The Omega Block

Friday, October 18, 2013
5:57 a.m.

There's a lot of things that suck in life. I'm not quite sure if I've gotten any sleep tonight, and that definitely sucks. But there is something that sucks even more than not being able to fall asleep, and that is called an "omega" block. The "omega" stems from the configuration of the 500mb heights in the atmosphere.

First, let's review what a capital omega looks like.

Here ya go.

Here is a capital Omega, the 24th and last letter of the Greek alphabet. Taking so many math and science classes, I get enough of these guys as is.

Below is an idealized diagram of the aforementioned block that I retrieved through UCAR's MetEd program. The program is free and is a great resource for not only weather enthusiasts but for those involved in larger educational and commercial fields. Check it out.

Now, take a look at a NAM chart all the way back from 2006. You can clearly see two closed lows on either side of a large ridge of high pressure.

A NAM representation of an Omega Block over the United States back in May of 2006. Created by NCEP. Retrieved from Wikimedia Commons. Chart URL: http://en.wikipedia.org/wiki/File:NAM_500_MB.PNG

See the correlation? Omega Blocks actually look pretty cool on models, but they will give any storm chaser a nightmare. Or two. Or three.

The reason? Once these blocks come up, they are stubborn as heck. Here's the chart for today:

It's not a "classic" Omega Block; it only has a closed low to the west of the high. Still, there is a very large trough to the east of the high, and the whole chart definitely still looks like it should be plastered on the outside of a fraternity. As I write this this sentence, it's actually 5:55 p.m. in the KOMO weather center (I was finally able to fall asleep at around 7), so let's take a look at this morning's 12z WRF-GFS 500mb height charts.

Valid 05:00 am PDT, Fri 18 Oct 2013: 500mb Heights, Absolute Vorticity. UW WRF-GFS 36km Resolution: Initialized 12z Fri 18 Oct 2013. Retrieved from the Pacific Northwest Environmental Forecasts and Observations website. Model URL: http://www.atmos.washington.edu/~ovens/wxloop.cgi?mm5d1_x_500vor+///3

This is the chart for the model initialization (forecast hour 0). As the succeeding charts show, we stay in a boring pattern for the next several days.

The above WRF-GFS charts show the Omega Block breaking down. To the untrained Pacific Northwest storm lover, this may look like good news. But in actuality, it's the worst thing that could happen. Why? Because a "Rex Block" will take its place.

This block does not resemble some brain-dead bloodthirsty beast, even if I do when one is situated over the area. Rather, it is named after Dr. Daniel F. Rex, a Commander in the Office of Naval Aerology and one of the founders of the NCEP (National Center for Environmental Prediction), which is the organization that develops and executes many different models that the United States (and many other countries around the world) use. Simply stated, a rex block has a high situated on top of a closed low. These blocks are even more stubborn than omega blocks. Let me put it this way... an omega block is to a filibuster as a rex block is to a government shutdown. And they will most definitely give any storm chaser a nightmare. Or four. Or five.

Let's take a look 180 hours in the future, which is the furthest the WRF-GFS goes out. Viewer discretion is advised.

Valid 05:00 pm PDT, Fri 25 Oct 2013 - 180hr Fcst: 500mb Heights, Absolute Vorticity. UW WRF-GFS 36km Resolution: Initialized 12z Fri 18 Oct 2013. Retrieved from the Pacific Northwest Environmental Forecasts and Observations website. Model URL: http://www.atmos.washington.edu/~ovens/wxloop.cgi?mm5d1_x_500vor+///3

That's a rex block, no doubt about it. grrr...

If there's a silver lining, this thing will break down eventually, and when it does, we'll be in for a neutral November. And looking back at November 2006, I think we can all appreciate how exciting those can be. :)

Have a good one! (inside KOMO joke) ;)

Charles