A few facts about fog

Cape Breton Post - - WEATHER - CINDY DAY weath­er­mail@weath­er­by­day.ca @CindyDayWe­ather Cindy Day is SaltWire Net­work’s Chief Me­te­o­rol­o­gist.

Did you know that New­found­land is widely con­sid­ered one of the fog­gi­est places on Earth? On av­er­age, you can ex­pect more than 200 foggy days ev­ery year. But you don’t have to live in New­found­land to know all about fog; it’s some­thing that all At­lantic Cana­di­ans are quite fa­mil­iar with.

How­ever, you might not know that there are 10 types of fog: ad­vec­tion fog, evap­o­ra­tion fog, freez­ing fog, frontal fog, ground fog, hail fog, ice fog, pre­cip­i­ta­tion fog, ra­di­a­tion fog, and up­s­lope fog. Fog ad­vi­sories are is­sued when low vis­i­bil­i­ties in fog are ex­pected to last for at least 18 hours. For fog to form, there has to be a lot of water vapour in the air, in other words, it has to be very hu­mid. To­day, it cer­tainly is. The trop­i­cal air mass that ac­com­pa­nies what’s left of Isa­ias has re­sulted in wide­spread ad­vec­tion fog.

Ad­vec­tion fog forms when warm, moist air passes over a cool sur­face. This process is called ad­vec­tion, a sci­en­tific name de­scrib­ing the move­ment of fluid. In the at­mos­phere, the fluid is wind. When the moist, warm air makes con­tact with the cooler sur­face air, water vapour con­denses to cre­ate fog. Ad­vec­tion fog shows up mostly in places where warm, trop­i­cal air meets cooler ocean water.

As the warm, moist air moves over the cold water, the air cools down rapidly. The cooler air can’t hold the same amount of mois­ture it could at its former warm tem­per­a­ture, so con­den­sa­tion forms. The in­vis­i­ble water vapour con­denses and forms a fog bank.

De­pend­ing on the hu­mid­ity and tem­per­a­ture, fog can form very sud­denly and then dis­ap­pear just as quickly. This is called flash fog.

Prior to our new re­al­ity, I was of­ten asked to go into the schools to help out with the weather unit, which is taught in Grade 5 in Nova Sco­tia. One ques­tion that came up quite reg­u­larly was, “What would it feel like to walk in a cloud?” We do it quite of­ten: fog is a cloud that touches the ground.

Late evening fog was start­ing to form when Charles Peach snapped this lovely photo. It was 10:30 p.m., and Charles was look­ing south­east­ward across the la­goon from the Ben Eoin Beach RV Park in Cape Bre­ton.

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