As meteorologists, we often stress the potential for “severe” weather, but do you actually know what a severe storm means? Does this mean it will rain very heavily, or the storm will produce a lot of cloud-to-ground lightning? Actually, the answer is neither!
Rain and lightning intensity is not how a severe storm is categorized. Many of the storms which produce deadly lightning, or have caused flash flooding events, were not severe-warned. A storm has to meet certain criteria before being designated severe. The storm has to have wind speeds greater than 58 mph or hail size greater than an inch in diameter, which is near quarter-sized. These can be observed by radar, as radar technology gives us the power to measure wind speeds within the atmosphere and estimate the size of hailstones within the storm, especially with the advances in dual-pol radar technology. This technology gives us the ability to not only see horizontally into the storm, but the vertical structure and makeup as well.
If the atmosphere is conducive for the development of severe storms, the National Weather Service will issue a SEVERE THUNDERSTORM WATCH. This means those living within the watch area need to be on high alert for the development of severe storms. If the National Weather Service notices a storm producing severe weather, a SEVERE THUNDERSTORM WARNING is issued, meaning severe weather within the warned area is imminent.
The Storm Prediction Center uses computer modeling to warn the public, in advance, when severe weather may occur. There are many different indices and signs to look for when determining the level of threat an area could potentially see. These forecasts are issued three days out. They issue these threats on a scale of 1 to 5, with one being the lower-end threats and five being the most extreme threats. Levels one and two typically cover days severe weather may be observed, but will most likely be isolated and short-lived, with relatively few incidents. Level three is the “enhanced” category, meaning severe weather may be more widespread and could be more damaging, whether it be stronger wind gusts or stronger tornadoes. Levels four and five are typically outbreak territory, meaning a severe weather outbreak is likely with widespread severe weather incidents and stronger tornadoes. These higher threats are typically rare and only used for the most dangerous of days.
Hail can be a destructive force inside severe storms. It can range from quarter-sized to grapefruit-sized, which can cause massive damage when falling from high up in the atmosphere. Hailsize within a storm is determined by the strength of the storm’s updraft, which is the belt of stronger winds moving upwards into the storm. The stronger this belt of wind, the more power it has to suspend these large hailstones, allowing them to grow bigger before the force of gravity brings them down.
Wind gusts of 60 mph can uproot trees and cause extensive damage to mobile homes.
When a severe storm is threatening your area, it’s best to stay away from windows and stay indoors. Do not travel within the warned area, and keep tuned to KLFY for the latest information. With Severe Weather Awareness week upon us, download the KLFY weather app, which will send alerts directly to your mobile device if your area is warned.
