Hi, Sharni,
I hope you will get some first hand information, but a good source for weather forecasts is eltiempo.es Though they don't have a listing for Fuente De, you can check for Potes and Espinama (about 4 kms before Fuente De). Then on the other side of the Picos pass, you can check Portilla de la Reina. All of these places show pretty cold (high 4-8, lows go to 0, -3, -6, all centigrade). Looks like some snow is in the forecast for Thurs, Fri, Sat.
If my memory serves, you still have a month till departure, no? By then, maybe spring will have sprung! Laurie