FYI, the Alamosa weather forcast says there is a 40% chance of rain (thunderstorms) Friday but only a 20% chance Friday night. Probably will be a bit too warm overnight (mid 40s) for morning frost but dew usually hangs around until the sun hits it. North and West facing aspects get direct sun later than East facing slopes, so plan your runs accordingly. Also there is a shop in Alamosa that will rent sand boards the evening before and they only charge for the next day as long as you return them before 6pm the next day. Since neither rental shop opens before 8am any pre-dawn starts would require having everything you might need the night before.
Myself I wear aqua socks because they can get wet crossing the river and they fit in the soft bindings on the sand boards and they protect my toes and heels while boarding. My wife ripped up her toes going barefoot last time so don't make that mistake.
It should be fun, hope you post your videos...