Glacier Point heeft een aantal interessante gedachten over de komende zomer. Onderaan wordt door een ander nog melding gemaakt dat we kans hebben op wederom een negatieve NAO winter.
Some loose thoughts as follows:
The last 6 months has featured a solidly negative NAO. Feedback loops have helped to reinforce this -NAO signature in the North Atlantic, especially a warm anomaly in the tropical seas off Africa which strongly teleconnects to an upper weakness over the Azores (low pressure). These generally telconnect to unsettled and variable summer time conditions.
El Nino conditions are still persistent in the Pacific although declining. The tropics and extratropics are becoming nicely tied together so the waxing and waning associated with upper level tropical waves are varying the strength of El Nino global teleconnections. During March this signal was for east trade winds (working against El Nino) whilst this has switched in the last week and thunderstorm activity and cloudiness has increased east of the Dateline as the upper tropical wave moves eastwards. Hence why numerical model tools are gunning for a reintroduction of the blocking to the north. The periodicity of these waves is 6-8 weeks. Therefore, the weakening of this wave should begin in mid May and continue through to early to mid June allowing the NAO to become more neutral and probably quite a nice spell of weather. The period mid June through late July will likely favour a return of -NAO conditions. With a -AO more favoured during east QBO phase, this looks unsettled and cool during this time - but need to research this further. Late July through August looks slightly better with the NAO becoming more neutral based.
At this stage, I would be very against the development of a strong Azores ridge - the usual harbinger of summery weather for the UK. The SSTs in the Atlantic and residual Nino (not to mention the increasing amount of colder than normal waters across large parts of the north Pacific) do not favour this.
This leaves the options of a significant ridge over western Europe delivering warm and sunny weather or a mean ridge centred towards Iceland and the central northern Atlantic leaving NW Europe in a cool mean trough. The balance of probability favours the latter.
But, the key is likely to be the strength of blocking the north tied into the Arctic Oscillation. If it's weak, then more finer weather is likely. If strong, then it will be 4 poor summers on the bounce.
the weather pattern does seem to be enforcing the the sst tripole pattern in the Atlantic or vice versa.
If this pattern holds over the next 6 to 8 weeks then according to the Met office this would favour another -NAO winter season 2010-2011.
http://forum.netweather.tv/topic/58354-in-depth-technical-model-discussion/page__st__238
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