Contents
- Weather in December
- Frequently asked questions
- Average temperature in December
- Average pressure in December
- Average wind speed in December
- Average humidity in December
- Average rainfall in December
- Average rainfall days in December
- Average snowfall in December
- Average snowfall days in December
- Average daylight in December
- Average sunshine in December
- Average sunshine days in December
- Average UV index in December
- Average cloud cover in December
- Average visibility in December
Weather in December
Temperature
December's arrival correlates with a reduction in the average high-temperature, down from a frosty 46.9°F (8.3°C) in November to an icy 33.8°F (1°C). Throughout December, Johnston registers a consistent average low-temperature of 22.1°F (-5.5°C).Humidity
In Johnston, Iowa, the average relative humidity in December is 79%.Rainfall
In Johnston, during December, the rain falls for 3.8 days and regularly aggregates up to 0.55" (14mm) of precipitation. Throughout the year, there are 114.6 rainfall days, and 15.51" (394mm) of precipitation is accumulated.Snowfall
Months with snowfall are January through May, October through December. In December, it is snowing for 5.5 days. Throughout December, 0.83" (21mm) of snow is accumulated. Throughout the year, there are 29.6 snowfall days, and 6.77" (172mm) of snow is accumulated.Daylight
December has the shortest days of the year, with an average of 9h and 12min of daylight.On the first day of December, sunrise is at 7:23 am and sunset at 4:45 pm. On the last day of the month, sunrise is at 7:41 am and sunset at 4:54 pm CST.
Sunshine
In Johnston, the average sunshine in December is 4.8h.UV index
In Johnston, the average daily maximum UV index in December is 2. A UV Index value of 2, and less, symbolizes a minimal health vulnerability from exposure to the Sun's UV rays for the ordinary person.Note: The maximum daily UV index of 2 in December interprets into the following recommendations:
While sun exposure does not greatly affect most, individuals with fair skin, babies, and children always need vigilant safeguarding. Avoiding direct sun during mid-day hours can prevent harmful UV radiation exposure. To cut down UV radiation exposure by about half, sport a wide-brim hat. Keep in mind! Snow's reflective quality can nearly double the intensity of the Sun's UV radiation.
Published by: Weather U.S. | About Us
Data Sources | Weather Forecasting & Climate
Frequently asked questions
How cold is it in December?
What is the average humidity in December?
How much does it rain in December?
How many days does it snow in December?
What is the month with the shortest days?
How many hours of daylight does Johnston have in December?
When are sunrise and sunset in December?
How many hours of sunshine does Johnston have in December?
What is the UV index reading in December?
Average temperature in December
Johnston, IA
- Average high temperature in December: 33.8°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 (27.9°F).
- Average low temperature in December: 22.1°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 December
Johnston, IA
- Average pressure in December: 30.12"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 December
Johnston, IA
- Average wind speed in December: 9.9mph
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 December
Johnston, IA
- Average humidity in December: 79%
The month with the highest relative humidity is January (83%).
The month with the lowest relative humidity is October (70%).
Average rainfall in December
Johnston, IA
- Average rainfall in December: 0.55"
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 December
Johnston, IA
- Average rainfall days in December: 3.8 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 December
Johnston, IA
- Average snowfall in December: 0.83"
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 December
Johnston, IA
- Average snowfall days in December: 5.5 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 December /
Average sunshine in December
Johnston, IA
- Average daylight in December: 9h and 1min
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 December: 4h and 5min
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 December
Johnston, IA
- Average sunshine days in December: 22.8 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 December
Johnston, IA
- Average UV index in December: 2
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 December
Johnston, IA
- Average cloud cover in December: 49
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 December
Johnston, IA
- Average visibility in December: 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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