When the sky throws lightning, but the rain never reaches the ground

These are not your feelings: this summer’s storms have been more brutal and destructive than ever. AND AEMET data says so. But to understand it well, we have to go one step further: we have to understand what is perhaps one of the key elements of the current enormous problem, dry storms.

What are dry storms

a storm It is, in essence, a crash, an impact, a violent ‘argument’ between two air masses with different temperatures and pressures. The warm, humid air rises quickly and this generates atmospheric disturbances accompanied by electrical discharges (lightning and thunder), strong winds and precipitation of rain, snow or hail.

However, sometimes, even though the storm does contain moisture in the upper levels of the atmosphere, it’s not raining. There are lightning bolts, there are angry winds, there are clouds of great vertical development; but there is no precipitation that reaches the ground. We call that dry storm.

Characteristics of dry storms

As we said, the main characteristic of this type of storm is electrical activity (lightning and thunder) without significant precipitation on the surface. However, explaining the process and its characteristics is a little more complicated:

• It’s not that it doesn’t rain, it’s that the precipitation evaporates before hitting the ground. This occurs because these droplets pass through a layer of very warm and dry air. It is what is known, in technical terms, ‘virga’.
• For obvious reasons, it usually forms in arid, desert environments or during extreme heat waves. If the air in contact with the ground is exceptionally dry, the probability of evaporation in the fall increases.
• None of this has to do with its electrical activity, which is a lot. If these types of storms attract attention for something, it is the amount of thunder and lightning that develop.
• And if they are worrying for anything, it is because of the downward gusts of wind (caused by this rain evaporation process) that very dangerously increase the risk of fires.

How a dry storm forms

In reality, there is nothing strange about dry storms. They are, for all intents and purposes, normal storms. The “strange” thing is what happens on the ground: high temperatures and low humidity that favor the evaporation of rain.

This simplifies things because the process is identical to that of any conventional thunderstorm: unstable air, sufficient humidity at high and mid levels, and a rising mechanism (intense heat, in this case). Everything else, including precipitation generation, is very similar.

Relationship between dry storms and fires

Let’s not beat around the bush: the relationship between dry storms and wildfires is direct and dangerous. In fact, these types of storms are one of the main causes (unintentional) of fires. What’s more, due to the meteorological conditions that characterize them (dryness, heat, etc…), these types of events also facilitate the rapid spread of fire.

You don’t have to be very imaginative: electrical activity without precipitation, low humidity, very high temperatures and strong (and gusty) winds are the perfect recipe for a macrofire.

How to detect a dry storm

A dry storm can be sensed by the presence of electrical activity without significant rain on land. But, as with almost everything in meteorology, to have an overview you need lightning detectors, weather radars (especially Doppler) and satellites.

Consequences of dry storms

The main consequences of this type of storm are also the most dangerous: fires. Its structural characteristics entail a high risk of forest fire (the combination of intense electrical activity and lack of rain) and, if that were not enough, promote the rapid spread of fire.

Not in vain, the atmospheric conditions associated with dry storms (high temperatures, low relative humidity and strong gusts of wind) create a favorable environment for an incipient fire to spread at high speed and become uncontrollable.

The main consequence of dry storms is, in short, to verify again and again that we do not have enough capacity for stop today’s fires.

Image | NICOLA

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