I was watching the first thunderstorm of the season tonight (I’m a big fan) and I noticed, for the first time, something I thought was a TV cliché. Whenever a clap of thunder would be heard, the rain immediately increased, sometimes from a smattering to a downright torrent, then slowly die away until the next thunderclap. Why is this? Does the noise of the thunderclap somehow precipitate the rain from suspension in the clouds?
The idea sounds ridiculous, but I just pulled my book All About Lightning by Martin Uman off the shelf, and Chapter 14 is titled “Do Gushes of Rain Follow Thunder?”
However, this talks about the gushes of rain that people have noticed, a minute or two after thunder. This implies that the gush is generated in the cloud and takes a while to fall.
He basically says that it’s postulated that droplets of water in the cloud can have a charge, and the lightning in the cloud sends droplets scurrying around more, based on their relative charges. When the droplets move around with respect to each other, they coalesce into larger droplets and fall.
Again, this is just what some people have postulated, and it involves a gush a minute or two after the thunder.
IANAMANAY*, but I’d venture to opine that the more magnificent thunderclaps and the torrents of rain are coexistent symptoms of the same occurrence – the passage of a strong frontal system. Anecdotally, I’ve seen plenty of instances where the torrents of rain preceded the bust-ass lightning and thunder, but the time differential was minutes.
*I am not a meteorologist and neither are you.
I’ve been noticing this phenomenon for years.
The thunder you hear is actually a large pressure wave formed from rapidly expanding air around a lightning strike. I always thought this pressure wave sort of “jostled” a bunch of drops loose. 
I’ve been observing the weather for some 16 years professionally (it’s my job) and I have never noticed this phenomenom. I asked the off-going duty observer, and he hadnt. The forecaster here hasnt heard of it either.
In all the thunderstorms I have reported, the intensity of the precipitation varies considerably as different parts of the thundercloud (cumulonimbus) pass overhead. Yes, you do get bursts of more intense rain, but I have never noticed that this happens after a thunderclap.
Remember too, that the thunderclap will be from a lightning strike that may be some miles away.
How many times has the rain gotten more intense without a thunderclap preceding it ? Maybe it just isnt noticed as much. A bit like you always notice when you get stuck in then longest queue at the supermarket, but dont notice those times when you didnt.
My tuppence-worth.
Well, while I was watching, I noticed it and then watched it for the remainder of the storm. There were variations in rain intensity in between thunderclaps (the thunderclaps were separated by two to five minutes), but each thunderclap brought a sharp increase in intensity, one so intense as to go from a fair smattering to an absolute torrent that lasted a few minutes.
Post hoc ergo propter hoc, matt
Yes, but it happened every single time, between five and ten seconds after the thunderclap.
And every time the rooster crows, the sun comes up! Proof positive! :rolleyes:
So you’re saying that the thunder clapped because the rain increased? Please, try to contain your effusions of brilliance.
Here’s a theory:
How do you tell if the rain got harder?
By the sound of it, right?
I think what happens is that the LOUD thunder causes your ears to adjust to loud sounds, then after the thunder your ears slowly adjust back to the volume of softer rain. While your ears are doing this adjusting, the sound of the rain seems to get louder, making you believe the rain is getting harder. But it is just an illusion.
Also, sometimes the rain may actually get harder right after a thunderclap, but this may be unrelated.
Does this seem plausable?
Steven
My experience with thunderstorms has been that the big downpour comes just after the last of the lightning and thunder. I’d guess that the same convection that is creating the static electric potential in the cloud is holding precipitation aloft at the same time. It is, after all, that sort of convection that allows rain drops to be repeatedly lofted to freezing levels to form hail stones.
As I said, I’ve usually seen T-storms just go through one cycle: Big Pile-up; Fireworks; Downpour. But I suppose if the storm was going through the cycle more than once it could go: Fireworks; Downpour; Fireworks; Downpour…
FWIW
No, by sight. I was sitting on my front steps and as I said, it quickly and visibly increased from a few drops to a very heavy downpour.
Have never noticed it here. We have quite a number of thunder storms over the wet season and when there is lightning and you’re close to it, it just buckets down all the time.
Two possible mechanisms:
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Since lightning is generated by charged raindrops, and since raindrops tend to FALL, perhaps a region of dense rain causes a cloud-to-ground lightning bolt before that larger hunk of rain finally makes it to the ground.
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Since lightning is generated by charged raindrops, and since the base of thunderclouds is typically charged negative while the earth below has an induced positive charge, we would expect the earth and cloud charges to apply forces to raindrops between them. There is a strong vertical e-field in the region below a thunderstorm! Suppose some positively-charged rain is falling. It would tend to fall more slowly than normal (attracted by the negative charge above, and repelled by the positive below, which affects its terminal velocity). If lightning is triggered, it would discharge part of the cloud and (sometimes) greatly reduce the electrostatic forces below the storm. The charged rain would fall faster. It would then slow down again as the storm cloud charged itself up.