Why is siberia much colder than western russia?

Siberia is much colder than Western Russia because ocean winds cannot reach Siberia. This wind is warm, which makes Western Russia warmer than Siberia. 

Another factor is that Siberia has huge mountainous region preventing warm air from traveling North while cold Arctic air travels South.  

While winters are rainy, summers are dry. regions with this climate are usually in the eastern part of the continents. they experience hot, humid summers and colder winters. precipitations have a regular distribution throughout the year, but hurricanes are common.