The poet Carl Sandburg wrote, "The fog comes/ on little cat feet./ It sits looking/ over the harbor and city/ on silent haunches/ and then moves on." The almost feline mystery of fog makes it enchanting, but fog can conceal a host of hazards.
For us motorcyclist, fog is one of those frequently encountered yet barely understood weather phenomena that can enhance or spoil our rides. What is fog, and why should we learn anything about it? Our safety may depend on our understanding, and the riding strategies we used when encountered by the mysterious stuff!
Fog is tiny droplets of water in the liquid state that form when moisture laden air is cooled below its dew point. Fog is like clouds in nearly every way except how it's formed. Clouds form when moisture laden air rises and is cooled. Fog forms when moisture laden air cools at or near the ground surface.
Since cold air is heavier than warm air, fog forms most easily in valleys and depressions, especially those moist places like marshland, along the banks of streams or near ponds. Fog forms most readily on clear, cloudless nights, for clouds tend to reflect rising heat back toward the ground. Strong winds disperse fog, but slight winds enhance its formation.
Because fog tends to be a local condition, accurate forecasting is rare. Your favorite drive time radio weather forecaster may be cheerfully commenting about "possible patches of fog this morning" just as your Gold Wing plunges into a mile long fog bank.
The most obvious risk to a motorcyclist is a sudden, drastic reduction in visibility. Abruptly, you don't know what (if anything) is stalled on the highway just ahead, or just how soon you'll reach the next curve in the road. If you're riding at night, your headlight beam is suddenly diffused, destroying your night vision with its glare. If you're riding in daytime the sunlight above the fog illuminates it, making you think you're surrounded by bright cotton candy. In either daytime or night, set your headlight to low beam; it will reflect less off the moisture drops.
Your best riding tactic is to roll off your speed rapidly, but not abruptly, by gradual braking. Not only does fog keep you from seeing the perils ahead of you; it also means the 18 wheeler behind you can't see either, and he may not have rolled off his speed!
If you choose to pull off the highway, do so quickly, carefully and completely. Then turn off your lights so that same 18 wheeler high balling into the fog behind you doesn't mistake you to be still underway ahead of him and smack into you! When riding in hilly country where dips and valleys fill with patches of fog while the hills and higher areas are clear, resist the urge to blast through the fog. WHAT YOU CAN'T SEE, CAN HURT YOU.
Another factor to keep in mind about fog is that if the dew point has been reached so fog can form in the air, there's a good chance moisture is also forming on the pavement. As you know, slightly damp pavement is often much more slippery than thoroughly wet pavement. Obviously, any time the pavement gets moist it's not a great time to be grabbing huge handfuls of brake!
A particularly treacherous type of fog is freezing fog. Made of super cooled liquid water, this fog appears when the temperature is below freezing and freezes as soon as it comes in contact with a cold surface, say a bridge surface or pavement.
Finally, though fog of uniform density transmits sound well, sound actually bounces off fog patches and produces echoes and ships have sunk because their captains couldn't be sure where the warning sound came from.
The distance of sound in foggy conditions can be misleading also. The British navy tested fog horns under various conditions and learned when humidity dropped from 77% to 71%, the distance the horn could be heard decreased by two miles.
Though you're unlikely to have a fog horn mounted on your Wing, you might have deer alert whistles, and a whole herd of deer might be in the midst of a bank of patchy fog wondering which direction you're really coming from. It might not be a bad idea to tap your horn once or twice to make your approaching sound somewhat more obvious.
By taking extra care when you encounter fog, you should be able to avoid adding to the risk of your ride.
RIDE SAFE