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Diamond Bar climate
Typical historical weather for Diamond Bar, United States, averaged across 10 years of hourly climate data. Pick a date for a specific day.
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Annual average
17.5°C
across all months
Warmest month
31.4°C
Aug average high
Coolest month
7.3°C
Jan average low
Annual rainfall
452mm
total per year
Diamond Bar is typically hottest in August and coolest in January, a swing of about 24.1°C across the year. About 59% of annual rainfall falls in the three wettest months (January is typically wettest, July driest).
Monthly averages
Average daily high/low temperature (band) and monthly rainfall (bars).
| Month | Avg high | Avg low | Rainfall | Wet days | Humidity | Wind | Cloud | Solar |
|---|---|---|---|---|---|---|---|---|
| Jan | 17.6°C · record 19.6°C–30.1°C | 7.3°C · record 1.9°C–4.4°C | 93mm | 6 | 59% | 1.5 m/s | 50% | 3.1 kWh/m² |
| Feb | 18.3°C · record 18.1°C–30.1°C | 7.7°C · record 1.2°C–5.7°C | 85mm | 6 | 56% | 1.6 m/s | 42% | 4.1 kWh/m² |
| Mar | 18.6°C · record 21.2°C–29.6°C | 8.8°C · record 2.8°C–5.7°C | 89mm | 9 | 65% | 1.6 m/s | 51% | 5.1 kWh/m² |
| Apr | 21.9°C · record 25.6°C–34.7°C | 11°C · record 3.9°C–9.2°C | 25mm | 4 | 61% | 1.7 m/s | 42% | 6.6 kWh/m² |
| May | 22.7°C · record 25°C–35.6°C | 12.9°C · record 6.5°C–10.9°C | 13mm | 3 | 67% | 1.8 m/s | 41% | 7.1 kWh/m² |
| Jun | 27.1°C · record 30.4°C–41°C | 15.9°C · record 11.2°C–14.1°C | 2mm | 1 | 62% | 1.7 m/s | 25% | 8 kWh/m² |
| Jul | 30.8°C · record 32.3°C–43.3°C | 18.7°C · record 14.5°C–17.3°C | 1mm | 0 | 57% | 1.6 m/s | 18% | 8 kWh/m² |
| Aug | 31.4°C · record 33.8°C–38.6°C | 19.2°C · record 14.8°C–18.8°C | 10mm | 0 | 56% | 1.5 m/s | 17% | 7.3 kWh/m² |
| Sep | 29.4°C · record 33.1°C–43.6°C | 17.8°C · record 10.5°C–16°C | 9mm | 2 | 58% | 1.5 m/s | 23% | 6 kWh/m² |
| Oct | 26.5°C · record 31.2°C–38.1°C | 14.3°C · record 6.7°C–12.6°C | 13mm | 2 | 51% | 1.4 m/s | 25% | 4.8 kWh/m² |
| Nov | 22.2°C · record 22.9°C–32.9°C | 10.2°C · record 3.9°C–8.9°C | 38mm | 4 | 48% | 1.5 m/s | 36% | 3.6 kWh/m² |
| Dec | 18.3°C · record 21.6°C–27.6°C | 7.8°C · record 1.7°C–6.3°C | 76mm | 5 | 55% | 1.5 m/s | 48% | 2.8 kWh/m² |
"Avg high"/"Avg low" is the mean daily high/low for that month, averaged across every year on file. The "record" figure alongside it is a different statistic — the single hottest (or coldest) hour ever recorded during that month across all years — so it can sit above or below the average and does not describe the average's year-to-year spread. A "wet day" is any day with at least 1.0mm of rain.
Year to year
Annual average temperature, 2016–2025.
Across these 10 years, the annual average has moved by about -1.3°C per decade. That’s a short window for a reliable long-term climate trend — treat it as indicative, not definitive.
Annual rainfall has moved by about +214.39mm per decade over the same period.
2025 (the most recent year on file) averaged 17.2°C, below the 9-year baseline of 17.6°C by 0.57 standard deviations.
Typical extremes per year
Rainy days
42.1 days
≥1.0mm rain
Heavy rain days
6.5 days
≥20mm rain
Extreme heat days
0.6 days
daily high ≥40°C
Frost days
0 days
daily low ≤0°C
Averaged across 10 years on file. Thresholds match PastClimate's data pipeline definitions — see data & sources.
Records on file
Ranked across 10 years of data currently on file (2016–2025).
Hottest day
43.6°C
5 September 2020
2020 was 1.05 SD above the 9-year average that year
Coldest day
1.2°C
25 February 2022
2022 was 0.82 SD above the 9-year average that year
Wettest day
75.9mm
5 February 2024
2024 was 1.36 SD below the 9-year average that year
Windiest day
4.6m/s
22 February 2023
2023 was 2.26 SD below the 9-year average that year
See the detail: Diamond Bar on 5 February 2024.
Nearby cities
Ontario
Same ERA5 grid cell
Pomona
Same ERA5 grid cell
Chino
Same ERA5 grid cell
Chino Hills
Same ERA5 grid cell
Upland
Same ERA5 grid cell
Yorba Linda
Same ERA5 grid cell
Want a side-by-side view instead? Compare Diamond Bar with another city.
Frequently asked questions about Diamond Bar's climate
What is the hottest month in Diamond Bar?
August is typically the warmest month in Diamond Bar, with an average high of 31.4°C. January is typically the coolest, averaging 7.3°C overnight.
How much does it rain in Diamond Bar?
Diamond Bar gets about 452mm of rain a year on average, with roughly 59% of it falling in the three wettest months (January is typically the wettest, July the driest).
How many extremely hot or cold days does Diamond Bar have?
On average, Diamond Bar sees about 0.6 day(s) a year at or above 40°C and about 0 day(s) at or below 0°C, based on 10 years of data.
Is Diamond Bar getting warmer?
Across the 10 years on file (2016–2025), the annual average temperature has moved by about -1.3°C per decade. That's a short window for a reliable long-term climate trend — treat it as indicative, not definitive.
What is the hottest day on record for Diamond Bar?
The hottest day on file is 5 September 2020 at 43.6°C, out of 10 year(s) searched.
Data & provenance
↓ Download monthly CSVData 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
- Diamond Bar — 34.000°, -117.750°, ERA5 grid cell center, 6.4 km from requested point
- Time zone
- America/Los_Angeles
- What's shown here
- Monthly and annual averages, and dated extreme-value records, derived from an hourly base record.
- 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 (2026-07-19). Historical climate data for Diamond Bar, United States (34.00°N, 117.75°W), derived from ERA5 (Hersbach et al., 2023, Copernicus Climate Change Service). Retrieved from https://www.pastclimate.com/
PastClimate. (2026). Historical climate data for Diamond Bar, United States [Data set]. Derived from ERA5 (Copernicus Climate Change Service). Retrieved July 19, 2026, from https://www.pastclimate.com/
"Historical Climate Data for Diamond Bar, United States." PastClimate, derived from ERA5 (Copernicus Climate Change Service), July 19, 2026, www.pastclimate.com.
@misc{pastclimate,
author = {PastClimate},
title = {Historical climate data for Diamond Bar, United States},
year = {2026},
note = {Derived from ERA5 (Hersbach et al., 2023), Copernicus Climate Change Service. Accessed 2026-07-19},
url = {https://www.pastclimate.com/}
}Notice something wrong with this data? Report a data issue.