How are thunderstorms formed? | Weather Wise S2E1

welcome to season two of weather-wise

where we'll be looking at severe weather

starting with thunderstorms exactly how

they form and what kind of extremes they

can grow to how does a puffy white

cumulus cloud turn into an immense tower

and cumulonimbus that can deliver

powerful winds dousing rainfall and even

hail and tornadoes to answer this

question let's isolate one warm humid

blob of air like this one and watch what

happens as it rises as long as the blob

is warmer than its surroundings it rises

expands due to the lower pressure and

cools due to that expansion until it

reaches the same temperature as the air

around it if the blobs temperature drops

to the dewpoint water vapor will

condense out of it and a cloud will form

and this condensation begins a cycle

that drives the growth of the cloud this

is because when water vapor condenses it

releases heat thus as soon as the cloud

forms the condensation gives the block

back some of the heat at loss due to

expansion and because the warmer air

holds more moisture the blob recovers

some of the water vapor it lost as well

when all that is done the blob is still

warmer than its surroundings so it rises

and the whole thing starts all over

again expansion and cooling condensation

recovery of heat and water vapor and it

rises again and this keeps happening

over and over and over until the blob

runs out of water vapor so when it's hot

and sticky out the abundant heat gives a

blob of air a strong impulse to rise and

the humidity provides a lot of water

vapor to drive the growth of the clouds

without anything to stop the process

this can produce clouds that can climb

all the way to the stratosphere now

expand all of this out and we say that's

not just one blob of air rising to make

the cloud but an ever flowing conveyor

of them drawing a constant supply of

warm humid air up into the developing

cloud in the form of powerful winds

known as updrafts when rain starts to

fall from the clouds this reduces down

drafts and the storm can persist for

some time like this especially if strong

upper-level winds caused the cloud to

become tilted which separates the

updrafts and downdrafts enough that they

won't cancel each other out it's at this

point during the storms mature phase

that will see abundant lightning and the

possibility of hail and even tornadoes

thunderstorms come in a variety of

shapes and sizes

they can end up looking like big clumps

of cauliflower as they run out of

moisture before they reach the top of

the troposphere if they do reach the

stratosphere they tend to spread outward

forming that characteristic flat and

ville shaped top of a cumulonimbus cloud

they can occur individually they can

cluster together or form up into squall

lines given enough heat and humidity

they can grow into immense rotating

super cells and then there's the

notorious mesoscale convective complexes

squall lines that can form one day

persist late into the night with heavy

rain hail and possibly tornadoes before

dying down by morning and then kick up

again into another line of powerful

thunderstorms by afternoon larger

thunderstorms are even capable of

producing such strong gusts of wind

flowing out from underneath them that

these gusts can form squall lines of

their own and these are known as

derechos now that we know all about

thunderstorms come back in episode 2 or

we'll dive deeper in and talk about

lightning what that is how it happens

and even some hints about what may cause

it as we all become a bit more weather


now storm formation can grind to a halt

with just one simple addition to the

whole scenario a layer of warm air

higher up above the ground

a typical temperature profile of the

atmosphere is that it gets cooler the

higher you go meteorologists call the

presence of this warm layer a

temperature inversion above the

inversion the normal temperature profile

takes over forecasters and storm chasers

often refer to this as the airmass being

capped this cap is most commonly

associated with warm air riding up over

cooler denser air such as near a warm

front or if there's a warm stagnant

airmass stuck over a region the air

closest to the ground will cool

overnight but this cooling may not reach

the air higher up before sunrise as

rising air reaches the cap more and more

warm humid air parcels become trapped by

this cap blocked from reaching the

cooler air above it this causes a

buildup of instability across this warm

layer and a buildup of frustration for

storm chasers because this entire

scenario will prevent storms from


however if conditions can break the cap

either the air beneath it warms up

enough to cancel out the inversion or

some particularly strong convection

bursts past it the sudden upward rush of

warm humid air causes explosive cloud

development and a sudden rush of storm

chasers to their vehicles as this often

results in severe thunderstorms