Foggy weather means hazards in winter

You really have to get accustomed to much less sun this time of year. Aside from the fact we’re down to only about nine hours of daylight each day, those daylight hours are likely to be much cloudier.

For both Spokane and Coeur d’Alene, the months of November, December and January are the wettest months of the year. On days when it is not raining or snowing, the moist ground, low sun angle, and cooler temperatures will also lead to higher instances of fog in the area. Unless we have a dry northerly flow – it is easy to be fooled into anticipation with early morning sunshine. Stratus can quickly fill the sky; however, as early morning sunshine evaporates moisture from the ground and returns it to us in the form of low clouds and fog an hour later.

Speaking of fog, it is definitely a hazard that should not be taken lightly, especially when accompanied by sub-freezing temperatures. Though forecasts for dense fog don’t cause a rush on grocery or hardware stores like other winter storms do, reduced visibility and the potential for slick roads can cause many travel problems for those traveling by car or plane.

Under certain weather patterns, dense fog can also persist for days on end, and you can’t plow it away like snow. When visibility of a quarter-mile or less is expected over a widespread area, the National Weather Service will issue a “dense fog advisory.”

On average, Spokane (fog records are not kept for Coeur d’Alene) sees 101 days of fog each year. Heavy fog, in which visibility is a quarter-mile mile or less, is reported on 48 of those 101 days.

What is fog, exactly? It is nothing more than a cloud that has its base on or close to the ground.

The difference between clouds/fog and rain have to do with the size of the water droplets. It takes about a million average-sized cloud droplets to make an average sized raindrop, so cloud droplets are small enough to stay suspended in the air. The density of these droplets determines whether the fog will be heavy or light.