April 07, 2012

Did You Know . . . (on Flash Fogs)

Fog on the Jounieh - Beirut Highway (where 2 lanes can turn into 5 lines)

. . . that there is a difference between fog and mist? I didn’t, until this morning when I tried to figure out how we ended up with this fantastic fog cloud yesterday afternoon, all along the coast. It gets hazy in summer now and then, but not foggy. Even the airport had to close for a couple of hours last night. That's something that usually only the Israelis manage to accomplish.

Beirut downtown (you can see the characteristic finishing of the St.George Hotel) at 6:00 PM local time. The sun is about to set in the thick layer of fog. Certain parts of town were free of fog.

Fog is defined as cloud which reduces visibility to less than 1 km, where as mist is that which reduces visibility to less than 2 km’. And so we had fog, and not mist. Right now, at 10 o’clock in the morning, it is still very hazy over much of Beirut’s coastal regions, but I can see East Beirut, so do we have mist now? Actually, I am above the fog from my house.

Fog forms when water vapor in the air at the surface begins to condense into liquid water. Fog normally occurs at a relative humidity of 100%. This can be achieved by either adding moisture to the air or dropping the ambient air temperature. (. . . ) Fog can form suddenly, and can dissipate just as rapidly, depending what side of the dewpoint the temperature is on. This phenomenon is known as Flash Fog.

Another type of formation also common is sea fog (also known as salt fog). This is due to the peculiar effect of salt. Typically, such lower humidity fog is preceded by a transparent mistiness along the coastline as condensation competes with evaporation, a phenomenon that is typically noticeable by beachgoers in the afternoon. (source)

The Byblos coastline at 5:20 PM
Learned something new today. 

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