On the weekend of April 29th and 30th this year, a series of thunderstorms slammed the
southern and midwestern US, spawning flooding and tornadoes that killed at least 20 people.
The Monday afterward, I saw this satellite animation on Twitter.
It showed the thunderstorms’ formation and movement across the US, and I was like, wow
… that is very cool and a little bit unlike any satellite image I’ve ever seen of a
storm.
I wrote a note to the National Weather Service saying that I wanted to know everything about
this storm’s formation, and they wrote me back and then I gave them my phone number
and then they called me because I have a very cool life.
So here’s why that satellite animation looks so impressive, and how it shows the perfect
combination of factors that led to those devastating storms.
The first thing to note is that this video looks different from other satellite videos
of storms not just because the storm was pretty epic, but because this is one of the first
visualizations created from a new weather satellite that launched last November.
It’s called GOES-16, where GOES stands for Geostationary Operational Environmental Satellite,
and it’s the latest in a series of weather satellites that first started launching in
1975.
GOES-16 is still in its testing phase, and this is some of the first imagery from the
satellite that’s been made public.
It provides significantly higher resolution than older satellites, both in terms of image
quality and number of frames taken.
We’re talking four times the resolution gathered five times faster than older satellites.
The satellite collects real-time data as frequently as every 30 seconds, allowing a better understanding
of exactly what happens with storms like this one.
But enough about this satellite; let’s talk about the storm.
In the first few seconds of the video, you can see a stationary front stretching across
the midwestern United States.
A stationary front forms when cool airmass and a warm airmass meet, but neither side
is able to overtake the other.
That can lead to cloudy weather and a lot of rain.
This particular stationary front was set up by a cool airmass across the northern and
western part of the country and unseasonably warm weather in the south and east.
Since both of these masses of air were similar sizes, neither could move the other.
So that’s our stationary front.
There was a lot of warm, wet air along the front, trapped under a cap of warm, dry air.
The warm, moist air wanted to rise, but it couldn't get through the hotter air above
it.
Until, finally, it broke through.
There were similar conditions across much of the midwest, which allowed thunderstorms
to develop really quickly along the entire front.
There were also winds running mostly parallel to the front, so these thunderstorms moved
in the same direction, one after another.
That’s what meteorologists call training, because you end up with a bunch of thunderstorms
moving along the same path, like train cars moving along a track.
The cap of warmer, drier air was broken in succession all down the front.
The warm, moist air at the surface shot up and cooled, and water vapor condensed, releasing
tons of energy, and also all that rain.
Some of the storms that developed were supercell thunderstorms — the really severe kind that
can have super strong winds, cause flash flooding … and sometimes produce tornadoes.
Thanks to the amazing resolution of the GOES-16 satellite, you can see one of the telltale
signs of a severe thunderstorm: those little dark splotches.
In intense thunderstorms like supercell thunderstorms, warm, moist air shoots up into the atmosphere,
cooling as it rises.
Eventually, its temperature becomes the same as the ambient air.
When that happens, the storm flattens out at the top, forming what’s known as the
thunderstorm’s anvil, because the clouds look kinda like an anvil, all flat at the
top.
But in the center, where the air was rising the fastest, the air shoots up past the top
of the thunderstorm anvil, in what’s called — appropriately — an overshooting top.
That’s what those little black splotches are.
And this is what they look like from above.
Meanwhile, this stationary front, unfortunately, remained stationary as more warm, wet air
was sucked up into the atmosphere.
And so not only did the rain keep falling, it kept falling in the exact same place, in
some cases more than 25 centimeters in one day.
The next day, the same system spawned tornadoes in east Texas.
You can see the parent thunderstorms here.
By the end of this video, the thunderstorms had been going on for almost 48 hours, stretching
across much of the south and east.
In a normal situation, by this time the jet stream, a high-level wind pattern that usually
runs west-to-east across North America, would have blown the whole thing substantially to
the east, possibly even out into the Atlantic.
But it just so happens that the jet stream dips and waves occasionally, and on the weekend
of April 29th and 30th those dips were highly amplified, making the jet stream move more
north to south rather than west to east.
So instead of quickly moving east, the storm moved very slowly, and there were multiple
days of thunderstorms across the same areas.
That led to a devastating flood and loss of life.
But with the new, high-resolution data that scientific instruments like NOAA’s GOES-16
are collecting and sending down to Earth in real-time, we’ll only get better at identifying
and reacting to these events.
This episode of SciShow, and also lots of other great things, was brought to you by
the federal government spending money on the National Oceanic and Atmospheric Association
so that everybody has access to this remarkable data like this.
And also by our supporters on Patreon.
Thanks y’all.
If you want to watch more SciShow, here’s a video about why tornadoes really, really
hate the United States...
so much.