Wednesday was a rather dreary day with overcast skies and drizzle for Iowa. The hourly observations from the Cedar Rapids Airport indicated overcast skies at 800 or lower feet above ground level throughout the day. For aviation, the cloud ceiling represents the level at which the sky is at least 50% covered by clouds as viewed from the ground. While the airport weather station does not explicitly report a ceiling value, an approximation is to find the first level with at least broken clouds reported. The featured chart presents a histogram of calculated ceiling levels for Cedar Rapids by week of the year. Instrumentation and reporting changes over the years makes this plot a bit noisy and please notice the irregular y-axis to capture reporting graduation. The annual signal is rather clear with much higher frequencies of lower ceilings during the cold season. This is due to cooler air being easier to saturate and reduced solar inputs leading to less lower atmospheric mixing, which tends to lower relative humidity.

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