Your nature year
Boulder, Coloradothrough the year
Also for Longmont, CO: the same nearby places.
When do frost, green-up and fall color come to Boulder?
Head northwest for the closest of the 3 places we follow around Boulder. The closest place we follow is Rocky Mountain, 28 miles away, for fall foliage, Sep 1–Oct 31 (local timing). Rocky Mountain (28 mi) is the pick for wildflowers, May 21–Aug 10 (local timing). Boulder usually sees its last spring frost around May 6 and its first fall frost around Oct 5, a frost-free stretch of about 152 days at NOAA's Boulder station, 2.3 miles away. Spring green-up reaches town around Mar 21, with first blooms around May 1. At some 5,253 feet up, Boulder is high enough that seasons run on a mountain clock. Across Colorado, fall color is usually well under way by mid-October.
Updated Sep 28. Sources: US Census Bureau, 2024 Gazetteer (places) ↗ (opens in a new tab), US Census Bureau, city and town population estimates, 2024 ↗ (opens in a new tab), NOAA NCEI U.S. Climate Normals 1991–2020 (annual/seasonal) ↗ (opens in a new tab)
Boulder's year at a glance
- Frost possible
- Frost-free, ~May 6 to ~Oct 5
- First leaf ~Mar 21
- First bloom ~May 1
- Fall color under way ~Oct 11 (CO)
- Today
Near Boulder right now
- Fall color is usually well under way by mid-October in ColoradoStatewide · USA-NPN volunteer observations, 2020–2025 · not a forecast~13 days
- First fall frost usually around Oct 5 · last spring frost around May 6NOAA 1991–2020 normals, Boulder (2.3 mi, 50% dates)~7 days
- Rocky Mountain · 28 mi · Local timing: Sep 1–Oct 31Fall foliage · in its window now
- Guanella Pass · 38 mi · Regional timing: Sep 1–30Fall foliage · in its window now
- Wildflowers · Rocky Mountain · 28 miLocal timing: May 21–Aug 10~8 months
Boulder's nature year
- Spring green-upMar
- Wildflowers · Rocky MountainMay–Aug
- Last spring frostMay
- Fall color (CO)Oct
- First fall frostOct
Nearby, season by season
Fall foliage
- Rocky Mountain · 28 miLocal timing: Sep 1–Oct 31
- Guanella Pass · 38 miRegional timing: Sep 1–30
- Maroon Bells · 111 miusually Sep 21–30
Wildflowers
- Rocky Mountain · 28 miLocal timing: May 21–Aug 10~8 months
- Guanella Pass · 38 miLocal timing: Jun 15–Aug 10~9 months
Snow in Boulder
Snow usually becomes possible around Oct 25 (our calculation from NOAA's daily snow chances: the first day the chance of 0.1" or more of snow reaches 10%). NOAA's normals at Boulder (2.3 mi away): 93 inches of snow in an average year, about 22 days with 1 inch or more.
NOAA's chance of at least 0.1 inch of snow on each date (one value per week, September to May), averaged over 1991–2020. A typical year, not a forecast.
Frost and green-up
Last spring frost
May 6
Average (50% date)
First fall frost
Oct 5
About 152 days without frost between
Spring green-up
Mar 21
First bloom around May 1
Frost: NOAA 1991–2020 climate normals at Boulder (2.3 mi from Boulder), the day a 32 °F night is as likely as not. Green-up: the USA-NPN Spring Index, 1991–2020 average at the town.
Questions people ask
When is the first frost in Boulder?
On average around Oct 5, and the last spring frost around May 6: about 152 days without frost between. These are NOAA's 1991–2020 normals at Boulder, 2.3 miles away (the day a 32 °F night is as likely as not).
When does spring green-up reach Boulder?
The USA-NPN Spring Index puts first leaf around Mar 21 and first bloom around May 1, on average for 1991–2020 at the town.
Where can I see fall foliage near Boulder?
Rocky Mountain, 28 miles (local timing: Sep 1–Oct 31); Guanella Pass, 38 miles (regional timing: Sep 1–30); Maroon Bells, 111 miles (usually Sep 21–30). Distances are straight-line.
Where can I see wildflowers near Boulder?
Rocky Mountain, 28 miles (local timing: May 21–Aug 10); Guanella Pass, 38 miles (local timing: Jun 15–Aug 10). Distances are straight-line.
When does it start snowing in Boulder?
Snow usually becomes possible around Oct 25: our calculation from NOAA's daily snow chances: the first day the chance of 0.1" or more of snow reaches 10%, at Boulder. An average year brings 93 inches (NOAA 1991–2020). A typical year, not a forecast.Sources: NOAA NCEI U.S. Climate Normals 1991–2020 (annual/seasonal snowfall) ↗ (opens in a new tab), NOAA NCEI U.S. Climate Normals 1991–2020 (daily snowfall probabilities) ↗ (opens in a new tab)
How we know
US Census Bureau, 2024 Gazetteer (places) (opens in a new tab) (Sep 27) · US Census Bureau, city and town population estimates, 2024 (opens in a new tab) (Sep 27) · NOAA NCEI U.S. Climate Normals 1991–2020 (annual/seasonal) (opens in a new tab) (Sep 27) · USA National Phenology Network, Spring Index 1991–2020 averages (opens in a new tab) (Sep 27) · USA National Phenology Network, colored leaves observations (opens in a new tab) (Sep 28)