Please answer the following question: Given the following passage  "In 1816 Byron, Percy Bysshe Shelley and his wife Mary Shelley visited Geneva and all three were inspired by the scenery in their writings. During these visits Shelley wrote the poem "Mont Blanc", Byron wrote "The Prisoner of Chillon" and the dramatic poem Manfred, and Mary Shelley, who found the scenery overwhelming, conceived the idea for the novel Frankenstein in her villa on the shores of Lake Geneva in the midst of a thunderstorm. When Coleridge travelled to Chamonix, he declaimed, in defiance of Shelley, who had signed himself "Atheos" in the guestbook of the Hotel de Londres near Montenvers, "Who would be, who could be an atheist in this valley of wonders". By the mid-19th century scientists began to arrive en masse to study the geology and ecology of the region.",  answer the following question. Note that the answer is present within the text.  Question: What was happening when Mary Shelley thought of Frankenstein?
A:
thunderstorm