What are the severe thunderstorm risk categories?

Photo: Jim Pennucci / CC BY 2.0 / MGN
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ALEXANDRIA, La. (KALB) - Whenever you hear the words, “Marginal Risk”, “Slight Risk” or something to that effect during a weathercast, you should pay close attention to what the weathercaster or meteorologist is talking about.

Those terms refer to the potential for severe weather in the forecast. The KALB First Alert Storm Team tries its best to nail down the overall timing and potential threats for Central Louisiana. This is especially for times within 24 hours of when the potential threat could occur, after looking over the most updated computer model data.

In some cases, it can be difficult to nail down the timing when there isn’t a potential squall line setting up, instead, the activity is isolated to scattered and has the potential to have a severe thunderstorm or two in its overall activity. Every potential severe weather threat has its own set of challenges and is different. It’s very much a case by case situation. It can definitely keep the KALB Weather Team on its toes when it is in the forecast throughout the year!

The terms of “Marginal Risk” or “Slight Risk” are a couple of the severe thunderstorm risk categories that the Storm Prediction Center puts out across the country throughout the year. The Storm Prediction Center puts out a day 1, day 2 and a day 3 severe weather threat that shows either a non-severe or severe thunderstorm areas across the country. There is also a day 4 through day 8 depiction of potential threats across the country.

Throughout this web article, I’ll be discussing the different levels of these categories that we mention on air and on social media when there are potential threats in our forecast.

Another thing to remember here is that these risks are estimates of a severe weather threat within 25 miles of a point, and not in one particular neighborhood. Also, note that day 1 is for today, day 2 is for tomorrow and day 3 is 2 days ahead.

The Storm Prediction Center puts out a light green color with no label for non-severe thunderstorms. No severe thunderstorms are expected but lightning and flooding can still exist with general and/or non-severe thunderstorms.

We move onto the dark green color, marginal risk. A marginal, low-end, risk for severe weather is when isolated severe thunderstorms are possible. These thunderstorms are either limited in nature or have very low overall power.

Next, we move onto the yellow color, slight risk. A slight, level 2 risk for severe weather is when scattered severe thunderstorms are possible. These thunderstorms are an area of organized severe storms, which are not widespread in their overall area with a variety of overall power.

Then, we move onto the middle of the road for risks, the orange color, which is called an enhanced risk. An enhanced, level 3 risk for severe weather is when numerous severe thunderstorms are possible. These thunderstorms are in an area of greater severe storm coverage with a variety of overall power just like with a slight risk. A side note here, the Halloween Night and November 1, 2018, Severe Weather Outbreak that Central Louisiana dealt with was when an Enhanced Risk of severe weather was in the forecast. Multiple tornadoes were confirmed across the area during this particular severe weather event in the fall of 2018.

The second highest level on this severe thunderstorm risk categories, the red color, is a moderate, level 4 risk for severe weather when widespread severe thunderstorms are likely. These particular thunderstorms for a moderate risk are in an area where widespread severe weather with either several tornadoes or severe thunderstorms are likely. Some of these thunderstorms are very likely to be intense.

Finally, we move onto the highest level on this severe thunderstorm risk categories scale, the magenta color, is a high, level 5 risk for severe weather when widespread severe thunderstorms are expected. This is where there’s an area of an expected severe weather outbreak from either numerous intense and long-tracked tornadoes or long-lived strong thunderstorm complexes that can generate wind gusts of hurricane-force and widespread destruction.

When it comes to the day 4 through day 8 timeframe for severe weather outlooks, there are two probabilistic thresholds of either a 15% risk or a 30% risk that can be forecasted for a particular area. The 15% risk area refers to a slight risk possible, while a 30% risk area refers to an enhanced risk possible.

Aside from these potential risks in the day 4 through day 8 outlooks for severe weather, on rare instances, these outlooks will begin with the headline for the possibility of a potential severe weather outbreak. If there is not a 15% or 30% risk area in place, which does happen throughout the year, there’s certain group of words used by the Storm Prediction Center for lower than a 15% risk area.

These groups of words are either PREDICTABILITY TOO LOW or POTENTIAL TOO LOW. The PREDICTABILITY TOO LOW phrase is used to indicate that severe thunderstorms may be achievable based on some of the computer model scenarios. The POTENTIAL TOO LOW phrase means that it is used to indicate that 15% or greater severe probabilities appear highly doubtful on that particular day.

Whenever there’s a severe weather threat in the forecast, it’s always important to listen to what the weathercaster or meteorologist has to say about the potential threats and overall timing. Remember, every severe weather threat is different and unique in its own way and is very much a case by case basis. Remain weather aware and alert whenever a severe weather threat is in the forecast! The KALB First Alert Storm Team will remain on top of things and keep you posted on the latest threats.



 
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