Might have been less fun if it had been in the depths of winter. The fact that it was a balmy sunny day in springtime made it a pleasantly novel experience, I agree. Of course, the "sunny day" seems to have been correlated.
From pleasants 20-25C to -30C in some peaks. Castilles? Snow for granted. The north? Chilly as hell. Not snowy, but the humidity fro the Atlantic will make you feel cooler than the Castilles themselves even if freezing.
Can be hard, and NOT just because of Filomena. Not all Spain it's a Mediterranean beach, trust me. Some winters in Leon can be harder than the average Winter in Poland.
How hard a Winter can be? Pick a height map of Spain... and you will deduce something by yourself.
Spain is more than Barcelona or Valencia. Both the North and the inner part of the country can have crude winters, specially in the mountains. The temperatures range between -22 and 116 Fahrenheit depending on the location. For comparison, Chicago minimum is -25 F, so even if the mean is lower there, some places can be still very cold. Is one of the most diverse countries in Europe.
TL:DR Spain is not just Andalusia, and the US is not just Texas.
Spain is like a condensed minigame map of the US. Remember when the Morrowind videogame looked megadiverse because of the mountains generating lots of different terrains and curves? That's Spain. You cross a mountain tunnel by car and your warm 28C degrees in May at Leon somehow shifted to a cloudy, gray sky with 15 degrees in Asturias in -literally, measured by clock- ~10 minutes.
You would think that you where somehow abducted and teleported from a UFO in the road. But no, it's just the rough nature.
And the Winters in Leon are bipolar being a dry, continental climate. So you can have scorching summers... and freezing winters with -10 degrees with ease.
So, yes, Winters outside the Mediterranean sea can be rough.