In a park in Fushimi-ku, about 4km from our house, I saw my first Sakura (Cherry Blossom) for this season. Almost a month before the Somei-Yoshino (the most common ones in Japan) come into bloom. This particular Sakura is a Hybrid with Somei-Yoshino and an another kind (which I can't recall at the moment). The colour of these ones is a lot pinker than the Somei-Yoshino.
What makes these blossom so early I don't know. The trees in this park are fairly young and I know the younger Somei-Yoshino blossom maybe a week earlier than older ones, but never so early as this. Other factors like being near sun facing walls or being surrounded by bitumen or concrete also can make the bloom come a little earlier, but these Sakura are in a park with grass.