This sharp change in temperature, albeit brief, is not unexpected to me. It’s been my experience over the last seven years living in Las Vegas that the summer heat generally begins to fall away the first, second, or third week of September.
And let me assure you that this will be a very welcome change! I do love the hot summers here, but this super hot summer season has been very long-lasting.
The heat came up, then it sustained much longer. Eighty-five degrees will feel slightly cool to some folks here like me who are very well acclimated to the desert environment!