Thundery wintry showers

The models are showing a very consistent signal for an evolution to a cold, blocked pattern now- it just remains to be seen how long the cold will sustain for over the UK, and whether or not the blocking will be in the right place to bring something snowy. The main stumbling blocks for a snowy result will be high pressure settling over the UK and/or low pressure being slow-moving in the mid to eastern North Atlantic- both of those resulted in the failure of December to bring a widespread snow cover. The ECMWF operational run is a stunner for snow lovers with an easterly (definitely cold enough for snow showers in the eastern half of the UK, even along east-facing coastal fringes, looking over the 850hPa temperatures) followed by a very robust-looking northerly and has quite strong ensemble support, but we've been there before, less than a month ago in fact. I won't take any snowy north-easterly type synoptic for granted unless it comes inside T+72. The UKMO would probably not evolve in quite the same way as the ECMWF post T+144 because the high pressure to the north is less well-developed (1015mb as opposed to 1025mb) but still points towards a blocked and colder-than-average outlook. The GFS 12Z run highlights the need for caution as it shows a cold but mainly dry high pressure setup followed by the eventual sinking of the high. It seems unlikely that the blocking will recede that quickly given the teleconnections and the sudden stratospheric warming, but then again the quick breakdown around mid-December seemed unlikely. Hence my original assessment- turning cold for a while, but how snowy and for how long is extremely uncertain.

I think the smoking ban was a positive step overall, but that we could have eliminated many of its downsides simply by allowing pubs, bars etc. to apply to have segregated smoking areas. This would have enabled "social smokers" to have a selection of outlets without having to go outdoors, and it would have protected some of the more marginal pubs/bars against being forced to close due to reduced income from the sort of people who would pop in and have a few cigars. Indeed, the only arguments that I've heard in opposition to the above proposal are:[list] [*]"I don't smoke so I'm alright Jack", [*]"the total smoking ban is a positive step overall so therefore there is no need to improve on it", [*]"smoke might drift into the non-smoking areas", [*]"laws in some other countries don't allow them, so we shouldn't either, for the law is the law". [/list] I'm sure that small amounts of smoke would diffuse into the non-smoking areas, but then again, that happens under the current legislation (smoke coming in through the front door from people smoking outside). Also, non-smokers often have to walk through a lot of smoke in order to get to the pub entrance. They are picking on drinkers, but they have a habit of punishing the wrong people and saying, "the minority have to spoil it for everybody else". For example, Labour's ID measures have resulted in me being unable to enter most city-centre pubs unless I have my passport on me, despite being aged 28 and a very moderate drinker.

Some great and insightful accounts of the 1962/63 winter here. The persistence of cold frozen snowy weather was well beyond anything that I've experienced- my nearest approaches were 17th December 2009-9th January 2010, and 25th November-26th December 2010. Having read through all of the accounts, I get the impression that I'd have really enjoyed the early part of that winter, but not sure about 9 weeks of it, as the references to dwindling food supplies, broken heating systems and repeated partial freeze-thaw cycles turning the snow icy are off-putting. However, there's a lot to be said for living through such a remarkable event and being able to tell the tale afterwards- I have no regrets about being in France during the August 2003 heatwave for instance, even though it was hell at the time. I think we'd certainly be forced to re-think some of our Health and Safety policies in order to keep moving were such a winter to happen again!

I agree- I remember looking back through the recently-updated Wetterzentrale archive charts from the 1870s to 1940s and being surprised by how many times some sort of northerly or easterly nearly came off but was scuppered by shortwave activity and cyclogenesis around Iceland. Winters were generally colder and snowier on average back then but there were still a fair number that were generally mild and snow free- 1920/21 springs to mind for instance.

It's been cloudy for three days in a row here, just the odd glimpse of the sun during yesterday and today, although judging by the satellite imagery many places to the south and east of here have had a fair amount of sunshine, especially yesterday. It may well have felt quite springlike in the sun, but in the cloudy zone temperatures have consistently been around 9 or 10C by day and night. Certainly looking set to become colder and brighter over the coming week- far too early to be expecting snowfall yet but the models are certainly showing a lot of "north-eastern promise". I recall one GFS run yesterday which had us in the freezer with a north-easterly flow bringing frequent heavy snow showers well inland and 850hPa temperatures of -10 to -13C- that would've had the forum in mega-ramp mode if such charts had appeared inside T+96!

As someone who is often quite critical of the modern BBC forecasts, I just thought I'd pop in here and express agreement- I just saw the forecast on the BBC Points West website and thought that it was fantastic, the right balance of detail & simplicity regarding the upcoming weather, and the stuff about the stratospheric warming is the sort of thing that gets many of those with a passing interest in meteorology to become more interested and understand it better. Makes up for missing John Hammond's forecast last night that made a reference to it.

I was thinking about that post when I saw a BBC forecast last night which was one of those designed to reassure people about "good" weather, particularly in view of the recent flooding- it talked of the mild and dry weather being "just what we need", used positive value judgements regularly and talked up the possibility of many of us seeing some sunshine. Unfortunately I didn't see the one by John Hammond referring to the stratospheric warming that I've seen others talk about. It does seem that breaks in the cloud are a bit more widespread today judging by the satellite imagery but it's still dull here at present, 9.8C.

I certainly wouldn't want Gray-Wolf's scenario of a war-like state to come about- it would force action, but at an extremely heavy price- I would much rather see a long-term plan of managed action to prod us into being more and more sustainable, while minimising the negative impacts on human life. There are many social and cultural barriers towards this, unfortunately, which we will need to address, but overcoming social inertia is extremely hard so I think my greatest hope is that AGW turns out not to be as big a factor as currently thought, and that global warming is near the low end of the IPCC's projected range (a warming of just 1 to 2C relative to pre-industrial levels wouldn't be much of a big deal). Geoengineering will of course not address the problem of dwindling fossil fuel reserves, and most methods are somewhat risky, although I am in favour of measures that involve capturing carbon dioxide out of the atmosphere- as the aim of those is not to "tinker further" but rather neutralise existing human imputs into the climate system. About anthropogenic global warming and climate change, the problem is not a changing climate but the rate of change over a small period of time, the ability of humans to adapt, and the risk of prematurely terminating the current ice age altogether and pushing the Earth into its ice-free state (a climate that has existed at times in the past, with surface temperatures several degrees above today's). The Earth will almost certainly survive, but can we? Some aspects of climate change can't be helped, but many aspects of the anthropogenic component can be. One of the most annoying arguments for inaction is, "either AGW doesn't exist, in which case inaction is justified, or it does exist but that's life, and thus inaction is still justified."

I think Scandinavian highs can deliver significant snowfalls to E Scotland and NE England, but generally only in association with a specific setup. The high must ridge across to the north of Scotland pulling in a cold easterly or north-easterly airflow, and bring in very cold arctic continental air, with the instability over the North Sea providing frequent and heavy snow showers. The two most famous examples occurred in February 1991 and January 1987. In both cases disturbances in the easterly flow caused snow showers to be replaced by more general areas of snowfall at times. http://www.wetterzen...00119910208.gif http://www.wetterzen...00119870111.gif We've had relatively slack easterly flows delivered by a Scandinavian high which brought big snowfalls to many eastern coastal areas but relatively limited falls in inland areas, on 20-22 November 1993 and 27-29 December 2005: http://www.wetterzen...00119931122.gif http://www.wetterzen...00120051228.gif Snow stuck around for 8 days at Durham and for 7 days at Aberdeen Airport and Leuchars from the November 1993 cold spell. I recall reading reports of some 15-20cm of lying snow in some spots near the east coast as well. On occasion though, if a really cold airmass accumulates over the Balkans, a south-easterly can bring a fair amount of snow- I remember that mid-February 1994 turned rather snowy at Tyneside: http://www.wetterzentrale.de/pics/archive/ra/1994/Rrea00119940215.gif I think the main issue with the Scandinavian high is that it often gives us a combination of surface cold off the continent and relatively mild air at 850hPa (often above -5C) and this translates to generally dry cloudy weather. In the SE, the short track over the North Sea means that temperatures hover around freezing and any precipitation falls as snow, but in the NE the longer sea track often pulls the surface air temperature up to 3-5C and showery activity near the east coast tends to be rain, sleet and graupel. The Scandinavian high is sometimes associated with "battleground" frontal snowfalls, for which you don't necessarily need particularly cold 850hPa temperatures- sometimes values just below 0C suffice. However these snowfalls tend to mainly affect central, western and/or southern parts of the UK, and as the frontal systems head into NE England and E Scotland they tend to weaken and the surface winds with a long track over the North Sea often raise the temperature above freezing and give a rain/sleet mix rather than snow.

Like many forecasts, my forecast for December started off well then veered rather wide of the mark. [quote]Changeable and generally cold, some snowfalls During December 2012, the jet stream will be tracking from north-west to south-east over the eastern North Atlantic and Europe for most of the month, and this will enable a succession of northerly and north-easterly outbreaks to affect the British Isles. It won't be as intensely cold as December 2010 was, but it will be cold enough for snow at times, particularly over the north and east of Britain but less so in the west. Following two cold bright days and then a milder interlude on the 3rd with some sunshine and a few showers in the west, another northerly outbreak will arrive on the 4th/5th December. A wintry mix of showery precipitation will spread southwards on the 4th, particularly affecting northern and central parts of England, though snow will mainly be confined to high ground. On the 5th most places will be cold, dry and sunny, but sleet and snow showers will affect eastern coastal counties with snow generally from Teesside northwards. Between the 6th and 8th December another low pressure system will slide south-eastwards, and will bring an active belt of rain (preceded by a brief fall of snow in eastern Scotland and north-east England) on the 6th, which will aggravate any flooding problems left over from November's rain. The rain will clear away southwards early on the 7th, with some possible snow on its northern flank, but the wintry showers that will follow behind into eastern areas on the 7th/8th will generally produce rain/sleet at low levels and snow on hills. Another depression will slide south-eastwards between the 9th and 12th and this low is associated with considerable uncertainty- the weather during the following week of the month will be strongly dependent on its precise track. A belt of rain and strong winds is expected, followed by another northerly/north-easterly outbreak with sunny intervals and wintry showers. Temperatures will be rather below average but not exceptionally so, and towards midmonth a north-easterly type is expected to prevail with high pressure extending from Iceland to Scandinavia. It will be generally dry and sunny in the west, while eastern areas will have some sunny intervals mixed with wintry showers, mostly falling as a sleety mix near the east coast but with snow inland. Around the 15th-18th low pressure will start to attack from the south-west which will eventually result in milder air coming up from the south, but not before many of us see some sleet and snow on the northern flank of the weather systems. The Midlands and central and western parts of northern England will be most prone to snow, while eastern coastal areas will mostly see rain due to the winds off the comparatively warm North Sea. The last third of the month is somewhat uncertain, as we will most likely see a burst of polar air coming down from the north around the 20th of the month, while depressions will continue to take a southerly track. Thus, a cold snap is likely shortly before Christmas, with north-eastern districts most prone to snow showers, while southern areas will be prone to belts of wintry precipitation associated with lows passing by to the south. It is hard to place much confidence on the chances of a white Christmas at this stage but the wintry spell may hang on for long enough to give some places a white Christmas, more likely the further north-east you are. A milder, changeable south to south-westerly type is expected to finally establish towards the end of the month. Overview Notably mild Decembers have been rare in recent years- the last one was way back in 1994 in the south, and 1988 in the north. This December won't be breaking that run, though nor will it be quite as cold as December 2010- temperatures will be about 2 to 2.5C down on the 1981-2010 average over most of the country, with a Central England Temperature of 2.4C expected. Much of northern and western Scotland and Northern Ireland and south-west England, however, will only be 1 to 2C short of average. Rainfall during December 2012 will mostly be below the long-term average, though with considerable regional variation. Western Scotland and north-west England will have the largest shortages, of 50% or more, but some parts of eastern and southern England will have slightly above average rainfall, and heavy rainfall in the second week of the month may cause further flooding issues in south-west England. Averaged nationally the shortfall will be aruond 20-30%. It will be a sunny December over most of northern and western Britain, with excesses of 50% or more over much of Ireland, western and northern Scotland, Wales, and western England. However, eastern and southern England, together with south-eastern Scotland, will only have slightly above-average sunshine. Averaged nationally sunshine will be about 30% above average. [/quote] The first 10 days of the forecast went pretty well in my opinion, but after that it went downhill. There was strong ensemble support for the link-up between the Siberian and Icelandic highs after the 10th which would have produced an east to north-easterly blast with sunshine and snow showers, perhaps a sleety mix near east-facing coasts and mostly dry in sheltered western areas. It would also have delayed the return of the Atlantic. However, in reality the Siberian high stayed put and the Icelandic high threw up a weak ridge down to Britain, giving a few dry cold sunny days and then a fast Atlantic breakdown. As an aside, I remember a couple of comments talking of a fast breakdown being a case of greatest risk/greatest reward. Whenever I see that phrase it always seems that the "greatest reward" involves, at best from a snow lover's perspective, a limited area of the UK having a shot at a major snowstorm like the one that hit the south-west in February 1978 or the Midlands one on 8 December 1990, while the rest of us make do with a brief snow-to-rain event. Mid-December showed us the other side of the coin- the breakdown was so rapid that most of us just saw rain. My forecast for around the 17th-20th fell into line with what actually happened, but then the trough in the eastern North Atlantic proved far more persistent than I had predicted (though I sensed that there was always a possibility of this- I just didn't consider it very likely). As a result there was no northerly pre-Christmas and a traditional mild west to south-westerly type increasingly became established towards the month's end. As a result of the greater Atlantic influence, mean temperatures were a couple of degrees higher than I predicted, rainfall was markedly higher, and sunshine totals were lower, though the sunny first half more than counterbalanced the dull second half in most parts of the UK. In the end, the forecast from the 11th onwards was pretty inaccurate, though in my defence, most forecasts got heavily de-railed this month.

The sort of weather that we've been taught to love at this time of year- dry, cloudy (lenticular cloud in the lee of the Pennines) and 11.4C. I wouldn't mind a mild settled spell if it included a fair amount of sunshine, particularly given the flooding situation, but it looks likely to be predominantly cloudy for the foreseeable as the near-continent is also pretty cloudy- time to concentrate on things other than weather observing maybe!

I think there's considerable uncerrtainty around the T+240 area- a lot of model runs have been keeping high pressure close by but the GFS has often been throwing in deep lows and a chunk of the polar vortex, which would mean very disturbed and blustery weather with the possibility of wet snowfalls in the north. Too far out in my opinion to be able to place much confidence in it at this range.

I will also add that if we get extensive northern blocking, but a slow-moving trough in the eastern North Atlantic, then the result will generally be a mild UK and a cold continent. The December just gone provided quite a good example of this- the persistance of the trough to the west and the lack of a link-up between the Icelandic and Siberian highs from around the 10th onwards threw most forecasts for the month offline, including mine. This is something that we'll need to bear in mind if we get a major stratospheric warming event- though of course increased northern blocking substantially increases the probability of something cold and snowy arising in the long run. The charts for the next 7-10 days in the vicinity of the UK remind me a bit of January 1989 although the Siberian High is much stronger than it was in Jan '89 and so the mild SW'lys are not expected to penetrate as far east and south into Europe and Asia- it doesn't strike me as particularly likely that this setup will show anywhere near the level of persistence that it did in 1989, but 7-10 days minimum seems likely. Current indications are that sunshine will be variable rather than plentiful for most of the UK, and generally deficient over Northern Ireland, Cumbria and the north and west of Scotland, but it will feel quite springlike wherever the sun does emerge.

4.4C

A bright and breezy New Year's Day lies in store for a large majority of the country, with some scattered showers in the west- I remember quite a few bright and breezy New Year's Days in the recent past. The anticyclonic period starting on Wednesday will be grey and drizzly initially as a frontal system moves east introducing tropical maritime air. I also think Thursday may turn out rather grey for most of us and the GFS is suggesting an area of rain over SW Scotland and Cumbria- so not necessarily dry for all of us. It's from Friday onwards that we are likely to see more of a continental influence come into southern areas in particular. Cloud amounts associated with any continental air remain very hard to pin down at this range, but the current GFS projections are suggesting variable amounts of cloud, so probably sunny on some days and cloudy on others. As others have noted, the cloudiest overall conditions are likely to be found in the NW. Some of the longer-term outputs, notably this evening's ECMWF run, are bringing in a strengthening continental influence which would bring relatively cold dry weather and some long-term potential for an evolution to something snowy, but the signs at present are only tentative. The ECMWF ensemble mean still has high pressure centred to the south at T+216/240.

Looking back to my own December forecast (which predicted a CET around the 2.5C mark, although I forgot about the CET prediction thread), the main points were as follows: Forecast was generally accurate until around the 10th Overestimated the strength of the link-up between the Icelandic and Siberian highs around the 10th-15th, which would have meant an easterly blast, and a slower subsequent return to milder weather from the Atlantic. In reality the Icelandic high sunk over the UK and the Atlantic came in relatively unopposed. From 15th-25th, expected a milder interlude with low pressure to the west, but then a surge of Arctic northerlies towards Christmas. In reality the trough stuck around stubbornly to the west and so the Arctic blast never reached us. Mild end to the month as predicted, though I did not envisage a sharp decline in the amount of northern blocking. One major point that comes out of this is that if we get extensive northern blocking but a persistent trough to the west of Britain, the outcome often tends to be mild. There was a good example of this during January 1969, although the blocking changed position into February and gave us a cold and, for many, snowy February.

Ian Brown's assessment seems fair. I think sunshine amounts in the south will largely depend on how cloudy it is over the near-continent, as the high pressure will pull in some continental air from central and southern parts of western Europe. Continental air is generally dry and clear in the summer half-year but in the winter half-year banks of cloud can get trapped underneath inversions and then drift in off the continent. Thus I cannot really commit regarding sunshine amounts in southern Britain at this range. Tropical maritime air off the North Atlantic is usually cloudy at this time of year so the further north you are, particularly to the west of high ground, the more likely it is that a cloudy quiet spell is impending.

Boxing Day 1984 might have had sleet/snow showers as we got quite a cold polar maritime incursion, but it doesn't seem likely that it would have lay on the ground at Manchester: http://www.wetterzen...00119841226.gif In the Tyne and Wear area lying snow was more common than in Manchester but those of 1994, 1999, 2002, 2004, 2006 and 2007 had no snow lying days under Met Office rules, while 2006 and 2007 were snowless. 2012 had a couple of days of snow lying there in the first week, but here at Sandhutton December 2012 looks like passing by without any Met Office snow days.

Christmas Day 1995 still stands as my favourite Christmas Day weatherwise (just edging out Christmas Day 2010) for at Cleadon I was well-placed to catch the heavy and frequent snow showers that ran down the east coast of England that day, started the day with about 3cm on the ground (from a decaying polar low on Christmas Eve) and ended it with about 8cm. Christmas Day 2010 had a deeper covering there (11cm) but no more than the odd flurry. However, snow showers were rather less widespread in inland areas on Christmas Day 1995 than was originally forecast, even on the evening before by the looks of it, so some will have ended up disappointed.

A good point- the anomalies relating to short-term synoptic variability will even out more readily over the globe as a whole. There may still be minor anomalies (e.g. a strongly positive NAO can cause enhanced warmth by a few tenths of a degree in the Northern Hemisphere, due to concentration of warm anomalies over the continents) but the magnitude of the anomalies will be somewhat smaller. Some good points also about reliability of earlier records and the anonalous warmth of the 1990s. I forgot to mention that the NCDC compares global temperatures with the twentieth-century average, which drowns out the warmth of the 1990s more effectively than a 1951-2000 base period but the downside is that the earlier years of that period have relatively limited data in parts of the globe. That said, the resulting anomalies are very similar to those relative to 1961-1990, perhaps fractionally greater due to the colder temperatures in the first three decades of the century, so it doesn't appear to make a significant difference (unlike, say, moving to 1981-2010 which would dramatically mask the warm anomalies).

Something to keep an eye on for the snow lovers in Scotland and Ireland for the 29th/30th December as the cold northerly blast to the east of Greenland might give us a 36-hour window of cold north-westerly winds with sunshine and snow showers: http://cdn.nwstatic..../h850t850eu.png That chart is from the GFS, but the ECMWF and UKMO and the ECMWF ensemble mean all show strong support for it. Nothing particularly remarkable, but I remember previous examples of similar polar maritime blasts bringing lying snow to parts of north and west Scotland, Ireland and on higher ground over Wales and NW England. There was one on the 28th December 1998 following the notorious gale on the 26th/27th, and 18th January 2005 was another good example. The GFS 06Z run is projecting wintry showers quite widely over northern England also. I'm placing it in the "worth watching" category although bear in mind that such blasts are often toned down as we get nearer the time. Before that, we have a few days of relatively quiet weather to come, but there will be a broad scoop of tropical maritime air preceding the possible 36-hour cold blast, as the 28th/29th December look like being particularly grey and wet for most of us, particularly the west of Britain, which will lead to further flooding. With a deep Icelandic low there will also be strong to gale force winds in many parts of the country, so the period 28th-31st December is worth keeping an eye on for various reasons.

I spent the period January to mid-June in Cleadon in the Tyne and Wear area, and from mid-June onwards I was based in Sandhutton (N Yorkshire). This will have made slight differences to the specifics but the general weather was much the same. January- Mild, dry and sunny, most memorable for a windy start and an anticyclonic spell midmonth with stunning sunsets, reminiscent of the February 2008 one. Otherwise, a month that won't stick in the memory, though the high sunshine amounts were welcome. February- Cold first half, much milder second half, very little snow, though an "ice-storm" on the 4th. March- Warm and dry with variable cloud until the last third, then exceptionally warm and sunny, with 20C on a couple of the days. April- A "switch-around" at the start with some wet snow and a strong NE wind, then the month became increasingly dull and wet. May- Cool and cloudy first two-thirds, a notable cold snap on the 5th/6th but not quite cold enough for sleet/snow. Memorable warm sunny spell in the last third which rather fortuitously coincided with a trip to Norwich to have a BBQ with some students. June- Dull and wet with low daytime maxima and frequent Atlantic depressions, some convective events at the end although Sandhutton's thunderstorms on the 28th were nothing compared with what Tyneside got. My birthday (22nd) was particularly autumnal this year, as were the preceding two Fridays. July- Dull and damp first half with a staggering number of drizzly "non-weather" days, got drier, brighter and warmer in the second half but still often cloudy. August- Warm sunny first half, the sunshine was mixed with showers and frequent thunder in the first week while the second week was mostly dry, but the second half saw dull wet conditions increasingly make a return. September- Dry and sunny until the last week, warm first third and cool middle third, but then exceptionally wet around the 23rd-25th with flooding. October- A varied and "episodic" month, with unexpected snow showers on the 26th/27th- the first time I've seen snow in October. Wet, due to a couple of active individual frontal systems, most notably overnight 11th/12th. Sunshine probably a little above average, though it was grey and drizzly around the 22nd-25th. November- An average month until the last week with little of note, then yet another exceptionally wet spell thanks to slow-moving frontal rain belts. December- A cold first half which promised snowfalls but failed to deliver more than a brief dusting on the ground, though it was notably sunny. Since midmonth, though, it's been mostly dull and wet with yet more slow-moving frontal belts and flooding. Overall I found late-March, late-May, the first half of August and much of October rather enjoyable, but otherwise pretty poor- the main points of note were the unrelenting greyness of much of June and July and the frequency of active slow-moving rain belts with prolonged moderate rain sustaining for upwards of 24 hours and resulting in flooding.

The current NOAA 8-14 day outlook suggests continued west to south-westerlies over the UK but with blocking around the North Pole and eastern Canada/western North Atlantic: http://www.cpc.ncep.noaa.gov/products/predictions/814day/500mb.php Potential for a pattern change from that setup I think, but certainly a recession of the northern blocking compared with recently.

The main issue with the current projected setup, as often happens in these situations, is that while we have a lot of cold air flooding out of the Arctic into the eastern North Atlantic, the strong jet stream just to the north of the British Isles is set to send a rapid succession of weather systems in off the Atlantic. This forces the cold air to travel a long distance over the Atlantic before it eventually reaches us as polar maritime or returning polar maritime air (as opposed to a colder arctic maritime version) and those incursions are brief and interspersed with tropical maritime incursions, especially the further south you are. Parts of Scotland, especially to the north of the Lowlands, may get some marginal snow events out of this setup though. Christmas Day itself looks like being one of the brightest days of the spell for most of us, and probably dry away from southern and western coastal areas, though there is the chance of a disturbance giving more general rain over southern England. Wet spells will include Christmas Eve and possibly the period 27-29th for N and W areas as we get a burst of mild and moist tropical maritime air. I'm not convinced about this pattern lasting 4-6 weeks, given the teleconnection support for a colder and more blocked spell towards mid-January, but I think we are unlikely to get out of this essentially zonal pattern until after the first week of January.

I agree with the general premise (for a climatological type of analysis it makes far less sense to keep updating the reference period than when, say, reporting the latest month's weather) but think that the World Meteorological Organisation's idea of having a 30-year mean updated every 30 years for that purpose is far from ideal. I would suggest a longer-term baseline such as 1951-2000, or maybe even 1901-2000 if the pre-1950s station networks were reliable enough back then. I remember when analysing the Central England Temperature series, finding that the period 1981-2010 had anomalously cold Decembers (relative to the other months, in the context of longer-term averages) and the 1961-1990 period had anomalously warm Octobers, whereas extending the average to 1951-2000 largely drowned out the short-term variability.