Winter 2017-18: Discussion

sryanbruen

Here it goes, the Sudden Stratospheric Warming.

bazlers

Sryanbruen,
From your research of an SSW taking place.
When do you see it's effects hitting Ireland?
(Eg. North, North East, East event taking place)

sryanbruen

bazlers wrote: »

Sryanbruen,
From your research of an SSW taking place.
When do you see it's effects hitting Ireland?
(Eg. North, North East, East event taking place)

I'll make some analogues and a table of historical SSWs, compare CETs/IMTs of months etc to answer that question.

I will hopefully post them later.

Oneiric 3

This day 4 years ago at around this time of day, Storm Darwin made landfall over Ireland:




Analysis at 6pm that evening:

George Sunsnow

https://twitter.com/twoweather/status/963017066008731648

BuilderPlumber

Oneiric 3 wrote: »

This day 4 years ago at around this time of day, Storm Darwin made landfall over Ireland:




Analysis at 6pm that evening:

Remember it well. It was a shortish but very nasty severe storm and the worst I saw since 24/12/1997 (I did not have to wait that long until the next bad storm came which was 16/10/2017 Ophelia). Ophelia lasted a lot longer than the other 2 but what made Darwin different to the other 2 was how late it came. By February, most of the worst of the weather is behind one and Darwin more or less brought 2 full months of exceptionally wet and windy weather to an end. There was one more mild storm 2 days later IIRC and then the weather improved a lot and we had a lovely summer. The last few winters have alternated between a cold, dry and at times snowy one for one year and then a mild, wet and windy one for another year. There were 3 cold ones in a row:

2008-2009: Cold, snowy.
2009-2010: Cold, snowy.
2010-2011: Cold, snowy. Severe cold/snow spell in November and December.

Then, things got mixed:

2011-2012: ordinary, nothing exceptional. Quite a wet one at times.
2012-2013: ordinary, nothing exceptional.
2013-2014: Mild, wet and windy. Severe storm Darwin Feb 12th worst storm since Christmas Eve 1997.
2014-2015: ordinary, nothing exceptional. Cold.
2015-2016: Mild, wet and windy. Lots of storms, nothing as bad as Darwin.
2016-2017: ordinary, nothing exceptional.
2017-2018: A real mixed bag of a winter. Ophelia starts thing off violently and there were further nasty storms but not as bad or as long. Cold and snowy weather has been a recurrent feature too.

It seems since 2013-14, every second winter is windy. Some wind events are more severe than others with Ophelia, Darwin and Christmas Eve 1997 standing out. The length of the winter varies too. This year, you could say it began with Ophelia and is still feeling like winter. Other years, winter may last only December and January with nice weather up until November and things improving by late January or February. Other times, winter can go and come back again later. I remember one year (2012 IIRC) it was feeling summerlike in March and then there was very cold wintry weather for Easter.

sryanbruen

No signs of the zonal winds regaining their speed.

sryanbruen

BBC outlook, wanted to highlight this part of it:

Monday 19 February—Friday 9 March
Increasing risk of cold with snow possible

After mid-month, there continue to be signs from a range of forecasting guidance for a more significant pattern change across Europe. One of the sources that meteorologists are currently monitoring closely is the strength of upper level winds in the stratosphere, which are forecast to weaken considerably from mid-February and could lead to significant consequences for surface weather patterns. In past years when such an event has occurred, it has at times led to a greater incidence of high pressure over northern Europe and vastly reduced the typical westerly air flow that often characterises the European winter. The potential impacts from such a development would be perhaps a greater frequency of cold outbreaks, but such conditions may only begin to occur through the final week or so of February into early March. Wind and rainfall are also expected to be below average with a lack of energetic Atlantic lows crashing into the UK, but should the wind direction swing easterly at times then this would bring the threat of wintry showers from the North Sea.

https://www.bbc.com/weather/outlook

sryanbruen

https://twitter.com/webberweather/status/963098070090240000

ECM forecast for the MJO.

nacho libre

sryanbruen wrote: »

No signs of the zonal winds regaining their speed.

Good news indeed in terms of prolonging any cold outbreak. With that in mind, those hoping for an early spring this year might be a bit disappointed:)

sryanbruen

Here's my table containing previous SSW events since 1962-63 I have been working on this afternoon. The exception being the April 1982 SSW event which I discounted because it was not worth including as a result of it not having much of an effect on us and the fact that I would have to include two separate columns just for that one event. I decided to not include the May mean temperatures either because there are very few March SSW events and well, they don't seem to have much impact on the month like May is a very easterly month regardless of SSW taking place.

The AO and NAO columns are averages for three monthly periods following SSW events. For example, if a SSW occurred in February, the AO/NAO index is averaged for that February, March and April's values into one figure. Or another example, if a SSW occurred in November, the AO/NAO index is averaged for that November, December and January - I had one exception where I included February in this equation (marked with a * on the table); Winter 1968-69. I included February 1969 because it had a very negative AO and NAO index just like the two preceding Winter months, it was also a very cold month. Some seasons, two SSW events occur and where they have done so, I've given two AO/NAO figures on the table.

The IMT and CET columns are of the mean temperatures for those respective months in the self explanatory regions. Irish Mean Temperature is the mean used for Ireland (figures here calculated by me), including Northern Ireland. The CET is for the Central England region and is the oldest dataset in the entire world. The main important mean temperatures in this case of course are those following SSW events. I'd like to put a disclaimer on the February 1985 figure though. As of a recent post looking at charts from this month, I am skeptical of this figure especially seeing how different it is to the CET value which is much colder. I need to recalculate this when I can because it does seem a bit odd given the synoptics and the CET value.

To no surprise, the results are very mixed. Every SSW event is unique, particularly this one that is taking place right now and the 1985 event. I don't have time to go through every one of them sorry but hopefully my table is easy enough to follow so you can analyse yourself with these disclaimers and information.



Here's a reanalysis of Marches following splits of the Polar Vortex - or at least close matches to the 2018 event here. It shows the prospects of northern blocking over Greenland and the Arctic Circle. However, at the same time, it has a very deep trough over the UK and Ireland, centred just to the southwest of England. It would take small adjustments for this to be a very cold 500mb height anomaly chart with the trough being centred that bit more southwards. Each of the Marches in the reanalysis are quite different from each other in some aspects - 1985 being a rather cool and unsettled month, 1979 being very cold and wet, 1991 being mild and wet and 2001 being cold with close to average rainfall. There does seem to be a trend here though in this reanalysis for March to be unsettled and wet with a small chance of it being mild.



This reanalysis is of Marches following Sudden Stratospheric Warming events that occurred in February of that year. This is very similar to the above reanalysis of Marches following PV splits but the low is centred closer over the country and just seems to me like a very wet or unsettled chart. Not particularly mild though either but there are some mild Marches in there as you can see yourself from the mean temperatures in the table above.

nacho libre

There is another warming forecast to take place now after the ssw split of the vortex. If it happens, then that just might shred the vortex completely, or at least ensure it takes longer to reorganise itself. All good in terms of prolonging any blocking.

sryanbruen

So the tables seem to have dramatically turned on the ECM ensembles since this morning with them now firmly going for negative NAO.

sryanbruen

https://twitter.com/judah47/status/963175131941044224

https://twitter.com/fergieweather/status/963173304247967745

Rougies

Some great work there again sryanbruen. Please tell me you're backing up all this data regularly, would be a shame to lose it to a hard drive failure or something.

sryanbruen

Rougies wrote: »

Some great work there again sryanbruen. Please tell me you're backing up all this data regularly, would be a shame to lose it to a hard drive failure or something.

Yes, thank you very much. A few years ago, I had lost some analysis courtesy of a hard drive problem. Fortunately, I have all my analysis kept on different sources whether it's here, Twitter, Dropbox, Google Drive etc.

Stratosphere charts updated to the 12th February. First SSW since March 2016. First Winter SSW since January 2013. First February SSW since February 2010.

sryanbruen

Again, no signs of the zonal winds reversing back today.

sryanbruen

Quite a massive upgrade for negative NAO on the ECM ensembles this morning. They are now showing the prospects of the NAO getting down to -3. We haven't seen that kind of level for NAO since January 2016 and we have to go back to the likes of March 2013 to find a persistent spell of NAO levels that negative. The turning point of the NAO on the ensemble chart is the 20th February so this time next week, albeit the preceding few days show it as neutral levels.

JCX BXC

sryanbruen wrote: »

Again, no signs of the zonal winds reversing back today.

The fact that it's forecast to go outside 2 standard deviation surely shows something major brewing?

sryanbruen

JCX BXC wrote: »

The fact that it's forecast to go outside 2 standard deviation surely shows something major brewing?

Yes, which is what some people are missing the fact of here.

Donegal Storm

JCX BXC wrote: »

The fact that it's forecast to go outside 2 standard deviation surely shows something major brewing?

Mean forecast from next week is high pressure to our north and low pressure in the Azores so that explains the negative NAO.

The orientation of the high will determine what sort of weather we end up with, could be cold easterlies, it could be calm settled weather or as often happens the high could be shunted east and we still end up with an atlantic influence

sryanbruen

In terms of the US setup, it's looking very good for us. Not a chance of the Polar Jet intensifying here for the next week at least including with negative NAO and SSW.

lolie

Bbc weather presenter just mentioned milder next week but could be colder weather on the way later this month.

George Sunsnow

lolie wrote: »

Bbc weather presenter just mentioned milder next week but could be colder weather on the way later this month.

Yeah Chris Falkes
He said ‘there are signs it could turn much colder by the end of the month we’ll keep you updated on that’

joe199

Hopefully it's not to late in the month again the easterly gets going were really cutting it fine

sryanbruen

https://twitter.com/MJVentrice/status/963426022770335744

sryanbruen

Everybody on board the easterly train? Choo choo :P

sryanbruen

Another similarity with 2001, the eastern USA ridge.

https://twitter.com/antmasiello/status/963243739459346432

sryanbruen

STATUS YELLOW

Wind Warning for Ireland
Southerly winds will reach mean speeds of 50 to 60 km/hr with gusts of 90 to 100km/hr. The strongest winds will be in coastal areas.

Issued:Tuesday 13 February 2018 17:00
Valid:Wednesday 14 February 2018 00:01 to Wednesday 14 February 2018 08:00

sryanbruen

Pretty bullish UKMO forecast. Thanks for inspiring me RobertKK to look at it.

UK Outlook for Sunday 18 Feb 2018 to Tuesday 27 Feb 2018:
After a frosty start, Sunday is likely to stay dry and fine for most, especially in England and Wales, but the northwest will be more changeable with further wintry showers. Dry and bright weather will predominate in England and Wales throughout next week, with a greater than average chance of overnight frost. Light rain or drizzle is possible at times, mainly in north and west Scotland and perhaps Northern Ireland. Temperatures at the start of next week will be around average for the time of year, but there will be a trend toward colder weather by the end of the week and into the start of the following week, as prevailing winds turn easterly. Where this happens, wintry showers may develop near the east coast.

UK Outlook for Wednesday 28 Feb 2018 to Wednesday 14 Mar 2018:
As we move into the first week of March, it is likely to stay cold but often dry and settled with widespread overnight frost. There will be a greater chance than usual of easterly winds, which would bring very cold weather at times and the potential for some snowfall in eastern and even southern parts. In the second week of March there are indications that it may eventually become more unsettled and less cold, with the wettest weather and mildest temperatures likely to be in the south or the southwest of the UK.