Irish Weather Online Summer Forecast 2012

Summer of 2012 -- reasonably warm with a variable pattern. 

IWO's Peter O'Donnell presents his summer forecast based on his ongoing research and a detailed numerical index method that is continuously upgraded from results of previous forecasts.

 In general terms, this summer should be somewhat improved over what has become the standard fare since warm and dry summers such as 2003 and (the first half anyway) 2006. Some of the more recent summers have been widely described as poor to sub-average, although when you look at the numbers it might be fair to say that after 2007, a true shocker, the past four have fallen into the average camp. So I am concluding from my research evaluation that this summer might be somewhere between average and the standard for a warm and dry summer. It would not even surprise me greatly if the reviews place it among those better summers of the past, although the numbers look a little closer to average.

 The spring started out warm and dry (and many would say in February) but the trends since early April have been towards cold and wet. This is because a large-scale blocking pattern developed, in part due to retrogression of a blocking high towards Greenland, which in turn trapped low pressure systems fairly frequently near France, England and the Biscay region. It gives me some confidence in my method and outlook to report that this development was predicted in the published spring forecast. Also, I plan to continue with the theme briefly mentioned there, for improvements into June and a much less gloomy pattern as this northern blocking should tend to evaporate while also, remnants of an eastward-moving trough component (which got added into the vile mixture) should also continue to migrate east and fill due mainly to seasonal height rises as it approaches the Baltic regions.

 These two developments will both assist a return to a more normal jet stream configuration but remnants of the pattern will probably lead to a somewhat chaotic flow pattern that sometimes develops strong semi-blocking highs fairly close to Ireland, and at other times degenerates into weak meandering lows. I don't foresee a return to a "raging Atlantic" although there may be a persistent storm track from south of Greenland towards the eastern Atlantic but this should often tend to weaken and split with components of formerly strong systems shunted around the growing European high.

 As a result of all that, and considering the detailed numerical output from the research, I foresee June being about 1 degree above normal in temperature, July also 0.5 to 1 degree above normal, and August fairly close to normal with perhaps a late burst of warmth leading into a very warm September that could average 1-2 deg above normal. That does not imply that all days will be above average, but suggests that warmer days will outnumber cooler days by about a 2:1 ratio, perhaps dropping to a more equal mixture in early July. The analogue years that are identified in the method tend to be clustered around this outcome but one or two are definite outliers -- I have had a look at possible reasons why, because we don't want to see an outlier provide the best analogue of the whole set.

I am fairly confident that the cooler 5-10% of the analogue years would have that colder pattern explained by variables that do not enter this analogue set (in other words, the reason they got in has been damped out by reasons that won't apply to 2012). To give some idea of what is considered in the forecast, there are about a hundred variables in the research model, each given a weight based on the theoretical framework, but probably about twenty of these are significant enough to influence the ouitcome noticeably (some of the variables have amplitudes of only 0.1 or 0.2 deg so whether they are in a warm or cold phase they can't really do much to the outcome unless 20-30 of them all pile on together -- this has been checked out). As many readers will know, my research interests are basically in the field of solar system magnetic field analysis, and how those patterns (which are essentially variations in structure of the solar wind) might predictably influence weather patterns.

Like some other researchers, I have also studied aspects of the lunar orbital variables and incorporated that research, which is semi-independent of the rest of the external variables. In addition to all that, I keep a close eye on the field of tele-connections and global weather pattern analysis and research but find that the data sets are probably masked in the external variable data sets (in other words, those things are covered in this forecast methodology). For those who like to view the climate set-up from that paradigm, I could mention that it appears likely that a strong dipole which has been pulsating across the pole at about the Greenwich-IDL (International date line) longitude couplet, should rotate slightly (to the east for each part) and that is the process referred to above as the filling in of the progressive part of the overlapping (prograde/retrograde) trough. Summer is often a time of year with reduced high-latitude blocking and a more simplified flow pattern, but with a long imprint of higher pressure west of the Azores, it seems likely that the rotation of troughs will therefore shorten the wave lengths. This is why I feel that the summer is about equally likely to turn out very warm and fine, or rather warm and slightly unsettled. Perhaps a compromise between these two as in say 2005 will be the type of summer on offer. Briefly, I could mention also that the sea surface temperature regime this spring has reflected outflow of very cold waters from the after-effects of the frigid three weeks in Europe, but this signal is being diluted by mixing with the more normal if restrained North Atlantic Drift component.

The net effect of sea surface temperature anomalies in my forecast scenario is therefore set at nearly equilibrium (in other words, no special effects). Spells of notable if not extreme heat are likely to develop on two or three occasions, the index values are strongly suggesting around 7-12 June as being quite warm, then also late June into early July, and parts of late July. A longer and more anomalous warm period is likely from about 20 August on through September (and the autumn extension of this research suggests a very mild November to follow a more average October).

 Rainfall may tend to drop back to if not below normal values in the patterns expected but this may be a rather variable regime where some places see drought developing and others have adequate or locally excess rainfalls. I would speculate that the inland southeast could see the higher rainfall amounts relative to normal as there will probably be enough of a rise in the jet stream to place the active frontal zone closer to 52-54 N at times. This may be a good summer for a very active thunderstorm outbreak at some point since we are looking for a weak southerly flow to develop in stages.

I also feel that the pattern is likely to bring above average sunshine but perhaps not by a huge margin. There will be some rather cloudy periods between the warm spells, as the flow reverts to weaker versions of the exceptionally dull set-up now in place.