Jump to content
  • entries
  • comments
  • views

Recap of 2014/15 forecast (2015/16 forecast to follow...)

Sign in to follow this  


Before I start on this year's forecast, it's worth recapping last year's one for a look at what went right, and (moreso) what went wrong, and why. If my 2013/14 forecast was wrong but for the 'right' reasons i.e. the synoptic pattern for the NH that materialised was similar to the one that was predicted even if it was milder than I'd predicted for here, last winter's was pretty much the opposite, for Scotland at least.
A look at the predicted/analogue (left) vs the actual height anomalies (on the right) show a rather poor miss:
[attachment=263251:blogentry-9298-0-92446000-1414943296.png][attachment=263250:2015 winter.png]
There are a few similarities, including a weakish negative height anomaly over southern Europe and mean ridging from Alaska to central Russia, but the main point of interest from the analogue, a stonking Greenland high with a negative anomaly stretching across from the US to southeastern Europe, is absent, replaced by a fairly typical +ve NAO pattern. Why was this, when so many indicators (-(very -ve QBO coupled with weak El Nino, positive Snow Advance Index, negative OPI [the latter index clearly needs a bit of work to say the least]) pointed towards a very blocked pattern? The clue, as is often the case, is in the stratosphere:
Much as it tried, and there was some pretty hefty wave 1 activity through the first half of winter, the SSW that we probably needed to fulfill the predictions simply never came through, and we ended up with a fairly strong Greenland based vortex. Part of that may be linked to solar activity - after a bit of a drop off in summer 2014 we again saw a peak during the winter [attachment=263263:solar-cycle-10-cm-radio-flux.gif]
This appears to have a particularly strong impact during the -ve phase of the QBO, where papers suggest the -ve QBO actually acts to enhance the solar signal and propagate westerlies northwards, strengthening the polar vortex ( [url="http://onlinelibrary.wiley.com/doi/10.1002/jgrd.50424/full"]http://onlinelibrary.wiley.com/doi/10.1002/jgrd.50424/full[/url] )
As Tony (Lorenzo as he's known on here) pointed out a month or so ago, taking an 'additive' approach to these variables(as I did last winter) may not be the most effective method, and I'll certainly take that into account this winter.
The other measure which seemed to buck the trend were the long range forecast models. I've long been sceptical of their performance, particularly of the CFS, but actually both it and the Met Office's GLOSEA5 model were pretty close to the mark. Given these were very much contradicting my own analogues last winter I will put a significantly greater weighting on their outlook for this winter's forecast. There will obviously be misses, but compared with the models' accuracy a mere 5 years ago when the Met Office's seasonal forecast had to be pulled after the 'barbeque summer' fiasco (and the CFS seemed to fare even worse overall) it looks as though recent upgrades have paid dividends.

The bit that, if you weren't paying that much attention to the overall NH picture and lived in Scotland, seemed like it might have made the forecast vaguely ok was the temperature - in spite of a lack of 'proper' high latitude blocking we managed to end up with temperatures around average overall (although a bit above in the south) and a number of snowfalls. These were mostly pretty marginal and were obviously nothing on the scale of 2009/10 or 2010/11 for longevity or depth, but given how long I'd personally been waiting for 'cold zonality' to deliver seeing charts like these was really quite fun:
[img]http://modeles.meteociel.fr/modeles/gfs/archives/gfs-2015011012-0-6.png[/img] [img]http://modeles.meteociel.fr/modeles/gfs/archives/gfs-2015011312-0-6.png[/img]
The second one gave me my first sighting of proper lying snow in central Edinburgh since March 2013.

Anyway, there's a good reason charts like those, which on the face of it don't look especially snowy, delivered to a number of low lying areas - this:
The cold Atlantic, while potentially acting to enhance those storms, inhibited temperatures sufficiently to turn what might otherwise have been cold rain into snow (though, for most of that period for most of central/southern England, simply turned mild and wet into cold and wet).
In comparison to 2013/14 the angle of attack of the storm systems was more favourable for cold, with the lack of blocking to our north allowing some proper Arctic air into the mix, and overall storms were less frequent with the jet tracking further north (though it hardly eased up much - see the horrific storm that hit Lewis on January 9th with 2 hours of sustained hurricane force winds), but there were definitely some similarities between the two for NW Europe.
So are we heading for a third straight winter where 'stormy' headlines dominate 'snowy' ones? Will we finally get the 'coldest (actually we really meant [s]wettest[/s] [s]windiest[/s] [s]sunniest?[/s]) winter in 1000 years' as the Express has been promising since just after the last genuinely cold one? Am I massively overhyping a forecast of a pretty average winter? All will be revealed in the next few days...
Sign in to follow this  


Recommended Comments

There are no comments to display.

  • Create New...