If you’re living in the midwestern United States, you were probably confused and possibly unmotivated because in this area there was a lack of sunlight for the entire week of January 27. There are multiple factors that can contribute to the consistent cloudiness that persists for multiple days, and weather patterns that have brought on coincidental cloudiness. The dreary days that have been in effect for that week may seem like the usual wave of January weather — but fear not, winter is no stranger to seeing the sun.
Projecting our weather analysis to the 300 mb level, which is where the jet stream lies, we can see patterns of where warm or cold air patterns are to be directed. At this level, we can see a closed low that is often very slow moving since it sits out of the general stream of westerly air that is seen. Consequently, the closed low has little to move it along and can persist over the course of multiple days. This can also be called a cut-off low because it is removed from the general flow pattern and moves slower than typical weather patterns. Since low pressure systems are associated with cloudiness, rain and snow — this is a cause of persistent cloudiness.
Image: Gathered from the 12z GFS on 2/28, this depicts a closed low that is separated from the general flow of the upper atmosphere at 300mb. (Photo courtesy of Pivotal Weather)
Of course, weather patterns work together throughout the atmosphere and pure coincidence could lead to extended periods of cloudiness. Coincidental passings of multiple low pressure systems to a certain area can occur, along with multiple cold frontal passages can lead to extended periods of cloudiness.
Warmth can even lead to persistent cloudiness with the formation of fog when warm air moves over a cold surface. Since the atmosphere is built of many different levels that are working at different rates, we can experience different weather systems closest to the surface, instead of deep through the atmosphere. For example, a small area could experience low clouds and fog which can exist in the depth of the boundary layer. This layer extends about one kilometer above the surface, most commonly where lake effect convection occurs and can be specific to a small area.
While these are all possibilities for cloudiness to occur in a given region, it’s not particularly common to see this happen for such a long period, but it certainly can. For the specific case of the week of January 27th in the midwestern United States — almost all of these factors made an appearance. From passing snow showers and a wintery mix, to slight warmth leading to fog, a strong enough front with a proceeding high pressure system is necessary to conclude a period of cloud coverage.
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© 2020 Meteorologist Jason Maska