The artifact came to me from an obscure secondhand shop in Deep Ellum in 1987; I do not recall the name, and have never been able to locate the place again. To all appearances, it is a perfectly ordinary (if slightly antiquated) umbrella, save for the motto which is etched into the handle: Dimitto procellis. It was that bit of writing that caught my eye and roused my curiosity; it was that inscription which eventually revealed the true nature of the device.
The first documented use of the umbrella was by Samuel Mathers in 1878. Mathers was one of the founders of the Hermetic Order of the Golden Dawn, and claimed to have created artifact himself. Other accounts dispute this, however, claiming that the umbrella is actually a relic of ancient Atlantis, which Mathers somehow rediscovered and claimed for his own.
The primary use of the umbrella is, of course, to keep the rain off. What distinguishes it from an ordinary umbrella is that instead of shielding the user from the rain, the presence of the umbrella acts as a talisman that actively prevents the rain from falling. For so long as I have the umbrella with me, it simply doesn't rain. There is, however, a price: the moment I leave the umbrella behind, the skies will immediately open up with a heavy rain.
Certain fragmentary parchments, when properly translated, hint that this was how Atlantis was destroyed. The umbrella was carried by the high priest, to guarantee fine weather for the entire land. Each high priest passed the umbrella, along with his title and certain other, unnamed regalia, to his successor. Thus was the umbrella carried by an unbroken line of high priests for nearly eight centuries. Then, one fateful morning, the current high priest (now remembered only as Ashavor The Dimwit) accidentally left the umbrella in his chambers. The rains began before he could return, and that was it for Atlantis...