Focus on severe weather forecasts

You’ve seen Spectrum News meteorologists talk about severe weather forecasts when stormy weather is forecast. They are published by the Storm Prediction Center in Norman, Oklahoma, and provide a general overview of the severe storm threat expected in a particular area.

But do you know what each of the five categories is, or the level of certainty they convey? Did you also know that the scale has changed over the years? We’ll tell you how to make sense of these severe weather forecasts and offer another way to interpret these maps.


What do you want to know

  • Storm Prediction Center releases one-day severe weather forecast
  • The outlook scale has five categories, from marginal risk to high risk
  • An older scale, used before 2014, used three risk categories

What do the five categories mean?

For many, they are colored spots on a map, but they have a distinct meaning for meteorologists at the Storm Prediction Center (SPC). The convective outlook consists of a map and explanation, showing severe thunderstorm threat areas across the continental United States.

The prospective explanations are written in technical language and give the meteorological reasoning of the risk zones. It is our job to explain these perspectives in a way that is easy to understand, yet conveys the significance of the threat.

All five threat levels start at Marginal, which represents the lowest risk of severe weather. It is rising high, a signal that severe weather is likely in this area, and a major severe weather outbreak with multiple hazards and life-threatening storms is possible.

This is an example of a convective outlook for Day 1, which describes the conditions expected from the early morning of the current day until the early morning of the next day. Notice how the five levels are presented.

Example of a severe weather forecast in five categories. (NOAA)

You may still be wondering why each category is called by this name. Why not just number the categories one through five? Why isn’t lightness the lowest on the list?

To be fair, the Storm Prediction Center has the difficult job of predicting hazardous weather conditions across the United States and the categories should be taken as a guide and not set in stone. In fact, the outlook for an ongoing severe weather event is updated up to five times. This is the best explanation we have found of how to interpret risk categories, directly from the RCP itself:

It is important not to rigidly associate the type of hazard area (eg, 2-SLGT-yellow) with the severe potential of a given thunderstorm in the hazard area. In other words, the mere fact that a 2-SLGT-yellow hazard is forecast does not necessarily mean that thunderstorms in the hazard area will be mildly severe.

What were the serious threat categories

In the spring of 2014, the RCP updated the scale to include two new risk categories: marginal (level 1) and increased (level 3). Previously, a three-level scale was used (mild, moderate, high).

The same severe weather outlook as above, but with only the original three categories. (NOAA)

The CPS saw this as a beneficial change, an opportunity to better describe low risks (below the light category) and high risks (above the light category). Emergency managers liked the change, but some questioned whether it was beneficial for weather enthusiasts and the general public, or whether it would just create messier graphics or harder-to-understand explanations.

From a meteorologist’s perspective, the names of the new categories themselves – fringe and enhanced – are somewhat difficult to explain to the general public. But again, it’s always our job as broadcast meteorologists to interpret the data ourselves and explain the potential dangers and risks of severe weather to our viewers, whatever the weather outlook is called. Spc.

Rethinking extreme weather outlook

Either way, everyone has access to and can interpret severe weather forecasts for themselves. This can lead to confusion and sending mixed messages, especially on social media (that’s a whole other conversation for a different blog). To add to the confusion, some local TV stations have their own severe weather hazard zones, using the areas drawn by the SPC, but using their own color scheme and even category names.

Some members of the weather community feel that the SPC convective outlook could have a more simplified naming convention. This humble author thought of a five-category naming convention that might be easier for the public to understand, hopefully eliminating the need for broadcast weather forecasters across the country to change it themselves. It might even retain the same colors the SPC currently uses. Tell us what you think.

LEVEL 1 – LOW: This would replace the ‘marginal’ label that currently exists, communicating the lowest threat from severe weather.

LEVEL 2 – MINOR: The word “slight” meant the lowest risk. Now that means the second lowest risk. I think we should get rid of that word completely.

LEVEL 3 – MODERATE: When I think of “moderate”, I think of the middle, and I bet most people do too. This would replace the “enhanced” tag that currently exists.

LEVEL 4 – HIGH: When meteorologists see a “moderate” risk now (which is a level four risk), it means big trouble. I think “high” should be the label used here, and save the higher risk with a catchier phrase.

LEVEL 5 – EXTREME: Yes, this word is often used to describe things that are not quite that. However, the truest definition of the word indicates how serious this risk would be: “to reach a high or the highest degree; very large “.

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