RadarScope, one of my favorite apps for Apple iOS devices, is a full-featured app that provides access to nearly the entire suite of Doppler weather radar products generated by the National Weather Service.
As a wildlife photographer I use RadarScope to make go/no-go decisions for photowalking outings. And when I’m already in the field, I use the app to decide whether it’s time to seek shelter from pop-up thunderstorms.
As a weather enthusiast, RadarScope enables me to track the approach and passing of weather systems such as the line of strong thunderstorms that affected the Washington, D.C. metropolitan region on Friday, 27 May 2022.
Composite Reflectivity
The first image shows “Composite Reflectivity.” This is the same type of weather radar imagery that has been used by TV weathercasters for years. In a nutshell, composite reflectivity shows precipitation intensity within range of a weather radar site, in this case KWLX — the NWS Forecast Office located in Sterling, Virginia.
27 MAY 2022 | 10:29 AM EDT | KWLX Sterling
Notice the line of heavy precipitation, indicated by a narrow band of red radar echoes, just to the west of my location in suburban Washington, D.C. (see blue reticle at the center of the screen). Forecast storm tracks (see incremented white lines) indicate individual storm cells are moving generally from southwest to northeast.
To view storm tracks in RadarScope, tap the settings icon in the lower right of the screen, then choose Layers and turn on the Storm Tracks option. The estimated times of arrival can be seen by touching anywhere along the track. Source Credit: RadarScope: How are Storm Tracks Computed? [Editor’s Note: In my experience, this feature works only when I tap the white circle at the origin of each storm track.]
Storm Relative Velocity
“Storm Relative Velocity” shows the wind velocity in a storm minus the forward motion of the storm. Greens show motion toward the weather radar site; reds show motion away from the radar (like car tail lights).
27 MAY 2022 | 11:21 AM EDT | KWLX Sterling
Look closely at the full-size version of the preceding image. Notice the yellow polygon located between Beaverdam and Fredericksburg, Virginia that delineates the boundaries of a severe thunderstorm warning area.
There is a red polygon (located inside the yellow polygon) that represents a tornado warning area. Within the boundaries of the red polygon, notice the juxtaposition of greens and reds — a good indicator of counterclockwise rotation in a storm cell. As it turns out, there were several official reports of a tornado on 27 May 2022 in the same location as indicated by the NWS Doppler weather radar.
It’s important to note that the orientation of side-by-side greens and reds typical of rotating thunderstorm cells varies depending upon the location of the storm cell relative to the weather radar site. In the example shown above the greens are on the right and the reds are on the left because the warning area is located to the southwest of KWLX. In contrast, if the warning area were located to the northeast of the radar site, then the reds would be on the right and the greens on the left.
Related Resources
The following resources from the National Weather Service provide excellent background information about Doppler weather radar.
RadarScope features good in-app documentation, as evidenced by the following screen captures.
RadarScope | Help
RadarScope | User’s Guide
RadarScope | User’s Guide – Velocity Products
The same resources (and more) are available online.
Copyright © 2022 Walter Sanford. All rights reserved.
walter sanford's photoblog 