Tornadoes

Tornadoes Tornadoes cannot be detected with radar alone – rely on your spotters for confirmation of a tornado. However, we can use radar to spot areas with enhanced rotation, where tornadoes are more likely. To locate areas of enhanced rotation, use BOTH Base Reflectivity and Storm Relative Velocity products in tandem. A hook echo on Base Reflectivity may be an indication of an area of enhanced rotation. Use Storm Relative Velocity to confirm whether or not there is rotation in the same area – which is shown as a couplet of inbound and outbound velocities that straddle the radar beam.

Classic Supercells One of the most easily recognizable supercells is the classic supercell. A classic supercell has several key features including a mesocyclone and hook echo. Some supercells display other features such as a V-notch or a bounded weak echo region (looks like a donut at higher elevations on Reflectivity) – both of these features are indicative of a strong updraft. Below is an example of a classic supercell on Base Reflectivity (left) and Storm Relative Velocity (right). This storm produced a tornado in Alfalfa County.

Remember: It is important to remember your radar limitations when viewing supercells – including decreasing resolution and increasing beam height with distance from the radar. This causes some features such as hook echoes to be less identifiable (or not present at all) at farther distances from the radar.

Storm

Base Relative Reflectivity Velocity

High Precipitation (HP) Supercells HP supercells contain an abundance of precipitation and can produce rain-wrapped tornadoes. Like classic supercells they have a distinct mesocyclone (visible on Storm Relative Velocity) but unlike classic supercells the hook echo may not be as distinctive or even visible at all due to significant amounts of heavy precipitation. In the below example, strong rotation on Storm Relative Velocity (right) and an obscured hook echo on Base Reflectivity (left) are telltale signs of an HP supercell. This storm produced a long-track EF-5 tornado in El Reno and Piedmont, OK.

Storm Base Relative Reflectivity Velocity

Tornadoes

Non-Supercell Tornadoes Tornadoes are not limited to just supercells. Some tornadoes form within squall lines or bow echoes. Not every storm that produces a tornado is going to have classic signatures on Base Reflectivity. Base Reflectivity only tells part of the story, so it is very important to view Base Velocity as well as Storm Relative Velocity. The below example is of a bow echo that not only produced strong straight- line winds, but several tornadoes in the Tulsa area.

Tornadoes Storm Base Relative Reflectivity Velocity

Tornadic Debris in Dual-Polarization Radar Data

Dual-Polarization (Dual-Pol) allows all NEXRAD radars across the country to better identify the shape, size, and variety of weather and non-weather targets. While these advancements most benefit the identification of different precipitation types (hail vs. rain, rain vs. snow, etc.), the technology can sometimes aid in the detection of tornadic debris under the right conditions.

Correlation Coefficient (CC) is a dual-pol product that measures how uniform or diverse atmospheric targets are. Most weather targets (rain, snow, hail) are fairly uniform and result in high CC values. Conversely, non-weather targets such as birds, chaff, debris, etc. are much less uniform and result in very low CC values. If a storm contains significant rotation and also happens to have low CC in the same spot, it may possibly be indicating tornadic debris. The example below shows this occurrence (Base Reflectivity – left; CC – center; Storm Relative Velocity – right) during a storm that produced an EF-5 tornado in Moore, OK on May 20, 2013.

While this may seem like a slam-dunk tool in detecting tornadoes, it has its limitations. The tornado has to be producing significant amounts of debris and the debris have to be lofted high enough for the radar to see. For tornadoes that are weak, farther from the radar, or not producing significant debris, the radar will not be able to detect debris. The Bottom Line: use CC only after consulting Base Reflectivity and Storm Relative Velocity and treat it as additional information. Continue to use and rely on your spotters to confirm the presence of tornadoes!!

Base Correlation Storm Relative Reflectivity Coefficient (CC) Velocity