time to visit japan for sakura in April

i am planning to visit Tohoku to see sakura within april. when should i arrive in Japan to have the best chance to see them? I've seen Sendai around 13th of april, so would the period between 10 and 23 would be ok? Can I also go to Nikko, the west coast like Niigata and japanese alps? Thank you so much for your advices

Flowering timing in the Tohoku region varies strongly from south to north. The current forecast for some Tohoku locations is published here:
http://www.japan-guide.com/e/e2011.html

I've seen Sendai around 13th of april, so would the period between 10 and 23 would be ok?

It is probably okay for southern Tohoku, but likely too early for northern Tohoku. But nobody can predict it accurately.

Can I also go to Nikko, the west coast like Niigata and japanese alps?

Why not? Whether you will see flowering cherry trees there is a different question. Nikko, for example, is not very famous as a cherry blossom destination, I believe.

thank you Uji, I would like to visit yamagata, niigata and I guess other places in the area to see sakura between the 8th and 20thy of april. Do you have any recommendation for places to visit during this period for sakura? Thank you