Severe Risk Categories – Something New

Starting with this coming week’s outlook going out on Sunday, it will start to follow revised outlook phrasing. Since these outlooks are not meant as a replacement for the SPC outlooks and tend to be a bit more broad in scope, a revision was in order. The six categories that will be used are seeing in the image above with some noticeable differences.

The risks levels now make more sense when actually looking at the definition of the words used. Currently there is debate on how SPC uses words like Slight, Marginal, and Enhanced in and order that really doesn’t make sense compared to the words’ actual meanings.

A quick reminder on what is actually considered severe weather criteria.

  • Hail over 1″ in diameter or quarter size (see chart). Anything below that isn’t considered severe.
  • Wind 58 mph or higher.
  • Tornado

Image result for hail size chart

“No Severe Storms Expected”

This is clear cut. There could still be storms that day, but they are expected to remain well below severe thresholds. People can still see some gusty winds and small hail with these storms.

“Very Low Risk”

Isolated severe storms are possible with a very limited number of reports. This will cover those situations where a pulse severe storm could occur, provide damaging wind and hail in a very small area. Not everyone in the risk area will see severe weather. Conditions are usually margin for severe weather. A tornado is not expected, but not completely ruled out.

“Low Risk”

Scattered severe storms are possible with multiple reports of damaging wind and hail. A couple tornadoes are also possible. Coverage is still fairly limited, but conditions will allow for storms to become severe. Another scenario this will be used for is when conditions would allow for storms to go severe, but the cap may be too strong to permit any storms to form. If they do, they will be severe.

“Elevated Risk”

Several severe storms are probable in this situation. Unlike the Low Risk area, there is little worry about a cap prohibiting any development. Could see one or two long lived supercells producing damaging wind, large hail, and tornadoes over a small area. This category can also be used in situations where widespread severe weather is expected, but the reports are expected to be more on the lower end of severe limits.

“Enhanced Risk”

Widespread severe storms are likely in this situation. Very large hail, destructive winds over 70 mph, and the possibility for some strong tornadoes would also exist. This category is meant to cover the events that are just below outbreak criteria.

“Extreme Risk”

Severe weather outbreak expected. All conditions are in place for widespread severe weather or extremely high end events. This included widespread destructive wind events (derechos) and tornado outbreaks with high number of tornado reports expected or several strong to violent tornadoes.

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