by: WGN-TV Weather TeamTom Skilling
Tropical weather systems, like the one that develops along and off the southeast coast of the United States, draw moisture and critical latent heat energy from warm ocean waters, like the ones we see in these ocean analyzes from CIMSS at the University of Wisconsin-Madison.
These two charts and analyzes are courtesy of CIMSS (the Cooperative Institute for Weather Satellite Studies) at the University of Wisconsin-Madison:
The seasons on Earth ARE DUE TO THE EARTH’S ORBIT OF THE SUN and the tilt of the Earth on its axis relative to the Sun.
This tilt of the orbit and axis causes a change in the amount of sunlight that falls on Earth at different times of the year.
As winter approaches, the most direct sunlight falls further and further to the south of the planet. We watch here in Chicago as the sun moves across the sky each day gradually moving south. The further south the sun’s path in the sky goes each day, which means we see the sun for shorter periods each day. This is why the days are getting shorter. This also means that the sunlight that arrives here at ground level each day as winter approaches does so at an increased angle. In doing so, we receive less energy from the sun each day. Shorter days and less energetic sunshine explain why temperatures cool throughout the fall and move closer to the start of winter. Winds around weather systems can blow warmer air into the area, causing “ups and downs” in the cooling rate, but the OVERALL FALL TEMPERATURE TREND is lower.
Historically, normal temperatures drop 10 degrees in September, 12 degrees in October, and 13 degrees in November, making these the first, second, and third fastest cooling months of the year here in Chicago.