Understanding severe thunderstorm risk categories

11/30/2020 (Permalink)

In the Pacific Northwest, thunderstorms can be familiar. However, it’s important to be aware of how dangerous they can be, and how you can interpret weather forecasts and warnings. Here at SERVPRO of Northwest Portland, we wanted to share some vital information on thunderstorms. We encourage you to save this blog for reference, as understanding the risk categories for thunderstorms and what can be expected from each category can be valuable information in your safety response. 

These categories are used by the National Weather Service and other weather agencies, such as NOAA.

General thunderstorms (no label) 

- Light green shading

- Depicts a 10% or higher probability of non-severe or near severe thunderstorms. 

- Damage to property or roadways can still occur at this level, so staying alert is still advisable.

Severe Category 1 - Marginal Risk

- Dark green shading

- Marginal (MRGL) risk of severe thunderstorms during the forecast period. 

- 2% probability or greater tornado probability OR 

- Probability for severe hail OR severe wind.

Severe Category 2 - Slight

- Yellow shading

- Slight (SLGT) risk of severe thunderstorms during the forecast period.

- 5% probability or greater tornado probability OR

- 15% probability for severe hail or severe wind probability WITH OR WITHOUT 10% or greater probability of hail 2 inches or greater in diameter OR

- Wind gusts 75 mph (120 km/h) or greater.

Severe Category 3 - Enhanced

- Orange shading

- Enhanced (ENH) risk of severe thunderstorms during the forecast period.

- 10% probability for any tornado WITH OR WITHOUT 10% or greater probability of an EF2+ tornado OR

- 15% probability for any tornado OR

- 30% severe hail or severe wind probability WITH OR WITHOUT 10% or greater probability of hail 2 inches or greater in diameter, or wind gusts 75 mph or greater, OR

- 45% probability of severe hail or wind.

Severe Category 4 - Moderate

- Red shading

- Moderate (MDT) risk of severe thunderstorms are expected.

- 15% tornado probability AND 10% or greater probability of an EF2+ tornado OR

- 30% probability of any tornado OR

- 45% severe wind probability AND 10% or greater probability of wind gusts 75 mph or greater OR

- 45% severe hail probability AND 10% or greater probability of hail 2 inches or greater in diameter OR

- 60% severe wind probability OR

- 60% severe hail probability WITH OR WITHOUT 10% or greater probability of hail 2 inches or greater in diameter.

Severe Category 5 - High

- Fuchsia shading

- High (HIGH) risk of severe thunderstorms are expected.

- 30% tornado probability AND 10% or greater probability of an EF2+ tornado OR

- 45% or greater probability for any tornado WITH OR WITHOUT 10% or greater probability of an EF2+ tornado OR

- 60% severe wind probability AND a 10% or greater probability of a wind gust 75 mph or greater.

To read more about thunderstorm safety and flood safety, visit Ready.Gov.

No matter the storm event, SERVPRO of Northwest Portland is ready to respond to the area immediately. Once you are safe and ready to receive service, call us at 503-283-3658.

Sources: weather.gov