Garrett’s Blog: Chemical Weapons and Weather


If you were a terrorist wanting to inflict as much damage as possible, and create as much shock as possible, where would you release chemical weapons?

The very topic is disturbing but you might be surprised at how much weather plays into warfare. After all, on D-Day we stormed the beaches of Normandy because of a recent cold front passage (see below) which ensured building high pressure and sunny weather for all of the troops going to battle.

Weather on D-Day

The recent conflict in Syria has resulted in the use of chemical weapons. While the use of Sarin gas is undisputed; it’s point of origin is still debated by world leaders; although many governments are pointing the blame at Syrian President Assad. Rather then go into the politics of foreign relations, this blog post aims to take a look at weather conditions surrounding the attack.

Before looking forward, let’s look back at the original question I posed above. Where would a terrorist carry out the attack? In 1995, terrorists in Tokyo released Sarin gas into the subway system killing 13 people and causing over 1,000 people to develop nervous system disorders; including loss of eyesight. The attack was the worst in Japan since World War II.

1995 Japan Attack

The attack in Ghouta on the outskirts of Damascus in Syria occurred in the predawn hours. Most media reports place the chemical release around 2:30 or 3:00am local time. The Guardian has reported around 20 unexploded missiles were found over a large area and were suspected of carrying and dispersing the chemical agent: Sarin.

Syria Missile:

Sarin gas was first discovered as a pesticide. It’s considered highly volatile and changes from a liquid to a gas in minutes; because of this, it’s typically mixed in flight or immediately before deployment. It’s also difficult to store because it degrades in quality quickly over the course of time.

The chemical switches off the neurotranmitter (acetylcholine) which is responsible for regulating nerves. The absence of the neurotranmitter causes unregulated nerve endings within the body. The result is collapse, twitching, loss of bowel/bladder functions, foaming at the mouth, and eventually suffocation and death since the lungs are a muscle and breathing becomes impossible due to the chemical.

So what does any of this have to do with the weather? In short, it has to do with the atmospheric boundary layer and the nocturnal inversion.

During the daytime hours, the Earth is unevenly heated by the sun. Think about black asphalt heating faster than green grass. As air off the asphalt rises… wind is generated and the atmosphere is effectively “mixed”. This is why stable weather patterns generate more haze on the horizon and smog becomes a greater concern. It’s also why you have more allergies during the day than at night when the atmosphere isn’t moving.

Environment Canada Image

During the late night hours, a thermal inversion is created which traps the air near the surface and prevents the wind from mixing the air. The boundary layer is most stable around 3 AM. Similar overnight weather conditions occurred during the 1984 Bhopal India Disaster when over 3,500 people were killed as a toxic gas cloud of methyl isocynate was accidentally released in the city from an industrial plant.


A chemical attack at 3:00am, in the geographical area of Syria, strongly implies knowledge of local mesoscale weather conditions. The weapons are most effective when deployed within a stable boundary layer at night.

As day turned to night in Ghouta, the surface cooled and the local wind patterns stopped. The inversion at the surface kept chemicals suspended in the atmosphere much longer and was more deadly than if the attack had taken place in a crowded square in the afternoon; when the local winds would have dispersed the chemicals.

Deploying chemical weapons within a noctural inversion with little to no wind would assure that the chemical would inflict maximum casualties. Instead of rising up and away from the town, it likely formed a toxic cloud that spilled out horizontally and covered a larger area. Don’t overlook the effect of weather in this attack, it was the primary reason so many people were killed.



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