July weather forecast
Herndon, VA

The peak of Herndon's summer arrives in July, bringing with it the highest temperatures of the year. July is the warmest month in Herndon, with the average high temperature reaching up to 87.8°F (31°C) and the low around 67.3°F (19.6°C). The warmth of July is complemented by clear blue skies and long daylight hours. These conditions make it an ideal time for a summer picnic or a swim in one of Herndon's pools. However, high humidity levels are also a part of the July weather package, making hydration a priority.

Temperature

With average temperatures fluctuating between a high of 87.8°F (31°C) and a low of 67.3°F (19.6°C), July stands out as the warmest month in Herndon.

Heat index

For most parts of July, the heat index is computed to be a very hot 100.4°F (38°C). Exercise extra preventive actions, heat cramps and heat exhaustion are plausible. Continuous activity could result in heatstroke.
The heat index's values are generally associated with conditions in shade and light breezes. The heat index may scale up by 15 Fahrenheit (8 Celsius) degrees with direct sun exposure.
Note: The heat index, also known as 'feels like' or 'apparent temperature', reflects the feeling of heat when considering both air temperature and humidity. Factors including metabolic differences, physical activity, and clothing are additional elements that influence the individual's temperature experience. Given the impact of direct sunlight, it's noteworthy that the felt temperature can rise by 15 Fahrenheit (8 Celsius) degrees. Heat index values are essentially critical for children. Children are often less aware of the need to rest and re-hydrate. Thirst is a late sign of dehydration - it's vital to remain hydrated, particularly during prolonged physical activities.
When temperatures rise, the human body turns to perspiration, using the cooling power of evaporating sweat. Increased relative humidity interferes with body cooling by slowing the rate of evaporation, resulting in a slower body cooling rate and a heightened feeling of heat. When heat uptake goes beyond the body's cooling mechanisms, there's a surge in body temperature, posing health risks.

Humidity

The least humid month is July, with an average relative humidity of 70%.

Rainfall

In July, the rain falls for 16.3 days. Throughout July, 3.03" (77mm) of precipitation is accumulated. Throughout the year, there are 158.1 rainfall days, and 31.46" (799mm) of precipitation is accumulated.

Snowfall

May through October are months without snowfall.

Daylight

In Herndon, the average length of the day in July is 14h and 35min.
On the first day of the month, sunrise is at 5:48 am and sunset at 8:39 pm. On the last day of July, sunrise is at 6:10 am and sunset at 8:21 pm EDT.

Sunshine

The month with the most sunshine is July, with an average of 10.7h of sunshine.

UV index

The months with the highest UV index in Herndon are May through August, with an average maximum UV index of 6. A UV Index estimate of 6 to 7 represents a high health vulnerability from unsafe exposure to UV radiation for the ordinary person.
Note: The maximum UV index of 6 during July translates into these guidelines:
Endorse precautions and be consistent with sun safety guidelines. Preventing sunburn is paramount. Remember that UV radiation from the Sun is strongest between 10 a.m. and 4 p.m. Make an effort to limit direct sun exposure during this time. For excellent sun protection for the eyes, ears, face, and neck, consider a wide-brim hat.