We talk about different types of severe storms all the time. Some bring hail, some bring strong winds, some even bring tornadoes, but the shape of the storm can have a huge impact on what type of severe weather threats we will see.
Squall lines may look like they only bring a line of showers, but they actually bring higher impacts than that. Matt Ziebell, forecaster at the Lubbock National Weather Service, explains. “A squall line of thunderstorms is literally just that. It’s a line of showers and thunderstorms, and they typically cover a large area as opposed to an individual thunderstorm or super cell thunderstorm. They’re typically the most organized thunderstorms that can last a long time and cover a lot of land and real estate. Usually a lot of severe wind and hail, and flooding. There is not so much a tornado threat, but the other threats of severe weather are certainly possible.”
Squall line winds typically average 70 miles per hour, but sometimes they can get up to 100 miles per hour. Damaging winds from a squall line are called straight line winds. This basically means that the winds are blowing in one direction, and not rotating like you would see in a tornado. However, sometimes, there can be some rotation in a squall line that can spin up a brief tornado.
“Unlike a supercell thunderstorm that has that really organized and long-lived area of rotation, squall lines can develop that rotation very quickly.“ Ziebell says. “It’s not always easily detected by radar. It can grow literally from the ground on up as it gets stretched up into the thunderstorm updraft. So that makes it very difficult to detect as we’re warning for these thunderstorms. But that does occur where you can have little inflection points, as we call them, that develop along that gust front and if it’s organized enough and it persists long enough it can actually develop into a tornado. Not unlike what we saw in Anton just a couple of weeks ago with severe weather and tornadoes there.”
And if the winds inside the squall line get strong enough, the line can ‘bow out’ where the storm looks like a bow on an arrow. This bowing in the squall line is what we call a bow echo. When a bow echo begins to take shape, this means that very strong and damaging winds, and sometimes even tornadoes, will develop.
For more information on bow echos head here: http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/svr/type/mline/mrbw.rxml