Snow in December 2017.
Met Éireann says the looming Siberian temperature crash and snow that will hit Ireland in the first week of Spring is a type of weather system that could last for weeks.
The forecaster has warned that such a so-called Sudden Stratospheric Warning' (SSW) event in January 2013 led to a very cold month of March that year with some significant snowfall.
The Met Éireann report for March 2013 said that almost all weather stations reported the coldest March since their station records began. Dublin Airport recorded the the lowest mean temperature for March since station records began in 1942. The lowest mean minimum temperature for the entire month at the airport was just above freezing.
Met Éireann says the type of system that is set to take hold can remain in place for several days or even weeks, causing the areas affected by them to have the same kind of weather for an extended period of time.
The forecaster has tweeted that a SSW is a factor in the arrival of the Siberian weather which is already the subject of week long Yellow Weather warning which could be upgraded to Red depending on how the weather front develops. READ MORE HERE
Met Éireann says SSW of the atmosphere refers to a rapid jump in temperatures in the stratosphere, the layer of the atmosphere extending from approximately 10 km to 50 km above the ground, which can then lead to the onset of cold weather in winter for the mid-latitudes. This rapid stratospheric warming (which can be up to about 50 degrees Celsius in a couple of days) is triggered by a disruption of the normal westerly flow by natural weather patterns or other disturbances in the lower atmosphere.
This disruption leads to a 'wobbling' of the jet stream. As these 'wobbles' or waves break, they can be strong enough to weaken or even reverse the westerly winds thus leading to easterlies.
Met Éireann says the easterly winds in the stratosphere eventually sink to the lowest layer of the atmosphere. This can alter weather patterns in the northern hemisphere by weakening and displacing very cold air around the north pole.
This in turn pushes the jet stream further south leading to the development of a blocking high pressure system at higher latitudes.
"Blocking highs can remain in place for several days or even weeks, causing the areas affected by them to have the same kind of weather for an extended period of time.
"If these blocking highs become established over Scandinavia or Greenland, such a synoptic pattern can lead to bitterly cold air from eastern Europe/Russia pushing in over Ireland.
"A SSW event in January 2013 led to a very cold month of March and some significant snowfall accumulations," said the forecaster," says Met Éireann.