September weather forecastHerndon, PA
September
Weather in September
September, the first month of the autumn in Herndon, is still a warm month, with an average temperature ranging between min 53.6°F (12°C) and max 73.8°F (23.2°C).Temperature
Herndon, Pennsylvania, in September undergoes a slight reduction in the average high-temperature, shifting from August's 80.2°F (26.8°C) to a still warm 73.8°F (23.2°C). Throughout the month of September, Herndon sees a steady low-temperature average of 53.6°F (12°C).Humidity
In Herndon, the average relative humidity in September is 79%.Rainfall
In September, the rain falls for 12.6 days. Throughout September, 2.13" (54mm) of precipitation is accumulated. Throughout the year, there are 165.3 rainfall days, and 30.55" (776mm) of precipitation is accumulated.Snowfall
In Herndon, snow does not fall in June through September.Daylight
In September, the average length of the day in Herndon is 12h and 27min.On the first day of September, sunrise is at 6:35 am and sunset at 7:39 pm. On the last day of the month, sunrise is at 7:03 am and sunset at 6:50 pm EDT.
Sunshine
The average sunshine in September is 8.8h.UV index
In Herndon, Pennsylvania, the average daily maximum UV index in September is 4. A UV Index of 3 to 5 symbolizes a moderate health risk from exposure to the Sun's UV radiation for ordinary individuals.Note: The UV index of 4 during September leads to these advisories:
Take heed. Individuals of lighter complexion can be burned in less than half an hour. The Sun's most harmful UV rays are emitted around midday; avoid staying outdoors for long during this time. Sun-related eye harm can be minimized with proper sunglasses offering UVA and UVB coverage.
Published by: Weather U.S. | About Us
Data Sources | Weather Forecasting & Climate
Frequently asked questions
Average temperature in September
Herndon, PA
- Average high temperature in September: 73.8°F
The warmest month (with the highest average high temperature) is July (82.4°F).
The month with the lowest average high temperature is January (32.9°F).
- Average low temperature in September: 53.6°F
The month with the highest average low temperature is July (61.2°F).
The coldest month (with the lowest average low temperature) is January (20.1°F).
Average pressure in September
Herndon, PA
- Average pressure in September: 30.07"Hg
The month with the highest atmospheric pressure is November (30.13"Hg).
The month with the lowest atmospheric pressure is June (29.94"Hg).
Average wind speed in September
Herndon, PA
- Average wind speed in September: 5.2mph
The windiest months (with the highest average wind speed) are March and April (7.8mph).
The calmest month (with the lowest average wind speed) is August (4.5mph).
Average humidity in September
Herndon, PA
- Average humidity in September: 79%
The month with the highest relative humidity is February (82%).
The month with the lowest relative humidity is April (76%).
Average rainfall in September
Herndon, PA
- Average rainfall in September: 2.13"
The wettest month (with the highest rainfall) is May (3.35").
The driest months (with the least rainfall) are February and November (2.09").
Average rainfall days in September
Herndon, PA
- Average rainfall days in September: 12.6 days
The month with the highest number of rainy days is May (18.4 days).
The month with the least rainy days is February (9 days).
Average snowfall in September
Herndon, PA
- Average snowfall in September: 0"
The month with the highest snowfall is February (5.67").
The months with the least snowfall are June, July, August and September (0").
Average snowfall days in September
Herndon, PA
- Average snowfall days in September: 0 days
The month with the highest number of snowfall days is January (11.3 days).
The months with the least snowfall days are June, July, August and September (0 days).
Average daylight in September /
Average sunshine in September
Herndon, PA
- Average daylight in September: 12h and 30min
The month with the longest days is June (Average daylight: 15h and 0min).
The month with the shortest days is December (Average daylight: 9h and 18min).
- Average sunshine in September: 8h and 48min
The month with the most sunshine is July (Average sunshine: 10h and 24min).
The month with the least sunshine is February (Average sunshine: 4h and 12min).
Average sunshine days in September
Herndon, PA
- Average sunshine days in September: 15.4 days
The month with the most sunshine days is November (16.4 days).
The month with the least sunshine days is May (9.9 days).
Average UV index in September
Herndon, PA
- Average UV index in September: 4
The months with the highest UV index are June and July (UV index 6).
The months with the lowest UV index are January, February, March, November and December (UV index 2).
Average cloud cover in September
Herndon, PA
- Average cloud cover in September: 37
The month with the most cloud cover is February (Cloud cover 54).
The month with the least cloud cover is July (Cloud cover 32).
Average visibility in September
Herndon, PA
- Average visibility in September: 5mi
The months with the highest visibility are March, April, June, July and November (6mi).
The months with the lowest visibility are January, February, May, August, September, October and December (5mi).
