Throughout 2017, April and October saw the most rainfall while December and September saw the least. During the wither, potential rainfall in Chicago is realized as snowfall.
In Chicago, there are significantly more Heating Degree Days than Cooling Degree Days as Chicago is a colder (Zone 5B) climate. Heating season lasts from October to May with some heating necessary in September and most heating needed in December. Cooling season lasts from April to October, with most cooling needed in July.
Winter winds in the “Windy City” have more higher speed winds than other seasons. Summer winds are generally calmer than other seasons’, and both spring and fall are generally on the moderate side.
Around the end of July, the trend of increasing diffuse radiation changes to decreasing diffuse radiation. This change is tied to increasingly shorter days (and thus less time for potential solar radiation).
Normal, or direct radiation, is not dependent on climate, but rather day-to-day weather. Thus, designs should not rely entirely on direct radiation because it is not reliable with the seasons.