Thunderstorms which produce tornadoes

They are responsible for nearly all of the significant tornadoes produced in the U. Supercells are also known to produce extreme winds and flash flooding. The most ideal conditions for supercells occur when the winds are veering or turning clockwise with height. For example, in a veering wind situation the winds may be from the south at the surface and from the west at 15, feet 4, meters. This change in wind speed and direction produces storm-scale rotation, meaning the entire cloud rotates, which may give a striated or corkscrew appearance to the storm's updraft.

Dynamically, all supercells are fundamentally similar. However, they often appear quite different visually from one storm to another depending on the amount of precipitation accompanying the storm and whether precipitation falls adjacent to, or is removed from, the storm's updraft.

In low precipitation supercells the updraft is on the rear flank of the storm providing a barber pole or corkscrew appearance to the cloud. Also, large hail is often difficult to discern visually. With the lack of precipitation, no "hook" seen on Doppler radar. The majority of supercells fall in the "classic" category. The classic supercell will have a large, flat updraft base with striations or banding seen around the periphery of the updraft.

Heavy precipitation falls adjacent to the updraft with large hail likely and has the potential for strong, long-lived tornadoes. Beneath the supercell, the rotation of the storm is often visible as well. Wall clouds are often located on the trailing flank of the precipitation.

The wall cloud is sometimes a precursor to a tornado. If a tornado were to form, it would usually do so within the wall cloud. With some storms, such as high precipitation supercells, the wall cloud area may be obscured by precipitation or located on the leading flank of the storm. Please Contact Us. You may have heard a meteorologist refer to these as "popcorn" or "pop-up" storms. They are commonly found in the spring and summer, and can bring brief periods of heavy rain and hail.

While these storms can be severe, depending on the instability, many times they are not and can bring a welcome relief to intense summertime heat. While these storms can contain the usual suspects, like hail and gusty winds, the threat of flooding is greater with these.

Multi-cell thunderstorms can line up and move continuously over the same area, dumping significant amounts of rain. This is called "training" and often leads to flash flooding. There have been instances where multi-cell thunderstorms dump more than 5" of rain in an area in just an hour or two! This is when the flash flooding not only becomes dangerous, but life-threatening.

Especially common in the Midwest, these lines can often times be found ahead of a powerful cold front. Heavy rain, hail, lightning and tornadoes can occur, but the biggest threat with these can be damaging straight-line winds.

We look for a line of storms that appears to bow outwards on Doppler radar. This can indicate intense, damaging winds sometimes in excess of 70 mph! Many times, when these winds cause structural damage, storm surveyors are sent out the next day to determine if the winds were from a tornado or a "derecho", the Spanish word for straight. That brings us to the KING of the thunderstorms, the supercell. No doubt, you've heard your local meteorologist use the term on the air before.

Tornadoes that come from a supercell thunderstorm are the most common, and often the most dangerous. A rotating updraft is a key to the development of a supercell, and eventually a tornado. There are many ideas about how this rotation begins. One way a column of air can begin to rotate is from wind shear — when winds at two different levels above the ground blow at different speeds or in different directions. An example of wind shear that can eventually create a tornado is when winds at ground level, often slowed down by friction with the earth's surface, come from the southwest at 5 mph.

But higher up, at feet above the same location, the winds are blowing from the southeast at 25 mph! Rising air within the thunderstorm tilts the rotating air from horizontal to vertical — now the area of rotation extends through much of the storm.

Once the updraft is rotating and being fed by warm, moist air flowing in at ground level, a tornado can form.