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Breakdown: Why the Storm Prediction Center’s ‘Graphical Probabilistic Risks’ may have a different meaning than you thought

Published: Apr. 7, 2022 at 8:53 AM CDT|Updated: Apr. 7, 2022 at 9:14 AM CDT
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MEMPHIS, Tenn. (WMC) - Severe weather is a common occurrence in the Mid-South, and when it comes to strong and severe storms, understanding what the colors and text means could better help you prepare for incoming severe weather.

You’ve more than likely seen the Convective Outlooks from the Storm Prediction Center (SPC). Below is SPC’s outlook for Tuesday, April 5, 2022.

This is NOT A CURRENT FORECAST.

SPC Convective Outlook for Tuesday, April 5, 2022
SPC Convective Outlook for Tuesday, April 5, 2022(WMC)

But have you seen their Graphical Probabilistic Risks? These show the probability for tornadoes, wind, and hail.

For all outlooks, the probability values represent the chance of severe weather occurring within 25 miles of any point, which is about the size of a major metropolitan area.

Let’s use SPC’s April 5, 2022 Graphical Probabilistic Risks as an example.

The risk area has outlined portions of Alabama and Georgia under a 10% (yellow) probability for Tornadoes.

This means those areas have a 10% chance of a tornado occurring within 25 miles of any location.

This may seem like a low number, but a tornado is very uncommon at any one location.

Normally, your chances of getting hit by a tornado or other severe weather are small, purely based on statistical average.

Let’s say you have a 1% statistical (climatology) history of tornadoes within 25 miles on this day, which still is large. Having a 10% probability means 10 times the normal odds of a tornado nearby, meaning it should be taken seriously.

The probabilities for severe thunderstorm wind and hail also have the same meaning as they do for tornadoes, but typically will be higher numbers than for tornadoes, since they are much more common.

SPC Tornado Risk for APRIL 5, 2022
SPC Tornado Risk for APRIL 5, 2022(WMC)

Below is the April 5, 2022 graphical probabilistic risk for Damaging Winds.

There is a 45% (pink) probability for damaging winds across portions of Alabama and Georgia.

This means those areas have a 45% chance of damaging winds occurring within 25 miles of any location.

SPC Damaging Wind Risk for APRIL 5, 2022
SPC Damaging Wind Risk for APRIL 5, 2022(WMC)

Below is the April 5, 2022 graphical probabilistic risk for Hail.

There is a 15% (yellow) probability for damaging hail for portions of Alabama and Georgia.

This means those areas have a 15% chance of damaging hail occurring within 25 miles of any location.

SPC Hail Risk for APRIL 5, 2022
SPC Hail Risk for APRIL 5, 2022(WMC)

While, of course, you don’t need to memorize these probabilities, it is important to stay weather aware as these outlooks are designed to give you a heads-up on areas of potential severe weather days in advance.

Ahead of incoming severe weather, make sure your weather radio is on, has fresh batteries, and the volume is up. Secure any loose or light outdoor items.

First Alert Weather Day preps
First Alert Weather Day preps(WMC)

And, be sure to download the WMC Action News 5 First Alert Weather app, especially on First Alert Weather Days.

You’ll have instant access to any watches or warnings that may be issued, live interactive radar, hour-by-hour forecast and special video updates from the First Alert Weather Team.

How to download the WMC First Alert Weather app
How to download the WMC First Alert Weather app

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