Boulder
United States · 20 May 2018
Average
6.7°C
low 2.9°C · high 10.6°C
Rainfall
5.3mm
rain recorded
Wind
1.7m/s
daily average
Humidity
87.7%
daily average
Cloud
93%
cover
Pressure
1021hPa
daily average
The temperature ranged from 2.9°C around 07:00 to 10.6°C around 14:00. Rain was recorded across 14 hours, from around 01:00 to 21:00 (5.3mm total).
How unusual was this day?
Compared against the same 135 calendar days (±7 days) across the other 9 years on file.
High temperature
10th percentile
Low temperature
27th percentile
Rainfall
76th percentile
Wind
24th 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 10.8°C, versus 6.7°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 | Feels | Rain mm | Wind m/s | Dir | Humidity % | Pressure hPa |
|---|---|---|---|---|---|---|---|---|
| 00:00 | 06:00 | 4.3°C | 2.2°C | 0.09 | 1.2 | ESE | 98 | 1024 |
| 01:00 | 07:00 | 4.1°C | 2°C | 0.11 | 1.1 | ESE | 98 | 1023 |
| 02:00 | 08:00 | 4.1°C | 1.9°C | 0.14 | 1.3 | ESE | 98 | 1023 |
| 03:00 | 09:00 | 3.1°C | 0.5°C | 0.12 | 1.5 | ESE | 100 | 1022 |
| 04:00 | 10:00 | 3.6°C | 2°C | 0.18 | 0.2 | NE | 100 | 1023 |
| 05:00 | 11:00 | 3.4°C | 1.1°C | 0.14 | 1.2 | ESE | 100 | 1022 |
| 06:00 | 12:00 | 3.2°C | 0.8°C | 0.05 | 1.4 | ESE | 100 | 1024 |
| 07:00 | 13:00 | 2.9°C | 0.2°C | 0.07 | 1.7 | ESE | 100 | 1025 |
| 08:00 | 14:00 | 3.5°C | 1°C | 0.08 | 1.4 | ESE | 98 | 1025 |
| 09:00 | 15:00 | 5.7°C | 3.3°C | 0.01 | 1.4 | ESE | 86 | 1024 |
| 10:00 | 16:00 | 6.5°C | 3.6°C | 0.02 | 2.1 | ESE | 82 | 1023 |
| 11:00 | 17:00 | 8.5°C | 5.5°C | 0.01 | 2.5 | ESE | 75 | 1022 |
| 12:00 | 18:00 | 10.1°C | 7.2°C | 0.01 | 2.5 | ESE | 70 | 1020 |
| 13:00 | 19:00 | 9.7°C | 6.4°C | 0.1 | 3.1 | ESE | 74 | 1019 |
| 14:00 | 20:00 | 10.6°C | 7°C | 0.27 | 3.7 | ESE | 72 | 1018 |
| 15:00 | 21:00 | 10.4°C | 7.3°C | 0.29 | 3 | ESE | 71 | 1018 |
| 16:00 | 22:00 | 9.4°C | 7.4°C | 0.29 | 1.6 | ENE | 80 | 1018 |
| 17:00 | 23:00 | 8.9°C | 6.8°C | 0.19 | 1.7 | E | 81 | 1019 |
| 18:00 | 00:00 | 9.1°C | 7.1°C | 0.19 | 1.3 | ESE | 77 | 1019 |
| 19:00 | 01:00 | 9.1°C | 7.5°C | 0.84 | 0.7 | SSE | 77 | 1019 |
| 20:00 | 02:00 | 9°C | 7.3°C | 1.01 | 1.3 | SSW | 84 | 1018 |
| 21:00 | 03:00 | 7.9°C | 6°C | 1 | 1.8 | SSW | 95 | 1016 |
| 22:00 | 04:00 | 7.2°C | 4.8°C | 0.08 | 2.2 | SW | 92 | 1017 |
| 23:00 | 05:00 | 6.3°C | 3.9°C | 0 | 1.9 | WSW | 95 | 1016 |
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 2018 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.