Good Example of the DCVZ Today… | CHASECASECO.NET - SCOTT HAMMEL

Good Example of the DCVZ Today… | CHASECASECO.NET - SCOTT HAMMEL

Good Example of the DCVZ Today…

• Written by Scott Hammel
• on 06/28/2013
• Filed under STORM

Of the many terms I’ve seen countlessly misidentified this year such as landspout, Bears Cage, gustnado, and so on, when people claim a DCVZ is setup when it’s clearly not, I tend to go a little nuts.  Now in all fairness, I’m sure I mis-speak and misidentify things all the time as well, so I get that we’re all human.  BUT, since the DCVZ is such a critical component of chasing here in Colorado, there’s really no excuse to not have at least a basic understanding of what it is, and how to tell if one is actually in place.  So let’s start from the beginning…
The DCVZ stands for the Denver Convergence Vorticity Zone.  The phenomenon also led to the term ‘Denver Cyclone.’  Now, why do we get these?  Like with a lot of things related to weather here in Colorado, our geography and topography, namely the Palmer Divide, is the critical part.  When we get a surge of moist, southeasterly winds that come up over the Palmer, they essentially get ‘trapped’ in the Front Range area due to the topography.  When these southeasterly winds make it over the Palmer, they run in to the winds coming off the foothills which tend to be northwesterly or uplsoped in the Summer.  So, when you have dry northwest winds, meeting moist southeast winds and they get trapped in our area, we get more vorticity.
Here’s a pretty good rough graphic that I found online…

But what does it tend to look like on radar?  Well, I grabbed this image from my radar software just about 20 minutes ago…

What I’ve outlined here with the yellow arrows is basically the flow of the wind once it gets trapped near the Denver metro.  You can see that a ‘cyclone’ forms surrounding the city.  The size of this cyclone can vary, and is generally not this big or visible on radar.  However today, because our dew points are higher you can actually see the convergence and boundary on radar which I’ve pointed to with the blue arrow.
In my experience with DCVZ days, storms that tend to form just outside the boundary (my red elipse in the photo) drift off to the east or northeast and eventually fizzle.  The storms that form ON the boundary are the one’s as a chaser you’re gonna want to stick with.  June 6th of last year was a great example of this.  A lot of people bit on a storm that formed just off the boundary and chased it as it drifted away and eventually died.  Meanwhile another storm formed on the boundary near Elizabeth/Ponderosa Park and just sat there dumping hail and eventually producing a decent tornado.

So anyways, that’s the basic gist of the DCVZ and what it looks like on radar.  I don’t expect much in the way of severe weather from it today.  The overall parameters are lacking, but it still is neat to see it show up so visibly on radar.