When dissecting the visual cues of a storm, it is particularly helpful to know what you are looking at.
Yes that is the most obvious sentence ever but let’s be honest, someone needed to read that.
At their most basic level, storms operate with updrafts and downdrafts. Through these two broad features most of the rest of the storm operates. So, when discussing the anatomy of a thunderstorm it is probably best to start with updrafts and downdrafts.
Updraft: Storm clouds form as warm and moist air lifts upwards. You often hear these called thunderheads — and they’re basically the storm breathing in and growing upwards.
Downdraft: This is cool, saturated air sinking quickly towards the ground — you may recognize a downdraft as where the rain and hail fall in a thunderstorm.
Anvils
Anvils are the flat, spreading top of a cumulonimbus cloud.
Thunderstorm anvils may spread hundreds of miles downwind from the thunderstorm itself. Sometimes, they may even spread upwind.
Think of anvils as a visual cue the thunderstorm updraft is ‘topping out’ in the upper reaches of the atmosphere. You can quickly assess where anvils are likely to form by looking at the equilibrium level (EL) on storm soundings.
Mammatus
A feature commonly found under the anvil are mammatus clouds.
Mammatus clouds are certainly pretty, but what do they signify in thunderstorms?
For the most part, mammatus do not indicate anything about a storm’s strength. They’re found in both strong and weak storms in both the strengthening and weakening phases of their life-cycles. Simply put, the presence of mammatus does not signify anything except that you might want to grab your camera.
Wall Clouds and Shelf Clouds
Wall clouds are localized, persistent lowerings in a rain-free base. They are sometimes only a fraction of a mile big, but other times can be several miles big. They’re commonly found on the south or southwest side of a thunderstorm, where the strongest part of the parent updraft meet the storm’s inflow. Wall clouds which are persistent are especially dangerous.
However, not all wall clouds rotate. Rotating wall clouds usually develop before strong or violent tornadoes, by anywhere from a few minutes up to nearly an hour. Watch any wall cloud featuring persistent, sustained rotation and/or rapid vertical motion.
Shelf clouds are usually associated with the leading edge of storm outflow — this is usually a sign of a line of storms or an HP supercell.
Oftentimes, shelf clouds feature lots of turbulent and rapid rising motion. This doesn’t mean that the storm is preparing to produce a tornado — it simply shows outflow and inflow are interacting in turbulent ways within the shelf cloud.
Shelf clouds may feature wall clouds where low level inflow is maximized along a line of storms. Keep an eye on wall clouds within shelf clouds for rapid tornado formation.
Supercell features to be mindful of
The rear flank downdraft (RFD) is a key ingredient in tornado formation in supercell thunderstorms. The RFD is a region of air (either dry or wet) subsiding on the back side of a mesocyclone that then wraps around the meso. Thus, it is often visible as a clear slot wrapping around the wall cloud.
Flanking lines are common in supercell thunderstorms. The flanking line is a line of cumulus or towering cumulus clouds connected to the parent updraft and extending outwards away from the parent updraft. They can also be the site of rapid tornado formation, and should be watched carefully when observing storms.
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