Severe weather has the potential to occur year-round in St. Louis. Thunderstorms can bring strong winds, hail, lightning and flash flooding, while winter storms may include sleet, freezing rain, ice and heavy snow fall.
By monitoring weather conditions and preparing in advance, many of the inconveniences and deadly impacts of winter weather can be avoided.
Severe thunderstorm watches are issued when severe thunderstorms are possible in and near the watch area. The watch area is typically large, covering numerous counties or even states.
Severe thunderstorm warning are issued when severe weather has been reported by spotters or indicated by radar. Warnings indicate imminent danger to life and property.
“Destructive” and “Considerable” Damage Threat Categories
We developed three categories of damage threat for Severe Thunderstorm Warnings. The categories, in order of highest to lowest damage threat, are destructive, considerable, and base. These tags and additional messaging are designed to promote immediate action, based on the threats.
- The criteria for a destructive damage threat is at least 2.75 inch diameter (baseball-sized) hail and/or 80 mph thunderstorm winds. Warnings with this tag will automatically activate a Wireless Emergency Alert (WEA) on smartphones within the warned area.
- The criteria for a considerable damage threat is at least 1.75 inch diameter (golf ball-sized) hail and/or 70 mph thunderstorm winds. This will not activate a WEA.
- The criteria for a baseline or “base” severe thunderstorm warning remains unchanged, 1.00 inch (quarter-sized) hail and/or 58 mph thunderstorm winds. This will not activate a WEA. When no damage threat tag is present, damage is expected to be at the base level.
On average, only 10 percent of all severe thunderstorms reach the destructive category each year, nationwide. Most of these storms are damaging wind events such as derechoes and some of the larger, more intense thunderstorms, called “Supercell” storms that can typically produce very large hail in their path. The new destructive thunderstorm category conveys to the public urgent action is needed, a life-threatening event is occurring and may cause substantial damage to property. Storms categorized as destructive will trigger a WEA to your cell phone.
How to prepare before it happens
- Keep an NOAA weather radio at a location that will allow alerts to be heard by occupants in the work area.
- Monitor the weather anytime there is a potential for severe weather.
- For winter weather, maintain an emergency kit that contains adequate clothing and blankets to keep warm.
What to do when it happens
- Stay updated with changing weather conditions.
- Stay inside during the storm.
- Minimize travel under difficult conditions.
- During thunderstorms, avoid contact with electrical equipment, corded phones/devices and plumbing.
- Walk carefully during snowy, icy conditions.
- Report any power losses to WashU Police (Danforth, West and North campuses) at 314-935-5555 or Protective Services (Medical School) at 314-362-4357.
What to do right after it happens
- Stay away from storm-damaged areas, including downed power lines.
- Report any damages to WashU Police or Protective Services.
- Restock any emergency supplies.