Here's a little something I came up with... criticism would be most helpful:
For centuries, Auril the Frostmaiden has rewarded her most faithful priestesses with a fraction of her divine power. These Chosen would then roam the North, seeking to bring eternal winter to Faerun. Inevitably, each and every one of them would fail, leading to the Frostmaiden’s disappointment. Each Chosen would be magically transported to the massive Temple of Ages in the far north, stripped of her powers, and forever encased in a block of ice as a warning for others to come.
It is the year 1374. The priests of Kossuth the Fire Lord are gathering at the Peaks of Flame, awaiting an ancient prophecy to be fulfilled. This prophecy will stir all of Faerun’s volcanoes to action, making them spew ash and smoke for months and years before finally erupting. The skies will be blackened by smoke, and lava will cover many inhabited areas. By 1380, the year of the Blazing Hand, Faerun will become a much more inhospitable place. Behind all this is the imprisoned slaad lord, Bazim-Gorag the Firebringer, who has spent years learning to manipulate Faerun’s fiery core from his prison.
Ironically, even though the cataclysm will be born of fire, the final effect will be that of winter - as the ash clouds block the sun, the temperature will begin to cool with acidic snows covering the planet’s surface until nothing is left but the wasteland. Auril will have won without any effort on her part.
As the dormant volcanoes began to wake, a series of earthquakes shook the entire planet. While not particularly violent, one of these earthquakes was strong enough to crack the icy walls of Auril’s Temple of Ages, freeing the former Chosen from their prisons. While the priestesses of Auril were never big on teamwork, this time, they realized that banding together will give them the opportunity to get even. In other words, they have to avert the prophecy. And the only way to do that is to discover what is causing volcanic activity and to stop it. So far, the former priestesses have pinpointed the source of this strange magic to northwestern Faerun.
To scour this huge area is no small task, and so the Circle of the Thawed (as the former Chosen are calling themselves) are now manipulating the orcs, frost giants, and other savage humanoids into doing their bidding. In return, they are supplying these creatures with foul rituals and magic items they took from the ruined temple.
They care nothing for the North and will gladly abandon it to the savage orcs after they fullfil their goal. Once they discover the source, they will try to destroy or banish Bazim-Gorag.