Spain in January

Europe's a big place.

Barcelona in January - if you are lucky, bright days, 15-16 degs, chilly nights.
Always a change of rain.

We were in Barcelona for Christmas last year. Yes - December, not January - but! Probably close in terms of weather, which was shirtsleeves weather for me. My husband needed a light windbreaker.

Crowds were not nearly as frantic as we thought they would be for Christmas. The city was absolutely lovely. We did not encounter any enraged locals with attack spray bottles.

We tend to do European jaunts in winter (December through March) because I am such a whiny baby when temps get much above 65F. So I will proffer my general opinion for January in Europe and say YAY! It’s amazing!

Fewer tourists shuffling along in tight, clueless clumps.

Fewer self-absorbed teens with selfie sticks hogging space in front of the Trevi Fountain/Eiffel Tower/along Las Ramblas, etc.

Folks in little shops seem more relaxed and convivial, since they’re not fielding quite as immense a horde of visitors.

We love it. Would highly recommend. :-)

My best friend lives in Barcelona and has told me that it stays lively all-year round. There are many things you could consider doing. I went last year beginnings of spring to visit him and really enjoyed the fewer crowds and it is in fact an amazing city to visit. We also took the ferry to Mallorca, and stayed there a couple of days. The climate is milder but still cold (I assume for you it might get even colder). But if you don't mind with that, I think you should go for it. Here https://www.ferryhopper.com/en/ferries/spain/barcelona you might find some good extra info in case you are also interested in taking the ferry to other places from Barcelona like we did and maybe here https://www.barcelona-life.com/barcelona/january specifically for January some things that might be happening. I hope that helps : )

On December 28, 2022, we had lunch outside at Terra Mia on our way to Park Güell. It was lovely out. The sun feels stronger than in the Northeast US where we live. While the days are shorter, the sun sets @an hour later in Barcelona than where we live, and we see that as an advantage.

We were in Barcelona in January.Barcelona is amazing, and it was quite lively even in January. We had sunny, 55 F days, no rain. Be aware they celebrate Epiphany. It is a national holiday. We were warned that some places would be closed, but we didn't have an issue finding places to eat. There were activites at Plaça Catalunya and lots of festive lighting in the city. Tourist sites were still busy and we needed to reserve tickets at Park Guell, Sagrada Familia and Casa Mila.

As a useful info, and maybe except on Christmas Day and New Year´s, when it´s a vacation day in Spain all bars and restaurants are very, very open and it´s normally a huge business day for them. Not only the "aperitivo" before lunch (lunch is the very main meal of the day, not dinner), but lunch and the "sobremesa" (that time after lunch when we sit for a couple of hours at the table, chatting and having our post-lunch drinks).

Thank you for all the helpful replies! I’m thinking about southern Spain now in January. Here is a potential itinerary:
Days 1 Malaga explore beach promenade maybe a boat tour
Day 2 Nerja and Frigiliana
Day 3 Malaga city tour
Day 4 Tarifa with Bolonia beach Roman ruins
Day 5 Tangier
Day 6 Seville City tour
Day 7 hiking in Grazalema or Caminito Del Rey

Let me know any thoughts! Thanks again!

I imagine you are planning to rent a car.
Grazalema could be chilly, I'd spend that day in Sevilla
This was our January trip, but we are slow!
https://community.ricksteves.com/travel-forum/trip-reports/spain-in-january-february-madrid-sevilla-cordoba-toledo-valencia-and-coast-n-s-of-alicante