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MATT: Hi, John.
Thanks for joining us again.
JOHN RAFFERTY: Hey, Matt.
How are you?
MATT: Good.
Good.
So a few weeks ago, we discussed climate change, specifically how
the pandemic was affecting climate change.
So I thought I would do a little bit of a follow-up
and ask you some other weather-related questions.
As we get into the summer months, I think people are often used to, OK, well,
the heat is going up, the temperature is going up.
But there are also some other weather systems that happen
or they start happening in the summer months, such as thunderstorms, tornadoes.
And it's the start of hurricane season.
How come this happens now?
JOHN RAFFERTY: How come this happens now?
Well, why don't we start with thunderstorms?
MATT: Sure.
JOHN RAFFERTY: Just because they're kind-of part and parcel of some of these other systems
you talk about.
It has a lot to do with how much liquid water is available
and how much energy there is available.
And specifically, the contrast between the energy available at the surface and the cooler
air conditions aloft above the surface.
So let's just talk about liquid water for a second.
In the winter months in a lot of parts of the Northern Hemisphere, the Southern Hemisphere--
a lot of that water is locked up as ice.
So it's not available to evaporate quite as easily.
But in the summertime, because temperatures are such that things are warmer,
you do have greater liquid water availability.
So what happens is it allows the water to evaporate.
And when water evaporates and it's warm, warm water vapor rises to a point
where at the upper levels of the atmosphere, it cools and condenses into clouds.
And when that happens, if the condensation is great enough, it forms the water droplets.
And if those water droplets are heavy enough, they fall out as rain.
MATT: Thunderstorms are usually shorter in length, but stronger in force.
Why is that?
JOHN RAFFERTY: Well, it has to do with how rapidly that convection, condensation
process takes place.
OK, so in the summer months around here in North America,
we get our prevailing winds from the Southwest.
And that's where the warmer temperatures are.
So that's the energy source.
Well, in addition, you've got all these growing plants.
You've got open water on lakes and rivers.
So you've got a lot of moisture that's available.
Over the course of the day, that water evaporates, temperatures heat up.
And so there is that perfect storm of those two things together
that causes this convection happen.
The strong thunderstorms result in this heated air that really wants to rise.
And it's also taking the water vapor with it.
As this warm parcel is warming the cooler air above it,
the cooler air is also interacting with it as well.
So it's cooling that parcel.
The more energy is available, the higher it goes.
So the higher it goes, the clouds happen.
You get more intense situations like a thunderstorm that would arise.
As quickly as it comes up in the late afternoon, it dissipates as it moves along.
Because we're running out of sunlight at that time.
That energy source is starting to go down in the early evening.
So that's why the greatest chance of thunderstorms
is right at that peak sunlight hour, peak sun time in the late afternoon.
That's where the heat is the greatest.
MATT: Right.
Usually, when we experience intense thunderstorms,
it is that late afternoon, early evening.
And then oftentimes, now we get all these alerts on our phone.
You get a severe thunderstorm warning.
Sometimes you may even get a tornado watch or tornado warning, depending on where you live.
Do thunderstorms and tornadoes go hand in hand?
Or in other words, can a tornado form without a thunderstorm?
Or does it need to--
does a thunderstorm have to happen first, before you get to a tornado?
JOHN RAFFERTY: Well, it actually comes down a lot to the definition.
OK, a thunderstorm is only called a thunderstorm if there's lightning that produces thunder.
So you could still have a cloud that does everything a thunderstorm does,
except for thunder and lightning.
And it wouldn't technically be called a thunderstorm.
But those kinds of things can produce tornadoes as well.
By and large, though, in practice, tornadoes and thunderstorms typically go hand in hand.
MATT: Got it.
And as I was doing some research before talking to you,
I did learn that the US has the most tornadoes out of anywhere in the world.
We actually even nicknamed an area in the Central United States called Tornado Alley.
Why do more tornadoes form in this area?
JOHN RAFFERTY: It has to do with just the recipe of conditions.
And it's not just the source of water and the energy, but it's also the topography--
the lay of the land, the landscape.
Tornado Alley occurs in the Great Plains.
It's an area that is pretty flat.
Some hills here and there, not a whole lot of forests.
And you also have the Gulf of Mexico that's nearby.
And that's the moisture source.
And with those southwesterly winds, southernly winds,
you get the moisture from the Gulf of Mexico coming over this frying pan.
And you get that convective storm action that we discussed earlier.
MATT: So tornadoes form over land.
If we move on to hurricanes, they actually form over oceans.
JOHN RAFFERTY: Yes.
MATT: Why do they need the oceans in order to form the tropical system?
JOHN RAFFERTY: Well, it's interesting.
Because if you think about it, if you compare tornadoes and hurricanes, the recipes for them
are fairly similar.
You're going to need a heat source.
You're going to need a moisture source.
However, with hurricanes in the tropical oceans, the tropical oceans
provide the heat source and an endless supply of moisture.
That water vapor is going to rise and form thunderstorms and ultimately,
hurricanes based on those same kinds of things that are going on over land with tornadoes.
MATT: We live in the United States, so we're used to the systems that we see here.
We call hurricanes hurricanes, but they have different names,
depending on where they developed across the globe, correct?
JOHN RAFFERTY: Yes.
MATT: So what's the difference between a hurricane, a cyclone, and a typhoon?
JOHN RAFFERTY: Nothing.
Nothing.
Actually, the technical term for all of these things, all of these phenomenon that everybody
has different names for is tropical cyclone.
So if you're talking to a nerdy scientist like myself, we might say tropical cyclone.
But in different regions, they call them different things.
So here in North America in the North Atlantic, we talk more about hurricanes
than we do about typhoons, because that's just what we call them.
Around China, Taiwan, Japan--
that's the typhoon zone, but it's basically the same thing.
The storms form the same way.
It's just what they call them.
And then typically, everywhere else it's a matter of a mix between typhoon and cyclone.
Pretty much more cyclone than anything else, because that's just what they call them.
MATT: Got it.
So they all start the same way.
They're just a tropical depression.
And it really depends on if it intensifies enough and becomes a storm
and then if it strengthens all the way to what we refer to it as a Category 1 hurricane.
The name can just change, depending on where this formation happens around the globe.
JOHN RAFFERTY: Yes.
Everybody has got different names for things.
In the common parlance between these different regions, they call them cyclones.
MATT: So, John, Hollywood loves a good disaster movie.
Oftentimes, these disaster movies are rooted in some type of weather event.
And in the movie, they depict the meteorologist or the storm chasers as action heroes.
They are exaggerated a lot of the time for entertainment value.
But there is some truth to what these experts have
to do in order to get the data to best predict these systems
and hopefully protect us as best they can.
Do you think that we'll ever get to a point with that technology, will
be so advanced that we don't have to send people into the eye of a storm?
JOHN RAFFERTY: What we need to do is we need to take measurements
in order to get a sense of the storm.
And some of those measurements-- you can get from space using satellites,
get a sense of the size of the storm, the heat level of the storm,
infrared that's coming off of the storm, those kinds of things.
But you're still going to need something to go through the cross section
to see how high the winds are, to gather pressure readings, et cetera.
So that's why we use those hurricane hunter aircraft to go through.
Now, are we going to ever get to a point where the satellites will
be so sophisticated that they can just take a snapshot of a developing storm and go,
OK, this is how strong the hurricane is going to be in a week
and this is where it's going to go?
Maybe.
But it's pretty speculative right now.
It's a combination of remote sensing from satellites,
but also ground truth or close to ground truth measurements through hurricane hunter aircraft,
and the measurements that those take.
MATT: John, thanks again for joining us.
I'm sure we'll talk again-- next couple of months.
It's been a very eventful 2020, but hopefully, the hurricane season
is not too intense this year.
JOHN RAFFERTY: Matt, thanks for having me on.
I share your sympathies.
Let's hope we catch a break this year.
MATT: All right.
Thanks, John.
JOHN RAFFERTY: You're welcome.
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