Thunderstorms — Page 269, Lesson 250

I want to walk you through the use of lightning discharge monitors for thunderstorm avoidance. This is a separate tool from airborne weather radar, but the core principle is the same: these instruments are for storm avoidance, not for flying through storms or over them. Let’s start with the basic principle. Instruments exist that can indicate and record lightning discharges. They work because, inside a mature thunderstorm, air turbulence has rearranged the normal distribution of charged particles. This creates large buildups of electrical charge. Lightning is the discharge that dissipates those buildups. The equipment detects these lightning discharges and normally shows them on a screen, with the centre of the screen representing the aircraft’s position. Now, here’s a critical point about interpreting that display. The distance of the lightning symbol from the centre of the screen is not the actual range of the discharge from your aircraft. Instead, it is an indication of the strength of the lightning discharge. The equipment calculates where to place the symbol using an algorithm based on the average strength of lightning discharges. So, a very powerful discharge far away could appear at the same distance on the screen as a weak discharge that is actually close to you. You cannot read range directly from the screen position. How do we use this information operationally? Because lightning is more likely to be associated with the most severe turbulence, an area showing frequent discharges in a particular direction should be avoided. However, there is a dangerous exception. The first lightning discharges from a recently formed cell — one where no discharges have been evident beforehand — may be particularly strong, or violent. This means that the lack of any indication of a discharge is no guarantee that lightning will not strike. A cell can be building up charge silently and then produce a very powerful first strike. One particular manufacturer gives a specific recommendation for pilots using their equipment: you should manoeuvre your aircraft so that all clusters of lightning discharges are kept at least 25 nautical miles away. So, to summarise the key takeaways: lightning monitors are for avoidance, not penetration. The displayed position indicates discharge strength, not range. Frequent discharges mean severe turbulence and should be avoided. And a lack of discharges does not mean a cell is safe — the first strike from a new cell can be especially violent.