Studying the potential for a 'Beast From The East' event in Ireland

You may hear the terms Polar Vortex (PV), PV split and Sudden Stratospheric Warming (SSW) mentioned over the coming days in relation to goings on in the stratosphere above the North Pole.

You will also come across online news articles and Twitter posts confidently suggesting stating that the 'B***t from the East' is imminent.

In short, the BFTE is not imminent, but weather models are hinting that the building blocks that produce such an outcome could materialise in around 2 weeks days from now with a potential cold spell impacting somewhere in the mid-latitudes, which includes Ireland, in early March.

It really is a case of ‘ifs, buts and maybes’ this far out. To Beast or not to Beast? That is the question.

About those building blocks.

The PV is a band of strong westerly winds that forms in the stratosphere between about 10km and 50km miles above the North Pole every winter.

When the vortex weakens, shifts, or splits, the polar jet stream often becomes extremely wavy, allowing warm air to flood into the Arctic and polar air to flood south.

A SSW refers to a swift jump in polar stratospheric temperatures. The warming is preceded by a slowing then reversal of the westerly winds in PV.

See the first graphic.

Such disruptions of the PV can lead to extreme cold air outbreaks in the mid-latitudes, in place like Eurasia, Europe and the United States. It should be noted that despite there being an estimated 25 major SSW events during the past 40 years, a relatively small number have led to a BFTE outcome in Ireland.

For example, a major SSW around February 10th, 2018, produced the infamous Beast From The East of late February and early March that year. A SSW in January 2019 had little impact on Ireland's weather, which, in fact, remained relatively mild for the rest of the meteorological winter. Another SSW in January 2021 produced cold conditions in Ireland and Britain, but it was much less severe that the 2018 outcome.

Back to what is happening in winter 2024-25 and, more importantly, between 10km and 50km above the North Pole. Right now, the PV is rather stable but models like the ECMWF and GFS indicate that a warming of the stratosphere will commence later next week and just about pull off a PV split in approximately two weeks, sending two lobes of cold air south into the mid latitudes. There is limited support for a Major SSW but growing support for a minor SSW. See animation below.

The ECMWF is more resolute on producing a definitive PV split as the next image shows.

This is one to watch and the outcome is far from certain. Models struggle with forecasts beyond 3-5 days out, never mind two weeks out. Furthermore, should the ECMWF output verify in two weeks, it will take another 2.5 to 3 weeks for the impact of PV split and any accompanying SSW to be felt in the mid-latitudes.

Stories about an imminent ‘Beast From The East just like 2018’ will be pushed at you over the coming days by your neighbours and friends who will parrot what they have read on social media or elsewhere online. The truth is that there is a small possibility of such an outcome in early March (there goes spring if it comes off). However, there is far more unknowns than knowns due to the uncertainties surrounding long range forecasting.

BFTE talk is akin to the Chinese whispers surrounding your local sports team who are supposedly “flying it in training”. We all need to wait and see for ourselves should Championship Day (SSW / PV split) eventually come around. Images c/o ECMWF, Meteociel, UKMO, NOAA.