Ah, thunderstorms. A typical sight in the summer months where warm moist air rises in unstable environments to produce heavy rain, lightning, and beautiful views. On Sunday, moist onshore flow from the Atlantic impacted the eastern seaboard of the U.S. while a series of disturbances in the atmosphere provided the lift to create scattered storms.
Up close, these storms present an ominous sky, with dark clouds moving overhead. Storms were in the vicinity of D.C. this day, and you can see their threatening undersides near the top of this photo. But looking out beyond these nearby storms, you can see others in the distance. To the far right, there’s the characteristic puffy tops of growing cumulus clouds. To the left in the far distance, a more mature storm can be seen.
So how far away was that storm in the distance? Well, Richard Barnhill not only captured this photo, but also a screen shot of the current radar at this time. You can see where this storm was relatively to D.C., nearly 75 nautical miles (140 kilometers) away.
Looking back at the picture of this distant storm, notice how the top of it seems to spread out horizontally like an anvil. Need a refresher on what we mean by an anvil? Well, here you go:
As the storm grows in the atmosphere, it is limited by how high it can reach by how the temperature of the surrounding environment changes with height. In the troposphere, where most of our weather occurs, temperature tends to decrease as you go higher in the atmosphere. Certain conditions can lead to levels where temperature begins to increase with height, called an inversion, which serves as a sort of “lid” for these storms. The most common lid in the atmosphere is at the top of the troposphere, where above that temperature begins to increase with height in the stratosphere. So a storm can tap into the energy available in the troposphere as long as it remains warmer than its environment and can continue to rise until this equilibrium level. Here’s a handy diagram that can help show what we mean by this.
The take-home message from this image is that once the cumulonimbus reaches that stable point, the ice crystals in the upper-levels of the storm will begin to spread out horizontally in the stronger upper-level winds, creating the anvil. This type of cumulonimbus, that has the characteristic anvil, is called the “incus” variety. Incus is another name for “anvil” and is not only used to describe these clouds, but is also the name for a part of our ear.
For those who regularly follow our page, notice another familiar term that’s used to describe clouds?
So the distant anvil of Richard’s picture is an indicator of a more mature storm that has reached its maximum vertical growth. The clouds overhead were not posing an immediate threat, but shortly after, more intense storms rolled through the region.