Have you ever wondered what it would be like to live among the clouds? Fog could be called clouds at ground level. Like clouds, fog is composed of condensed water in the air. Sometimes fog can be so thick, it's hard to see anything. It's San Francisco or London or a Stephen King story.
Here, the city disappears. Then the skyline emerges, rising along the lake again. It is beautiful, atmospheric, eerie.
Here is the statement from the National Weather Service for this morning, May 6--
FOG IS WIDESPREAD ACROSS NORTHERN ILLINOIS AND NORTHWEST INDIANA THIS MORNING. SOME OF THE FOG IS DENSE WITH VISIBILITY UNDER ONE QUARTER OF A MILE... ESPECIALLY IN LOWER LYING AREAS OR NEAR BODIES OF WATER.AREAS OF DENSE FOG WILL CONTINUE THROUGH 9 OR 10 AM WITH GRADUAL IMPROVEMENT THROUGH NOON. EXERCISE CAUTION DURING THE REST OF THE MORNING COMMUTE... PLANNING FOR POSSIBLE LONGER TRAVEL TIMES...AND BE PREPARED FOR LOW AND RAPID CHANGES IN VISIBILITY.
What causes fog? Weather questions.com explains it this way--
Like clouds, fog is made up of condensed water droplets which are the result of the air being cooled to the point (actually, the dewpoint) where it can no longer hold all of the water vapor it contains.
For clouds, that cooling is almost always the result of rising of air, which cools from expansion. But for fog, which occurs next to the ground, there are usually other reasons for this cooling.
For instance, rain can cool and moisten the air near the surface until fog forms.
Or, as is more often the case, infrared cooling of a cloud-free, humid air mass at night can lead to fog formation - this is called "radiation fog". Radiation fog is most common in the fall, when nights get longer, air masses begin to cool, and land and water surfaces that have warmed up during the summer are still evaporating alot of water into the atmosphere.
Finally, a warm moist air mass blowing over a cold surface (usually snow or ice, or over a cold ocean surface) can also cause fog to form-this is called "advection fog".
Morning fog dissipates later in the day. As the air and ground warm up, the air temperature becomes warmer than the dew point temperature, causing the fog droplets to evaporate.
Fog is common here in the spring, as explained in this article in the Chicago Tribune. It is even more intense with the arrival of warm gulf air, which may bring temps in the 80's on Thursday.
Perhaps the most famous Chicago fog happened on December 31, 1988-- the Fog Bowl, the NFL playoff game between the Philadelphia Eagles and the Chicago Bears.
A dense fog rolled over Soldier Field during the 2nd quarter, cutting visibility to about 15–20 yards for the rest of the game. In spite of difficult conditions, the game continued and the Bears ended up winning the game 20–12.
You can watch the Fog Bowl again on You Tube.
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