07/31/2003
Only a Microburst
Last week, I said a mini tornado had swept through our area on Tuesday, July 22. That wasn’t a good day right from the start. It began with a report from my dermatologist’s office that a biopsy on a lesion on my leg indicated a squamous cell carcinoma and that a surgeon should remove the remainder of the lesion. Acting promptly, I got an appointment that afternoon with a surgeon, thinking he would do the job in his office. My wife dropped me off for the appointment on her way to pick up our grandson from a day camp at a school a couple blocks from our house. The sun was shining when she dropped me off.
It turned out that the surgeon said I would have to schedule the surgery to be done as an outpatient in our local hospital so I was out of his office in ten minutes. The sky was darkening and, when my wife pulled up to take me home, it was raining. In a couple minutes, a severe thunderstorm was in progress and I saw the mother of all lightning bolts, possibly the one that set a nearby utility pole on fire. We were just pulling into our garage when hail the size of “small ice cubes” (quoting a local paper) pelted us. As we entered the house, the power went out, the hail was swirling like a tornado and we promptly went to the basement with our grandson.
In a minute or so, it was over and we came upstairs to see our back yard covered with fallen branches and two very large limbs down in our neighbors’ yard. Looking out the front, we found a major limb in our front yard, another large limb on our driveway and yet another on the street. Had we arrived home a couple minutes later, we could have been killed or injured by any of the three limbs hitting our car! The area around us, probably an area about a half to three quarters of a mile square, was full of large fallen trees, some on houses and cars. Not wanting to open our refrigerator without any power that evening, we went out to find a bite to eat and found another patch of a neighboring town in similar circumstances.
We ended up the next evening at Brian Trumbore’s condo to use his George Foreman grill to cook some frozen steaks that were thoroughly unfrozen by that time. When we opened our refrigerator, I was impressed by the technology that must go into the manufacture of packaged ice cream. Even though melted, the ice cream in each of four containers of a couple different brands had maintained its shape and volume. The ice cream makers must know just how much air and gel-like material to add to the ice cream to achieve that effect. It was 39 hours before our power was restored the next morning.
We were convinced that we had experienced a tornado, especially after hearing on our battery powered radios that a widespread area of New Jersey had experienced even worse damage. In fact, our town’s damage did not even merit mention in our daily newspaper, The Star Ledger. However, an article in the July 24 Ledger by Peter Spencer and Maryann Spoto titled “The Weather Goes Haywire” attributed the extensive destruction not to tornadoes but to “microbursts” and “macrobursts”. The National Weather Service says that these bursts are straight lines of fierce low-lying wind that can be just as devastating as tornadoes. A macroburst differs from a microburst in the extent of the destruction; a macroburst’s destruction extends more than two and a half miles. By that definition, we had experienced a mere microburst but the damage was far from micro, in my opinion.
It was interesting to me that these micro- and macrobursts didn’t follow any definite path. Whereas our microburst struck at about 4 PM, a macroburst struck an area only 10-20 miles west of us some five to six hours later that night. There were roofs blown off and at least one report of a car being lifted and moved some 15 feet. In the intervening period a Jersey shore community well to our southeast was hit by a severe microburst.
I imagine that readers in some parts of the country, where real tornadoes are common, may be thinking that you guys in Jersey don’t know what devastation is. You’re right, of course. However, I decided to do some more research on these bursts and visits to the Web sites of the National Weather Service, NOAA (National Oceanic and Atmospheric Administration) and University of Nebraska Lincoln confirmed that these bursts can be quite deadly under the right circumstances.
What causes a microburst, which is sometimes called a downburst? And what is “virga”? Virga is simply rain that evaporates before reaching the ground. This doesn’t sound particularly threatening but the evaporation of the rain cools the air. Heavy rain can also cool the air. Cooler air is heavier and falls, creating a downdraft. In a thunderstorm, under the right conditions, this downdraft can be quite strong. Heavy hail falling through the downdraft can also push the wind in the downdraft to high velocities. When the column of wind in what is now a downburst hits the ground, it spreads out horizontally in all directions. As it spreads out there may be areas where the wind curls up in vortexes that can be a couple thousand feet high.
These horizontal winds can be quite damaging. And microbursts can be embedded in a macroburst, as was the case in Florida on July 20, 2000. The macroburst was unusually wide, 5 miles, and contained winds of 50-60 miles an hour. These winds weren’t particularly damaging but the embedded microbursts had winds clocked at 100 and 125 mph that caused extensive damage.
Undetected microbursts can be a real problem if you’re flying. In retrospect, I think we encountered a couple of them on a flight from Florida to Newark some years ago. Within a period of five minutes we had two precipitous, heart-stopping drops of I would guess a couple hundred feet. Downbursts? I can’t imagine the feeling passengers must have in those rare drops of several thousand feet. Scary as those are, a microburst can be a potentially more serious problem when a plane is landing or taking off, and its speed is relatively slow.
Let’s say you’re the pilot on a glide path to the runway and you encounter a microburst. You will find that the aircraft will rise as it runs into the headwind from the burst. But this means you might miss the runway so you cut the power to bring the plane back down to its proper glide path. However, by this time you’ve passed through the microburst to the other side and the headwind becomes a tailwind, which pushes the plane down. If you’re already close to the ground, you may be in serious trouble! In view of the admirable safety record of commercial airlines, I’m assuming that our airports have suitable radar facilities to detect microbursts and that pilots are trained to handle such situations.
As for our own microburst, it’s eight days later and the sounds of chain saws and tree shredders still abound. In fact, our city’s tree people are at this very moment taking down our neighbor’s very large tree that was damaged by the storm. Our town is known for its many large trees but, at this point, life in a treeless condo development seems rather appealing!
Allen F. Bortrum
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