what parameters you used to predict the bloom dates of sakura.

The Sakura blossoms are dependant on the wind, rain, and temperature, which can make the blossoms appear either earlier or later than average and can lengthen or shorten the blooming season, making the cherry blossom forecast vary a little every year.
Blooming typically occurs between late March and early April throughout most of Japan. The regions with the milder winter climate usually produce earlier bloomer trees because it needs to be cold and then get warm for the trees to understand it is spring and start blooming.

You can check about the cherry blososm forecast here:
https://planetyze.com/en/japan/tokyo/blog/sakura-cherry-blossom-forecast-2018
it says that the Estimated best viewing periods by Planetyze based on data collected in previous years, especially 2016 and 2017, by the Japan Weather Association.