UK Winter 2014/15 Weather Forecast predictions Well, it’s that time of year again when all attention starts to focus on winter 2014/15. Will it be mild and stormy winter 2014/15 or will it be cold and snowy, or maybe something in between? Well let’s find out. First of all, these are just our preliminary thoughts as to how the winter will play out. Our full and final forecast will be released in November, however, we will be updating in between for you and addressing any changes that may come about in the next month or two. El Nino: We have started here due to the simple fact that El Nino will play a major role in the outcome of our winter forecast. At the beginning of the year, the forecast models were predicting a moderate El Nino. It now transpires that there will only be a weak El Nino, however, not all of the equatorial Pacific region will be under El Nino conditions. Below is an image explaining the different regions across the equatorial Pacific that an El Nino can develop. ENSO Regions The area we are going to focus on is region 3.4. In the past couple of decades, scientists have discovered that in some El Nino years, only the 3.4 region showed the warm anomalies. They have called this a ‘Modoki’ El Nino. Below, the two different forecast models are suggesting that by January, the region 3.4 will indeed be under El Nino conditions, albeit rather weak (on the chart 0 to 1 is considered a weak El Nino). Jamestec El Nino 3.4El nino 3.4 forecast The model below is the forecast for region 1 & 2 of the equatorial Pacific. As you can already see, the anomaly has taken a significant drop recently and this incline is forecast to continue. This is an indication that a ‘Modoki’ set up is indeed likely by January. Now we have established that a Modoki set up is likely, we can now work towards what pattern this set up will bring across the UK this winter, the results are rather interesting. El nino 1.2 Historical Modoki Patterns: Let’s start with the 500mb geopotential height anomalies. Below is a plot that takes in to account all the 3.4 (Modoki) El Nino’s ranging from 1949 – 2010, during December to February. The plot suggests that during this set up, higher than normal heights build in over Greenland and parts of Scandinavia. This suggests a blocking pattern (Northern Block) which will bring periods of cold weather to the UK. Geo heights 3.4 el nino The next image is a plot of the 200mb zonal winds (jet stream) using the same techniques as the 500mb heights. The plot suggests that the jet stream during this setup, will run well to south of the UK, as indicated by the green and yellow colours. Whenever the jet stream runs south of the UK, then we are on the cold side of the jet, thus conditions will be cooler. This is another indicator of cooler conditions. 200mb zonal wind Long range forecast models: (500mb Height Anomalies) Now we are going to see what the long range models are suggesting for the period from December to February. Although these models are not to be taken too seriously at such length, they can be used for trend purposes. Below is the chart from the Beijing climate Centre. We have circled the UK as the chart is a little difficult to read. Lower than normal heights are predicted for much of Western Europe, however, higher than normal heights are predicted over Greenland. This is a cold signal as northern blocking is indicated, with the flow coming from the N/NE, which as we know is a cold direction in winter. We must stress however, that northern blocking will not be a feature throughout the whole of the winter period, this model is just indicating that this pattern will be more dominant. BCC DJF The next model run is from the Korean Meteorological Agency. This model is also suggesting higher than normal heights across Greenland and lower than normal heights across Western Europe. Another cold signal with northern blocking in place, promoting an NE/E flow across the UK. Korean DJF Next up is the CFSv2 model. The interesting factor with this model is that until mid-August, the CFS had no interest in any sort of blocking event. It wasn’t necessarily forecasting a mild winter, but there was no signal at all for blocking over Greenland. However, in recent weeks it has now started to signal that blocking will take place over Greenland, with lower than normal heights over Western Europe, as the chart below clearly indicates. This theme is becoming quite a trend across the models. CFSv2 DJF Why did the CFS flip? It’s not uncommon for long range models to flip as a forecast period nears. However, I suspect the CFS was too keen on keeping warmer than average temperatures throughout August within its forecasting parameters, as the last 8 months have recorded warmer than average temperatures. However, August was rather cool, in fact this was the coolest August for the UK since 1993. I think once the forecast model took this into consideration, then the forecast output changed. It will be very interesting to see it this model continues to throw this scenario out. The last model we are going to take a look at is a rather experimental model. This model was created by Huug Van Den Dool and this model bases its forecasts on current SST (sea surface temperatures) across the globe. The model then runs this data against previous years that had similar SST and then it creates a forecast prediction. Although this model is different in the way that it produces its predictions, it’s no surprise to see that the prediction is very similar to all the other models we have analysed. A clear signal for northern blocking, with lower than normal heights across Europe, again promoting an easterly flow across the UK. hugg DJF UK Winter 2014/15 Model Conclusion. It’s hard to argue with that fact that most of the long range models are in some sort of agreement, that there will be a blocking event this winter. However, this pattern will not be dominant all winter, there will be breakdowns to milder conditions at times, although the transition will be difficult as cold air is notoriously difficult to displace. It may also be possible that the blocking set up will return, after any brief mild incursion. So from what the seasonal forecast models are predicting, coupled with historical data, the conclusion at this moment in time, is that winter will indeed be colder than average. The pattern being predicted is likely to produce some lengthy cold periods, which will no doubt produce periods of snow. Other factors to consider: Will solar activity be a factor? Solar cycle 24 reached solar maximum around the start of this year. The current predicted and observed size of this maximum makes this the smallest sunspot cycle since Cycle 14, which had a maximum of 64.2 in February of 1906. Going back to 1755, there have been only a few solar cycles in the previous 23 that have had a lower number of sunspots during its maximum phase. So low solar activity continues to be a factor and it is no secret that low activity has indeed coincided with previous cold winters. Why won’t Winter 2014/15 be as mild and stormy like winter 2013/14? Well let’s first look at why the 2013/14 winter turned out so persistently wet and windy. There have been strong suggestions that persistent Indonesian rainfall had a huge impact on the Pacific jet stream, causing the jet to buckle and allowing a dominant high-pressure system to reside just off the Northwest coast of America and Canada. This in turn started to drag very cold air from the Arctic, filtering down the eastern side of the USA and plunging these areas into a very cold and bitter winter. Due to the eastern USA being unusually bitter, the cold temperatures caused a huge temperature contrast between the warm flow of the Atlantic Ocean (via the Gulf Stream) and the cold air mass filtering out of the USA. This contrast was partly responsible, along with an unusually strong QBO (Quasi-biennial oscillation) for a strengthening of the jet stream, which in turn strengthened the low pressures systems that affected the United Kingdom. The QBO also produced a very strong polar vortex, which despite many attacks, stood firm and continued to push very cold air into the Eastern United States. Now this winter the QBO will be in a different phase to start with, which supports an overall less potent stratospheric vortex. Another factor will be the Indian Dipole, albeit indirectly. The Indian dipole is an irregular oscillation of sea surface temperatures in which the western Indian Ocean becomes alternately warmer and then colder than the eastern part of the ocean. During a positive phase of the Indian Dipole, conditions around Indonesia are significantly drier than normal. During this winter the Dipole will continue in a positive phase, so there will be no repeat of the Indonesian rains that cause such a dramatic and lengthy shift in the pacific jet. So we leave you with that for now, we hope you enjoyed all the information supplied and don’t forget we will be producing further updates when necessary. - See more at: ukweatherforecast.co.uk/uk-winter-201415-weather-forecast-predictions/#sthash.eJM92Fsy.dpuf
Posted on: Fri, 05 Sep 2014 08:24:49 +0000
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