I flew to Valladolid (return) from Stansted, UK last Autumn. The flight took off more or less on time but as there was fog in Valladolid we were diverted to Santander airport. Ryanair already had coaches waiting there to transfer us to Valladolid - a journey of over 3 hours! I enjoyed the trip as you first experienced warm sunshine on the coast, then passed through the northern snow-capped mountains before ending up on a very foggy meseta.
I think if you are flying to Valladolid in winter you have to take account of the fact that fog is quite common (and the airport does not have the equipment to allow planes to operate in such fog). Add a possible 4 hours to your journey time. On the other hand, it's such a quiet airport that other types of delay are uncommon. As a point of interest, the bus transfer to the city costs around 3Euros (a taxi ride 20 or less) and a return bus ticket to Madrid (I think) is a little under 20 Euros.
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An English Bookseller in Madrid