As IWO reported on Monday, Ireland
is on course for a period of much colder weather from Sunday through
the early days of next week with potential for disruptive snowfall in
the eastern half of Ireland in particular.
Cold air
will be drawn in from the Eurasian landmass, bringing cold conditions
across Ireland with snowfall for Leinster, east and north Ulster and
east Munster in particular. This evening's model output suggests a
return to milder conditions from the Atlantic on Thursday which could be
preceded by more extensive snowfall for a time before precipitation
turns back to rain in all but the far northeast.
Since early
January, headline writers across Ireland and the UK have made numerous
mentions of the ‘Beast from the East’ and how it could be set to return
to our shores for the first time since the epic snowfalls of February
2018. These predictions came after the Sudden Stratospheric Warming (SSW) event of early January. However, as iWeather Online indicated on 15th January,
a SSW does not always mean we will be shovelling snow off our driveways
two weeks later. The swift jump in temperatures in the stratosphere
over polar regions can often take many weeks to impact our weather. In
fact, history tells us that less than half of all SSWs lead to an
outbreak of severe cold weather here.
So, is the 'Beast from the East' on the way?
If
current computer model output for Sunday into the early days of next
week verifies, then we would be looking at subzero temperatures at night
and daytime temperatures struggling to get above freezing. The finer
details of this cold spell have yet to be determined but
present indications that significant snowfall is possible in Leinster,
east and north Ulster and east Munster. Western counties would be drier with good sunny spells at times but extremely low overnight temperatures. The trend is your friend in the
forecasting world and right now, the output is trending towards a
period of significantly cold weather from this weekend.
Will it snow in my back garden?
Forecasting
snow totals at this range would be a fool’s errand but in a
north-easterly to easterly setup east and north Ulster, Leinster, and
east Munster would be favoured. Due to a strong easterly breeze some shower activity may result in
snowfall further inland, including in eastern parts of Connacht. Snowfall down to sea level is expected
from Monday with a sleety mix likely at lower levels on Sunday.
Tonight's model output would give rise to streamer activity which that
brought heavy snow to the eastern half of Ireland in particular during
2010. Streamers are lines of showers
that form over a body of water and align themselves with the wind-flow,
bringing a constant "stream" of showers over a certain area. They are
also known as Sea or Lake Effect showers, as they are a common
wintertime occurrence near the Great Lakes region of the USA. In Ireland
they generally form over the Irish Sea and affect north and
east-facing coastal regions of Leinster and eastern Ulster. Snowfall
totals can vary greatly from one location to another even in a
relatively small geographical area, as was witnessed in 2010 and again
in 2018.
How long will the cold spell last?
Current
indications are that colder conditions will extend from the northwest
on Thursday night into Friday. Conditions will get progressively colder
during the weekend as the coldest air reaches the east coast later on
Sunday bringing heavy and frequent snow showers. A transition to milder
weather is currently earmarked for Thursday but we will keep an eye on
this over the coming days.
What Met Éireann Says
Met Éireann's Gerry Murphy says, "We will have very cold weather for Sunday, Monday, Tuesday and
Wednesday. The winds will feed in showers over the eastern half of the
country and those showers will be of sleet and snow. As the cold weather persists, each day and each night will be
colder. The showers will become wintery. A fair few of those are likely
to be of snow from Sunday into Wednesday.”
Speaking to The Irish Times, the forecaster cautioned that it was too early to “pin down a number” as to how many centimetres of snow will fall.
“That’s
why we have said there will be significant accumulations, but it will
be more than a few centimetres,” he stated. “I don’t want to put amounts
because it is only going to frighten people at this stage. I can’t give
an exact figure."
The UK Met Office
says, “Although amounts of snow across England are likely to be less
than seen across Scotland, the potential is there for some heavy snow
across eastern England later in the weekend, and perhaps elsewhere in
southern Britain as we head into next week, with very cold easterly
winds.”
Mark for IWO.
USEFUL LINKS:
Sea Effect Showers ("Streamers") Explained
How Snow Is Formed
The Isle Of Man Shadow
Find out what altitude you live at here
Satellite & Radar