Hardening is the bio-physiological process whereby winter cereals become tolerant of low temperatures, which allows them to withstand the freezing conditions that occur during their winter dormancy period. Our model simulations indicate no or weak frost tolerance in most of the EU, except for some parts of Finland, Sweden and the Baltic States, as well as in a few spots in southern Germany, the Czech Republic, Slovakia and eastern Poland, where the winter crops are in a partial or advanced hardening state. In a wide area around the North, Baltic and Black Seas hardening is delayed, as the process began only in late November. In addition, in several regions dehardening also occurred because of the warmer-than-usual weather conditions. The situation improved in the first half December, but the hardening of winter cereals is still considerably delayed. The current situation is delicate, as a cold air intrusion could cause considerable frost-kill damage in the areas that do not have an adequate depth of snow cover and have winter crops with low frost tolerance. In Belarus, northern and western Ukraine, winter wheat is only partially hardened. Further eastwards, such as in the northern parts of the Central Okrug and most of the Near Volga Okrug in Russia winter cereals have reached advanced hardening or have almost achieved maximal frost tolerance. At the same time, winter wheat is still only partially or slightly hardened in western and central Turkey and southern regions of Russia, as well as in central and southern Ukraine. Due to the absence of damaging low temperatures, frost kill has been very limited so far. Local frost-kill events have been simulated in some spots in southern Russia. Taking into consideration the latest weather forecast, an increase in hardening is probable in central, northern and eastern regions of Europe. No frost kill is expected over the coming days. 

Source - https://ec.europa.eu