Big Time Weather...For Washington

    Last Saturday (Oct 20) from about 4:00 pm to 4:10pm, the residents of western Washington were treated to a surprise: a waterspout. It occurred just off the shore of Everett, which is about 25 miles north of Seattle. One little waterspout is nothing to write home about across most of the United States, but in western Washington, where even a single stroke of lightning is a big deal, such an event makes breaking news. I decided to investigate the funnel cloud more closely, so I downloaded raw radar data from KATX, a weather radar located on Camano Island about 15 miles to the northwest, which is actually really close. Besides the normal reflectivity data, which is what if often shown on TV, I also looked into the radial velocity data. This kind of data shows the speed of the rain coming towards or away from the radar. What makes this so useful is that rotation in the cloud can be spotted since one side of the rotation will be moving towards the radar very fast, and the other side will be moving away very fast. Since the rotation is small one just needs to find a few pixels in the data that are very different, yet very close together. Typically, the radar will not see the actual funnel cloud, whether it be a tornado or a waterspout, since the radar's beam will be well above the cloud base at the distance the storm is at. Despite this, with KATX so close, I thought I might give something a try...

-All of the following photographs were taken by others, but unfortunately I do not have the sources. If these images belong to you, I mean no disrespect.

-All of the radar images were made by me using Unidata's IDV program with Level II NEXRAD data. Note that all my images are from a 4:08pm radar scan.

 

 

Here, the spout is roughly south of the observer, who apparently is in a downpour.

 

This image is probably at about the same time as the previous one, but looking basically north. It is likely the photographer of the last image was located on the piece of land behind the funnel in this picture.

 

 

This is the best one. Notice how the funnel can be seen extending up through the lowest level of clouds. Also, to the left of the waterspout appears to be another one forming, as evidenced by the disturbed water.

 

 

This is the topography map I used for my images. The KATX radar is located just off the top left corner of the image and Everett is located on the center right.

 

 

Here is the reflectivity data, like what is often shown on the news. Notice the hook in the clouds just north of the island, that is the general region I suspect the waterspout was.

 

 

Next is the radial velocity data from the same radar scan with the same field of view. Near the center of the image are some very boldly colored pixels, but some are red and some are blue. This is likely a sign of concentrated rotation.

 

 

Using the same data as the last image, I constructed a cross-section right though those bold pixels. Even in the vertical, there is some bold blue right next to bold red. I might really be on to something...

 

 

So now I get a little tricky. The tangled white mess is called an isosurface. This means that everywhere on the surface some parameter has the same value. In this case, everywhere on the white surface, the radar measured the same reflectivity value. This somewhat shows the distribution of clouds.

 

 

Now I've turned that velocity data back on. If you look closely, there is a little hollow area near the center. In that area are those bold pixels.

 

 

Now the cross-section has been turned back on. Once again, those bold pixels are located in that little cavity.

 

 

This is the same series of data as the previous three images, just zoomed in more.

 

 

 

Now it’s really zoomed in. It is very clear something is going on in here. And look at little speck at the bottom of the data, just below the bold red pixel, interesting.

 

 

Ta da! With the cross-section off, it is clear that the little speck is really some pointed feature right in the middle of the cavity. That, I believe, is the radar signature of the waterspout itself. All of this even agrees with the actual photos. Remember the heavy rain from the first one? That would be the wall of white in the back of the cavity. Furthermore, it was nearly sunny in the second picture, which matches the radar image, where no rain is detected south of the cavity.

Wow, I never expected to find data this good. I'm glad I checked.