September weather forecastWaltham, MA
September
Weather in September
September in Waltham, Massachusetts heralds the arrival of autumn. As this transitional month edges towards fall, weather conditions change considerably with a slight drop in temperature. The highs and lows range from 73.2°F (22.9°C) down to 56.3°F (13.5°C) respectively. The shift can be felt in the crisp morning air and a significant decrease in daylight hours.Temperature
The commencement of September indicates a gentle shift in the average high-temperature, receding from August's warm 81°F (27.2°C) to a pleasant 73.2°F (22.9°C). The average temperature drops to a refreshing 56.3°F (13.5°C) during the night in the month of September.Humidity
The average relative humidity in September is 76%.Rainfall
The month with the least rainfall is September, when the rain falls for 8.3 days and typically collects 0.35" (9mm) of precipitation.Snowfall
In Waltham, snow does not fall in June through October.Daylight
In September, the average length of the day is 12h and 28min.On the first day of the month, sunrise is at 6:10 am and sunset at 7:18 pm. On the last day of September, sunrise is at 6:41 am and sunset at 6:27 pm EDT.
Sunshine
In September, the average sunshine is 8.5h.UV index
In September, the average daily maximum UV index is 4. A UV Index value of 3 to 5 symbolizes a moderate health risk from exposure to the Sun's UV rays for the average person.Note: An average maximum UV index of 4 in September leads to these recommendations:
Undertake protective steps - Obligation to safeguard skin and eyes from harm is in place. The most potent solar radiation is around mid-day, so one should minimize exposure to direct sunlight during this period. For effective sun eye protection, rely on sunglasses certified for UVA and UVB resistance.
Published by: Weather U.S. | About Us
Data Sources | Weather Forecasting & Climate
Frequently asked questions
Average temperature in September
Waltham, MA
- Average high temperature in September: 73.2°F
The warmest month (with the highest average high temperature) is July (82°F).
The month with the lowest average high temperature is January (33.3°F).
- Average low temperature in September: 56.3°F
The month with the highest average low temperature is July (64°F).
The coldest month (with the lowest average low temperature) is January (21.6°F).
Average pressure in September
Waltham, MA
- Average pressure in September: 30.05"Hg
The month with the highest atmospheric pressure is November (30.07"Hg).
The month with the lowest atmospheric pressure is June (29.92"Hg).
Average wind speed in September
Waltham, MA
- Average wind speed in September: 6.3mph
The windiest month (with the highest average wind speed) is January (9.1mph).
The calmest month (with the lowest average wind speed) is August (5.8mph).
Average humidity in September
Waltham, MA
- Average humidity in September: 76%
The month with the highest relative humidity is February (78%).
The month with the lowest relative humidity is April (70%).
Average rainfall in September
Waltham, MA
- Average rainfall in September: 0.35"
The wettest months (with the highest rainfall) are April and November (0.87").
The driest month (with the least rainfall) is September (0.35").
Average rainfall days in September
Waltham, MA
- Average rainfall days in September: 8.3 days
The month with the highest number of rainy days is July (12.4 days).
The month with the least rainy days is January (5.3 days).
Average snowfall in September
Waltham, MA
- Average snowfall in September: 0"
The month with the highest snowfall is December (1.14").
The months with the least snowfall are June, July, August, September and October (0").
Average snowfall days in September
Waltham, MA
- Average snowfall days in September: 0 days
The month with the highest number of snowfall days is February (5.4 days).
The months with the least snowfall days are June, July, August, September and October (0 days).
Average daylight in September /
Average sunshine in September
Waltham, MA
- Average daylight in September: 12h and 30min
The month with the longest days is June (Average daylight: 15h and 12min).
The month with the shortest days is December (Average daylight: 9h and 6min).
- Average sunshine in September: 8h and 30min
The month with the most sunshine is August (Average sunshine: 10h and 30min).
The month with the least sunshine is February (Average sunshine: 4h and 42min).
Average sunshine days in September
Waltham, MA
- Average sunshine days in September: 19.4 days
The month with the most sunshine days is January (22.2 days).
The month with the least sunshine days is June (15.8 days).
Average UV index in September
Waltham, MA
- Average UV index in September: 4
The months with the highest UV index are June, July and August (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
Waltham, MA
- Average cloud cover in September: 37
The month with the most cloud cover is March (Cloud cover 50).
The month with the least cloud cover is August (Cloud cover 32).
Average visibility in September
Waltham, MA
- Average visibility in September: 6mi
The months with the highest visibility are January, February, March, April, May, June, July, August, September, October, November and December (6mi).
The months with the lowest visibility are January, February, March, April, May, June, July, August, September, October, November and December (6mi).
