Are Mist and Fog the Same?


The now-infamous 1988 NFC Divisional Playoff game between the Philadelphia Eagles and the Chicago Bears is known as the Fog Bowl because of the bank of thick fog that covered Soldier Field. Ronald C. Modra/Sports Imagery/Getty Images

On Dec. 31, 1988, the Philadelphia Eagles met the Chicago Bears at Soldier Field. The matchup promised a lot of drama. Not only was this a playoff game, but the two teams had publicly-feuding coaches: Buddy Ryan and Mike Ditka.

So yeah, NFL fans expected to see bad blood that day. However, for a good portion of the game, people in the stands couldn't see anything. Late in the second quarter, a bank of fog rolled in from Lake Michigan and smothered the field. And refused to budge. After halftime, coaches on the sidelines actually lost sight of their own players at critical moments. And as The New York Times later reported, live TV footage of the showdown "had the grainy quality of a Western movie from the 1930s."

This infamous game is now remembered as the "Fog Bowl." But was it truly fog that descended upon Chi-Town that day, or just a thick layer of mist?

Well, "fog" and "mist" are two terms that describe different degrees of the same phenomenon: condensation. The science here is pretty interesting. Condensation is the process by which gas is turned into liquid. This happens when gas molecules lose energy and slow down. Said molecules then bond together, forming a liquid.

Now let's backtrack for a second. The gas molecules lose energy when they make contact with other, cooler molecules. Condensation is therefore linked to differences in temperature.

Most people associate the process with water vapor — and this is where fog comes into play. Fog is created when cold and warm air meet at or near ground level. There are many ways for this to occur, and therefore, several different types of fog exist.

Types of Fog

One well-known variety is called advection fog. It's caused by warm, moist air passing over a colder surface. The interaction cools the warm air down, and in the process, condensation sets in and little droplets of water begin to form around dust particles in the atmosphere. Then, those droplets remain airborne. Floating beads of water reflect light in all directions, impairing human visibility. And that's why it's so difficult to see through a thick fog.

The 1988 Eagles vs. Bears game is a perfect example of advection fog at work. That day, a current of warm, humid air blew over Soldier Field. Because the air around the stadium was much cooler by comparison, conditions were ripe for advection fog. Ergo, Chicago fans were treated to an eerie, murky NFL football game.

Sometimes, a sun-warmed ground is responsible for foggy days. If heat trapped in the ground radiates into cool air, you'll get what meteorologists call "radiation fog." This is most commonly seen at night when there is little to no wind. Also, just in case you feel like taking a little field trip, the best places to find radiation fog are in valleys and around still bodies of water.

Now just to mix things up a bit, both of these processes we've just described can also produce mist. The sole difference between mist and fog is visibility. Want to know which one you're dealing with? Take a good hard look through the gloom.

Let's assume you're standing on a flat surface when a ground-level cloud of suspended water droplets appears. If you can see another object on the same, horizontal plane that's further than 1 kilometer (0.62 miles) away from you, then the murk you're experiencing would technically be classified as mist. On the other hand, if you can't see beyond 1 kilometer (0.62 meters), it's considered fog.

The Dangers of Mist and Fog

Sometimes, mist and fog strike an ominous appearance — which helps explain horror films like John Carpenter's 1980 chiller, "The Fog." Both can also be quite dangerous in the real world. The U.S. Federal Highway Administration reports that between 2002 and 2012, foggy conditions were responsible for 31,385 vehicular crashes, including 511 deaths. Heavy fog can also ground airplanes and cause boating accidents.

High-beams are a big reason that mist and fog are so hazardous to motorists. Again, those suspended water particles reflect light. As a result, when drivers enter a bank of fog or mist and throw their high-beams on, the intense light causes a blinding glare. If you absolutely must take the wheel under such weather conditions, use your low-beam headlights instead.

Don't start hating mist or fog just yet, though. You see, a little gloom now and then does have its upside. In Morocco, Chile and other locales, fog is being harvested from the air with fine, mesh nets so it can be converted into drinking water. Additionally, northern California's famous redwood trees get 24 to 40 percent of their moisture from fog and mist.

So while airborne drizzle might not be conducive to good football, it's an absolute must for some of Earth's most charismatic plants.



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