Herndon in Summer
In summer (June, July and August), Herndon sees average daytime highs around 85°F and overnight lows near 67°F, with 10.6 in of rain over about 33 wet days across the season. It is the warmest season of the year and the 3rd-wettest season.
Over the season highs climb from about 80°F in early June to 84°F by late August. The sky is clear or mostly clear about 27% of the time across summer, and the air most often feels muggy.
Summer is Herndon's 3rd-best season to visit on our travel score. For the whole year in context, see Herndon's year-round climate.
- Avg daytime high
- 85°F
- warmest season of the year
- Avg overnight low
- 67°F
- Rainfall
- 10.6 in
- 33 wet days
- Avg wind
- 5 mph
- Travel score
- 5.0
- 3rd-best season
- Months
- Jun · Jul · Aug
Temperature in Herndon in Summer
Over the season highs climb from about 80°F in early June to 84°F by late August.
A typical summer day in Herndon reaches about 85°F and drops to 67°F overnight. The warmest of the three months is July, the coolest June.
How summer really feels in Herndon
Once humidity and wind are folded in, summer brings about 8 days that feel above 90°F and 0 that feel at or below 32°F.
The story in summer is heat — humidity pushes the afternoon "feels like" well above the raw temperature.
Herndon weather by month
How the three summer months (June, July and August) compare with the rest of the year — the season's months are highlighted.
| Month | High / Low (°F) | Rainfall (inches) | Wet days | Snow days | Daylight (hours) | Travel score |
|---|---|---|---|---|---|---|
| Jan | 42° / 28° | 3.0 | 8.6 | 3 | 9.6 | 0.3 |
| Feb | 45° / 29° | 2.8 | 8.1 | 3 | 10.5 | 1.1 |
| Mar | 54° / 36° | 3.8 | 10 | 2 | 11.7 | 3.3 |
| Apr | 66° / 46° | 3.4 | 10.3 | 0.1 | 13 | 5.8 |
| May | 74° / 56° | 3.8 | 11.3 | 0 | 14.1 | 6.5 |
| Jun | 83° / 65° | 3.4 | 11.2 | 0 | 14.7 | 5.5 |
| Jul | 88° / 69° | 3.9 | 11.8 | 0 | 14.5 | 4.4 |
| Aug | 85° / 68° | 3.3 | 10.4 | 0 | 13.5 | 5.1 |
| Sep | 78° / 60° | 4.4 | 9.5 | 0 | 12.3 | 6.7 |
| Oct | 67° / 49° | 3.4 | 7.8 | 0 | 11 | 6.5 |
| Nov | 55° / 38° | 3.0 | 7.6 | 0.3 | 9.9 | 3.9 |
| Dec | 46° / 32° | 3.5 | 9.1 | 2.1 | 9.3 | 1.3 |
Cloud cover in Summer
The sky is clear or mostly clear about 27% of the time across summer.
Chance of precipitation in Summer
Herndon gets around 10.6 in of rain over 33 wet days across summer. The line is the day-by-day chance of measurable precipitation.
Humidity in Summer
Most of summer feels muggy — the stacked bands show each day's mix of comfort levels, read off the dew point.
Wind in Summer
Winds average 5 mph across summer.
Sunrise & sunset in Summer
Daylight runs from about 14 h 30 min in early June to 12 h 54 min by late August. The lit band spans sunrise to sunset each day.
Solar energy in Summer
Average shortwave solar energy reaching the ground each day across summer, about 5.8 kWh/m².
Is summer a good time to visit Herndon?
Our two travel scores rate summer for general sightseeing and for beach or pool weather — 0 (poor) to 10 (ideal), averaged across the three months.
summer is a reasonable time to visit Herndon for sightseeing. The water and warmth also suit a beach or pool day.
What to pack for Herndon in Summer
From summer's temperature range, rain chance, sun and wind — what's worth putting in the bag.
In summer, Herndon sees daytime highs around 85°F and nights near 67°F. Pack light clothes and sun protection. Worth having: rain gear. About 33 days see rain.
UV index in Herndon in Summer
Clear-sky midday UV across summer averages around 8 (very high — sun protection essential). The full-year curve, shaded by WHO exposure level, is below.
Under clear skies, the midday UV index in Herndon peaks around July 11 at about 9 (very high) — sunscreen, a hat and midday shade are essential. It bottoms out near December 19 at about 2 (low).
The index reaches 3 or more — the level where the WHO recommends sun protection — in 9 months of the year.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| UV index (midday) | 2 | 3 | 5 | 6 | 8 | 9 | 9 | 7 | 6 | 4 | 3 | 2 |
| Level | Moderate | Moderate | High | High | Very high | Very high | Very high | High | High | Moderate | Moderate | Low |
| UV index (midday) | Level | |
|---|---|---|
| Jan | 2 | Moderate |
| Feb | 3 | Moderate |
| Mar | 5 | High |
| Apr | 6 | High |
| May | 8 | Very high |
| Jun | 9 | Very high |
| Jul | 9 | Very high |
| Aug | 7 | High |
| Sep | 6 | High |
| Oct | 4 | Moderate |
| Nov | 3 | Moderate |
| Dec | 2 | Low |
Air quality in Herndon in Summer
Average fine-particle pollution (PM2.5) through the year — so you can see where summer falls, not just the annual average.
Air quality in Herndon is worst in July — around 17 µg/m³ PM2.5 (moderate), about 1.9× the cleanest month (November, 9 µg/m³).
Modeled monthly averages (CAMS reanalysis, 2015–2024).
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| PM2.5 (µg/m³) | 11 | 12 | 13 | 13 | 15 | 16 | 17 | 15 | 12 | 9 | 9 | 10 |
| Level | Good | Moderate | Moderate | Moderate | Moderate | Moderate | Moderate | Moderate | Moderate | Good | Good | Good |
| PM2.5 (µg/m³) | Level | |
|---|---|---|
| Jan | 11 | Good |
| Feb | 12 | Moderate |
| Mar | 13 | Moderate |
| Apr | 13 | Moderate |
| May | 15 | Moderate |
| Jun | 16 | Moderate |
| Jul | 17 | Moderate |
| Aug | 15 | Moderate |
| Sep | 12 | Moderate |
| Oct | 9 | Good |
| Nov | 9 | Good |
| Dec | 10 | Good |
Where is Herndon?
Herndon sits at 39.0°N, 77.4°W, 361 ft above sea level, in United States. The nearest listed city is Reston, 2.5 mi away.
Topography around Herndon
How much the land rises and falls, and what covers it, within 2, 10 and 50 miles of Herndon.
Within 2 miles, the terrain around Herndon has only modest variations in elevation — a maximum elevation change of 505 ft around an average of 377 ft above sea level; within 10 miles, only modest variations in elevation — a maximum elevation change of 558 ft; within 50 miles, large variations in elevation — a maximum elevation change of 3,615 ft.
The land around Herndon is covered by trees (57%) and artificial surfaces (35%) within 2 miles, trees (67%) within 10 miles, and trees (65%) within 50 miles.
United States travel facts
- Power plugs
- Type A / B
- 120 V · 60 Hz
- Prices
- ≈ 100% of US
- price level, 2025
- GDP per capita
- $90,027
- 2025
- Happiness
- 6.8 / 10
- World Happiness, 2025
- Safe drinking water
- 98%
- of population, 2024
- Homicide rate
- 5.8
- per 100k, 2023
- Road deaths
- 12.7
- per 100k/yr, 2019
- Income group
- High
- World Bank
- Religion
Sources: World Bank, US State Department, World Happiness Report, WHO/UNICEF, EF EPI, CIA World Factbook.
Data sources
Temperature, precipitation, cloud, humidity, wind and solar figures are a 1991–2020 climatology for Herndon (38.9695°, -77.3861°, elevation 361 ft), computed from hourly ERA5 reanalysis — contains modified Copernicus Climate Change Service information. Sun figures are astronomical calculations, not observations. City data © GeoNames, CC BY 4.0. Map outlines from Natural Earth (public domain); interactive map © Google.