Thunderstorms of September 6th, 2012

Bow Echo Thunderstorm

Bow Echo Thunderstorm systems are exciting :^) This is a screenshot taken on an iPad using the Intellicast app and which I have annotated using Paint.Net.

Bow Echo thunderstorm systems for quickly and move fast. They form from large differences in pressure between the surface and winds aloft creating wind shear. Bow Echo thunderstorms can generate winds in excess of 60MPH during their brief lives. They generally do not spawn tornadoes unless they are part of a larger series of Bow Echo thunderstorms like …

Double Bow Echo thunderstorm

…this one. Multiple Bow Echo thunderstorm systems are not comforting. Besides bringing strong straight-line winds, these can spawn tornadoes, and be part of a larger weather system called a “derecho” (dah-RAY-cho). Derecho are not a comforting sight, either.


Derechos are often called “shelf clouds” due to their very flat appearance with a clearly defined leading edge. They are generally 10s to 100s of miles in length, a long ribbon of clouds which foretell the immediate arrival of very bad and potential dangerous weather, strong winds and tornadoes.


The above image is the derecho which ran through our region in April 2011. I think this is the one which provided us with straight line winds of nearly 70mphs – almost like a Category 1 hurricane.

Using weather apps, Unisys, Intellicast, for example, can provide you with a cool way of watching thunderstorm development. Thunderstorms can have diagnostic features which help in their classification. Knowing what a few of these diagnostic appearances are can help even an “Armchair Meteorologist” determine what the coming weather system might be like, whether a simple shower is in the offing, or if you should bring in Toto and head for the storm shelter.

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