THE TYPE OF weather event that caused the ‘Beast from the East’ five years ago may potentially bring snow to Ireland in late February or early March.
A sudden stratospheric warming (SSW) event, which occurs when temperatures rise rapidly in the stratosphere well above the earth’s surface, is capable of causing a spell of cold weather in northern Europe.
In February 2018, a SSW event combined with Storm Emma brought heavy snow and cold winds across the country. Temperatures dropped below zero, reaching nearly -10 degrees Celsius, while snowfall reached heights up to 60cm.
Sudden stratospheric warming was also responsible for the ‘Big Freeze’ in December 2010, which brought significant disruption to day-to-day life.
Now, a major SSW event is forecast to occur over the next week, with around two or three weeks of lag time before the impact would be felt in Ireland.
Met Éireann Climatologist Paul Moore explained that major SSW events increase the chances of cold weather but don’t guarantee it.
In a statement, Moore said that global weather models “can usually forecast, quite accurately, what is going to happen in the polar stratosphere 1-2 weeks in advance, so the upcoming SSW event is highly likely”.
“Forecasting how a SSW event imprints on the tropospheric weather patterns below is much more difficult to resolve, especially prior to the SSW event itself,” he outlined.
“Therefore, for now, it is unresolved how the upcoming SSW event will affect the weather patterns over north-western Europe. The timing for any impacts, if they do occur, will likely be towards the end of February or the beginning of March.”
Up in the air
Meteorologists in Ireland, the UK and elsewhere in Europe are closely monitoring the situation.
The UK Met Office expects there is more than an 80% chance of a major SSW event occurring.
Paul Moore of Met Éireann explained that the SSW event occurs “where the zonal winds at the 10hPa level (approximately 30km high) and at 60° North reverse from westerly to easterly and the temperatures in the stratosphere over polar regions rise significantly in just a few days”.
“It usually takes 2-3 weeks for a major SSW event to have an effect on the tropospheric circulation below because it takes time for the easterly zonal winds to descend through the stratosphere,” he said.
He outlined that every SSW event is different and not all of them disrupt tropospheric patterns, pointing to an SSW event in January 2019 that did not affect the weather patterns over north-western Europe.
The SSW event in February 2018, however, caused “major disruption to the tropospheric patterns below and led directly to the colder than average temperatures in Ireland during February and March 2018, including the very cold outbreak from the east culminating with storm Emma at the end of February and beginning of March 2018″.
Meanwhile, the weather forecast over the coming days is mostly mild with some patches of rain.
Tomorrow is due to be “rather dull” in the morning with low clouds and spots of drizzle but brighten up later in the day, with highest temperatures of 9 to 11 degrees Celsius.
Sunday will bring a “cloudy morning with some drizzle in place, becoming mainly dry for the afternoon”, Met Éireann forecasts, while Monday will be “dry with a mix of cloud and sunny spells for most, however cloudier conditions with a little drizzle may affect easter and southern counties”.