Urban Heat Island Effect - Warmer Near the Lake

Urban Heat Island Effect - Warmer Near the Lake
December 3rd 2012 temps reached 74 degrees with water temps around 45 degrees

Doesn't matter if you catch your weather forecast on CBS 2, NBC 5, ABC 7 or WGN 9 with Tom Skilling, you realize that in December it is normally warmer near the Lake. Yesterday was one of the warmest December days I can recall, ever! As I checked around 5:00 pm it had reached 74 degrees. This was a few degrees warmer than the rest of the city, primarily do to the fact the lake water has not reached the real cold level. Current Lake Michigan water temperature is about 45 degrees. I have one word to describe this "SWEET". Below are some interesting facts I ran across after my evening at the lakefront.

Strolling along McCormick Place heading down Chicago's lakefront towards Solider Field

So why is it warmer near the lake? 

** According to the Illinois State Water Survey, four factors control the climate of Chicago: 1) the sun, 2) weather systems, 3) urban areas, and 4) Lake Michigan. Two major controls are latitude (reflecting the amount of solar input) and weather systems (air masses and cyclonic storms). The effects of Lake Michigan and the urban area are of lesser significance but they influence local climate conditions to varying degrees within the Chicago metropolitan area, rather than uniformly across the entire region.

Walking near Adler Planetarium you realize it's December from the holiday colors used in the building lights, not from the unusually warmer than normal temperatures

The first local feature is the urban climate in the Chicago metropolitan area. Buildings, parking lots, roads, and industrial activities make the urban climate noticeably different than that of surrounding rural areas. For example, Chicago tends to be warmer by 2°F, on average, especially at night. In some cases, this difference can be higher. This particle feature of the urban climate is usually called the "urban heat island effect". Urban areas also cause changes in humidity, cloudiness, wind speeds and directions. Not only do the built up areas cause warmer temperatures but they also increase the runoff of rainwater, leading to increased flooding.

Since 1892, Winter, spring, summer, and fall, Columbia Yacht Club offers parties and events for everyone, especially nice on 70+ degree December nights.

An urban heat island (UHI) is a metropolitan area which is significantly warmer than its surrounding rural areas. The phenomenon was first investigated and described by Luke Howard in the 1810s, although he was not the one to name the phenomenon. The temperature difference usually is larger at night than during the day, and is most apparent when winds are weak. Seasonally, UHI is seen during both summer and winter. The main cause of the urban heat island is modification of the land surface by urban development which uses materials which effectively retain heat. Waste heat generated by energy usage is a secondary contributor. As a population center grows, it tends to expand its area, and increase in its average temperature. The less-used term heat island refers to any area, populated or not, which is consistently hotter than the surrounding area.

One of the warmest December nights in Chicago reaching 74 degrees.

Lake Michigan influences the climate of Chicago and most of northeastern Illinois. The large thermal mass of the lake tends to moderate temperatures, causing cooler summers and warmer winters. One of the major benefits is cool lake breezes that provide some relief from summer heat. The lake also tends to increase cloudiness in the area and suppress summer precipitation. Winter precipitation is enhanced by lake-effect snows that occur when winds blow from the north or northeast. These winds allow air to pass over the relatively warm lake, boosting storm system energy and water content, and leading to increased snowfall.

December Sunrise on Chicago's Lake Michigan.

So basically I am not going to worry why it gets this warm in December, I am just going to enjoy it. Today's expected high is around 55 degrees, I can live with that!

** Sources: Excerpt from The Weather and Climate of Chicago, The Geographic Society of Chicago, Wikipedia

Photo's by: Rick Lobes

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