Thursday, July 7, 2011

Aha! An OBSERVED MCV--just the other day

I was pleasantly surprised to see the University of Wisconsin -- Cooperative Institute for Mesoscale Satellite Studies (CIMSS) blog post on July 6th.  It discusses a mesoscale convective vortex that just occured over the southwestern US on July 5th and 6th.  Moreover, they have a stunning GIF animation of visible and IR satellite images that shows how the storms first organized as a mesoscale convective complex then later evolved to a mesoscale convective vortex.

The blog post is at:

And that GIF animation (which is the first image in the blog post) is here.

I encourage you to watch the animation to really get a good idea of the evolution of these sorts of storms.  The synoptic-scale flow aloft was relatively weak, indicating that this complex of storms organized away from any strong upper-level forcing.  What began as clusters of thunderstorms during the day (with very distinct outflow boundaries) congealed into an organized mass as night fell.  You can see in the overnight hours (when the animation switches to the lower-resolution IR images) how the cloud structure does indeed take on the characteristic round shape of a MCC. 

By the morning hours (when the animation returns to the higher-resolution visible images), the remaining circular cloud shield (and a fair amount of the convection going on) dissipates.  But, it leaves behind the warm-core vortex that lies at the heart of the complex.  Internal interactions within the cyclonic flow about this vortex are able to maintain some convection about the vortex center.  However, because this is a vortex, the convective structure has the characteristic "swirl" shape we see in MCVs.  Once again, not unlike a hurricane...

It's incredible how fragile MCVs actually are.  As I mentioned in my last post, studies indicate that on average only three or four MCVs are observed in the US each year.  Any strong upper level winds will tend to shear apart that warm-core vortex long before it gets very organized.  You can tell in the animation that the synoptic flow is weak, though, and atypical of a progressive, strong jet pattern.  The MCV itself drifts westward, which is not the typically direction we see storms move--this shows the relatively "mild" conditions aloft.

Anyhow, I just thought it was pretty amazing that the day after I do a post about MCVs (a relatively rare phenomenon), one happened to be observed.  So, please enjoy this fascinating type of storm...

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