A large part of Indiana has a level two (out of five) risk of severe weather today (April 20, 2017) and this evening, according to the National Weather Service (NWS) Storm Prediction Center. The primary threat today is damaging straight-line winds or gusts of 58 mph or greater, but an isolated tornado cannot be ruled out in much of northeastern and east-central Indiana.
That makes now an especially good time for Hoosiers (and everyone else who lives in an area that ever receives severe weather) to make sure they have good ways to know about any warnings their local NWS offices issue.
So, here’s my list of the best ways to get tornado, severe thunderstorm and flash flood warnings. Continue reading →
Half of Indiana (shaded in dark green on the map, above-left) has a marginal risk of severe thunderstorms between 9 a.m. EDT today and 8 a.m. EDT tomorrow, according to the “Day 1 Convective Outlook” that the National Weather Service Storm Prediction Center (SPC) issued at 8:52 a.m.
The primary risks are damaging straight-line thunderstorm winds of 58 mph or stronger and hail of one inch or more in diameter. The probability of either occurring within 25 miles of any point in the slight risk area is five percent.
The normal hail probability for any May 12 is about one percent, so today’s probability is roughly five times normal.
There’s no reason to be alarmed by a marginal risk, but if you live in that half of Indiana, it’s wise to remain weather-aware today, especially if you’ll be involved in any outdoor activities (e.g. baseball games, etc.). Remember that all thunderstorms, severe or not, bring lightning, which kills people who are outdoors.
The SPC plans to update its outlook for today by 12:30 p.m. EDT.
The U.S. National Weather Service has been issuing tornado and severe thunderstorm watches and warnings since 1965. More than 50 years later, however, people still fail to fully understand the difference between a watch and a warning. You probably know some of them, I certainly do.
In fact, before 1965, the NWS called what we now know as “tornado watches” “tornado forecasts.” A tornado watch indicates the possibility of tornadoes forming, just as a rain forecast indicates the probability of rain. Similarly, a severe thunderstorm watch indicates the possibility of severe thunderstorms forming. A watch does not mean these things are already happening, it means they could happen.
Like a forecast, a watch covers a period of many hours and usually covers a large area of at least several counties, if not several states. We should watch for possible dangerous weather in the near future.
A warning is an indication of immediate danger
It’s a call to take shelter now, because the tornado or severe thunderstorm is already happening. Depending on where you are, you might only have couple of minutes to protect yourself and your family. Or, you might have 10 or 15 minutes, if you’re at the far edge of the “warning polygon.” If you want to survive a tornado or a severe thunderstorm, don’t waste time seeking more information. When a warning comes out, take shelter immediately.
Because dangerous weather has already formed and is on its way, a warning usually covers a period of less than an hour and a small area that’s sometimes smaller than a county. The time to watch is over. It’s now time to heed the warning and take shelter.
Want even more lead time?
If you’re really interested in weather, or want to know even earlier whether severe weather is possible, there are two other NWS products to check out.
The NWS Storm Prediction Center (SPC) usually issues a “mesoscale discussion” before it issues a watch. This product lets you know that the SPC is thinking about (or planning to) issue a watch, the geographical area of concern and the reasons. Some of the text of a mesoscale discussion can get pretty technical, but anyone can figure out from this product whether a watch is likely to be issued. If any mesoscale discussions are in effect, you can find them on the SPC website.
For even more lead time, the SPC issues “convective outlooks” that indicate the amount of risk of severe weather as much as eight days in advance. You can also find these products on the SPC website.
Typically, a storm that warrants a severe thunderstorm warning has straight-line winds or gusts of 58 mph or stronger. A big tent is the last place I’d want to be when winds of that speed hit.
We don’t know yet whether anyone at the circus knew about the warning. Severe thunderstorm warnings don’t trigger Wireless Emergency Alerts on smartphones the way tornado warnings do. Likewise, most localities don’t activate outdoor warning sirens for severe thunderstorm warnings.
Weather alert radios – which are available for as little as $30 – certainly sounded off when the National Weather Service issued the warning for Lancaster. Very few people, however, carry portable weather alert radios with them to a circus.
Still, the entire audience could have known about the coming storm and taken shelter in fairgrounds buildings, or at least in their cars, had a circus staff member had been monitoring a weather radio and had the circus implemented an emergency weather plan.
Every organization that stages any kind of outdoor event has a responsibility to its participants, spectators, etc. to know about and respond appropriately to all weather warnings.
That includes circuses, state and county fairs, sports stadiums, etc.
In New Hampshire, the following chain of events would very likely have prevented all the injuries and deaths:
Circus staff members program a weather alert radio for the county in which the circus is located.
A circus staff member (e.g. ticket office staff) remains within earshot of the weather radio.
Upon hearing the severe thunderstorm warning, a circus staff member alerts a member of management.
Circus management makes an announcement over the circus public address system, in which they ask all patrons to seek shelter and provide advice on where to do so.
Of course, awareness of a severe thunderstorm warning is only part of the solution. People must also understand how dangerous a severe thunderstorm is, so they take shelter just as they would during a tornado warning. But that’s a topic for a different blog post.
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