Yesterday, the Storm Prediction Center (SPC) released more information on the long-anticipated redesign of their severe weather forecasts. The revamp of the agency's outlooks is a much-needed boost towards helping people truly understand the risk for dangerous weather before it happens.

For reference, severe thunderstorms are defined as having damaging winds in excess of 60 MPH, hail at least the size of quarters, or a tornado.

The SPC's current forecasts have three threat levels for severe weather: slight, moderate, and high. The revamp adds two levels — "marginal" and "enhanced" — on either side of the "slight" risk level to better communicate the true threat for dangerous thunderstorms.

The biggest difference between the information I posted in March and now is that the new outlooks will also have a scale from 1-5, with 5 denoting the highest risk for severe weather.

  • General thunderstorms = 0 (no severe weather expected)
  • Marginal Risk = 1
  • Slight Risk = 2
  • Enhanced Risk = 3
  • Moderate Risk = 4
  • High Risk = 5

This new numerical scale is an awesome feature that will help clear up some of the confusion caused by the wording that the SPC uses. Saying "there is an enhanced risk for severe weather today, which is a 3 on a scale from 1 to 5" makes it much easier to explain severe thunderstorm forecasts to people who have zero interest in the weather.

The SPC's release shows several examples from past severe weather events. Below is how the severe weather outlook for May 22, 2011 (the day of the Joplin tornado) would have appeared one day before, on May 21.

Here's that forecast using the current layout and scaling system:

...and here's how the proposed changes would look:

Here's another before/after example from a severe weather outbreak on June 1, 2011.



The update conveys more information than the current outlooks, and the redesign also shows that there's a risk for severe weather outside of the slight risk zone. This important bit of information is left out of current graphics, which both lulls people into a false sense of security and forces users to dig into the scientific discussion to find out the same information presented by the updated scale.

You can provide feedback on the updated forecasts at this link. The SPC is accepting public comments on the revamp through June 17. Provided the agency gets positive feedback on the product and it doesn't require any major tweaks, the updated forecasts should go into effect later this year or next.

[Images via SPC]