January CET

[Optimus Prime]

06z certainly is a cold run. Period 24th-31st comes in at 1.0c. Assuming to the 23rd it's 1.3c. The CET would end up at 1.2c to the 31st.

[kold weather]

As others have stated with regards to the sub 3C we've had spells where had they either fallen earlier/later in the winter or not been lobed across months we'd have come in sub 3C. Heck even this cold spell was lumbered between two months (from 11th Dec- 15th Jan) and whilst the CET will come in very below average, its still not a true reflection of how cold it really was.

An example would be March 2006 which had it been earlier in the winter would have very likely led to a sub 3C month given its relative to the average, December 01, 08 and 09 all would have been cold enough relative to the average to give what was needed.

Still this is going to be our first signifcantly cold Jan for a very long time, the severe winter month (1.5) benchmark is a much more important benchmark IMO, only one month has reached it since Jan 87, and that was Feb 91 and only *just* as well, no other month other then December 1995 has even come close.

[reef]

As others have stated with regards to the sub 3C we've had spells where had they either fallen earlier/later in the winter or not been lobed across months we'd have come in sub 3C. Heck even this cold spell was lumbered between two months (from 11th Dec- 15th Jan) and whilst the CET will come in very below average, its still not a true reflection of how cold it really was.

An example would be March 2006 which had it been earlier in the winter would have very likely led to a sub 3C month given its relative to the average, December 01, 08 and 09 all would have been cold enough relative to the average to give what was needed.

Still this is going to be our first signifcantly cold Jan for a very long time, the severe winter month (1.5) benchmark is a much more important benchmark IMO, only one month has reached it since Jan 87, and that was Feb 91 and only *just* as well, no other month other then December 1995 has even come close.

Its certainly true that we've been unlucky especially in periods like March 2006 and last winter. However, the same will have also happened in the past, so its not just that we've had an extra dose of bad luck in the last 20 years, but rather the regularity of such cold spells that allow a sub-3C/severe month have decreased markedly. It was always going to be the case that we'd record a sub-3C month again at some point, mainly because as recently as 1986 we recorded a month well below freezing and background warming can only account for some half a degree or so since then. Indeed, theres no reason in a 'perfect storm' scenario that we couldnt record a sub-zero month now, its just slightly more difficult and would require patterns (AO, NAO etc) and luck with the time period (spanning a month perfectly) that allow it.

Hopefully this isnt just a rare occurance and we're returning to a more favourable pattern than the last 20 years. The globe would have to warm up a hell of a lot more before recording sub-3C became impossible. I do wonder however if people would be prepared to return to a 60s/80s sort of pattern but have to put up with similar summers aswell?

[kold weather]

Yeah Reef thats certainly the case, we have had a big decrease over the last 15 years in those cold spells that have lasted for more then 10 days and the intensity of cold spells haven't generally been that impressive, in terms of relative temps the most impressive would probably be the 2nd half of November 05, the 1st 20 days of March 06 and obviously Jan 10, those are the ones that really stand out IMO.

Indeed Reef I think we may have got a 30 day sub zero spell this winter though I'm not totally sure of the stats?

Saying that I recall something that TWS has said in this thread about those inter-montherly cold spells and pretty all of our coldest periods i the 00s did straddle months, whilst those of the 50s seemed to more often fall neatly into calander month periods on a much higher rate then in the 00s. Dec 1950 saw cold air arrive for the start, so did Jan 54, Jan 55, Feb 56 and to some extent Jan 59 though that didn't get colder till a few days into the month. However it is fair to say our winters in the 00s were milder anyway in general then those of the 50s.

I suspect Reef most people's perfect year would be 1947 which had a very severe Feb and also a very good summer, as well as some very noteable other weather events inbetween such as protracted dry spells as well as some exceptionally heavy rains in March.

Edited January 24, 2010 by kold weather

[Thundery wintry showers]

I do wonder however if people would be prepared to return to a 60s/80s sort of pattern but have to put up with similar summers aswell?

Good question, but I have a feeling that we're already there. The summers of the 2000s were not any drier or sunnier than the summers of those colder decades- the only difference was the 0.5C or so of extra warmth that has accumulated over the Northern Hemisphere resulting in them being slightly warmer. Similarly if we move into an era of colder snowier winters we will have that 0.5C to add on.

Regarding the lack of sub 3C months, it's remarkable how often the cold spells of the winters of 1977-87 coincided exactly with calendar months. But there were also numerous cold spells in the 1950s and 1960s which bridged between calendar months, resulting in the CET outturns not being particularly low. I think it's just one of those quirks that evens out with time, but in the meantime the Northern Hemisphere has certainly warmed.

[damianslaw]

Increasing chance of the CET coming in below 2 degrees I feel. Tomorrow and Tuesday look quite cold in the CET zone so we could see a slight drop even from current values. Wednesday and Thursday will be fairly mild it seems, maxes of about 7-8 degrees nothing exceptional, so a slight increase we could be quite close to 2 degrees by Friday, but then the last 3 days will see a drop, finishing number perhaps 1.8 degrees with room for downward adjustments may just scrape a 1.6 degrees, 1.5 degrees is probably the lowest realistically we can get too, much will depend on how cold the nights can get at the end of the week.

[kold weather]

Even Wednesday and Thursday are still likely to come in cold, we do have a mild sector coming in ahead of the cold for Wednesday but any milder temps in response to this (6-8C as you say) will be easily balanced out by what looks like being a pretty cold night. I'd say 1.4-1.8C is the range now, any major downward adjustments (0.2 or more) will make a Severe winter month very probable.

Also this Jan means that we are pretty much certain to get a below average winter as well, even some of the horrid mild Febs of the past 20 years still won't cut it...

[The PIT]

Generally the GFS has under the temps by a large margin while the Beeb has over done them by a margin. Well for here anyway but it maybe not the case for other places.

[Weather-history]

.

Still this is going to be our first signifcantly cold Jan for a very long time, the severe winter month (1.5) benchmark is a much more important benchmark IMO, only one month has reached it since Jan 87, and that was Feb 91 and only *just* as well, no other month other then December 1995 has even come close.

Applying a 1.5C benchmark has problems.

You can't really apply that value to December because that month is on average the warmest winter month. Its about 0.9C warmer than January and February on average, so not surprisingly, it is harder to get a December having a CET that low.

Applying it to January, has its pitfalls because there are far more colder Januarys than Februarys, for instance there are 69 Januarys that have a CET of 1.5 or less to 43 for February.

If you look at the rankings, February 1991 was actually colder than January 1987 in terms of its position within its rankings.

It maybe better to determine a severe winter month by its position in its rankings rather than a cross the board value.

[kold weather]

Yeah a ranking system probably isn't bad, its why a relative system isn't a bad one to use IMO.

Anyway 18z GFS once more again suggests something between 1.2-1.4C as an outcome though I suspect thats a touch low myself, I'd personally say 1.4-1.6C is the most likely range looking at tonights models bar any major downgrade.

[Weather-history]

11th December - 24th January CET: 1.4C

Which is half the winter (45 days out of 90)

Pretty good chance that this winter could be colder than last winter which had a CET of 3.5C

Edited January 25, 2010 by Mr_Data

[Kentish Man]

Hadley has updated and stands on 1.3C (Jan 1 - 24)

There will be a nudge up today after a relatively mild night under cloud cover and on Wednesday as the warm sector passes through. However some colder weather towards the end of the week may keep the final unadjusted figure just below the 1.5C extreme month criterion.

Edited January 25, 2010 by Kentish Man

[Thundery wintry showers]

Interesting that sunshine is still above average across most of the country despite the dull weather since the 10th January. It shows how exceptional the sunshine of 1st-9th January (something like 228% of normal) was!

Philip Eden still has the CET at just 0.7C for 1-23 January. I think Hadley will definitely undergo a bit of downward revision at the month's end, and with a northerly likely to start up from the 28th (albeit only likely to produce CET outturns near 0C rather than the extreme cold earlier in the month) a final outcome of around 1.5C is looking pretty likely.

[phil nw.]

11th December - 24th January CET: 1.4C

Which is half the winter (45 days out of 90)

Pretty good chance that this winter could be colder than last winter which had a CET of 3.5C

That`s impressive Mr D.

Let`s hope that Feb.doesn`t let us down.

It will be good just to get one well below av, Winter for a change.

[summer blizzard]

Personally i define a severe month as having a +/- 3C departure from the 1971-2000 average, so on that basis, we would need a CET of 1.2C or below.

[The PIT]

If the GFS comes off 1.2c cet or less is very possible.

[Stratos Ferric]

Quite a change since my last update. As the narrative in the attached suggests, it's hard to place this month properly in context. Assuming a month end mark of 1.4C, then by recent standards it's exceptionally cold. Taking the deviation from the running ten year mean for the month (= -3.8C) then it ranks 4064/4106, i.e. just about in the coldest centile (1%) of all months since 1668. Feb 1986 (-4.5); Dec 1981 (-5.1); Jan 79 (-5.1); Jan 1963 (-5.6); and Feb 63 (-4.5), in recent times all came in colder on this measure, but they set in context that, relatively, this month is much colder than it has been in absolute terms.

Amongst Januaries alone, it would rank 329/343 on the same anomaly basis. Expand the reference period to 30 years and the rating drops to 322/343 - reflecting the impact of recent warming on the comparative baseline.

This month will also end the record breaking spell without a sub 3.0C month (ditto sub 2.0C, though almost certainly not sub 1.0C).

It may be a long time before we see its like again - unless, of course, we are entering a period of sustained cooling. Personally I doubt it, but then I would have doubted that we could come in this far below 3.0C again.

[kold weather]

The really interesting thing SF is the fact that the monthly figure of roughly 1.5C includes quite a decent length of temps close to average/slightly above which shows just how potent the cold spell in early Jan was, as others have said before its the coldest first 10 days since 1894 and thats a rather impressive figure really!

I think for the first time in a long time we've seen a cold spell that can claim to be of the same strength as those from the 80s at least, I suspect once the adjustments are done we will have 2 days close to -5C in the CET zone, something almost unheard of in these recent times....and lets not forget in theory we can go colder esp given we came off the back of an exceptional November, imagine a November like 05 with SST's a good 2C colder from the off and what could have been possible from then on.

As for sub 3C, I think its quite obvious it could fall given we came soooo close in Jan 09 on the back of what was a rather cold, but far from exceptional cold spell...December 09 proved that it was even more likely given we came so close after the first 10 days being very much on the mild side...however whether or not its an anomaly who knows....

I'm personally hoping we can get to 1.5C...it'll prove severe winter calander months are still very much possible, I have to admit I was becoming unsure of whether we could achieve those sorts of months, I had no doubt sub 3C was possible after Jan 09....but 1.5C or lower is another kettle of fish totally, that usually needs proper deep cold air sources lasting at least 10 days...something that we have finally managed in the peak period of winter rather then way out in either November or late Feb like previous years...

Even compared to past colder winters I think its fair to say this month has been very cold, not exceptional compared to the long term set-up but in the last 20 years its a pretty big outlier, with only Feb 91 to keep this month company...

Edited January 26, 2010 by kold weather

[West is Best]

Quite a change since my last update. As the narrative in the attached suggests, it's hard to place this month properly in context. Assuming a month end mark of 1.4C, then by recent standards it's exceptionally cold.

It's remarkable indeed Stratos. I didn't think we'd see the like of this in our lifetime. However, I think the signs have been there in the last few years, which is one of the reasons I changed the way I did. I remember that cold March back in, what, 2005? (Don't have the data to hand.). Then we've had some potent cold snaps that haven't quite managed to produce whole month cold data (last winter was notable for some very cold spells). This month is truly and properly cold. Remarkable.

[VillagePlank]

Very interesting times, I think.

Here's a ranking system that compares the similarities of a single calendar year to every other year. In this case using 2009 as a baseline, and the comparison technique is Pearson's product moment coefficient. Essentially, which years compare the ups and downs best with 2009?

It's nice to see 1979, and 1942 making it into the top ten. If I get time I will do a month by month rather than calendar year analysis which will include January.

Edited January 26, 2010 by VillagePlank

[Weather-history]

I think what has been notable and has helped kept the CET down is that when it has got milder, it hasn't been that mild.

For instance with the winter of 1981-82, between the two cold spells, there was a short very mild spell where CET daily means got above 8.0C. That alone was enough to add 0.8C onto that January's CET

1984-85 is another example. There was a very mild spell between the two cold spells of that winter with the first 4 days of February 1985 being very mild. Take out that mild spell and the rest of that February had a CET of 0.9 compared with the 2.1 it ended up as.

We have no such spells with this January, indeed since the 11th of December. The mildest daily CET mean since the 11th of December is a provisional 5.3 on the 17th of January.

Interestingly Janaury 1979, managed a 5.4 as its highest daily CET mean for that month.

Edited January 26, 2010 by Mr_Data

[Guest North Sea Snow Convection]

The 'impact' of Jan CET return has simply been that such a cold month has not occured for a while, and therefore it is magnified - but I don't see such impact in the same way in terms of expectations being greatly surpassed because it has always been the case that sooner or later a very cold month would emerge. In that sense it is no outlier at all - such cold months could appear again at any time, and colder than this one too. I see no lower limit that cannot be breached, but then my perception is grounded around what has been in the great scheme of things not the great warming trend, relatively speaking, that others see it to be. Hence why it has, imo, been over estimated and over hyped.

We are, and always have been a maritime country, and with the cyclical patterns that have determined our relatively warmer period over the late stages of the 20th century, it is quite logical that being situated at a crossroads between a large ocean and a large continental landmass, our weather and weather patterns always have been of a capricious nature. Cyclical trends and patterns, over a number of years will simply exacerbate the effects of such a capricious nature even more. Much as we have seen. Nothing more, or less, than that.

Much has been said by some of us about the meteorological and solar factors and drivers that are behind much of this natural variation of our climate and in that sense the signals of the last two winters are just a reminder of that and will continue to be so, and therefore no lower (or upper) limits of constraints should be applied imo in terms of expectations of monthly CET returns.

[Thundery wintry showers]

I remember that cold March back in, what, 2005? (Don't have the data to hand.).

March 2006. The period 25 February-23 March 2006 returned a CET between 2.5 and 3C- which is some 3C down on the 1971-2000 average for the same period. Based on this, I hypothesised that we could still, realistically, get a calendar month falling 3C below the 71-00 mean during the current climatic regime, which translates to a January CET of 1.0-1.5C. We now look like we're about to get one.

Some good points from both Kold Weather and Mr_Data, the milder weather since 10 January has been prolonged but it has never been particularly mild.

The burning question is whether this winter is a one-off, or whether the change in synoptic patterns around 1988 is starting to reverse- there have been some papers recently highlighting the possibility of a move towards the winter synoptics that we saw during the 40s, 50s, 60s and 80s. If so, while our winters won't be as cold or snowy overall as in those earlier decades because of the 0.5C (and increasing) of warming in the Northern Hemisphere, we should end up with a mix of mild and cold winters rather than the mild homogeneity of most recent winters.

[Duncan McAlister]

Quite a change since my last update. As the narrative in the attached suggests, it's hard to place this month properly in context. Assuming a month end mark of 1.4C, then by recent standards it's exceptionally cold. Taking the deviation from the running ten year mean for the month (= -3.8C) then it ranks 4064/4106, i.e. just about in the coldest centile (1%) of all months since 1668. Feb 1986 (-4.5); Dec 1981 (-5.1); Jan 79 (-5.1); Jan 1963 (-5.6); and Feb 63 (-4.5), in recent times all came in colder on this measure, but they set in context that, relatively, this month is much colder than it has been in absolute terms.

Amongst Januaries alone, it would rank 329/343 on the same anomaly basis. Expand the reference period to 30 years and the rating drops to 322/343 - reflecting the impact of recent warming on the comparative baseline.

This month will also end the record breaking spell without a sub 3.0C month (ditto sub 2.0C, though almost certainly not sub 1.0C).

It may be a long time before we see its like again - unless, of course, we are entering a period of sustained cooling. Personally I doubt it, but then I would have doubted that we could come in this far below 3.0C again.

Well last January and December also came very close, and it had been a long time before a month had even come close to breaking the sub 3 barrier (January 2001). It could just be a coincidence, but I think we are seeing somewhat of a correction to the winters of the previous decade (anomalously warm, even taking GW into account).

[kold weather]

The big question for me is whether we are going through another version of 95-97 which had a couple of colder winters that stick out like a sore thumb in the data or whether we have a longer run with more cold winters then mild, just too early to tell.

Still this winter will be a big outlier compared to all winters since probably 91, and probably if things keep going the way they are a good bit colder then even 08-09.