Spring ‘dance’ includes thunder

You weren’t imagining things if you thought you heard a distinct rumbling sound in the air this past Sunday. The area’s first thunderstorm of the year blew through bringing with it some hefty downpours along with some graupel.

If you had your eyes to the sky, you might have also noticed some beautiful cloud formations. Two features of particular interest were the “mammatus” clouds and the rain/snow shafts. If you don’t know what mammatus clouds are, you will know whether or not you have ever seen them after learning the word origin and hearing a description of the clouds. Mammatus comes from the Latin root “mamma” for mammary, as in mammary glands. They are baglike, bulbous clouds that hang on the underside of another cloud. These clouds are indicative of pouches of sinking colder air and are associated with turbulent air motions.

Also spectacular to look at were the rain and/or snow shafts, especially from the decaying storms. These were the vertical columns of gray or white that appeared below a cloud where the precipitation was falling. As some of the storms began to fall apart, and become more isolated, the precipitation shaft was often surrounded by blue skies. An untrained observer might have even mistaken these columnlike features for tornadoes, but their sinking rather than rising motion, and lack of rotation would be definitive that tornadoes they were not.

You might have experienced a cool gust of wind, however, emanating outward from around the rain/snow shaft, especially if the precipitation evaporated before it reached the ground. Evaporation cools the air, which makes it more dense than the air around it. This causes the air to descend faster, eventually spreading out in all directions as a wind gust once it reaches the ground.

Like many, I heard thunder that afternoon but did not see any lightning. There is no such thing as thunder without lightning, whether you happen to see it or not. Thunder occurs because the heat from the lightning bolt so rapidly expands the air around it (a lightning bolt can be as hot as 54,000 degrees Fahrenheit), that it creates a shock wave or a booming sound wave which we call thunder.

There are many types of lightning, such as cloud to cloud (or intracloud), cloud to ground, ground to cloud, and a rare type called ball lightning. Some folks use the term “sheet lightning” or “heat lightning.” These terms just describe the broad flash of light from a distant lightning strike (likely intracloud), and are not another form of lightning.

Don’t get too excited about lightning just yet, though, as Coeur d’Alene only averages about 16 days of thunderstorms per year. We are “lucky” to get a storm or two in March and April. The peak occurrence of storms is not until June. I will discuss lightning more in depth in a later column.

Mother Nature is definitely doing her spring “dance” with thunderstorms one day and snow the next. Though a few flakes fell during the past week, accumulating snows are highly unlikely as we head into April, which averages less than an inch of snow each year. Looking back at the whole month of March, precipitation came in a little more than a half inch above normal with 2.57 inches received as of March 29. April averages 1.75 inches of rainfall. I expect the first week of April to see some below-normal temperatures, but look for a significant warming trend toward the end of next week. Average high temperatures are in the mid 50s right now and will warm into the low 60s by the end of the month.