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
The commencement of December indicates a shift in the average high-temperature, receding from November's fresh 53.1°F (11.7°C) to a cold 42.6°F (5.9°C). December nights experience a consistent temperature drop to a freezing cold 30.6°F (-0.8°C).Humidity
In December, the average relative humidity is 76%.Rainfall
The month with the least rainfall is December, when the rain falls for 4.6 days and typically collects 0.31" (8mm) of precipitation.Snowfall
January through March, November and December are months with snowfall. In O'Fallon, in December, during 2.4 snowfall days, 0.08" (2mm) of snow is typically accumulated. In O'Fallon, during the entire year, snow falls for 13.3 days and aggregates up to 1.14" (29mm) of snow.Daylight
The month with the shortest days is December, with an average of 9h and 30min of daylight.On the first day of December, sunrise is at 6:59 am and sunset at 4:38 pm. On the last day of the month, sunrise is at 7:17 am and sunset at 4:48 pm CST.
Sunshine
The average sunshine in December is 4.6h.UV index
The months with the lowest UV index are January, February, November and December, with an average maximum UV index of 2. A UV Index reading of 2, and below, represents a low threat to health from exposure to the Sun's UV radiation for average individuals.Note: In December, an average UV index of 2 transforms into the following instructions:
Most individuals face no major issues with lengthy exposure to the sun, but children, infants, and individuals with fair skin always require protection. When the Sun is at its strongest around midday, find shade and limit exposure. To cut down UV radiation exposure by about half, sport a wide-brim hat. Be advised! The UV radiation from the Sun can be almost doubled due to the reflective properties of snow.
Published by: Weather U.S. | About Us
Data Sources | Weather Forecasting & Climate
Frequently asked questions
How cold is December?
What is the average humidity in December?
What is the driest month?
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 O'Fallon have in December?
What time are sunrise and sunset in December?
How many hours of sunshine does O'Fallon have in December?
When is the lowest UV index?
What is the UV index intensity in December?
Average temperature in December
O'Fallon, IL
- Average high temperature in December: 42.6°F
The warmest month (with the highest average high temperature) is July (85.6°F).
The month with the lowest average high temperature is January (37.8°F).
- Average low temperature in December: 30.6°F
The month with the highest average low temperature is July (68.2°F).
The coldest month (with the lowest average low temperature) is January (24.6°F).
Average pressure in December
O'Fallon, IL
- Average pressure in December: 30.13"Hg
The month with the highest atmospheric pressure is January (30.16"Hg).
The month with the lowest atmospheric pressure is June (29.93"Hg).
Average wind speed in December
O'Fallon, IL
- Average wind speed in December: 8.9mph
The windiest month (with the highest average wind speed) is January (9.5mph).
The calmest month (with the lowest average wind speed) is July (5.6mph).
Average humidity in December
O'Fallon, IL
- Average humidity in December: 76%
The months with the highest relative humidity are May, July and August (79%).
The month with the lowest relative humidity is October (70%).
Average rainfall in December
O'Fallon, IL
- Average rainfall in December: 0.31"
The wettest month (with the highest rainfall) is July (1.42").
The driest month (with the least rainfall) is December (0.31").
Average rainfall days in December
O'Fallon, IL
- Average rainfall days in December: 4.6 days
The month with the highest number of rainy days is July (13.1 days).
The month with the least rainy days is December (4.6 days).
Average snowfall in December
O'Fallon, IL
- Average snowfall in December: 0.08"
The month with the highest snowfall is January (0.51").
The months with the least snowfall are April, May, June, July, August, September and October (0").
Average snowfall days in December
O'Fallon, IL
- Average snowfall days in December: 2.4 days
The month with the highest number of snowfall days is January (4.7 days).
The months with the least snowfall days are May, June, July, August, September and October (0 days).
Average daylight in December /
Average sunshine in December
O'Fallon, IL
- Average daylight in December: 9h and 3min
The month with the longest days is June (Average daylight: 14h and 48min).
The month with the shortest days is December (Average daylight: 9h and 30min).
- Average sunshine in December: 4h and 4min
The months with the most sunshine are June and July (Average sunshine: 10h and 24min).
The month with the least sunshine is January (Average sunshine: 4h and 30min).
Average sunshine days in December
O'Fallon, IL
- Average sunshine days in December: 23.6 days
The month with the most sunshine days is December (23.6 days).
The months with the least sunshine days are May and July (15.5 days).
Average UV index in December
O'Fallon, IL
- Average UV index in December: 2
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 December
O'Fallon, IL
- Average cloud cover in December: 49
The month with the most cloud cover is January (Cloud cover 51).
The month with the least cloud cover is August (Cloud cover 28).
Average visibility in December
O'Fallon, IL
- Average visibility in December: 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).
O'Fallon, Illinois, USA
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