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
Johnston's progression into September involves a minor drop in the average high-temperature, slightly receding from a warm 81.3°F (27.4°C) in August to a still moderately hot 75.6°F (24.2°C). Nighttime temperatures in September average to a moderate 55.9°F (13.3°C).Humidity
In Johnston, the average relative humidity in September is 76%.Rainfall
In Johnston, in September, it is raining for 9.7 days, with typically 1.73" (44mm) of accumulated precipitation. Throughout the year, there are 114.6 rainfall days, and 15.51" (394mm) of precipitation is accumulated.Snowfall
June through September are months without snowfall.Daylight
In Johnston, the average length of the day in September is 12h and 28min.On the first day of September, sunrise is at 6:41 am and sunset at 7:47 pm. On the last day of the month, sunrise is at 7:11 am and sunset at 6:57 pm CDT.
Sunshine
In Johnston, the average sunshine in September is 9.4h.UV index
In Johnston, the average daily maximum UV index in September is 4. A UV Index value of 3 to 5 symbolizes a medium health hazard from exposure to the Sun's UV radiation for average individuals.Note: The maximum UV index, 4 during September, leads to the following recommendations:
Be vigilant - A duty to shield skin and eyes from injury exists. Sun exposure should be minimized, especially during midday, to avoid harmful UV radiation. During bright days, sunglasses that offer UVA and UVB defense are recommended.
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 in Johnston?
How much does it rain in September?
When it does not snow?
Does it snow in September?
How many hours of daylight does Johnston have in September?
When is the sunrise / sunset in September?
How long on average sun shines in September?
What is the UV index reading in September?
Average temperature in September
Johnston, IA
- Average high temperature in September: 75.6°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 (27.9°F).
- Average low temperature in September: 55.9°F
The month with the highest average low temperature is July (65.1°F).
The coldest month (with the lowest average low temperature) is January (14.4°F).
Average pressure in September
Johnston, IA
- Average pressure in September: 30.01"Hg
The month with the highest atmospheric pressure is January (30.16"Hg).
The month with the lowest atmospheric pressure is June (29.88"Hg).
Average wind speed in September
Johnston, IA
- Average wind speed in September: 8mph
The windiest month (with the highest average wind speed) is April (10.4mph).
The calmest months (with the lowest average wind speed) are July and August (7mph).
Average humidity in September
Johnston, IA
- Average humidity in September: 76%
The month with the highest relative humidity is January (83%).
The month with the lowest relative humidity is October (70%).
Average rainfall in September
Johnston, IA
- Average rainfall in September: 1.73"
The wettest months (with the highest rainfall) are May and June (2.52").
The driest month (with the least rainfall) is January (0.47").
Average rainfall days in September
Johnston, IA
- Average rainfall days in September: 9.7 days
The month with the highest number of rainy days is May (16.3 days).
The month with the least rainy days is February (3.5 days).
Average snowfall in September
Johnston, IA
- Average snowfall in September: 0"
The month with the highest snowfall is January (2.2").
The months with the least snowfall are June, July, August and September (0").
Average snowfall days in September
Johnston, IA
- Average snowfall days in September: 0 days
The month with the highest number of snowfall days is January (8.4 days).
The months with the least snowfall days are June, July, August and September (0 days).
Average daylight in September /
Average sunshine in September
Johnston, IA
- Average daylight in September: 12h and 3min
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 12min).
- Average sunshine in September: 9h and 2min
The month with the most sunshine is July (Average sunshine: 10h and 24min).
The month with the least sunshine is January (Average sunshine: 4h and 18min).
Average sunshine days in September
Johnston, IA
- Average sunshine days in September: 17.8 days
The month with the most sunshine days is December (22.8 days).
The month with the least sunshine days is June (11.2 days).
Average UV index in September
Johnston, IA
- Average UV index in September: 4
The months with the highest UV index are June and July (UV index 6).
The month with the lowest UV index is January (UV index 1).
Average cloud cover in September
Johnston, IA
- Average cloud cover in September: 28
The month with the most cloud cover is January (Cloud cover 53).
The month with the least cloud cover is September (Cloud cover 28).
Average visibility in September
Johnston, IA
- Average visibility in September: 6mi
The months with the highest visibility are January, February, March, April, May, June, August, September, October, November and December (6mi).
The month with the lowest visibility is July (5mi).
Johnston, Iowa, USA
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