Winter 2017-18: Discussion

sryanbruen wrote: »

GFS hinting at something big developing in the stratosphere, could develop by January:

sryanbruen wrote: »

Sudden stratospheric warming is an ongoing theory Oneiric 3, it was only made in late 2012 and early 2013 during the January 2013 SSW. A stratospheric warming is where temperatures in the stratosphere rise high very fast and extremely so in a short period of time. However, for a sudden stratospheric warming to be considered, it has to obliterate the Polar Vortex or reverse the zonal westerlies. It is a very strict definition. According to scientists who had discovered this theory, the effects of SSW on the North Pole do not propagate down into the troposphere (where weather occurs obviously) until at least two weeks after the SSW. However, the effects can take up to 2-3 months to take place also. That's not to say we'll always get cold in our favour though because the blocking caused by the SSW could end up on the wrong side of the Arctic Circle like eastern Europe, Siberia, North America etc blowing up the Polar Jet for us.

You are correct with saying most Winters tend to have a SSW event but it was a much more frequent event in the 20th century than the 21st century so far - which shouldn't be to no surprise given the limited amount of cold Winters in this century and the theory of SSW.

Since 2010/11, there have been two SSW events, January 2013 and March 2016. January 2013 was easily the most severe SSW event for quite some time as it obliterated the Polar Vortex. Any mild was rather short lived and the Winter was cold overall in spite of a rather mild December - and in some places, a rather mild January too.

January 2017 was initially regarded as an extremely weak SSW but due to how weak it was, it was then reconsidered as a failed SSW. Of course, we received the (very disappointing) February easterly two weeks after it occurred.

SSW events in different months tend to play out different conditions for our Winter interestingly enough. November, January and February SSW events tend to be good for cold Winters whilst December SSW events on the other hand do not. I do not know why this is the case at all.

If a cold spell is already occurring before a SSW event however, the SSW can ruin the cold spell and bring much milder weather. This is a rare occurrence though. February 2009 was such an example.

Good examples of SSW events and cold spells following them:

• January 2013 (February was a cold month but nothing impressive, March was one of the coldest on record with a record breaking March -AO)
• January 2006 (late February and early March cold snap)
• February 2001 (late February and early March snow/cold)
• February 1981 (April blizzards)
• November 1962 (Winter 1962/63 - coldest of the 20th century)

However, as I said, this is an ongoing theory and still requires quite a bit of research.

You can check out all the SSW events that occurred since 1950/51 in my Winter methodology tables in the Irish Weather Statistics thread.

sryanbruen wrote: »

Yes they do - as you saw from previous signs of the stratosphere warming on the GFS that I've posted before hand which had disappeared. This one is much more significant but it's still a long way into the FI range.

nagdefy wrote: »

From a personal point of view possible largest snowfall since 31st March 2010.

Calibos wrote: »

I'll believe it when I see it. I remember Dec 09 there was a frontal snow situation that seemed to be nailed down. Instead it lashed rain for 48 hours straight. Had that been snow it would have been a 1982 beater.

Donegal Storm wrote: »

It'll almost certainly be rain in the southern half of the country, too early to tell whether the north will be affected. Current guidance showing snow over Ulster but I can't recall a single Atlantic battleground snow event in my lifetime so naturally I'm a bit skeptical

Meteorite58 wrote: »

Wow that is cold !