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
Transition into September subtly marks a drop in the average high-temperature, moderately moving from 85.6°F (29.8°C) in August to a still warm 78.3°F (25.7°C). Herndon's nights in September cool down to an average low-temperature of 59.7°F (15.4°C).Humidity
In September, the average relative humidity is 75%.Rainfall
The month with the least rainfall in Herndon is September, when the rain falls for 12.6 days and typically collects 1.93" (49mm) of precipitation.Snowfall
May through October are months without snowfall.Daylight
In Herndon, the average length of the day in September is 12h and 26min.On the first day of the month, sunrise is at 6:39 am and sunset at 7:39 pm. On the last day of September, sunrise is at 7:05 am and sunset at 6:53 pm EDT.
Sunshine
In September, the average sunshine is 8.7h.UV index
The average daily maximum UV index in September is 5. A UV Index reading of 3 to 5 represents a medium health hazard from exposure to the Sun's UV rays for ordinary individuals.Note: The average daily UV index of 5 in September transforms into the following instructions:
Undertake precautions - It is suggested to shield oneself from sunburn. Direct exposure to the Sun's intense radiation around midday should be avoided for health reasons. A wide-brimmed hat is a shield, deflecting up to 50% of harmful UV radiation from eyes.
Frequently asked questions
What are September temperatures in Herndon?
What is the average humidity in September in Herndon?
What is the driest month in Herndon?
How much does it rain in Herndon in September?
When it does not snow in Herndon?
What is the average length of the day in September in Herndon?
When are sunrise and sunset in September in Herndon?
How long on average sun shines in September in Herndon?
How high is the UV index in September in Herndon?
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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