Tornado Intensity and Tropical Tornado Reference Guides
Posted on June 6, 2015
Lately there has been a variety of good research coming out in meteorological journals and presentations related to real-time tornado intensity estimation based on certain radar signatures. Such guidance can be valuable when attempting to estimate potential impacts from an ongoing tornado. Obviously, that comes with a variety of caveats that must be understood if you want to use the research and guidance in an intelligent way that can add value. I will outline a few of those below.
Additionally, the National Weather Service’s Warning Decision Training Branch (WDTB) provided training on tropical cyclone tornadoes in 2014. It was intended to provide guidance for forecasters who are warning for low-topped supercells in the bands of a tropical cyclone. I wanted to combine all this useful information into simple one page reference guides that could be used in an operational setting.
I made an initial version and posted it to social media, which allowed a few people to provide some good feedback. That feedback turned into a few tweaks, and the next iteration is now available. The reference guides seemed popular enough that I have posted them here for those that want to download.
Radar Tornado Intensity Estimation Reference Guide
This reference guide is available as a higher resolution PNG image file by clicking the image above, or as a PDF by clicking here. Caution should be used so that you don’t interpret these rules of thumb too specifically in real time. I repeat, caution should be used. However, they can still give you a good sense as to whether or not a strong or violent (EF2+) tornado is possible in a given situation, and therefore they do have some operational utility. The reference sheet is based on the following the following research, as well as some feedback that I received.
- [link] “Diagnosing the Conditional Probability of Tornado Damage Rating using Environmental and Radar Attributes.” Smith et al (2015), online release in Weather and Forecasting.
- [link] “The relationship between automated low-level velocity calculations from the WSR-88D and maximum tornado intensity determined from damage surveys.” Kingfield and LaDue (2015), online release in Weather and Forecasting.
- [link] Tornado Warning Guidance (2013) from the Warning Decision Training Branch.
- “The Relationship Between Tornadic Debris Signature Height and Tornado Intensity.” A WDTB Storm of the Month presentation from Chad Entremont and Daniel Lamb
Remember, this is a reference guide with some rules of thumb so the numbers listed aren’t intended to be taken literally in every situation. For example, a 60 knot maximum rotational velocity with a tornadic supercell doesn’t guarantee a strong tornado, but it does indicate you are in a situation where a strong tornado would be more likely. As one of the tips points out, that would be especially true if the tornado was moving fast, in a very favorable environment for strong tornadoes, or the signature was sampled poorly. The “overlap” ranges listed on the chart in the bottom left corner do not encompass all cases of overlap. Therefore, the general principle is that as your rotational velocity and/or tornadic debris signature height increases, so too does the likelihood of a more intense tornado on average.
An extra note for the maximum tornadic debris signature heights: the strong tornado range tended to be a bit lower for QLCS tornadoes, with more overlap below 10,000 feet, than in supercellular cases.
Tropical Cyclone Tornadoes Reference Guide
This reference guide is available as a higher resolution PNG image file by clicking the image above, or as a PDF by clicking here. The material was specifically based on 2014 training provided by the Warning Decision Training Branch on tropical cyclone tornadoes. You can view all the training on the WDTB website by clicking here. It’s detailed and provides some good information beyond even what is contained in the reference guide, so I would recommend checking it out if you have any further interest.
Combined Two Page Reference Guide
If you plan to use both of the reference guides together – possibly useful in locations that experience tropical cyclones on a somewhat regular basis – you can also download a two page PDF file with both guides together by clicking here. I have printed off a copy double-sided and then laminated it for easy use and reference.