In March in Barcelona you can really tell you are leaving behind Winter, maybe is not so much the temperatures, as they are not completly warm they go from 45 º F at night to to 64º F in the midle of the day (from 8 to 18 in Celsius), but more because of the lenght of the day, we have many more hours of light than in Winter.
Also we have in March funny activities, maybe they are not a enough reason to visit Barcelona but if you are already in the city in those days it is a good oportunity to see local traditions.
On the 3rd of March there is a popular parade with horses, charriots and floats in Honor of Sant Medir (Saint Emetherius), since 1828, year in which a bakerman that was cured of an illness thanks to this saint, decided to go in procession to Sant Medir hermitage up in the hills north of Barcelona, every year that day there is this popular parade, 6 tones of candy are thrown to people who go to see it.
For me one of the nicest tradition in Barcelona is the one that takes place on the week end of 11-12 of March (Rally Internacional de Coches de Época Barcelona – Sitges – Página oficial (rallybarcelonasitges.com), that day more tan 60 owners of vintage cars (before 1926) get together in a set place in Barcelona to go to Sitges which is a coastal village 35 kilometers south of the city, they drive on a bending road along the sea and they must be dressed as in the old times as they will have an “elegance contest”. On Monday they also go together to visit an emblematic catalan site. Even if you are not here that week end, from the 3rd to 21st of March you can see 6 of those cars exhibited in a popular shopping center in Barcelona.
Then in March there is one event related to beer. This is not really a catalan tradition, but it so happens that Barcelona is full with Irish pubs, so in Saint Patick day (17th of March) there are little parties in all those pubs.
And for the sweet-toothed, here in Catalonia and its capital, Barcelona, all the festivities have a tipical sweet product, this month, the 19th, is Saint Joseph, the father’s day in Spain, so it is the month of the “buñuelos”, a fried, round, soft bred dought with sugar on top or cream inside that you can find in all the bakeries and in many supermarkets too.