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Validation of Useful Info Winter 2005/2006 Forecast

Original forecast can be found here

Objective Climate Data used for Validation

winter Central England Temperature (CET) was spot on the 1961-90 average: December -0.3 C; January +0.5 C; February -0.1 C
winter England & Wales Rainfall (EWR) was 64% of the 1961-90 average: December 75%; January 36%; February 89%
winter PSC quintiles (1, 2: below average; 3: average; 4, 5: above average) were P₁S₁C₂: December P₃S₂C₃; January P₂S₃C₁; February P₁S₁C₄
winter NAO was -2.15: was close to neutral/slightly negative for most of December & January and mostly negative in February.
monthly weather summaries may be found on Philip Eden's website, Climate UK: December; January; February
daily synoptic charts may be found here
mean temperature anomaly for Europe as a whole was -0.4 C below the 1961-90 average: data here

The General Weather Pattern

PREDICTED: although the NAO is considered difficult to predict, Atlantic SSTs are favourable for negative NAO at the moment, are more favourable than last year with respect to the Greenland & Barents Seas and the annual profile of NAO through this year (Figure 1) is more similar to cold years (1963-69 & 1979-87) than warm years (1989-2004). So the probability is that the NAO will be negative for more days than it will be positive during the coming winter. (High Confidence)
OBSERVED: the overall winter NAO was -2.15 which is the 14th most negative since 1900 although for much of December and January, near neutral conditions prevailed with a lot of high pressure over the UK rather than located to the NW as in the classic negative NAO which prevailed in the latter half of February.
PREDICTED: the expected neutral SOI in the coming winter favours weak westerlies across the Atlantic and increases the likelihood (relative to last year when SOI was somewhat negative) of cold easterly type spells when a positive PNA pattern prevails across North America
OBSERVED: the winter across the UK was very blocked (weak westerlies) indicated by the PSC quintiles: P₁S₁C₂ with both January and February having below average westerlies and December average westerlies and several easterly spells did occur: just after Xmas, 4-8 January; and 20-28 February. As was the case in winter 2004/2005, the brunt of some easterly spells went further south across Europe which was the case in the latter half of January when extreme cold occurred in eastern Europe and Russia.
PREDICTED: winter forecasts for the US again expect a cold winter in the east and warm in the west indicating a recurrent positive PNA pattern which is likely to be associated with northerly & easterly spells across the UK (High Confidence)
OBSERVED: winter forecasts for North America turned out to be poor as a very zonal pattern developed during January giving record warmth in both the USA and Canada which resulted in winter 2005/2006 being fifth warmest on record in the US (NOAA). So the PNA was very variable over the winter and did not give the recurrent positive PNA pattern which was expected, and consequently northerly spells were less frequent than in recent winters (brief northerly mid-December and a few days in the latter half of February) but easterly spells certainly did occur as mentioned above..
PREDICTED: the occurrence of cyclonic spells this year, the neutral SOI and the above average hurricane season all suggest that when the positive PNA pattern occurs across Europe, it has more chance of being a cyclonic/west PNA rather than an anticyclonic/east PNA which has been characteristic of recent winters. This is an important point as it implies the UK would be included in the cold & snowy weather rather than it being confined to eastern Europe (Moderate Confiidence)
OBSERVED: this part of the forecast highlighting the occurrence of cyclonic spells and a bias to cyclonic PNA/west patterns across Europe rather than anticyclonic PNA/east was wrong as the winter as a whole was anticyclonic with only February having a cyclonic bias and it was only in the last ten days of February that a cyclonic PNA/west pattern prevailed.
PREDICTED: the weather patterns across North America are expected to oscillate markedly between cold and warm spells and this will no doubt have some effect downstream across the Atlantic & Europe but perhaps in Europe we can expect less volatility than in recent winters because of the expected neutral SOI (Moderate Confidence)
OBSERVED: while the weather patterns across North America were volatile, the pattern across Eurasia was remarkably static and blocked resulting in a cold winter across large parts of Eurasia. Perhaps the most notable feature of the winter across England & Wales was the total absence of any very mild days with temperatures above ~12 C owing to the failure of Atlantic low pressures to pump warm tropical maritime airstreams into western Europe against the persistent blocking. Instead the mild air went further north across Scotland at times and mainly into the Greenand & Barents Seas
PREDICTED: the probability of persistent mild westerly winds looks to be low as all factors appear to point to weak westerlies so such spells are likely to be brief (High Confidence)
OBSERVED: westerlies were below average in January and February and the winter as a whole was very blocked: winter P was quintile 1
PREDICTED: the predicted pattern above suggests a cold winter for Europe and the coldest airstreams are likely to come further west and north than in recent years when SE Europe (Greece/Turkey) has received the coldest airmasses. Drought in Iberia is a big concern at the moment and from the water shortage point of view, strongly negative NAO is good news as it means lots of low pressure and precipitation in the Mediterranean.
OBSERVED: although the winter across Europe was coldest since 1996, there was still a marked tendency for the coldest airstreams to affect the south-eastern half of the continent and to miss the north-western half: both the UK and Scandinavia has an average to mild winter. However, during January and February, there was certainly plenty of cyclonic activity across Iberia and further east in Europe giving some notably heavy snowfalls. So in fact, this cold, snowy weather only missed the UK by a fraction so the predicted cyclonic PNA/west pattern did occur to some extent.

The Weather

PREDICTED TEMPERATURE: with the occurrence of both northerly and easterly spells, some very cold weather is likely and with neutral SOI, less volatility in the pattern may occur than in recent years which means some long cold spells are possible (last winter managed a four week cold spell in the UK but 6-7 weeks in eastern Europe) but how cold it gets and how long the cold spells last will be dictated by random events which at this long range cannot be predicted. What can be said is that there is a real potential for cold spells this winter as was the case last year and the potential this year (from the point of view of the analyses above) appears to be greater.
75% Confidence Range for winter CET Anomaly (from 1961-90 average): -1.5 to +0.5 C (Moderate Confidence)
OBSERVED: although no extreme sub-zero spells of weather occurred in the UK (they did on the continent), several cold spells with sub-zero maxima did occur: 27-29 December; 30-31 January; 1-5 February & cold weather with below zero temps on hills occurred 20-28 February. So there was cold weather around at times but as in winter 2004/2005, much colder weather narrowly missed the UK while it passed to the south. The winter CET anomaly was 0.0 C so within the 75% confidence range.
PREDICTED RAINFALL: the trend to increasing incidence of cyclonic spells this year and the neutral SOI suggests a cyclonic/west PNA pattern may be recurrent across Europe this winter which would mean a wetter winter than last year which was markedly anticyclonic. Central & eastern regions are therefore likely to have average or slightly above average rainfall while western regions below average rainfall, especially the north-west. (Moderate Confidence)
75% Confidence Range for % of 1961-90 average of England & Wales Rainfall: 90-120%
OBSERVED: the winter as a whole was a dry one with most regions having 60-80% of the average rainfall (winter chart) but the latter half of February did show the cyclonic tendency which the forecast highlighted might be characteristic of the winter with eastern regions having average or above average rainfall (February chart). Also, France, Germany and many other European countries saw a number of heavy snowfalls during January & February so southern UK only narrowly missed out on a wetter cyclonic pattern
PREDICTED SNOWFALL: the trend of recent winters to increasing snowfall looks likely to continue. Northerly spells are likely to give some heavy snowfalls to northern Scotland and eastern & western coastal regions exposed to the north and easterly spells are likely to give some heavy snowfalls to eastern Scotland and central & eastern England
above average snowfall generally but average in some western regions (High Confidence)
OBSERVED: there were quite widespread snowfalls in the last week of November before the winter began and then there were a number of snow episodes but no major widespread heavy snowfalls except for a major snowfall in Scotland 11/12 March. Snow spells were: 16-18 & 27-30 December; 4-7 January; 8-10 & 20-28 February. Owing to the relative lack of northerlies this winter, snow was less widespread than in recent ones.
PREDICTED GALES: weak westerlies and the expected negative NAO suggest the incidence of gales and severe gales is likely to be below average (Moderate Confidence)
OBSERVED: the absence of gales was a notable feature of this winter. The only gale of note occurred 2 December in SW England when a southerly gale coincided with high tides to cause coastal flooding which damaged the railway line at Dawlish.

Prospects for the Scottish Ski Centres

PREDICTED: The prospects for winter 2005/2006 look very good with frequent northerly spells bringing regular snowfalls to the Scottish ski resorts and with perhaps a higher tendency for cyclonicity this season relative to last, snowfalls could be heavier. The likelihood of both northerly and easterly spells means some long cold, dry and sunny spells of weather ideal for skiing with not too many skier days lost to high winds. The early part of the season last year was ruined by a period of strong westerly winds from late December to mid-January but such a spell of weather is considered less likely this winter because SSTs anomalies in the Greenland & Barents Seas are negative currently compared with positive anomalies last year. And other factors do not appear to favour persistent mild westerlies.

The season last year was brought to an early and abrupt end by persistent warm southerlies from mid-March till the end of the month which quickly melted the unconsolidated snow pack. While it is certainly the case that negative NAO can lead to spells of warm southerlies when lows to the SW of the UK stall for a few days, the sustained period of warm southerlies last winter was unusual and is unlikely to be repeated this winter. With the potential for a strongly negative NAO this winter, the 2005/2006 season is likely to start much earlier and end much later than last year's short but sweet season and hopefully be the best since 2001 (Moderate Confidence).

OBSERVED: the winter 2005/2006 season was opened by Glenshee and the Lecht on 26 November after a potent northerly dumped over a foot of snow in low lying parts of north-east Scotland with much more on high ground. After digging itself out, Cairngorm opened on the 27 November and all three eastern centres had excellent deep powder on offer. For so early in the season, the snow lasted well with around a week of top to daylodge skiing at Cairngorm and two weeks skiing on the upper and middle slopes. Unfortunately, after the first week of December, there was no top to bottom quality skiing to be had in Scotland until 17 & 18 February when Nevis Range and Glencoe opened for the season: Cairngorm offered some thin runs on the upper slopes in late January and the first half of February and the Lecht & Glenshee were able to offer some limited artificial snow terrain. The eastern centres didn't benefit from the heavy snowfalls that enabled the western centres to open 17/18 February but some snowfall over the next week did improve conditions somewhat. But happily, snow-laden northerlies set in on the 27 February and all five centres were able to offer their full terrain. Excellent conditions then prevailed throughout March at all five centres and througout April at Glencoe, Nevis Range and Cairngorm. Glenshee closed 17 April, the Lecht 23 April, Nevis Range and Glencoe 30 April & Cairngorm 1 May which meant all five centres were open over the Easter weekend and these were the best late season conditions since 2001. So after an early start to the season in the east and a very poor January & most of February, March and April offered uninterrupted excellent skiing somewhat making up for the poor middle season.

Scores

BIAS TO BLOCKING: the winter was very blocked with both January & February having below average P indices: 2/3
NEGATIVE NAO: prediction of overall negative winter NAO was correct with all three months being negative: 3/3
ABOVE AVERAGE INCIDENCE OF NORTHERLIES: both December & February had low S indices: 2/3
SLIGHT BIAS TO ABOVE AVERAGE CYCLONICITY: the winter was overall anticyclonic but February had above average cylonicity 1/3
TEMPERATURE: predicted 75% Confidence Range for winter CET Anomaly (from 1961-90 average): -1.5 to +0.5 C. Observed was 0.0 C - 1/1
RAINFALL: the winter was very dry with just 65% of average EWR rainfall which was outside the predicted range of 90-120 and all three months were much drier than average 0/3
SNOWFALL: this is not based on objective data (not easy to assess UK wide), but a number of snowfalls did occur and most of these were in eastern areas although snow was not as frequent as predicted - 2/3
GALES: incidence of gales and severe gales were well below average 1/1
SCOTTISH SKIING: with an early start and excellent March & April, this season was not the disaster it appeared to be in the middle of February: 2/3

SUMMARY

THE overall score of 15/23 or 65% is the same as last winter's forecast and indicates some skill in the winter forecast. The idea of neutral SOI favouring blocking across Europe and much less volatility in the pattern compared with the last few negative SOI winters appeared to be spot on. And the idea of a colder than average winter across Europe was also correct but the idea of the cyclonic/west PNA pattern did not quite come off as anticyclones in December, January and early February were located close to the UK but on the other hand, countries on the nearby continent including our neighbour France did have lots of cyclonic and snowy weather in January & February so the error margin was small in global terms. However, it should be acknowledged that global seasonal forecasting models did predict that the UK would be on the margin of the cold air across Europe and that Scandinavia would have a mild winter which was spot on. The widely publicised winter forecast by the Met Office was partly based on such a model and correctly identified that Scotland would probably have a milder than average winter in contrast to a colder than average winter in southern England. Quite why these seasonal forecasting models forecast these characteristics was not specified in the UK Met Office forecast but it was an impressively accurate forecast. But the Useful Info forecast did not forecast this with a UK-wide colder than average winter expected.