Winter 2018/2019 - General Discussion

Billcarson wrote: »

Hope ecm is right and we at least get a few frosts next week with sunny days. Dec 2018 one to forget.

Clonmel1000 wrote: »

Spurs were title contenders yesterday lads. Some of the wishful thinking on here for bad weather is laughable.

Oneiric 3 wrote: »

Some notably warm Decembers though history.

1988: 8.5c
2015: 8.4c
1934: 8.4c
1974: 8.3c
1921: 8.2c
1953: 8.0c

Defaulter1831 wrote: »

Must have a look at some data I have on my PC to see cold Jan, Febs preceded by mild Decembers. There are a fair few too from what I remember.

Defaulter1831 wrote: »

The majority of cold follow ups in Jan and Feb seem to be over 100yrs ago.. curiously..

sryanbruen wrote: »

Long range models

To start off, let's discuss the long range or seasonal model output. The vast majority of the known long range models were pointing towards the occurrence of northern blocking up over the Arctic, some more extensive than others with a particular emphasis over Greenland. Models like the UKMO Glosea5 and JMA went especially bullish on Greenland blocking in the second half of the Winter around February. These models in their November updates as a result anticipated the chance of a very cold to even severely cold February if we were to go solely off of their 500mb height anomalies and or mean sea level pressure anomalies. Using Hanna's Greenland Blocking Index (GBI), similar Februaries to the extent of blocking shown on these models include 1947, 1901, 2010, 1902, 1895, 1942, 1960, 1855, 1900 and 1965. Several of these Februaries were either notably snowy (for example, 1947), cold (for example 1895 and 1947) or anticyclonic (for example, 1965 which later became cold and snowy too into March). Models were fairly mixed on the early part of the Winter but they generally pointed towards a rather zonal December with relatively mild and wet conditions especially the ECM. January looks anticyclonic but a bit split on the temperature aspect. If the high pressure aligns itself over top of the country, just to the north or to the east then it's likely to be a chilly January with clear skies leading to frost and fog. If the high is more aligned to the south then it will be a mild month. February holds the greatest potential for blocking (and therefore cold conditions) on the models with quite a strong signal for three months away. One would normally think the first month (December) would hold the highest confidence of what is likely to happen but in contrast, it is actually the most uncertain of this forecast. Models like the DWD and the CFSv2 which show zonal and wet conditions cannot be discounted as their solutions are certainly possible given factors like the QBO, El Nino (especially early in the Winter) and the Atlantic sea surface temperatures.

Atlantic sea surface temperature anomalies

The Atlantic sea surface temperature (SST) anomalies continue to show this strange profile of cold-warm-cold-warm in the North Atlantic with the cold anomalies forming the shape of a horseshoe which has been the case since Spring generally. This is not favourable for a negative North Atlantic Oscillation (NAO) going strictly by the SSTs alone as they would have to be warmer around Greenland to do so. In case you do not know, the NAO is an index showing the difference in mean sea level pressure between the Icelandic Low and Azores High, two elements which make up the normal zonal pattern for western Europe. A positive NAO involves both of these elements being strong and normally translate to mild, wet conditions in Winter time whilst a negative NAO involves both of these elements either being weak or sometimes, non-existent as the pattern can completely reverse, which usually translate to cold conditions in Winter. This is not always the case with either side of the NAO index as there have been instances of cold conditions with positive NAO just as much as mild conditions with negative NAO. Every Winter since and including 2013-14 has had a positive NAO which has been one of the reasons why Winter hasn't been particularly cold recently and sometimes, record mild or wet as such happened in 2013-14 and 2015-16. Summer has been the opposite for most years since 2007 with every Summer since bar 2013 and now 2018 having a negative NAO. In fact, Summer 2018 was record breakingly positive. Will Winter 2018-19 see a similar flip to negative NAO? Not very likely given the Atlantic sea surface temperature anomalies though not impossible. I did an analogue on Winters following very positive NAO Summers and in fact, the signal was strong for an Atlantic driven Winter. Therefore from this point of view, there is an increased chance of a mild, wet Winter.

El Niño-Southern Oscillation

The El Niño-Southern Oscillation (ENSO) is an irregular index with variation in winds and sea surface temperatures over the equatorial Pacific Ocean. The warming phase is known as El Niño whilst the cooling phase is known as La Niña. Southern Oscillation is the accompanying atmospheric component coupled with the sea temperature change. These phases of ENSO have various impacts on weather patterns around the world but the impacts from it on Europe are unknown due to event to event variation. However, it has been said that El Niño increases the chances of cold later in the Winter whilst La Niña does the opposite of increasing the chances of cold earlier in the Winter. Examples of El Niño Winters doing this include 2014-15 (where February was the coldest of the Winter with a frosty spell during the first half) and 1977-78 (where February produced a severe cold spell with one of the worst blizzards on record to hit the West Country).

Verdict

What is the final verdict from all of what I described above? What do I think is likely? Well, the signs from my analogues and long range models are very compelling aren't they for a cold Winter. However, I just don't think it will be as straightforward as some would interpret from these. I don't think this will be a classic cold Winter. Rather, I think a changeable Winter is more likely similar in vein to 2017-18 especially earlier in the season with more of a lean towards a risk of prolonged cold later in the season.

December - A close to average month in terms of temperature if a little bit on the milder side (Edit: I underestimated how mild it would be). Above average precipitation is more favoured than below average despite my analogue showing an anticyclonic month on the cards, due to a more zonal flow earlier on and there is a possibility of this continuing through the month.

acequion wrote: »

So in lay man's terms what are people predicting? More of this or more normal temps?