National Preparedness Month is recognized each September to raise awareness about the importance of preparing for disasters and emergencies that could happen at any time. This month, the Case Western Reserve University Division of Public Safety will share tips related to severe weather events. This week’s advice focuses on thunderstorms.
Thunderstorms typically develop in the warmer months of spring, summer and fall, but can occur at any time of the year. There are three basic ingredients needed for thunderstorm development: moisture, an unstable atmosphere, and some way to get the atmosphere moving.
The following steps take place:
- Moisture is necessary to produce the thunderstorm clouds and precipitation. In the summertime, most areas have sufficient moisture to generate thunderstorms if the other ingredients are present.
- Atmospheric stability, or more importantly, instability, also plays an important role in thunderstorm development. Rising air is needed to produce clouds, and rapidly rising air is needed to produce thunderstorms. For air to rise rapidly, it must become buoyant compared to the surrounding air. When the atmosphere is unstable, air near the ground can become buoyant and rise rapidly through the atmosphere. In general, the warmer the air is near the earth’s surface and the colder the air is aloft, the more unstable the atmosphere is. In addition to temperature, moisture near the ground can also contribute to the instability of the atmosphere.
- The third ingredient needed for thunderstorm development is something that will trigger motion in the atmosphere. This may be some sort of boundary, such as a front, heating caused by the sun, or cooling aloft. Once a thunderstorm has developed, it will continue to generate boundaries that can trigger additional storms.
The National Weather Service (NWS) issues severe thunderstorm watches and warnings based on the following criteria:
- Severe thunderstorm watch: Be prepared. Severe thunderstorms are possible in and near the watch area. Stay informed and be ready to act if a severe thunderstorm warning is issued. The watch area is typically large, covering numerous counties or even states.
- Severe thunderstorm warning: Take action. Severe weather has been reported by spotters or indicated by radar. Warnings indicate imminent danger to life and property. Take shelter in a substantial building. Get out of mobile homes that can blow over in high winds. Warnings typically encompass a much smaller area (around the size of a city or small county) that may be impacted by a large hail or damaging wind identified by an NWS forecaster on radar or by a trained spotter/law enforcement who is watching the storm.
Learn more about thunderstorm development. Next week’s advice will focus on how severe thunderstorms can produce tornadoes.
Are you interested in becoming a Storm Spotter for the National Weather Service? A free training session will be held on campus Friday, Sept. 6. Attendees will learn about thunderstorm development, storm structure, reporting and more. Register for the session via CampusGroups.