The fourth 節気 “sekki” division of the traditional Japanese calendar is:
vernal equinox, spring equinox
The third and final “kō” microseason within this division is:
(かみなり すなわち こえ を はっす)
“kaminari sunawachi koe o hassu”
That makes 雷乃発声 the twelfth microseason of the year!
It typically lasts 31 March~4 April.
This is #12 in a regular subseries of 365 Days of Japanese, where every five or six days I post about a Japanese microseason that has begun around the same date as the entry. I am taking all information from the list of 72 in this article. There is also a 36 microseason list here, which may be more authentic (rather than being based primarily on Chinese sources).
Image credit: iWeather.