By Jim Stefkovich, Meteorologist, Alabama Emergency Management Agency
CLANTON – March 18, 2018
Most have seen outlooks days in advance of severe weather from the Storm Prediction Center (SPC), your local television meteorologist, National Weather Service (NWS) forecast office, or perhaps even from a phone app. At times, these areas have different colors and areas that don’t seem to match up perfectly. Confusing? It can be!
So, let me start off by giving some detail of what these colors and areas mean, then simplify it so you know how to use them properly. I’ll use the upcoming severe weather event of March 19-20 as an example.
The SPC is a national center providing severe weather outlooks for the entire country. Here is their outlook for AL on Monday and what each color represents:
Severe weather is defined as a tornado (TORN), straight-line or non-tornadic winds near or above 60 mph (WIND), and/or HAIL the size of quarters or larger. “Significant Severe” means a forecast of a tornado that produces EF2 or greater damage, straight-line winds of 75 mph or greater, or hail two inches or larger.
Here is a chart of what each color represents:
The associated probabilities are NOT the same as a general forecast, like the chance of rain today. These probabilities represent the chance a severe weather event will occur anywhere within a 25 miles of a specific point. The chance of severe weather at any point from day to day is very low. So, for example, if there is a 30% chance of severe weather at any point, that is actually a very high chance of occurrence.
There are four NWS forecast offices that serve AL; NWS Huntsville, Birmingham, Mobile and Tallahassee.
Let’s take a look at NWS Birmingham’s graphic to see their outlook area:
If you compare it to the SPC graphic, notice that the orange or “Enhanced” area is much farther south than the SPC outlook. Once again, the SPC is responsible for severe weather for the entire country, and they are defining general areas where severe weather will occur. Your local NWS offices are defining more specific areas where the severe weather will occur.
Your local television meteorologists may use the SPC, NWS offices, or their own graphics to define these areas. As far as phone apps, I have to be honest and say with so many out there, I’m not sure what outlook information they are providing. That’s why you need to make sure you are receiving your weather information from a trusted source.
So, with all this technical information, let me simplify things for you:
1) Don’t focus on the specific color or specific area. Devastating storms can and do occur in Marginal (MRGL) risk areas. Just know if you are in or near one of these risk areas, severe storms are possible, and the higher the probability, the more likely severe storms will occur where you are.
2) Predicting when and where severe storms will occur is very difficult. These outlooks are updated often and frequently change before the event actually occurs. Check with your local NWS office or television meteorologist often for the latest information on the threat and timing.
3) Have a least two sources to receive severe weather warnings. Every single method has the potential to fail, but if you have multiple sources, your chances of getting the information is much greater.
4) Make sure you have an action plan in place BEFORE severe weather strikes, and if all possible, be in a safe location during the event. Trying to figure out what to do when a warning is issued is too late. Be in a sturdy building, get to the lowest floor possible, and into an interior closet or bathroom when a warning is issued. Wear a bicycle or other type of helmet if you have one, and use other items to protect yourself in case falling debris occurs.
We are now entering the heart of severe weather season. It’s been a quiet season so far, but this upcoming event is just one of several that will occur over the next couple of months. Now is the time to be prepared!