What's the difference between a tornado watch and a tornado warning?
Knowing the difference between the two can prepare people for the necessary steps to take when considering the threat of severe weather after a watch or warning has been issued.
A funnel cloud moves across the field near Dodge City in Ford County, Kan. (Image credit: KWTV-KOTV via AP)
While the peak occurrences for severe weather events in the United States happen between March and October, severe weather can occur at any time.
Because of the destructive and potentially deadly nature of tornadoes, knowing the critical difference between a tornado watch and a tornado warning when an alert comes through on your phone or on TV is crucial. It can mean the difference between life and death.
Tornado watches: Be Prepared! Watches are issued for broad areas where weather conditions exist for the development of twisters. Commonly issued a few hours before a severe storm could hit, tornado watches are meant to alert the public of a developing threat for tornadoes and indicate the need to be prepared and remain vigilant in case you need to act quickly.
Tornado warnings: Take action! Warnings are urgent alerts in which there is imminent danger to life and property; people need to seek and take shelter right away. Tornado warnings are issued when a tornado has been spotted, indicated by weather radar or is about to touch down. Move to an interior room on the lowest floor of a sturdy building. Avoid windows. If in a mobile home, a vehicle, or outdoors, move to the closest substantial shelter and protect yourself from flying debris.
Knowing the difference between the two can prepare people for the necessary steps to take when considering the threat of severe weather after a watch or warning has been issued.
Who issues tornado watches and warnings?
Watches are issued by the NOAA’s Storm Prediction Center (SPC). Typical watches cover about 25,000 square miles, or about half the size of Iowa, according to the SPC.
“A watch is issued when conditions are favorable, for example, either for a severe thunderstorm or tornadoes,” AccuWeather Senior Meteorologist Dan Kottlowski said. “It doesn’t mean severe weather is imminent.”
Kottlowski added there are no set criteria for issuing watches, but if the conditions seem consistent with a developing severe weather pattern, watches can be changed and altered by monitoring ongoing developments.
“There is not just one set of ingredients; every watch may have a different set of parameters from one day to the next since it is based on a synoptic situation that may change within several hours.”
Warnings are issued by local offices of the National Weather Service (NWS). Warnings are based on specific criteria and existing reports received by the NWS. For a severe thunderstorm warning, the criteria include hail that is more than 1 inch in diameter and wind speeds of 55 mph.
“Lightning is not a criteria for a severe thunderstorm warning. Heavy rain is not either,” Kottlowski explained. “The way a warning is issued is that a meteorologist will monitor the weather by radar and look for particular areas where there could be high impact damage.”
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