I don't have Weatherflow Tempest but as a generic guideline I am assuming you are using a .mail template in the \data\templates folder?
.mail template is simply an ascii file edited by a text editor. Make a copy of the .mail file you are using before editing. Comparing the .mail contents/layout to what you see in the received email should give you a rough idea of how things translate from .mail to email?
If you check the MB Releases March 3, 2018 you will see reference to three (3) senors for handling lightning events as provided by Weatherflow AIR station, same as Weatherflow Tempest then not sure? These three (3) sensors also list under the WiKi Template Sensors section.
As with any Sensor combine with appropriate Selector/s and add to .mail template.
If all else fails then might need a Weatherflow Tempest with specific Sensor/Selector knowledge relative to the Tempest?