 record lows show how far.
The official thermometer sits about 3 meters (roughly 10 feet) above the surface, and the ground can be colder than the air up there. A garden bed, a lawn or a windshield can frost on a night when the station stays above freezing. Cover tender plants when the forecast low is in the mid-30s. Do not wait for it to show 32°F.
What Are the Odds of the First Snow in October?
Boulder's first snow is the first day with measurable snow, more than a trace, at the official station. The average date since 1948 is October 17 and the median is October 20, with a standard deviation of 18.6 days. A quarter of years get it by September 30 and three quarters by October 30. One year in ten gets it before September 20, and one in ten waits past November 9. These summary figures still give September 12, 1974 and November 17, 2016 as the extremes, so they do not yet count the September 8, 2020 and November 29, 2025 first snows, now the earliest and latest in the 1948–2025 list.
The year-by-year dates from 1948 through 2025 give 77 seasons with a date, because 1989 is missing. First snow came in October in 41 of them, in September in 17 and in November in 19. So the chance that the first snow falls in October is a little better than even, about 53 percent, and about one season in four waits until November.
Through 2025, the last five seasons have run late. The 2020 season started on September 8. After that, first snow came on November 17 in 2021, October 27 in 2022, October 28 in 2023, November 4 in 2024 and November 29 in 2025. Three of those five waited until November, and both October dates fell in the last week of the month.
How Much Snow Falls, and Why the Average Misleads
The 1991–2020 mean October snowfall at the NIST site is 6.95 inches. September's mean is 1.03 inches, November's is 12.69 inches and the yearly mean is 89.71 inches. The October standard deviation is 9.17 inches, which is larger than the mean. Octobers swing between nothing and several times the average.
The big months:
- 1969: 49.3 inches. Six October daily snow records still belong to 1969 (October 3, 4, 5, 11, 12 and 15), along with record lows on October 12, 13, 14 and 16. The 10°F reading on October 13 is one of them.
- 1997: 30.1 inches. The season's first snow came on October 24 and set a daily record of 7.7 inches. The next day brought 22.1 inches, the largest one-day total in the October table. Those two days account for 29.8 of the month's 30.1 inches.
- 2009: 30.1 inches, including a 16.7-inch record day on October 28.
- 2019: 26.4 inches, with a 3.9-inch record on October 27 and record lows of 3°F on the 30th and 31st.
- 1942: 23.0 inches.
The lean months are recent. October snowfall was 0.0 inches in 2021, 0.1 in 2022, 6.8 in 2023, and 0.0 in both 2024 and 2025. Four of the five Octobers from 2021 to 2025 got a tenth of an inch or less. The rest of the year is in Boulder snow by month.
October 2020 fell between those extremes, with 12.5 inches, after 5.7 inches in September. Late that month a strong cold front moved through Colorado, and heavy snow developed behind it early on October 25. Accumulations were generally 12 to 18 inches across the Boulder and Larimer mountains and foothills, and 8 to 14 inches were common across the rest of the two counties. A spotter 1.8 miles east-southeast of Boulder measured 12.9 inches by 7 a.m. on October 26, and one 2.3 miles north of Allenspark measured 14.3 inches. Boulder's record lows of 10°F, 5°F and 4°F fell on October 25, 26 and 27, the same days.
Rain, Dry Spells and October Fire Weather
October is drier than September. The 1991–2020 normal precipitation is 1.62 inches for October, against 2.07 inches for September and 1.18 inches for November. The yearly normal is 21.16 inches. The last two Octobers came in well under normal: 0.13 inches in 2024 and 0.67 inches in 2025. The 2024 total was about 8 percent of normal.
Boulder County's largest fire by acreage in recent history started in October. At 12:22 p.m. on Saturday, October 17, 2020, the Sheriff's Office received a report of a one-acre wildfire outside Jamestown. A Red Flag Warning had taken effect at noon. That was the Cal-Wood Fire. It burned about 10,112 acres and destroyed 20 homes and 2 cabins.
The next day, Sunday, October 18, a second fire was reported outside Ward, in Lefthand Canyon. The Lefthand Canyon Fire burned 460 acres with minimal fire behavior because conditions were snowy and cold. A week later, the October 25–26 storm dropped 6 to 18 inches, depending on elevation, on the Cameron Peak and East Troublesome fires.
What to Pack for Boulder in October
Pack for a wide daily range. The normal gap between high and low is 27 degrees on October 1 (72°F and 45°F) and 25 degrees on October 31 (58°F and 33°F).
- Layers. A base layer, a fleece or sweater and a wind shell, so warmth can go on and come off as the day changes.
- A warm jacket, hat and gloves. Bring them for evenings and early starts, above all in the second half of the month.
- Waterproof footwear. One snow day can leave slush on sidewalks and trails for days afterward.
- A plan for snow on the drive. Check road conditions before heading to higher towns after a storm.
- Fire awareness on dry weeks. Check for Red Flag Warnings and local burn rules before lighting a camp stove or fire.
References
- Boulder October daily climatology and records, NOAA PSL
- Boulder first and last frost dates, NOAA PSL
- Boulder first snow dates, NOAA PSL
- Boulder monthly snowfall, NOAA PSL
- Boulder monthly precipitation, NOAA PSL
- Boulder weather station history, NOAA PSL
- Late October 2020 snowstorm, NWS Boulder
- Cal-Wood and Lefthand Canyon fires, Boulder County