A strong tornado churns south of Dodge City, Kan., on May 24. (Ian Livingston)

The National Weather Service has a long and dedicated history of warning people in the path of severe weather. The first tornado forecast was issued in the late 1940s, when forecasters predicted that a tornado would strike Tinker Air Force Base.

Over time, the process has been refined and transformed into what it is today. In addition to the dozens of other ways that warnings are disseminated to the public, they are now also fed to the world through social media.

If you live in a storm-affected region and use Twitter, you may have already seen @NWSSevereTstorm or @NWSTornado on your feed. If not, you probably will notice them soon as their reach grows.

Despite being a slow adopter to social media, the Weather Service has been taking it by storm over the past couple of years. Geeky government predecessors in NASA and the Interior Department have done tremendous outreach on these platforms, and now the Weather Service is increasingly among the innovators in digital communications across the federal government.


Stylized view of short-fused warnings (severe thunderstorm, tornado and flash flood from June 2014 through June 2016. For this map with boundaries and large cities, see here .)

As someone fascinated with the warning process and how it is communicated to the public, I have followed the severe warning accounts since inception in June 2014. Seeking out the zero warning, or one with no ambient population, is actually something of a hobby. (I know, don’t judge.)

Looking for more, I made a data request on what has been issued since the Twitter accounts became operational. I was fortunate enough to connect up with the National Weather Service, and they supplied the raw data they’ve obtained while developing these channels.

Work on the automated system began in 2012. After lengthy testing, NWS went live with the accounts in June 2014. Over time, the way they have been pushing warnings and watches to Twitter has evolved. The accounts continue to gain steam, and based on current plans, eventually these warnings will also go out through the local office accounts, increasing the overall reach substantially.

With June 2016 behind us, we now have data on three peak severe weather seasons. The data shows seasonal trends and gives us an idea of where the severe weather hot-spots are and what the typical warning looks like in terms of population.

A few things are apparent when we look at warning trends over the last two-plus years.


There is a striking variation between monthly warnings during the quiet times (a low of 61 so far) and the active ones (a high of 5,838 so far). As you might expect, knowing that storms occur the most in the spring and summer, there tends to be a fairly regular curve with a peak in May or June and a minimum during the winter months.

The sample here is quite small, but it also shows that there was a significant bump in severe warnings last December when multiple anomalous severe weather events occurred, like tornadoes in the Dallas area, as a strong El Niño was nearing peak. We can also see that by the warnings metric, May and June 2016 combined were considerably quieter than years prior.

Another interesting point we can glean from this graph is that the peak in flash flood warnings seems to lag the peak of general severe weather like wind, hail and tornadoes. Flash flood warning issuance has generally peaked in mid-and-late summer across this sample, albeit small. But it follows the expected trend — consider that the Southwest United States monsoon season in mid to late summer is a significant contributor to these events.

When it comes to the population impact for warnings, it’s somewhat evenly distributed from the smallest of places to populations up to about 100,000 people.


The National Weather Service’s mission is to “[p]rovide weather, water, and climate data, forecasts and warnings for the protection of life and property and enhancement of the national economy.” Which is why, in the minds of forecasters, a place with a population of three people deserves a warning just as much as one with a million. It appears the current sweet spot for warnings is the population total of 10,000 to 25,000, but this is likely at least partly a product of population distribution in regards to severe weather hot-spots on the whole.

A few meteorologists on Twitter are often scanning the feed for a “zero warning” — a warning for an area that has no population. It’s amusing that warnings are issued for places with no people. Of course, we can’t be sure there are no people traversing through it.

Interestingly enough, these warnings are somewhat more common than the major population warnings. For instance, in the sample analyzed here, there have only been 22 severe thunderstorm warnings with populations of 5 million or more, compared to 85 with zero.

Perhaps unsurprisingly, the highest-population warning since these accounts were created was in the New York City metro area, when more than 12 million people were under a severe thunderstorm warning in July 2014.

The highest-population tornado warning came in December 2015 in the Dallas metro area during a particularly deadly severe weather week. Tornadoes were reported to the National Weather Service on each day from Dec. 21 to Dec. 27. The seven-day streak was the most consecutive days with tornadoes on record in the month of December.

This Dallas tornado warning was issued  Dec. 26, when severe weather ripped through northeast Texas in the dark. The event spawned nine tornadoes, including an EF-4 with estimated winds of up to 180 mph and a continuous damage path of 13 miles across two counties. Eleven people lost their lives in tornadoes  that night.

Looking at total warnings issued by NWS offices over the course of the 25 months in this sample, we see much of the Plains and South leading the overall list.

The National Weather Service office in Norman, Okla., which covers a big chunk of central and western Oklahoma as well as parts of northwest Texas, have issued the most warnings. That area is quite active in most severe weather seasons, but it was particularly so during the spring of 2015 and parts of the other years in the sample.


Other thunderstorm-prone areas we would expect to see high on the list are indeed there, like Jackson, Miss. (No. 2 with 1,389 warnings) and Dallas-Fort Worth (No. 3 with 1,328 warnings).

Offices that stand out a bit in their respective regions include Las Vegas, where a lot of flash flooding occurs in the summer. NWS Grand Junction, which covers the border of Colorado and Utah, doesn’t issue many land-based convective warnings because it’s in the heart of the Rockies. NWS Seattle only has four issuances because of a generally stable environment, the Key West office even fewer because of minimal land mass and the frequency of their big weather being just offshore (waterspouts!).

Following trends with these accounts and what they tell us about warnings in the United States will be a fascinating endeavor in the time ahead.

While the current iteration of warning graphics keeps it simple and to the point, I have seen hints of the next evolution, and it takes it another step in the right direction. This is just one of multiple facets of NWS hazard simplification that are more apparently converging in recent times and will continue to do so ahead.

Where the big storm winds blow the most frequently …


Warnings you’ll really (really, really) want to take cover from…


Observed tornado warnings…


Warnings, in case someone stumbles in…