The kickoff of spring on March 1 marks the start of the severe weather season and an escalation of the risk of tornadoes over the lower 48 in the US. Here’s how to be prepared.
March is the start of Severe Weather Season
Meteorological spring kicked off on March 1 and ran through May 31.
Meteorological seasons differ from astronomical seasons. Meteorological spring is based on annual temperature cycles, and as the fronts of colder air and warmer air meet, it can result in severe weather.
What is a severe thunderstorm?
A thunderstorm that creates hail 1 inch in diameter or greater, or has wind speeds of 58 mph or greater, is categorized as a severe thunderstorm, according to the National Weather Service (NWS).
What causes severe and extreme weather?
According to IBM, severe weather is caused by changes in the atmosphere related to temperature, wind, or air pressure.
The changes in the atmosphere can result in extreme weather, which is defined as any type of weather that is out of the norm for a particular area, based upon past historical weather data in the region.
Types of extreme weather include blizzards, ice storms, hail storms, floods, hurricanes, and tornadoes.
What are the severe weather risk levels?
Severe weather is categorized on a level of risk on a scale of 1-5, with 5 being the highest risk, as established by the Storm Prediction Center (SPC) of the NWS.
The five categories are: Marginal, slight, enhanced, moderate, and high.
Marginal risk
- Defined as: Isolated severe storms.
- Possibilities: Heavy rain, winds, and hail are main threats. Isolated severe storms possible.
- Hazards: Winds 40-60 mph, up to 1″ hail, low tornado risk.
- Scope: Limited in duration, coverage, and intensity.
Slight risk
- Defined as: Scattered severe storms.
- Possibilities: Damaging winds and hail are typically the main threats. Scattered severe storms are possible—low threat of isolated tornadoes.
- Hazards: Damaging winds, 1″-2″ hail, 1-2 tornadoes.
- Scope: Not widespread, isolated intense storms, short-lived.
Enhanced risk
- Defined as: Numerous severe storms.
- Possibilities: The main threats are significant wind damage, large hail, and a few isolated tornadoes. Numerous severe storms are possible.
- Hazards: Likely wind damage, 1″-2″ hail, several tornadoes.
- Scope: Widespread with a few intense storms, more persistent.
Moderate risk
- Defined as: Widespread severe storms.
- Possibilities: Widespread wind damage, significant hail damage, and several strong tornadoes are the typical main threats.
- Hazards: Widespread wind damage, destructive hail, strong tornadoes.
- Scope: Widespread severe storms and long-lived intense storms.
High risk
- Defined as: Widespread and long-lived destructive storms.
- Possibilities: Damaging winds, major structure damage from large hail, and strong tornadoes are typically the main threats. Strong and destructive storms of a long-duration are possible.
- Hazards: Catastrophic hail, tornado outbreak, Derecho.
- Scope: Widespread, long-lived, destructive storms.
Tornado risk doubles beginning in spring
As spring escalates severe weather, it also marks the beginning of a doubling in the risk of tornadoes, which continues to increase as the months advance toward summer.
For example, the average number of tornadoes in February is 41, and the activity doubles in March for an average of 83.
In the United States, there is not a single month of the year when tornadoes do not occur. However, they are most active in spring, followed by summer and fall.
Using data accumulated over the past twenty years, between the years 2000-2019, here is a look at how tornado activity increases in spring, based on data from the storm prediction Center (SPC) of the National Oceanic and Atmospheric Association (NOAA).
- Spring: March (83), April (194), May (281).
- Summer: June (196), July (103), August (76).
- Fall: September (71), October (62), November (59).
- Winter: December (36), January (32), February (41).
Severe weather threats: Keeping safe
When severe weather occurs, get indoors as quickly as possible if you are outside. Strong winds can send projectiles flying, break off tree branches or uproot trees, and take down power lines.
Injuries can occur from hail striking you, and you can also be struck by lightning.
Indoors, stay away from windows. In the case of tornadoes, seek shelter in a basement or the lowest level of your home. If these aren’t available, shelter in the central room of your home without windows or shelter in the bathroom. Get inside the tub and lay down, placing padding over the top of you.
More resources
To get additional information about how to be prepared for severe weather and tornadoes, visit these US government websites for articles on preparedness at:
