Name the biome that has cold winters, warm summers, moderate
seasonal precipitation, fertile soils and occasional wildfires.

Temperate Grasslands!

Explanation:

Mild prairies have sweltering summers and cold winters. Precipitation is moderate. The measure of yearly precipitation impacts the stature of field vegetation, with taller grasses in wetter districts. As within the savanna, regular time of year and infrequent flames are imperative to biodiversity.

So based on the description you have gave me, the temperate grasslands matches what you asked for!