# Can you explain humidity?

Why is water vapour so important? We shall explain humidity and its consequences.

Humidity measures the amount of vaporized water in the air, and we use a hygrometer to get that measurement. When the air becomes saturated, it contains as much vapor as possible.

If saturated air cools off, water condenses into droplets and gives off a lot of heat in the process. Latent heat.

This extra heat is enough to dramatically change the shape of the curve this air would follow on the a tephigram or skew T diagram.

A what? A chart used to calculate wet bulb temperature and other parameters. The curve tells you how quickly the temperature changes as the pressure drops off in the current atmosphere. This can help create a good storm out of almost nothing.

## Explain humidity and Lifting Condensation Level

A fancy title for cloud base? Pretty close. As air goes up, it gets cooler. Eventually it reaches saturation because the vapour capacity decreases.

Condensation occurs, and here we define the lifting condensation level, LCL. One way to explain humidity of low altitude levels and its effects on weather is that the more moist the lower level is, the lower the cloud base will be. Then we will have stronger clouds and precipitation.

Even higher is the…

## Level of Free Convection

What happens if the transport of a small parcel of warm air somehow makes it through a stable layer immediately above? This does occur quite regularly.

If it gets caught in an updraft or forced up a hill, it can go against the forces of buoyancy that would normally push it back down.

The air parcel may make it into a layer above which is cooler and heavier. If this happens, spontaneous convection can take place. Atmospheric scientists call the point where this begins the level of free convection or LFC.

If the stable layer is too difficult to overcome, we have too much convective inhibition, or CIN. This gives us good stability for the time being.

## When the sun shines

After a good summer morning of heating, things can look a little different.

The temperature at the surface increases by several degrees during this period.

Then the vertical temperature gradient becomes strong. Now the height of the LCL increases and that of the LFC decreases simultaneously throughout the day, perhaps until they meet.

This is when our best summer storms occur. They are further enhanced by extra moisture at ground level, like after an overnight rain. Vapor is really fuel for the fire, which can explain humidity charts and data and why they are so essential for severe weather forecasting. If that happens, there is no longer any CIN to overcome. Ground-based spontaneous convection starts, and it can be big. You can call the surface temperature at which this occurs the convection temperature.

Humidity explained. Go back from Explain Humidity to the Chasing Storms web page.

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