Winter outlook - what the stats suggest

[Stratos Ferric]

Here's the updated projection for winter.

The headline is an overall CET for winter in the range 4.5-6.0, with my projection of the likely overall outcome being 5.0-5.5C. Bucking the likely trend of one or two other forecasts I'm projecting December to be the mildest month of the season, and February to continue the recent pattern of being the coolest; purely wet finger indications might be something like 5.5, 5.0 and 4.5C outcomes. Overall slightly above the ten year mean, but with one of the three months likely to come in below its own ten year mean - February being the likeliest to do so.

This first plot shows the outturn for each winter in the CET series c.f. the winter before. We're obviously entering this year in uncharted waters, so the anticipation has to be for a drop. Realistically, the absolute floor looks like something as cold as 1996, though I suspect this is beyond us this year, requiring a drop that has happened only 6 times in history, most recently in 1879.

This next plot explains why I wouldn't favour a continuation of the recent cool run (apart from reasons laid down elsewhere regarding the effective length of the cold run that would be required); it shows that recent warming is more apparent in winter than in summer, making the cool run since June seem less notable, and also last winter's warmth (its magnitude aside) likewise.

This plot shows a couple of items. Firstly the actual D-M CET values for the last thirty or so years. Note the ever increasing baseline, as described by the rising minimum on the previous plot. Also note the rolling monthly averages for winter. A single month sub 4.0C is starting to look very unlikely, and, staggeringly, anything below 3.0C now seems out of reach (I have previously put the floor at 2.0C). There may be only last hurrah some time, but as I've been saying this for four years now, and meantime with the overall average figures rising (this is NOT pure bad luck), this needs to happen in the next 3-4 years I'd say, or it's probably not going to happen again in any of our lifetimes.

This last plot just shows monthly mean CET for the pat ten years. It neatly shows the recent pattern for February to come in coolest. I'd stick with this for the forthcoming winter as I'm also increasingly of the view that warmer SSTs are meaning that the level of cold required for genuine UK wintriness to be sustained can only now occur by late winter.

There you have it. Probably a slightly different view to the Nina based suggestion of December being the coolest month, but the caveat would be that this is a fairly centre-line projection. LIke forecasting the football results, whilst most results go broadly to form, one or two don't. What would I offer as the likeliest deviation? Not overall temperature, but perhaps the sequence of cold: we're overdue a surprising January, so it would be for Jan to be the coldest month.

[johnholmes]

interesting projection there SF

I'm just a bog standard type forecaster doing basic forecasting out to 7 possibly 10 days ahead on aoccasion so have no idea what that far ahead may bring.

Its certainly been a rather different November to last year, not just for the UK but the overall weather patterns for the N Atlantic sector.

[Stratos Ferric]

interesting projection there SF

I'm just a bog standard type forecaster doing basic forecasting out to 7 possibly 10 days ahead on aoccasion so have no idea what that far ahead may bring.Its certainly been a rather different November to last year, not just for the UK but the overall weather patterns for the N Atlantic sector.

Neither do I John - all I'm doing is casting the boundaries based on what's gone before. I think (re the recent pattern) that's why I'm happy to open up some clear water from the teleconnection boys who, reading between the lines, were suggesting the form for winter on a moderate Nina is a cold start then milder later.

That said, and to be expected after a long settled spell, we're looking at a more zonal start to December. Although one or two scoffed at the point, the observation that some of November's cold was 'artificial' (more properly, shallow) is borne out by present circumstances in which the PF has nudged south, yet the surface is getting warmer. The reason; depressions that were being pushed well north of the UK are now managing just to make their presence felt, allowing a mT feed to prevail. The upside of this is that genuinely colder air will be closer to our north, but that is no use if, say, we have the pattern of last year with secondary depressions repeatedly cutting off the cold feed.

I sincerely hope it doesn't all go belly up for cold fans, and whatr happens a week hence may be an interesting indicator of the period to follow; whether or not we get any ridging to our W to maintain - albeit briefly - the mP flow, or whether it gets cut off.

Edited November 25, 2007 by Stratos Ferric