Snow Q&A: Things will get worse before they get better

Q&A: Expect no relief until the weekend when floods from melting snow could arise

The National Emergency Co-Ordination Group for Severe Weather has asked the public in Leinster and Munster to stay indoors from 4pm on Thursday until noon on Friday and to monitor further updates from Met Éireann. Video: Merrion Street

 

Was this worse than predicted so far?

No, it was always expected and clearly communicated that there would be snow starting Tuesday evening and that is what happened. It was also stated that snow amounts would vary as they arose from bands of snow showers. Dumb luck has the snow impact maximised in Dublin and the surrounding commuter-belt regions.

Is it harder as a rule to predict snowfall events?

Snowfall totals are much harder to predict. Snow is much less dense than water. When the 10cms or so lying outside my window as I type this melts it will yield a water equivalent of only a few millimetres. When a rainfall forecast is out by a few mm nobody much notices or cares. That error gets magnified 10-fold when falling as snow and not rain (a rule of thumb is 1mm of rain is equivalent to 10mm of snow).

It is one of several reasons why accurately forecasting snow and its impacts is much trickier.

Will it get colder and snowier still?

The coldest air in the entire outbreak will be overhead tonight, so it’ll get a little worse before it starts getting better.

It is going to take temperatures warming up and staying above freezing to appreciably improve the situation in the worst impacted areas. Latest indications are that this shall likely occur at some point over the weekend. How this will occur is still not entirely clear so regular recourse to the latest guidance is advised.

What will happen when its over?

It is likely to be a slushy mess during the transition to warmer weather. But even when it melts the impacts may not be over. Some of the biggest historical flood events in Ireland have occurred with rapid thaw of snow cover together with rain. People at risk of river flooding should be starting to think about possible impacts at this point.

Once its gone is there a threat it’ll return?

The current indications are that in the next ten days or so we’ll see a return to the normal order with westerlies winning out again, but it’s unclear exactly when and also how messy the transition will be. You should keep up to date with the latest guidance from Met Éireann.

Does this have any ramifications for the coming spring and summer?

It is unlikely that the current event markedly changes what will happen this coming spring and summer. It will delay the onset of the growing season but beyond that this is not, in any sense, a portent of the kind of spring or summer we can expect.

What about impacts outside Ireland?

Europe is also shivering along with us. But, on the flip side, the northernmost weather station in the world in Greenland has seen a huge record set in number of days above freezing in February (in perpetual darkness). Moreover, areas of the Arctic Ocean north of Greenland and between Russia and Alaska are ice-free which is unprecedented in the period for which we have records.

These events are all linked. We may be cold, but other regions are unusually warm. The Northern Hemisphere as a whole is very warm right now even as our corner of it shivers.

Why is this month so strange?

It all started several weeks ago 50km or so up in the atmosphere above the Arctic. The winds suddenly switched and the atmosphere warmed tremendously. Ever since this stratospheric warming event meteorologists have been watching its progression down to the surface.

Such events typically occur once or twice a year, but they don’t always reach the surface. Even if they do, they don’t always impact Europe. The sudden stratospheric warming was particularly marked this year.

So meteorologists suspected this may happen for some weeks?

Indeed. Since mid-January when the sudden stratospheric warming was forecast meteorologists, including Met Éireann, have been primed for the increased likelihood of this event. With such predictability it has been possible to prepare in the best way possible and minimise impacts.

Given that knowledge, did the authorities properly prepare for this event?

These type of events are very rare. It’s why we reach to events in 1982, 1962/3 and 1947 for analogies. We could buy a huge amount of snow clearing / management infrastructure but is that a sensible use of finite resources the Government could spend on a raft of other issues?

We could buy equipment next week which would be obsolete by the next time it is ever needed.

Preparation in this case can also simply be ensuring supplies to hospitals, schools closed in an orderly fashion, and public transport impacts minimised. We can never truly isolate ourselves from the impacts of extreme weather. To some extent we have to roll with the punches.

* Peter Thorne is Professor of Physical Geography (Climate Science) at Maynooth University