Thursday, April 30, 2015

Thunderstorms Part 2

Welcome back!
I will be continuing this week talking about severe weather and specifically supercell thunderstorms!
Supercell thunderstorms are individual cells with rotation. These storms form in strong vertical wind shear environments and the strong wind shear causes the thunderstorm to rotate (potentially leading to the formation of a tornado). 

This image below shows some of the features of a supercell thunderstorm:
Image from: Essentials of Meteorology: An Invitation to the Atmosphere.
Supercells are composed of many parts. The mesocyclone is a vertically rotating column of air that is typically 5-10 km across. The mesocyclone causes the updraft to rotate. 

The wall cloud is a rotating column of clouds under the base of a thunderstorm. This is where a funnel cloud and tornado may form. 

Image from: Heather Janssen 

Precipitation with supercells from south to north goes from hail, to heavy rain, and then light rain. 
Like multi-cell thunderstorms, supercells have the gust front, mammatus clouds, an overshooting top, and anvils. 

Supercell thunderstorms typically form in the late afternoon. What causes this? Well during the morning hours, storms are unable to grow vertically due to stable air. In the afternoon a conditionally unstable atmosphere becomes presents which can cause large growth in the vertical. This vertical growth will help with the formation of thunderstorms that eventually may become a supercell depending on the conditions in the atmosphere. 

If the conditions are right, a supercell may produce a tornado. A tornado is a rapidly rotating column of air extending down from the base of a supercell thunderstorm to the ground. Tornadoes can be of different shapes and sizes. The beginnings of a tornado is a funnel cloud in which the circulation has not reached the ground yet. Once the circulation had reached the ground, it can be classified as a tornado.

Image from: Essentials of Meteorology: An Invitation to the Atmosphere.
Tornadoes form most often in the presence of a supercell thunderstorm. Warm, humid air goes through the updraft of the storm while strong winds push heavy precipitation to the northeast portion of the storm. These winds help to produce a strong downdraft in the supercell.

The wind shear generates horizontal spin of air. The strong updraft in the thunderstorm can tilt the air vertically, creating the mesocyclone. Precipitation causes the creation of the forward flank downdraft and rear-flank downdraft. The rear-flank downdraft cuts off the warm, moist air causing the updraft to shrink horizontally and stretch vertically. This process forms the wall cloud where a funnel cloud develops and potentially a tornado if the circulation reaches the ground. 
Image from: Essentials of Meteorology: An Invitation to the Atmosphere.
This image shows these processes in a classic tornadic supercell thunderstorm: 
Image from: Essentials of Meteorology: An Invitation to the Atmosphere.
I hope you enjoyed this week’s posting! Make sure to comment down below with any weather-related you want answered by me. You can also ask your questions on Twitter using the hashtag #WeatherwithHeather. See you all next week!

Works Cited
Ahrens, C. Donald. Essentials of Meteorology: An Invitation to the Atmosphere. 6th ed. Andover: Cengage Learning, 2012. Print.

Creative Commons License
What's the Weather, Heather? by Heather Janssen is licensed under a Creative Commons Attribution-NoDerivatives 4.0 International License.

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