Boulder
United States · 17 May 2021
Average
9.9°C
low 6°C · high 13.5°C
Rainfall
12.9mm
rain recorded
Wind
1.5m/s
daily average
Humidity
86.7%
daily average
Cloud
98%
cover
Pressure
1013hPa
daily average
The temperature ranged from 6°C around 23:00 to 13.5°C around 13:00. Rain was recorded across 17 hours, from around 00:00 to 23:00 (12.9mm total).
How unusual was this day?
Compared against the same 135 calendar days (±7 days) across the other 9 years on file.
High temperature
25th percentile
Low temperature
73th percentile
Rainfall
90th percentile
Wind
12th percentile
A percentile of 100 means this was the hottest/wettest/windiest of the comparable days on file; 50 is right in the middle. This window's average temperature was 10.6°C, versus 9.9°C on this specific day.
Sun & daylight
Sunrise
05:43
Sunset
20:11
Day length
14h 28m
Hour by hour
Temperature (line) and hourly rainfall (bars), local time — America/Denver.
Cumulative rainfall through the day.
| Local time | UTC | Temp | Feels | Rain mm | Wind m/s | Dir | Humidity % | Pressure hPa |
|---|---|---|---|---|---|---|---|---|
| 00:00 | 06:00 | 8.1°C | 6.5°C | 0.12 | 1 | SW | 91 | 1016 |
| 01:00 | 07:00 | 8.1°C | 6.6°C | 0.08 | 1 | SSW | 90 | 1016 |
| 02:00 | 08:00 | 8.5°C | 7°C | 0.11 | 1 | SW | 89 | 1015 |
| 03:00 | 09:00 | 8.5°C | 7°C | 0.03 | 1.2 | WSW | 90 | 1015 |
| 04:00 | 10:00 | 8°C | 7°C | 0 | 0.5 | SW | 92 | 1014 |
| 05:00 | 11:00 | 8.2°C | 7.2°C | 0 | 0.5 | WNW | 93 | 1014 |
| 06:00 | 12:00 | 8.2°C | 6.8°C | 0 | 1 | NW | 92 | 1015 |
| 07:00 | 13:00 | 9.1°C | 7.8°C | 0.02 | 1 | NNW | 88 | 1015 |
| 08:00 | 14:00 | 9.6°C | 8.5°C | 0 | 0.7 | WNW | 88 | 1014 |
| 09:00 | 15:00 | 10.3°C | 9.3°C | 0.13 | 0.7 | ENE | 85 | 1014 |
| 10:00 | 16:00 | 10.2°C | 8.4°C | 0.36 | 1.9 | E | 88 | 1014 |
| 11:00 | 17:00 | 11.8°C | 9.8°C | 0.3 | 2.5 | ESE | 83 | 1013 |
| 12:00 | 18:00 | 12.2°C | 9.7°C | 0.53 | 3.1 | ESE | 80 | 1012 |
| 13:00 | 19:00 | 13.5°C | 10.9°C | 0.86 | 3.6 | SE | 78 | 1012 |
| 14:00 | 20:00 | 12.3°C | 10°C | 0.89 | 3.1 | SE | 81 | 1012 |
| 15:00 | 21:00 | 13.5°C | 11.5°C | 0.75 | 2.5 | SE | 74 | 1011 |
| 16:00 | 22:00 | 12.5°C | 10.1°C | 0.84 | 3 | SE | 77 | 1011 |
| 17:00 | 23:00 | 13.1°C | 11.4°C | 0.72 | 2.1 | ESE | 76 | 1011 |
| 18:00 | 00:00 | 11.5°C | 10.5°C | 2.96 | 0.7 | E | 79 | 1012 |
| 19:00 | 01:00 | 10°C | 8.4°C | 1.69 | 1.5 | ESE | 86 | 1013 |
| 20:00 | 02:00 | 8.8°C | 7.2°C | 1 | 1.5 | ESE | 92 | 1014 |
| 21:00 | 03:00 | 7.4°C | 6.2°C | 0.77 | 0.7 | N | 97 | 1014 |
| 22:00 | 04:00 | 7.3°C | 6°C | 0.53 | 0.8 | W | 97 | 1014 |
| 23:00 | 05:00 | 6°C | 4.3°C | 0.2 | 1.1 | W | 97 | 1013 |
Nearby cities
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Data source & coverage — ERA5 reanalysis, 2016–2025 (10 years)details
- Source
- ERA5 reanalysis, accessed via the Copernicus Climate Change Service (C3S) Climate Data Store
- Data type
- Reanalysis — a physically consistent reconstruction combining a forecast model with historical observations, not a live station reading or a forecast
- Coverage
- 2016–2025 (10 years) for United States
- Location
- Boulder — 40.000°, -105.250°, ERA5 grid cell center, 2.4 km from requested point
- Time zone
- America/Denver
- What's shown here
- The hourly and daily record for 17 May 2021 specifically — not a monthly average. See the Boulder climate overview for typical conditions.
- Spatial resolution
- 0.25° (~25 km) distributed grid — ERA5's native model resolution is finer; this is the publicly distributed regridded product
- Version / refreshed
- Methodology v2026.07 · data last refreshed December 31, 2025
- Limitations
- A model reconstruction, not a station observation — hyper-local extremes (a single storm cell, an urban heat pocket) can differ from a nearby gauge. See the full methodology.
- Attribution
- Generated using Copernicus Climate Change Service information
Cite this data
PastClimate (2026-07-21). Historical climate data for Boulder, United States (40.00°N, 105.25°W), derived from ERA5 (Hersbach et al., 2023, Copernicus Climate Change Service). Retrieved from https://www.pastclimate.com/
PastClimate. (2026). Historical climate data for Boulder, United States [Data set]. Derived from ERA5 (Copernicus Climate Change Service). Retrieved July 21, 2026, from https://www.pastclimate.com/
"Historical Climate Data for Boulder, United States." PastClimate, derived from ERA5 (Copernicus Climate Change Service), July 21, 2026, www.pastclimate.com.
@misc{pastclimate,
author = {PastClimate},
title = {Historical climate data for Boulder, United States},
year = {2026},
note = {Derived from ERA5 (Hersbach et al., 2023), Copernicus Climate Change Service. Accessed 2026-07-21},
url = {https://www.pastclimate.com/}
}Notice something wrong with this data? Report a data issue.