Boulder
United States · 20 May 2017
Average
5.4°C
low -2.7° · high 12.8°
Rainfall
0.3mm
dry day
Wind
1.4m/s
daily average
Humidity
66.2%
daily average
Cloud
74%
cover
Pressure
1017hPa
daily average
The temperature ranged from -2.7°C around 05:00 to 12.8°C around 16:00. Rain was recorded for one hour, around 18:00 (0.3mm total).
How unusual was this day?
Compared against the same 135 calendar days (±7 days) across the other 9 years on file.
High temperature
18th percentile
Low temperature
4th percentile
Rainfall
30th percentile
Wind
5th 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 11.2°C, versus 5.4°C on this specific day.
Sun & daylight
Sunrise
05:41
Sunset
20:14
Day length
14h 33m
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 | -0.3 | -3.9 | 0 | 1.9 | WSW | 87 | 1022 |
| 01:00 | 07:00 | -0.3 | -3.9 | 0.01 | 1.8 | WSW | 86 | 1021 |
| 02:00 | 08:00 | 0.2 | -3.3 | 0 | 1.8 | WSW | 86 | 1020 |
| 03:00 | 09:00 | -0.4 | -3.9 | 0 | 1.7 | W | 86 | 1020 |
| 04:00 | 10:00 | -2.6 | -6.4 | 0 | 1.8 | W | 94 | 1020 |
| 05:00 | 11:00 | -2.7 | -6.6 | 0 | 1.9 | W | 92 | 1019 |
| 06:00 | 12:00 | -2 | -6 | 0 | 2.2 | W | 90 | 1019 |
| 07:00 | 13:00 | -1.3 | -5.4 | 0 | 2.6 | W | 89 | 1019 |
| 08:00 | 14:00 | 0.9 | -2.6 | 0 | 1.9 | W | 83 | 1019 |
| 09:00 | 15:00 | 6.1 | 2.9 | 0 | 1.2 | WSW | 52 | 1018 |
| 10:00 | 16:00 | 6.7 | 3.7 | 0 | 0.9 | WSW | 51 | 1017 |
| 11:00 | 17:00 | 7.8 | 5.2 | 0 | 0.5 | W | 49 | 1016 |
| 12:00 | 18:00 | 8.5 | 5.9 | 0 | 0.4 | N | 46 | 1016 |
| 13:00 | 19:00 | 10.6 | 7.7 | 0 | 0.9 | NNE | 42 | 1015 |
| 14:00 | 20:00 | 11.5 | 8.4 | 0 | 1.3 | NNE | 41 | 1014 |
| 15:00 | 21:00 | 12.3 | 8.9 | 0.01 | 1.7 | NNE | 39 | 1014 |
| 16:00 | 22:00 | 12.8 | 10.1 | 0.01 | 1.1 | NW | 41 | 1014 |
| 17:00 | 23:00 | 12.6 | 10.3 | 0 | 0.6 | NE | 44 | 1015 |
| 18:00 | 00:00 | 11.9 | 10.1 | 0.28 | 0.1 | NE | 50 | 1015 |
| 19:00 | 01:00 | 11.6 | 9.3 | 0 | 0.8 | E | 50 | 1016 |
| 20:00 | 02:00 | 9.2 | 6.7 | 0 | 0.9 | E | 57 | 1016 |
| 21:00 | 03:00 | 6.1 | 3.5 | 0 | 1.2 | SW | 73 | 1017 |
| 22:00 | 04:00 | 5 | 2.2 | 0 | 1.6 | WSW | 81 | 1018 |
| 23:00 | 05:00 | 4.9 | 1.6 | 0 | 2.2 | WSW | 80 | 1019 |
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 20 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 (2026-07-17). 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 17, 2026, from https://www.pastclimate.com/
"Historical Climate Data for Boulder, United States." PastClimate, derived from ERA5 (Copernicus Climate Change Service), July 17, 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 2026-07-17},
url = {https://www.pastclimate.com/}
}Notice something wrong with this data? Report a data issue.