Today is the start of Alabama's 2021 Severe Weather Awareness Week. Tennessee's Severe Weather Awareness Week is next week. Mississippi just had its Severe Weather Awareness Week, but winter storm coverage got in the way of us being able to do anything then. Starting today, the Tennessee Valley Weather Channel will be taking these next three weeks to talk in detail about severe weather awareness, preparedness, and safety information. It is our mission to have every viewer in our coverage area ready for the coming spring severe weather season, but this is information you need to know at all times, regardless of how active this coming spring might be.
The first topic we will cover as a part of our campaign is the difference between severe weather watches and severe weather warnings (tornado watch vs tornado warning, severe thunderstorm watch vs severe thunderstorm warning). Despite the fact that "watch" and "warning" have been used since 1965 and the weather community has explained the difference between the two every year since then, a too-large number of the general public does not understand or remember the difference between a watch and warning. It may not seem like it, but that is important and critical information because you need to know that in order to know when you need to take shelter from an approaching dangerous storm!
Watch: A watch (tornado or severe thunderstorm) means that conditions are favorable for severe weather to happen over the duration of the watch, but it's not necessarily occurring yet. The ingredients for severe storms are there, meaning that they are possible, but they aren't imminently threatening your immediate area just yet. This is when you need to be extra aware of threatening weather, be aware of your surroundings, make sure your severe weather plan is already in place (we will detail that this week), and be ready to immediately act when a warning is issued. Watches are issued for large groups of counties at a time, often portions of multiple states. They are typically, but not always, issued 1 to 2 hours before severe weather is expected to start, and most watches last anywhere from 4 to 8 hours before they expire, but individual counties in the watch may be canceled as the severe weather threat ends. Watches are issued for whole counties at a time.
Warning: A warning (tornado or severe thunderstorm) means imminent danger and you need to TAKE ACTION NOW. A warning means that severe weather has either been detected by radar or reported by trained weather spotters. Severe weather is happening now, or it is rapidly developing and expected to be minutes away! A warning is your urgent CALL TO ACTION to seek shelter immediately. Warnings are issued with only minutes of advance notice and typically last in duration anywhere from 20 to 60 minutes. Since 2007, warnings have no longer been issued for whole counties. They are instead issued for only the portions of the county or counties that will be impacted. This type of warning is called a storm-based or "polygon" warning, and we will talk about that soon.
For those that get confused by the difference, maybe this graphic will help explain it. A watch simply means that the ingredients are there. Notice that all the cupcake ingredients are on the counter and ready for putting the recipe together, but we haven't started incorporating everything yet. A warning, however, means that the severe weather has formed and is an immediate threat. In comparison to the cupcake, the cupcakes are being finished and the final product is ready to be delivered. A warning means IMMINENT DANGER, TAKE SHELTER NOW. A watch means that severe weather is possible, be alert to changing conditions, and be ready to immediately act if needed.
The next important thing is, when a warning is issued for a part of your county, you need to know whether or not you are even included!
Since late 2007, tornado warnings, severe thunderstorm warnings, and flash flood warnings have no longer been issued by whole counties. Yes, you heard that right. Severe weather warnings are NOT issued by whole counties at a time any longer, and they haven't been for going on 14 years! These types of warnings are only issued for portions of the affected county or counties now. This is an effort to narrow down who is actually at risk from the threat, and only alert those people, and cut down on the number of false alarms to the people in the other portions of those counties who are never in danger from the storm. And yes, room for error is ALWAYS accounted for when the warning has drawn out. These warnings are called "storm-based warnings" and they are drawn with "polygons". We typically refer to these as "polygon warnings".
The example above is from a tornado warning issued on December 16, 2019. This is the warning that was issued for the deadly EF2 tornado that hit Town Creek and Courtland in Lawrence County, Alabama. Notice how Town Creek, Courtland, Hillsboro, Hatton, and Wheeler Dam are in the red shaded area, but Moulton, Wren, and Hepsidam are not. That is IMPORTANT. You need to know whether or not you are included in the warning when it is issued! Weather radios are critical but sound on the legacy system for whole counties. Sirens in many counties do as well (although some are transitioning over to polygons). This means that there may be times where your weather radio goes off or you hear a siren, but your town IS NOT ACTUALLY IN THE WARNING. The warning may be for another part of the county instead. Take the same warning above and look at it from the perspective of Lauderdale County, Alabama. That warning includes Killen, Center Star, Elgin, Rogersville, and Anderson. However, downtown Florence, Green Hill, Oakland, Underwood-Petersville, Cloverdale, Zip City, Waterloo... they are all not included in the warning. This concept is important to know and understand.
Apps like our Tennessee Valley Weather App and the Wireless Emergency Alerts built into your phone refer to the latitude and longitude of your location. Our app can either use your GPS location's latitude and longitude if you allow it, or you can select your location, and it uses that location's latitude and longitude. Those systems then compare those coordinates to the polygon warning. If the location is within the polygon, you get an alert notification. If your location is not included in the polygon, you are NOT alerted, even if some other portion of your county is included in the warning. This is how the warning system is designed to work. This is designed so that you get an alert if you are in danger, but you don't get alerted if you are not in danger. Room for error, change in storm direction, and uncertainty is all included when a warning is issued.
Here at the Tennessee Valley Weather Channel, we have a set of policies for providing live updates for watches and warnings:
- If a tornado watch or severe thunderstorm watch is issued for any of our viewing area counties, we will have LIVE updates at the top and bottom of every hour (every 30 minutes) for as long as the watch is in effect.
- If a severe thunderstorm warning is issued for any of our viewing area counties, we will have frequent LIVE updates, with the intensity of the severe storm and the level of danger dictating how frequently those updates occur. There may be times when the threat of damage in a severe thunderstorm warning is significant enough that we have to provide live non-stop coverage for a period of time.
- If a tornado warning is issued for any of our viewing area counties, we will provide LIVE NON-STOP coverage until the warning has expired, it has been canceled by the National Weather Service, or the storm is no longer a danger (it has moved out of the viewing area or it has completely fallen apart and hasn't tried to reorganize at all for several minutes).
- We DO NOT issue our own warnings. Those come ONLY from the National Weather Service. However, with our live radar that is able to scan lower in the skies over southern middle Tennessee and northwest Alabama, there may be times where we see a suspicious signature in a storm when a warning is not in effect. In those instances, we may advise you that we see something suspicious, and as a course of least regret, it may be a good idea to head to your safe place... but we do not and will not ever issue our own warnings. You will NOT hear "tornado warning" or "severe thunderstorm warning" from us unless it is officially issued by the National Weather Service.