I saved some images as the storms rolled through Oklahoma on Tuesday and just like April 27, they are amazing. Forecasters can work 20 years and see these kind of signatures on radar only once or twice, especially if they work outside of tornado alley. A short description accompanies each image. I will be in Europe on holiday for the next ten days, but I will try to post a few interesting snaps along the way.
Huge hook echo approaching Piedmont Okla. at 3: 50 PM Tuesday. The echo below the tornado triangle is a debris ball, indicating a large tornado is on the ground.
Storm relative velocity data at the same time showed over 100 kts. of wind shear. Blue is wind toward the radar and red is away. This is called a tornado vortex signature (TVS). TV stations were showing a large tornado live via helicopters at this moment. The visual likely convinced people to take shelter and reduced the loss of life.
Normalized rotation from the GR Analyst radar software. This is the highest rotation I have ever seen on this algorithm. The red triangle is a warning that a TVS is present.