Potomac
United States · 4 July 2018
Average
28.6°C
low 25.1°C · high 33.5°C
Rainfall
0.9mm
dry day
Wind
1.5m/s
daily average
Humidity
76%
daily average
Cloud
53%
cover
Pressure
1024hPa
daily average
The temperature ranged from 25.1°C around 05:00 to 33.5°C around 15:00. Rain was recorded for one hour, around 17:00 (0.9mm total).
How unusual was this day?
Compared against the same 135 calendar days (±7 days) across the other 9 years on file.
High temperature
75th percentile
Low temperature
98th percentile
Rainfall
52th percentile
Wind
11th 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 26.2°C, versus 28.6°C on this specific day.
Sun & daylight
Sunrise
05:48
Sunset
20:38
Day length
14h 50m
Hour by hour
Temperature (line) and hourly rainfall (bars), local time — America/New_York.
Cumulative rainfall through the day.
| Local time | UTC | Temp | Feels | Rain mm | Wind m/s | Dir | Humidity % | Pressure hPa |
|---|---|---|---|---|---|---|---|---|
| 00:00 | 04:00 | 27.2°C | 32.4°C | 0 | 1.6 | ESE | 87 | 1023 |
| 01:00 | 05:00 | 26.5°C | 31.4°C | 0 | 1.7 | SE | 88 | 1023 |
| 02:00 | 06:00 | 25.9°C | 30.3°C | 0 | 1.8 | SSE | 89 | 1023 |
| 03:00 | 07:00 | 25.6°C | 29.9°C | 0 | 1.8 | SSE | 89 | 1023 |
| 04:00 | 08:00 | 25.3°C | 29.6°C | 0.03 | 1.7 | SSE | 89 | 1023 |
| 05:00 | 09:00 | 25.1°C | 29.7°C | 0 | 1.5 | SSE | 92 | 1023 |
| 06:00 | 10:00 | 25.9°C | 31°C | 0 | 0.9 | S | 89 | 1024 |
| 07:00 | 11:00 | 26.1°C | 31.2°C | 0 | 0.9 | SE | 88 | 1024 |
| 08:00 | 12:00 | 26.5°C | 32°C | 0 | 0.8 | SSW | 88 | 1025 |
| 09:00 | 13:00 | 27.3°C | 34°C | 0 | 0.3 | ESE | 92 | 1025 |
| 10:00 | 14:00 | 28.8°C | 34.9°C | 0 | 1 | ENE | 83 | 1025 |
| 11:00 | 15:00 | 31°C | 35.7°C | 0.06 | 1.2 | ENE | 65 | 1025 |
| 12:00 | 16:00 | 32.2°C | 36.8°C | 0.05 | 1.7 | E | 62 | 1025 |
| 13:00 | 17:00 | 33.1°C | 37.3°C | 0.01 | 2.2 | ESE | 58 | 1025 |
| 14:00 | 18:00 | 33.4°C | 37.1°C | 0.01 | 2.6 | ESE | 56 | 1024 |
| 15:00 | 19:00 | 33.5°C | 37.1°C | 0.06 | 2.6 | ESE | 55 | 1024 |
| 16:00 | 20:00 | 31.8°C | 35.5°C | 0.04 | 2.4 | ESE | 61 | 1024 |
| 17:00 | 21:00 | 30.8°C | 36°C | 0.65 | 2.3 | ESE | 74 | 1024 |
| 18:00 | 22:00 | 30.2°C | 34.7°C | 0 | 1.4 | ESE | 67 | 1025 |
| 19:00 | 23:00 | 29.1°C | 34.1°C | 0 | 0.8 | NE | 72 | 1025 |
| 20:00 | 00:00 | 28.7°C | 33.1°C | 0 | 1.1 | NE | 70 | 1024 |
| 21:00 | 01:00 | 28.4°C | 31.8°C | 0 | 1.3 | NE | 65 | 1025 |
| 22:00 | 02:00 | 27.7°C | 30.4°C | 0 | 1.6 | ENE | 64 | 1025 |
| 23:00 | 03:00 | 26.5°C | 30.2°C | 0 | 1.7 | ESE | 78 | 1025 |
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
- Potomac — 39.000°, -77.250°, ERA5 grid cell center, 4.1 km from requested point
- Time zone
- America/New_York
- What's shown here
- The hourly and daily record for 4 July 2018 specifically — not a monthly average. See the Potomac 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 (2026-07-20). Historical climate data for Potomac, United States (39.00°N, 77.25°W), derived from ERA5 (Hersbach et al., 2023, Copernicus Climate Change Service). Retrieved from https://www.pastclimate.com/
PastClimate. (2026). Historical climate data for Potomac, United States [Data set]. Derived from ERA5 (Copernicus Climate Change Service). Retrieved July 20, 2026, from https://www.pastclimate.com/
"Historical Climate Data for Potomac, United States." PastClimate, derived from ERA5 (Copernicus Climate Change Service), July 20, 2026, www.pastclimate.com.
@misc{pastclimate,
author = {PastClimate},
title = {Historical climate data for Potomac, United States},
year = {2026},
note = {Derived from ERA5 (Hersbach et al., 2023), Copernicus Climate Change Service. Accessed 2026-07-20},
url = {https://www.pastclimate.com/}
}Notice something wrong with this data? Report a data issue.