In June 2024 extremely hot weather was observed in Southeast Europe and the Eastern Mediterranean. Based on ensemble seasonal forecasts of the INM RAS Earth system model (INMCM6M), that is run operationally at the Hydrometeorological Research Center of Russia for monthly calculation of global seasonal forecasts, the prediction of tropospheric temperature anomalies in this region is studied. Obtained results show that, among the causes of this heatwave, the most important role was played by the reduced accumulation of soil moisture during the preceding months and the reduced cooling of the lower troposphere due to evaporation stress. The analysis of observational data indicates the increased (especially in the first half of June 2024) meridional transport of warm air masses along the western edge of the heatwave region towards the central Volga region and the north-east of European Russia (north-westward of Ural Mountains). Model experiments allow to conclude, that the meridional transport of air masses from the warmer region to the north, rather than particularly extreme warming in the Eastern Mediterranean, led to the formation of a region of positive temperature anomalies in the north-east of European Russia.