INDIANAPOLIS (WISH) — Here’s a question Storm Track 8 meteorologists get asked a lot this time of year: When are we finally going to see the sun?
Winter is central Indiana is typically known as a relatively gloomy season.
The tilt of the Earth’s axis and the angle of the sun as it hits the surface helps explain why the winter months are typically more cloudy than the summer months.
During winter in the Northern Hemisphere, the sun angle is much lower. This angle contributes to colder temperatures and less daylight, but also affects why we see more clouds and specifically a consistent layer of cloud cover for much of the winter.
In a typical atmospheric environment, mainly in the spring, summer and fall, temperatures at the surface are warmer than the upper levels of the atmosphere. Warm air rises and in turn will cool and condense into clouds — usually in the form of puffy cumulus, which also leaves plenty of room for sunshine as well.
In the winter, the opposite is true. Because of the lower sun angle, temperatures at the surface are typically colder than that higher in the atmosphere. This will cause a more stratiform cloud along the boundary layer of the colder lower-level air, and the warmer air aloft. Stratus-type clouds are more like a blanket and widespread, leaving larger areas cloudy and gloomy with minimal sunshine.
While cloud cover isn’t an official statistic kept by the National Weather Service, some records go back for the last five years on cloud conditions for a particular day. They are categorized as clear, partly cloudy and cloudy. For this research, I classified both clear and partly cloudy days as “sunny,” since we would be seeing some sunshine under partly cloudy conditions. Here’s what I have found:
- So far this winter (dating back to Dec. 1), 55% of our days have been sunny, with 64% of the days with at least some sunshine in December, and just under half of our days being sunny in January.
- The winter of 2018/2019, we had exactly 50% cloudy days and sunny days. In 2017-18, 45% of days were reported sunny. In 2016-17, it was 52% sunny days. In 2015-16, 62% of our winter days were reported as sunny.