The Two Severe Weather Events You Don’t Know (But Should)
July 15, 2022
If you haven’t noticed, severe weather is more frequent and more severe than ever before.
There is a reason why severe weather is always in the top 10 or even the top five hazards of every hazard vulnerability analysis. We are documenting more tornadoes, more tropical weather, and more irregular storm systems than ever before.
As we think about the weather, I want to tell you about two types of storms that emergency managers should have on their radar.
Microbursts: Tornado-like winds on a smaller scale
A microburst is a downdraft (sinking air) in a thunderstorm that is less than 2.5 miles in scale that may only last a few seconds or a few minutes. I’d describe it as a tornado without the rotation.
Microbursts are relatively small and won’t cause the widespread damage we see with tornadoes. Still, the gusts produced in these microbursts can reach tornado criteria in the form of straight-line winds.
In extreme cases, they have the potential to be as fast as an EF-3 tornado, with gusts getting between 158 and 206 miles per hour. A microburst can really occur during any severe thunderstorm depending on the conditions in the atmosphere. Out of the two weather phenomena we are discussing here, the microburst is more common, and actually more common than a tornado. There are about 10 microburst reports for every one tornado nationwide.
Even with advanced forecasting and radars, it is very hard to predict where a microburst will occur, but we can tell when an environment is favorable for them.
Derecho: Look for the hunter’s bow
A derecho is a widespread, long-lived wind storm. These storms are found inside severe thunderstorms with the right atmospheric conditions. The destruction of a derecho could be similar to a tornado, but the damage path is far greater.
A derecho is determined after the storm has passed, as it has to meet specific criteria, including a wind damage swath extending more than 240 miles and wind gusts of at least 58 miles per hour or greater along most of its length. These also can be referred to as an inland hurricane due to the strength and wind speeds generated.
Emergency managers should note the distinctive identifiers that a derecho may be heading your way, such as the shape of the system on the radar. A derecho will form a shape similar to a hunter’s bow. This is referred to as a bow echo. Ahead of that bow is the gust front which represents the straight-line winds. Looking outside, you’ll see ominous clouds. Think of the movie “Independence Day.” The derecho clouds look as though an alien spaceship is about to come out of it. A bow echo may evolve from a single strong storm, but many times it will be a cluster of strong storms with multiple bow echoes in it.
Combining the two
If all of this isn’t bad enough, derechos can have embedded microbursts inside of them. A bow echo can also have a bookend vortex. This is when the poles (top and/or bottom of the bow) begin to counter-rotate and actually hook around, forming a near-circle. The areas impacted by this have the greatest risk of severe wind damage, as this generates far greater wind speeds than the rest of the system.
May through August have the highest risk for these storms in the United States. Thankfully, the radar usually will show these storms, and they can be predicted as a risk several days in advance.
These are just some high-level examples of a few of the more extreme weather events that may affect your community. As emergency managers, we must anticipate unpredictable events, and the worst and best possible outcomes every day.
As always, knowing what to look for is half the battle. Preparing and understanding the weather gives us the time we need to be at our best and to protect our staff and our facilities.
For questions about getting ready for severe weather, contact me or HAP’s Emergency Management team for more information.