Hi Jay, Spiti Valley temperature in August varies from 15° Celsius to 4° Celsius, and contrary to the popular opinion, it seldom rains. So, don't let yourself fall for the myth because while a lot of other places receive heavy downpour during this month, Spiti usually doesn't. Attached below with my comments you can see few packages offered by Tripoto for hassle free travelling. Please take a look, fill the form and someone will get in touch with you. Thanks!
April to mid-May: At this time, the snow starts to melt. A number of roads are opened too like road from Kaza to Losar. However, road from Kunzum Pass towards Manali open only in the June month. This is the time when reaching Spiti is feasible and a number of adventure enthusiasts make their plans regarding tour to Spiti. This is an ideal time to admire snow-clad mountains and play in the snow. If you do not really mind low tourist count, can stay amid basic facilities and do not mind certain road blockages, you can travel at during these months.