According to the heavens–more specifically, the Sun–astronomical winter is about to get underway in the Northern Hemisphere. Also known as the Winter Solstice, the new season will begin at 4:49 Universal Coordinated Time on December 22nd, which is Monday night, December 21st in North America, and Tuesday morning, December 22nd in Europe. That is when the sun will be at its southernmost point in relation to the equator. The first day of astronomical winter is also the shortest day of the year in terms of daylight in the Northern Hemisphere.
Source: NOAA/NASA’s SciJinks
The reason we have seasons in the first place is because of the 23.5 degree tilt of Earth’s axis. This causes the Northern Hemisphere to be tilted away from the sun during the winter months, receiving less energy overall, leading to the colder conditions we associate with winter. The opposite is true for places south of the equator, which are now receiving more direct light and energy from the sun. Because of that, the solstice is hemisphere dependent. While next week will mark the Winter Solstice in the Northern Hemisphere, the Summer Solstice will be occurring in the Southern Hemisphere, marking the start of their summer season.
As for daylight, many places in the mid latitudes of the Northern Hemisphere, such as the United States and central Europe, will have only about 7-9 hours of total daylight on the day of the Winter Solstice, which is 6-9 hours less compared to the Summer Solstice in June, which is the longest day in terms of daylight hours. It’s even more extreme for places in higher latitudes, some of which will be permanently locked into darkness for most of December. The opposite is true around the Summer Solstice, when places in Scandinavia and Alaska will go days with constant daylight without the sun ever setting below the horizon. The chart below shows the difference in daylight hours for select cities between the winter and summer solstice.
| City | Hours:Minutes of Daylight on Winter Solstice | Hours:Minutes of Daylight on Summer Solstice | Difference |
| Mexico City, Mexico | 10:58 | 13:18 | 2:20 |
| New York, NY, USA | 9:15 | 15:06 | 5:51 |
| Vienna, Austria | 8:20 | 16:05 | 7:45 |
| Berlin, Germany | 7:39 | 16:50 | 9:11 |
| Edmonton, Alberta, Canada | 7:28 | 17:03 | 9:35 |
| Oslo, Norway | 5:54 | 18:50 | 12:56 |
| Barrow, Alaska, USA | 0:00 | 24:00 | 24:00 |
While the start of astronomical winter is related to the Sun’s angle, forecasters will tell you meteorological winter has already started. The discrepancy is simply for record keeping purposes. The date of Winter/Summer Solstices and Spring/Autumnal Equinoxes can vary by a day or two from year to year. In order to be consistent and to allow for proper comparisons from one season to the next, meteorologists in the northern hemisphere consider the start of winter to be the first of December.
However, there is no rule that Mother Nature has to follow either date for the actual start of winter. For example, while meteorological winter has already begun, don’t tell that to people who live in the Great Lakes or northeastern United States, where record warmth has been the weather story so far this month. However, there have been years where major winter storms have dumped several inches of snow in October, several weeks before the official start of winter.
Due to all the seasonal and day-to-day variations associated with weather, you can check your Morecast App to get your latest forecast, whether it’s warm or cold, dry or snowy!