ROCHESTER, N.Y. (WROC) — Strong storms pushed through parts of the region on Tuesday afternoon and evening, but not everyone saw them. What you may have seen if you lived in Monroe county was the sky growing dark, but little to no rain was to be found. What gives?
This large cloud that overspread into areas like Rochester is called an anvil. It’s a cloud formation caused by the spreading out of strong winds within the upper part of a thunderstorm. It typically has a flattened, smooth appearance in the sky with more fibrous characteristics on the outer fringes. It can turn a completely sunny sky into an overcast one within minutes, and is a sign that strong storms may be nearby.
Depending on how strong the storm is and how long it lasts, these clouds can stretch for over one hundred miles downwind of the storm. Remember that when you see one of these clouds nearby there’s most likely a pretty strong storm not too far off, but you’ll typically find calm and sometimes partly sunny conditions underneath one of these clouds.
You can see the evolution of this anvil in the clip below with the storm blossoming over Wyoming and moving through Livingston county. See all that white on visible satellite below that seems to come out of nowhere next to the storm? That’s the anvil!
How does this happen? When a storm is particularly strong you know it has a nice updraft, which is the part of the storm that consists of strong rising motion. However, in the atmosphere there is a limit as to how high these storm clouds can go. As you go high enough into the atmosphere the temperature goes from decreasing with height, to increasing with height. We call this a stable layer in the atmosphere, and once this cloud reaches this layer it has the tendency to not want to rise anymore as the air becomes warmer and wants to sink. As a result, it gradually flattens and spreads out since it has no where to go but outwards instead of upwards.
Screenshots below are of the developing anvil as it made its way north of the thruway and overspreading nearly the entire counties of Monroe and Genesee.
Sometimes you can get other neat cloud formations to form within an anvil if there is a lot of turbulence going on in the air such as mammatus clouds. It takes a very unique environment to get cloud formations such as these, and typically occur in severe weather hotspots such as the Great Plains and Midwest United States. Take a look at an anvil forming these neat cloud formations from a storm I saw in Kansas a few years back in the photos below. Pretty neat right?
~Meteorologist Christine Gregory