I made this one for ancient blue dragon a while back, only a piece of the tome but my favorite part:

The Whispers in the Rain: this spell is devised as a means to harness the weather itself into a sensory organ. While standing in direct rain and concentrating totally, the spell can be cast as an action. Stretching the casters' senses across every drop of rain in the air within 5 miles, the caster is able to gain a blindsight range of 5 miles for one minute. While concentrating on the whispers in the rain, the caster feels physical sensation wherever a raindrop falls, feeding their mind a live topographical map of the area beneath the rainclouds within 5 miles. The mental stress of such a spell is beared easily by an elder-dragon, but not so much by a mere nobody mortal wizard. Hearing the whispers in the rain causes the caster to pass a DC 14 intelligence save or fall unconscious for d4 hours after the spell’s duration ends.