The paper reports the assessment of the spatiotemporal trends of climatic changes favoring the spread of West Nile fever (WNF) in the southern part of the European Russia. Data from 58 meteorological stations (1997–2018) and ERA-Interim reanalysis data (1981–2018) were used. The degree-day method was employed to assess whether the climatic conditions favor the spread of the West Nile virus (WNV). As a result an increase in the sum of the effective temperatures (ETs) was demonstrated. No increase in the length of the efficient infectivity season was observed. A coincidence of the trends of ET sum growth and the increase in the average air temperature for the epidemic season was noted. This creates favorable conditions for virus development in mosquitoes, because virus circulation becomes more efficient with an increase in ET. The most favorable temperature conditions for WNV form in the Caspian Sea region and the Ciscaucasia, where WNV circulation conditions are further improved due to an increase in the total ET. conditions favoring WNV transmission form more rapidly in the central part of European Russia than in the Cis-Ural region, which may cause further spread of WNF in this region.