Contents
- Weather in September
- Frequently asked questions
- Average temperature in September
- Average pressure in September
- Average wind speed in September
- Average humidity in September
- Average rainfall in September
- Average rainfall days in September
- Average snowfall in September
- Average snowfall days in September
- Average daylight in September
- Average sunshine in September
- Average sunshine days in September
- Average UV index in September
- Average cloud cover in September
- Average visibility in September
Weather in September
Temperature
September indicates a minor shift in the average high-temperature, from August's warm 85.6°F (29.8°C) to a still moderately hot 78.3°F (25.7°C). During September, Herndon witnesses a consistent average low-temperature of 59.7°F (15.4°C).Humidity
In September, the average relative humidity is 75%.Rainfall
September is the month with the least rainfall in Herndon. Rain falls for 12.6 days and accumulates 1.93" (49mm) of precipitation.Snowfall
May through October are months without snowfall.Daylight
The average length of the day in September is 12h and 26min.On the first day of September, sunrise is at 6:39 am and sunset at 7:39 pm. On the last day of the month, sunrise is at 7:05 am and sunset at 6:53 pm EDT.
Sunshine
In Herndon, the average sunshine in September is 8.7h.UV index
The average daily maximum UV index in September is 5. A UV Index estimate of 3 to 5 represents a moderate threat to health from unprotected exposure to Sun's UV rays for ordinary individuals.Note: The UV index of 5 in September translates into these instructions:
Take heed. Individuals of lighter complexion can be burned in less than half an hour. Direct Sun exposure should be minimized especially during midday when radiation is most intense. For minimizing sun-related eye damage, always choose sunglasses with UVA and UVB coverage.
Published by: Weather U.S. | About Us
Data Sources | Weather Forecasting & Climate
Frequently asked questions
What are September temperatures?
What is the average humidity in September?
What is the driest month?
How much does it rain in September?
When it does not snow in Herndon?
How many hours of daylight does Herndon have in September?
What time are sunrise and sunset in September?
How many hours of sunshine does Herndon have in September?
What is the UV index reading in September?
Average temperature in September
Herndon, VA
- Average high temperature in September: 78.3°F
The warmest month (with the highest average high temperature) is July (87.8°F).
The month with the lowest average high temperature is January (39.7°F).
- Average low temperature in September: 59.7°F
The month with the highest average low temperature is July (67.3°F).
The coldest month (with the lowest average low temperature) is January (25.9°F).
Average pressure in September
Herndon, VA
- Average pressure in September: 30.05"Hg
The month with the highest atmospheric pressure is November (30.14"Hg).
The month with the lowest atmospheric pressure is June (29.95"Hg).
Average wind speed in September
Herndon, VA
- Average wind speed in September: 5.3mph
The windiest month (with the highest average wind speed) is March (7.5mph).
The calmest month (with the lowest average wind speed) is August (4.7mph).
Average humidity in September
Herndon, VA
- Average humidity in September: 75%
The month with the highest relative humidity is December (78%).
The month with the lowest relative humidity is July (70%).
Average rainfall in September
Herndon, VA
- Average rainfall in September: 1.93"
The wettest month (with the highest rainfall) is August (3.78").
The driest month (with the least rainfall) is September (1.93").
Average rainfall days in September
Herndon, VA
- Average rainfall days in September: 12.6 days
The month with the highest number of rainy days is May (17.5 days).
The month with the least rainy days is January (9.3 days).
Average snowfall in September
Herndon, VA
- Average snowfall in September: 0"
The month with the highest snowfall is January (3.54").
The months with the least snowfall are May, June, July, August, September and October (0").
Average snowfall days in September
Herndon, VA
- Average snowfall days in September: 0 days
The months with the highest number of snowfall days are January and February (5.1 days).
The months with the least snowfall days are May, June, July, August, September and October (0 days).
Average daylight in September /
Average sunshine in September
Herndon, VA
- Average daylight in September: 12h and 2min
The month with the longest days is June (Average daylight: 14h and 54min).
The month with the shortest days is December (Average daylight: 9h and 30min).
- Average sunshine in September: 8h and 4min
The month with the most sunshine is July (Average sunshine: 10h and 42min).
The months with the least sunshine are January, February and December (Average sunshine: 5h and 0min).
Average sunshine days in September
Herndon, VA
- Average sunshine days in September: 15.9 days
The month with the most sunshine days is November (19.5 days).
The month with the least sunshine days is July (11.8 days).
Average UV index in September
Herndon, VA
- Average UV index in September: 5
The months with the highest UV index are May, June, July and August (UV index 6).
The months with the lowest UV index are January, February, November and December (UV index 2).
Average cloud cover in September
Herndon, VA
- Average cloud cover in September: 38
The month with the most cloud cover is March (Cloud cover 48).
The month with the least cloud cover is July (Cloud cover 31).
Average visibility in September
Herndon, VA
- Average visibility in September: 6mi
The months with the highest visibility are January, February, March, April, June, July, August, September, October, November and December (6mi).
The month with the lowest visibility is May (5mi).
Herndon, Virginia, USA
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