I've noticed a phenomenon all my life. After thunder (30 seconds or so) the rain falls harder...?

Question

The rain falls harder or seems more enhanced, particularly when the thunder (i.e. lightning) is right over head. I am accounting for the fact that this could be the beginning or front edge of a storm, but this occurs even during a shower or after one has commenced. It doesn't happen all the time, but quite often. My question is, does the expansion of the air/rushing back effect after lightning cause this?

Answer 1

Most probably your theory is, for the most part, right.

Thunder is merely the audible result of an electrically induced atmospheric explosion reaction.
Any explosion is simply the hyper-speed creation of a high pressure gas expansion which dissipates with distance.

Explosions can impart extreme velocity to projectiles at source and thereafter progressively dissipate.
This may well explain why rain is heaviest in the immediate vicinity of thunder and less so further away.

However consider ther instance of the submarine depth-charge.
Because depth-charges are not designed to penetrate submarine hulls they are drum shaped, not like projectiles. They operate by creating an explosion in the water making a gaseous hole. Since nature abhors a vacuum matter rushs to fill the void. If in close proximity of the gas hole a Submarine hull momentarily expands to fill the space, is weakened, and then assualted by the many tons of water returning to occupy the same space unsupportedly. It is this massive water return that finally crushes the hull.

Thus it is more likely that post thunder air rushing back to fill the explosion-created air-hole would be more likely to retard the freefalling rain as it was sucked into the space to restore pressure balance.

In conclusion: yes the initial explosion WOULD impart greater velocity to rain momentarily, until the air "rush back" then momentarily restrained fall force. Thus would be explained the "seems more enhanced" -- or brevity -- observation.
This situation probably occurs continually, but in some smaller showers is so rapid and minor not always perceived, hence your "doesn't happen all the time, but quite often" statement.

Answer 2

Nice observation. The answer, however, is no.

Here is why what you observed often occurs.

Lighting is a static electrical discharge that is formed due to a buildup of electrical potential within a thunderstorm. The differential within the electrical field is caused by the separation of charges within the thunderstorm. It is not precisely understood how this separation of charges occurs and is a subject of study and debate. However the separation of charges occurs, we do know that this occurs fastest and with the most rapid increase in electrical potential in the areas of the updraft/downdraft interface near the core of the storm. The updraft is the area where the conversion of water vapor to liquid or solid (ice) is the most pronounced.

Thus, the area where there is the fastest growth of electrical potential is also the area or region where the most rapid change of water vapor to precipitation is taking place as well. In other words, the core of the storm is where the most lightning is, as well as the most rain.

The actual lightning strike process is somewhat separate from the precipitation process and does not increase or decrease the precipitation rate. But both lightning and precipitation are maximized in the updraft/downdraft region.

Answer 3

There is a momentary increase in raindrop size that coincides with the thunder (not the lightning). This is because the vibrations (i.e., sound waves) cause the smaller water droplets to coalesce into larger droplets because they "bump into each other" as they are jiggled by the thunder vibrating the air/clouds.

As a result there is a brief heavy rainfall (i.e., larger raindrops) which lasts just a few seconds.

When there are already large raindrops falling or a heavy downpour already taking place, this slight increase is not noticeable, but when the rain has just started and/or there are small raindrops, a slight increase is very noticeable.

Answer 4

No, the air rushing back in has nothing to do with it. That's a very localized effect--it's the length of the lightning channel but only a few inches wide, so it's not going to affect rainfall in any substantial way. However, lightning is often associated with developing rain shafts, so I think that's what you're noticing, the rain growing harder as the lightning occurs.

Answer 5

Hmmmm...Never noticed this but here's an educated guess. The expansion of the air or pressure increase or maybe the heating of the air within the cloud causes the moisture to either condense sooner due to temperature change??

Answer 6

Nope!