Cool weather loving sweet potatoes?

Hi!

Does anyone know of a sweet potato variety that can grow in cooler climates? I'm at nearly 8,000 ft elevation, with a short warmish growing season, (85F day time highs with 60-50F night lows during a 3-4 month growing season.

I want to grow sweet potatoes in addition to white potatoes because the tubers and the leaves are edible equaling more food/nutritional value for the effort...