Weather Blog: New, Expanded Weather Risk Categories
Starting Wednesday, the Storm Prediction Center, an arm of the National Weather Service responsible for issuing all severe thunderstorm and tornado watches and warnings, will utilize expanded severe weather risk categories for 1 to 3 day convective outlooks.
WCCO-TV meteorologists use this information in weathercasts to communicate a severe weather threat, so be sure to familiarize yourself with these revised outlook categories!
The previous four categories were:
1. See Text (general thunderstorms)
2. Slight
3. Moderate
4. High
Here's an example of a convective outlook with the old categories (Outlook for day of April 27, 2011 Super Outbreak):
There will now be five categories of risk with the former "See Text" category now defined as "Marginal," and the addition of an "Enhanced" category:
1. Marginal
2. Slight
3. Enhanced
4. Moderate
5. High
Thus, the same example outlook would now look like this:
The Storm Prediction Center conducted a public comment period on these now implemented changes this past summer, and after assessing the feedback, the center determined that the public sought more clarity in the terminology utilized to communicate severe weather risk.
Here are the parameters of the new severe weather risk categories for Day 1:
1. Category 1 - Marginal
- 2 percent or greater tornado probability, or
- 5 percent or greater severe hail or severe wind probability
2. Category 2 - Slight
- 5 percent or greater tornado probability, or
- 15 percent or greater severe hail or severe wind probability
3. Category 3 - Enhanced
- 10 percent or greater tornado probability, or
- 30 percent or greater severe hail or severe wind probability
4. Category 4 - Moderate
- 15 percent or greater tornado probability AND 10 percent or greater probability of an EF2+ tornado, or
- 30 percent or greater tornado probability, or
- 45 percent or greater severe wind probability AND 10 percent or greater
probability of a wind gusts 75 mph or greater, or
- 45 percent or greater severe hail probability AND 10 percent or greater
probability of hail 2 inches or greater in diameter, or
- 60 percent or greater severe wind probability, or
- 60 percent or greater severe hail probability
5. Category 5 - High
- 30 percent or greater tornado probability AND 10 percent or greater probability of an EF2+ tornado, or
- 45 percent or greater tornado probability, or
- 60 percent or greater severe wind probability AND a 10 percent or greater probability of a wind gust 75 mph or greater
New Day 1 outlook parameters:
New Day 2 outlook parameters:
New Day 3 outlook parameters:
If you have any questions on these changes, please feel free to tweet me, @LaurenCaseyWCCO!