BOSAI: Be Prepared - Cumulonimbus Clouds That Bring Disaster

Are you ready if disaster strikes?

Find out what you need to do by watching this program... "BOSAI: Be Prepared."

The topic this time is "Cumulonimbus Clouds That Bring Disaster."

Hi, I'm Bobby Judo, and today I'm on a rooftop in Shinjuku looking at the clouds.

Known as a symbol of summer in Japan, cumulonimbus clouds can bring about serious weather disasters.

They cause four hazardous phenomena: intensive heavy rain...

lightning strikes...

hailstorms...

and tornadoes.

How can we protect ourselves from these kinds of disasters?

Weather forecaster Sasaki Kyoko will tell us how.

Nice to meet you!

Nice to meet you, too.

Sasaki Kyoko provides municipalities and companies with weather information to help them take disaster prevention and other safety measures.

Cumulonimbus clouds can cause disasters, so you should be prepared for the sudden changes in the weather they cause.

I have a quiz question for you!

Which of the following phrases in weather forecast is notable for suggesting cumulonimbus cloud development?

1. The weather will turn bad from the west.

2. Atmospheric conditions are unstable.

"The weather will go downhill, starting from the west" means bad weather will spread toward eastern Japan, right?

What does "atmospheric conditions are unstable" actually mean?

Well, "unstable atmospheric conditions" refers to when a lot of water vapor flows up from near the ground to low in the sky or cold air flows into the sky above us.

I'll take that one!

Final answer?

Yes, final answer. Final answer, No.2!

The correct answer is No.2!

When atmospheric conditions are unstable, cumulonimbus clouds tend to form and develop.

Sudden downpours occur directly below a developing cumulonimbus cloud.

One well-developed cloud contains the same amount of water as about 10,000 25-meter swimming pools.

You don't want all of that coming down on you!

Are there any signs that we can watch out for that indicate a cumulonimbus cloud is approaching?

Yes, a certain type of cloud may be a sign.

So here's the second question!

Which of these two types of clouds could be an indication that a cumulonimbus cloud is approaching?

No.1, Mammatus, and No.2, Cirrostratus.

Which one do you think?

Uh... No.2.

Cirrostratus? Well, the correct answer is...

Mammatus!

I can't even hit a 50-50 chance!

Mammatus clouds can be formed at the base of clouds spread in the direction cumulonimbus clouds are traveling.

So, when the sky darkens and you see mammatus clouds, that's a sign of cumulonimbus clouds approaching.

You should check the radar forecast screen for confirmation, with the question "Is a cumulonimbus cloud approaching?"

Then you may be able to reduce the risk.

So what should I watch out for when a cumulonimbus cloud approaches?

One cumulonimbus cloud is not so big.

You may get a downpour as the cloud passes by and then it's over.

But there are times when a number of well-developed cumulonimbus clouds form in a row.

In that case, what do you think will happen?

Instead of having one cumulonimbus at a time, the clouds are connected in succession?

So then, the rain will keep falling.

Yes. It's called "Bands of heavy rain clouds."

Cumulonimbus clouds form one after another on the windward side.

They extend linearly to create a band of heavy rain clouds.

Each one causes a torrential downpour at the same location.

And that can lead to disasters, so they are very dangerous.

In recent years, torrential rain caused by a band of heavy rain clouds has caused flooding disasters every year.

For this reason, since June 2022, weather reports have started forecasting bands of heavy rain clouds as early as six to twelve hours in advance.

So, once you hear that, you have a little bit of time to prepare.

That's right.

If you get this information, you may need to evacuate yourself.

I think it's good to check if your evacuation bags are OK, which shelter you should go to if necessary, things like that, and then take action.

You need to act fast, especially at night.

However, the prediction accuracy of bands of heavy rain clouds is still not perfect.

Just because the information is announced doesn't necessarily mean they will form, and, conversely, they can form even if no alert is announced.

Also, remember that heavy rain doesn't necessarily happen only when there is a band of heavy rain clouds.

The best way to be prepared is to listen carefully to all the weather information issued, especially advisories and warnings.

The second of the dangerous weather phenomena brought about by cumulonimbus clouds is lightning strikes.

Cumulonimbus clouds are thunderclouds, so there are lightning strikes.

Now, here's another question.

Lightning only strikes right below a cumulonimbus cloud.

True or false?

I think it would be seen lightning spreading in many directions at once, so I'll say "False."

Correct! Please look at this.

- Oh, wow! Yeah...
- Isn't it amazing?

That... that's crazy! It shoots out sideways and falls straight down.

Lighting falls right below a cumulonimbus cloud, where rain is pouring as a matter of course.

However, it doesn't necessarily mean you're safe because it's not raining where you are.

Lightning strikes fall sideways like this.

So, if you hear thunder, you should think there is the possibility of a lightning strike, and immediately take shelter inside a building.

The energy of one bolt of lightning is about 1,800 kWh.

That's the equivalent of six months' worth of electricity for an average household.

Never shelter from the rain under a tree.

That's very dangerous because of the possibility of side lightning strikes.

Also, prepare flashlights and cell phone batteries in advance ready for power outages.

The third of the dangerous weather phenomena is hailstorms.

Next question! Which season is most prone to hailstorms?

- Hail is ice, right?
- Yes.

No.1, Winter, No.2, Summer.

I mean, I only imagine hail falling when it's cold, so it's Winter, right?

- The correct answer is...Summer!
- What!?

Hail is blocks of ice that grow in cumulonimbus clouds.

I had no idea!

Developed cumulonimbus clouds can produce large amounts of hail or even huge hailstorms.

Before hail starts falling, take shelter in a sturdy building!

Number four is tornadoes, especially when the cumulonimbus become very large.

Have you heard of "supercell?"

Yeah, like when stores have big discounts, like 70% or 80% off?

Well, yes... But that's not the same thing!

Oh, sorry, I meant a "super sale!"

Wow, you're not enjoying being a part of that!

Not a ”super sale” but a ”supercell” is a cumulonimbus cloud that is much larger than ordinary.

When they get this huge, they can cause disaster-level waterspouts and tornadoes!

Regular cumulonimbus clouds can also produce tornadoes, but supercells tend to bring very powerful ones, like this one.

They are extremely dangerous.

A supercell tornado observed in Ibaraki Prefecture in May 2012 was so powerful, it toppled entire houses to their foundations.

If you see funnel-shaped clouds like this or flying debris soaring in a tubular shape under a cumulonimbus cloud, a tornado outbreak is possible.

Immediately evacuate to a sturdy building or go underground.

Check out weather information in English on sites such as Nowcasts of the Japan Meteorological Agency.

Disaster prevention measures really can take many forms, but I think just being aware of the weather information counts for a lot.

Yes. And I think it's fun to look up at the sky and understand what you see.

I hope that an extension of that feeling of enjoyment will be your ability to ensure safety and secure evacuation.