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  1. Winter 2018/2019 Forecast And Updates (United Kingdom & Europe) Winter 2018/19 NAO Forecast Released on 1st July 2018 this is the NAO (North Atlantic Oscillation) Forecast for Winter 2018/19. We reanalyze the sea surface temperature (SST) anomalies across the North Atlantic during the month of May 2018 to see what impact these SST's could have on the UK and European winter 2018/19. For a negative NAO (which means high pressure around Greenland and Iceland and low pressure through the Azores and the Mediterranean) during the Winter we want to see a tripole in the north Atlantic during May. It's the negative NAO state that, when associated with a negative AO (Arctic Oscillation) state, can produce cold weather during the Winter for the UK and Europe. A tripole means that we have three distinct bands of temperatures anomalies - Warm SST's to the south of Greenland, cold SST's through the central north Atlantic (specifically focused around Newfoundland and down the eastern seaboard coast of America) and another warm band of SST anomalies through the tropical Atlantic. This year's North Atlantic Sea-Surface Temperature anomalies during May 2018 were the reverse of the tripole. So we did have three distinct bands of SST's through the north Atlantic but instead of the warm/cold/warm triploe we actually had a pattern of cold/warm/cold. Colder than average SST's were found to the south of Greenland and down past Ireland/UK to Spain and Portugal. We then had an area of warmer than normal SST's through the central north Atlantic and backing over towards the eastern seaboard of United States of America. A third band of colder than average SST's was then seen through the tropical Atlantic. These SST anomalies persisted through the whole of of May 2018 and in-fact we saw them intensifying through the month so by months end we actually had a very intense cold/warm/cold set-up in terms of the north Atlantic sea-surface-temperature anomalies. This reversal of the tripole during May 2018 means that the GWV Winter 2018/19 NAO forecast can only be for a positive NAO (as the SST pattern is clearly the reverse of the pattern that we'd use to forecast a negative NAO Winter) - And due to the intensity of the SST's we would probably have to forecast either a positive or even very/strong positive NAO for Winter 18/19. A positive or strong positive NAO would mean we'd likely see a strong Azores High combined with an intense polar vortex around Greenland and Iceland. The resultant pressure gradient would intensify the westerly winds and jet stream making for a strongly zonal Winter for the UK and Europe. This would be a mild or very mild Winter signal - Although exceptions can occur and cold European Winters have been achieved with a positive NAO. For North America is not as straightforward as brutal cold outbreaks can still occur even in a very positive NAO Winter due to ridging that can sometimes occur over Canada and Alaska (this would be a positive NAO combined with a negative AO (arctic oscillation) There-fore the NAO is a much more useful forecasting tool for the UK and Northern Europe than it is for North America where the AO is more useful (actually for the UK and Europe the AO and NAO are probably both as equally important) One very large caveat to this NAO forecast is that the "horse shoe" shape of cold/warm/cold SST's through the North Atlantic is very indicative of a cold phase of the Atlantic Multi-Decadel-Oscillation (AMO) Since 1995 we have generally been in the warm phase of the AMO but the switch back to the cold AMO now seems to be well under-way (we might not truly enter the cold AMO phase until the 2020's, but 2018 is clearly the start of real cold AMO conditions) - The last time we were in the cold AMP phase was around 1964 to 1995. Despite the mid 1960's to the mid 1990's being a cold AMO period, with presumably very few tripole's occurring in the north Atlantic, cold winter Winters still occurred. Indeed there several cold winters in the second half of the 1960's, the late 1970's, as well as the early and middle 1980's. This tells us what we already know, namely that cold Winter are still very possible without a tripole (we know that as otherwise cold UK and European Winters would only be associated with tripole's and the warm phase of the AMO) - So even though, on the methodology alone we can only forecast a positive NAO for Winter 2018/19 - We are by no means ruling out a cold Winter 18/19. We know that several other factors are important for increasing the chance of a cold Winter in the UK and northern Europe and these are the factors we'll be focusing on during this years Winter updates. One critical aspect we'll have to focus on will be solar minimum as Winter 2018/19 will likely be *THE* solar minimum Winter of solar cycle 24. The cold Winters of the mid-1980's (84/85, 85/86 and 86/87) all occurred during the solar minimum of solar cycle 22 and did so despite being in the period of the cold phase of the AMO (so none of those Winters had a tripole) So at this stage we rule nothing in and we rule nothing out for Winter 2018/19 despite the positive NAO forecast based on this methodology. This is merely the starting point on which everything else will be built. We suggest everyone enjoys the rest of the Summer and we meet back here in September for the start of the Winter 18/19 updates. The first Winter update will be released on Sunday 2nd September 2018. The journey to Winter 2018/19 has begun... Courtesy GAVS weather vids
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