EXTREME COLD / COLD WAVE
A cold wave is a weather phenomenon that is distinguished by marked cooling of the air, or the invasion of very cold air, over a large area. It can also be a prolonged period of excessively cold weather, which may be accompanied by high winds that cause excessive wind chills, leading to weather that seems even colder than it is. It is marked by a drop of average temperature well above the averages of a region, with effects on human population, crops, properties and services. Cold waves can be preceded or accompanied by significant winter weather events, such as blizzards or ice storms. Other names of a cold wave include cold snap and deep freeze.