Boulder
United States · 21 May 2017
Average
7.9°C
low 0.2° · high 13.7°
Rainfall
1.7mm
rain recorded
Wind
2m/s
daily average
Humidity
65.7%
daily average
Cloud
61%
cover
Pressure
1020hPa
daily average
The temperature ranged from 0.2°C around 03:00 to 13.7°C around 15:00. Rain was recorded across 5 hours, from around 15:00 to 23:00 (1.7mm total).
How unusual was this day?
Compared against the same 135 calendar days (±7 days) across the other 9 years on file.
High temperature
21th percentile
Low temperature
7th percentile
Rainfall
54th percentile
Wind
56th 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 11.3°C, versus 7.9°C on this specific day.
Sun & daylight
Sunrise
05:40
Sunset
20:15
Day length
14h 35m
Hour by hour
Temperature (line) and hourly rainfall (bars), local time — America/Denver.
Cumulative rainfall through the day.
| Local time | UTC | Temp °C | Feels °C | Rain mm | Wind m/s | Dir | Humidity % | Pressure hPa |
|---|---|---|---|---|---|---|---|---|
| 00:00 | 06:00 | 4.4 | 0.9 | 0 | 2.4 | W | 80 | 1019 |
| 01:00 | 07:00 | 3.3 | -0.3 | 0 | 2.5 | W | 83 | 1019 |
| 02:00 | 08:00 | 1.7 | -2.1 | 0 | 2.5 | W | 85 | 1019 |
| 03:00 | 09:00 | 0.2 | -3.8 | 0 | 2.5 | W | 86 | 1019 |
| 04:00 | 10:00 | 1.6 | -1.8 | 0 | 1.5 | W | 77 | 1019 |
| 05:00 | 11:00 | 1.2 | -2.1 | 0 | 1.4 | W | 78 | 1019 |
| 06:00 | 12:00 | 1.5 | -2.2 | 0 | 2 | W | 76 | 1020 |
| 07:00 | 13:00 | 2.9 | -1.3 | 0 | 2.7 | W | 70 | 1020 |
| 08:00 | 14:00 | 6.4 | 2.8 | 0 | 2.3 | WNW | 63 | 1021 |
| 09:00 | 15:00 | 10.3 | 8.3 | 0 | 0.2 | SSW | 52 | 1020 |
| 10:00 | 16:00 | 11.8 | 8.6 | 0 | 1.8 | E | 47 | 1020 |
| 11:00 | 17:00 | 12.5 | 9.4 | 0 | 2.1 | ESE | 49 | 1020 |
| 12:00 | 18:00 | 12.9 | 9.5 | 0 | 2.5 | ESE | 48 | 1019 |
| 13:00 | 19:00 | 13.4 | 9.6 | 0.04 | 3.1 | ESE | 49 | 1018 |
| 14:00 | 20:00 | 13.6 | 10 | 0.05 | 3 | ESE | 49 | 1018 |
| 15:00 | 21:00 | 13.7 | 10.9 | 0.11 | 2.1 | ESE | 52 | 1018 |
| 16:00 | 22:00 | 13.7 | 10.7 | 0.06 | 1.7 | E | 43 | 1017 |
| 17:00 | 23:00 | 13.1 | 10.1 | 0.06 | 1.6 | NNE | 43 | 1018 |
| 18:00 | 00:00 | 12.3 | 9.2 | 0.04 | 1.9 | NNE | 47 | 1020 |
| 19:00 | 01:00 | 11.1 | 7.7 | 0.01 | 2.7 | NNE | 56 | 1021 |
| 20:00 | 02:00 | 9.5 | 6.7 | 0.3 | 2.1 | NNE | 69 | 1022 |
| 21:00 | 03:00 | 7 | 5.1 | 0.25 | 1.1 | NNW | 87 | 1023 |
| 22:00 | 04:00 | 6.2 | 4.4 | 0.26 | 0.8 | SW | 90 | 1024 |
| 23:00 | 05:00 | 5.9 | 4.2 | 0.5 | 1 | WSW | 97 | 1024 |
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 21 May 2017 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 (2026-07-18). 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 18, 2026, from https://www.pastclimate.com/
"Historical Climate Data for Boulder, United States." PastClimate, derived from ERA5 (Copernicus Climate Change Service), July 18, 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 2026-07-18},
url = {https://www.pastclimate.com/}
}Notice something wrong with this data? Report a data issue.