Sometimes you can see on the world map what looks to be lightning. In the following screenshot you can see it above the word ZOOM, about half way to the cursor embedded in the image.
I am wondering if Asobo hasn’t set a max limit to the number of discharges per unit time. If you watch the world map, and you see the lightning discharges, you’ll see that it often does dozens of discharges in the same location all at one time. My theory is that all or most of the likely lightning strikes that you might see during your session are being ‘used up’ (max count reached) before you ever even get into the actual sim and that’s why seeing lightning in game seems so rare. Its just my theory though and I have no idea how Asobo actually handle lightning.