Dear Tom,
I've been enjoying Chicago's above-average level of sunshine this year. Which part of the Midwest usually receives the highest average percentage of sunshine during the year?
Joel Porterfield, Park Ridge
Dear Joel,
The climate of the Midwest (and the central United States) becomes progressively more sunny westward from Chicago and less sunny to the east and south. This is so because dry air tends to bring more sunshine and moist air less. On average, the climate is drier to the west of Chicago and wetter to the east and south. Dry air descends the Rocky Mountains, its moisture having been wrung out in passage over the various Western mountain ranges, and spreads across the Great Plains. Moist air heading north and northeast from the Gulf of Mexico affects the weather to a progressively greater degree east and south from Chicago.
