March to June nd October to February is best time to Visit Spiti valley. You should avoid monsoon time (July-August) Season. As This area is prone Landslides.
Spiti Valley temperature in August varies from 15° Celsius to 4° Celsius Spiti Weather during August is not that bad, as the valley lies in the rain shadow area and sees little to no rainfall. But the roads leading up to the valley, especially those in Manali and Kinnaur, are extremely dangerous due to the volatile rains these regions experience in August.
You can Visit Spiti Valley in All Seasons
in Winter (November to March)
you will Witness Snow Covered Mountains in Summer (March to October)
You will witness Greenery Beautiful Landscape Lots Of Waterfall in spiti Valley