Get ready for less sunshine

After a relatively dry October, we are certainly making up for it this month.

In Spokane, rain was reported on 11 of the first 12 days of the month for a total as of Wednesday of 1.33 inches. Amounts closer to 1.5 inches were reported in the Spokane Valley, and in Coeur d’Alene a soggy 2.45 inches of rain has fallen so far this month. Fortunately, though rainfall was heavy at times, flooding has not been an issue across the Inland Northwest.

It’s time to start getting used to a lot less sunshine. Aside from the fact we’re down to only about nine hours of daylight each day, those daylight hours are likely to be a lot 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. On average, Spokane (fog records are not kept for Coeur d’Alene) sees 101 days of fog each year. Heavy fog, in which the visibility is a quarter-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. If you were out for a walk on a foggy day, you would literally have your head in the clouds.

Will you get wet from walking through fog? Perhaps, as clouds are made up of millions of tiny water droplets. The difference between clouds/fog and rain have to do with the size of the water droplets. It takes about one million average-size cloud droplets to make an average size 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.

Fog dissipates when the relative humidity goes down. This occurs as available sunlight warms the ground, which in turn warms the air above it. Water droplets evaporate; in other words, change from liquid water back into water vapor. Since water vapor is invisible, the fog begins to disappear, often from the ground up. This is probably why people refer to fog as “lifting,” though there is actually no physical lifting involved. Though it is often said that fog “burns off,” there is no burning involved either, just the warming of the ground and then the surrounding air by the sun.

For those folks interested in a little weather education beyond what is in these weekly articles, I want to mention an opportunity coming up this spring semester at North Idaho College. My friend and colleague, Randy Mann, will be teaching a course there on weather and climate. Topics include basic meteorology, the climate of the Inland Northwest, global climate change, and severe weather as well.

I expect it will be informative and fun.