Now that we are squarely in thunderstorm season, I want to describe two important cloud features, which sometimes occur with a thunderstorm, so that you can better understand what is happening when they do occur, and how you might be impacted. The features are called the Shelf Cloud and the Wall Cloud. Again they do not occur with all thunderstorms, but they do occur with some, and they do occur right here in The County!
A shelf cloud is very visually arresting. It looks like a long, continuous dark cloud that can be somewhat curved. Shelf clouds mark the leading edge of a thunderstorm’s precipitation. Often, just before the rain begins, very strong wind gusts, from the direction from which the rain is coming, will occur, and these can be very dangerous for those out in kayaks and other small craft on our lakes and waterways. It’s very easy for to get dumped out of a canoe or kayak before the first raindrops ever fall.
A good way to remember it is: “The wind before the wet.” By the way, please don’t ever go out on the water without a life jacket. You may think you’re a good swimmer, but when’s the last time you had to swim 200 yards in cold water?
A final word on the shelf cloud: if you see one of them where the center is pushing noticeably forward of the rest of the line and then, if you look at the radar on your phone or computer and see a backwards-C that is red or orange, if that “pushed forward” part is heading right for you, you are about to have damaging winds and, if out on the water, life-threatening conditions.
A wall cloud is the place to look for a possible developing tornado. Special attention should be paid to wall clouds that rotate, because a tornado could quickly develop out of this feature. While the rotation in a rotating wall cloud is clearly evident, it is also rather slow, kind of like a carousel, rotating in a counter-clockwise direction.
So, when looking at a thunderstorm, where do you look for a possible wall cloud? First, picture a side view of a classic isolated thunderstorm, one of those incredibly tall towers of billowing white clouds, with the edges sharply sculpted, resembling the surface of a cauliflower. Now visually slice the side view down the middle, with the rain coming down on the right half of your side view, while on the left half of your side view, there is no rain coming down at all. All you see there, on that left side, is the base (bottom) of the thunderhead, and what a wall cloud is, is a lowered (i.e. closer to the ground) portion of that rain-free base. The wall cloud is the place where the updraft of warm moist air is feeding the thunderstorm.
That’s good for starters I think. Do please google those two terms and look over some of the images. And if you see either this summer, please let us (and your nearby communities) know by posting on the Wall of my Facebook Page, facebook.com/tedsweather. Thank you in advance for your reports!
A final nifty note: some of the stronger thunderstorms we see in The County sometimes have the top of the thunderhead (the part where it flattens out and spreads forward into the familiar anvil shape), over 40,000 feet high. That is almost eight Mt. Katahdins, stacked one atop the other. In the Great Plains, the most intense thunderstorms can tower as high as 60,000 feet. That’s more than two Mount Everests high!
Ted Shapiro holds the Broadcast Seal of Approval from both the American Meteorological Society and the National Weather Association. An Alexandria, Va. native, he has been chief meteorologist at WAGM-TV since 2006. Email him at tshapiro@ wagmtv.comtshapiro@wagmtv.com.
