December CET

[reef]

The Hadley CET is now 4.3C to the 23rd. Yesterday came in at 7.6C.

An average of 3.0C is required for the final 8 days to reach 4.0C by month's end before adjustment.

Looking at the temperatures on the GFS, the maximum temperatures are marginally higher (3-6C) and frosts very hit and miss depending on cloudcover, so we may actually see very little change now. Around 3.8-4.0C might actually be a good landing point right now.

[kold weather]

Possibly Reef, though the beeb are pretty keen on temps between 3-4C, but much depends on what the mins do really I suppose. Should just get below 4C I reckon.

[The PIT]

Well a warmer day than expected and this morning figures on TV suggest this cool spell may not be as cold as originally thought. If the nights are as cloudy as this morning (In fact very sunny) there's hope yet for us.

[Optimus Prime]

 but much depends on what the mins do really I suppose.

Not really Kold. Even if there's an average minima of -2c, that'll be only 3c below the current average of 1.4c. If there's a 24 hour maximum of 3c, that'll be 4c below the current 7.4c.

It's all down to daytime maxima now. I don't think they'll be a great deal of change to minima. Maybe as little as 0.6c from here until the end. Could see over a 1c drop in maxima though.

Around 3.8-4.0C might actually be a good landing point right now.

Far too high still. 3.4c to 3.7c as the absolute high.

Edited December 24, 2008 by Optimus Prime

[kold weather]

Good point OP, 3.4C is too low at the low end IMO though given mins look like they are only just going to be in minus figures and I think looking at the general temps an average around min 0C is far more probable, despite that maxes do look rather surpressed and so I'd guess around 3.6-3.8C currently would be my range.

Edited December 24, 2008 by kold weather

[reef]

Not really Kold. Even if there's an average minima of -2c, that'll be only 3c below the current average of 1.4c. If there's a 24 hour maximum of 3c, that'll be 4c below the current 7.4c.

It's all down to daytime maxima now. I don't think they'll be a great deal of change to minima. Maybe as little as 0.6c from here until the end. Could see over a 1c drop in maxima though.

Far too high still. 3.4c to 3.7c as the absolute high.

To attain a mean of 3.7C now would require the final 8 days to average 1.8C. Today and tomorrow arent going to get anywhere near that, so outside of a massive correction at the end of the month by Hadley, it looks very unlikely indeed. If anything, when Hadley updates tomorrow we'll be more likely to see an increase to 4.4C, as today is in reality 4.33C.

[Snowly does it]

4.3 to the 24th = 103.2 cumulative degrees (I am assuming today is a no-changer)

2 per day from ere (optimistic if you ask me) = 14

117.2/31 = 3.8ish

Its not going to average less than 2 from here on in unless something drastic happens on the model output

at best a 0.2 adjustment (Phillip has already adusted up towards Hadley) = 3.6 low end for me, which is that tantalising 1.5 below average we keep not getting.

[Kentish Man]

Merry Christmas to all on N/W.

Climate UK (Manley) has updated

CET: (Dec 1-24): 4.1°C (-1.1 degC)

Although Hadley is still running higher than this, in most of 2008 after final month-end adjustment the two have finished within 0.2C or less of each other. This still leaves hope that the month will average the 4.0C or less required for the annual CET to end up below 10.0C. The only danger is the unexpected influx of mild southerlies into the CET zone in the final 2 days of the month as progged in the latest model runs.

[Kentish Man]

Hadley is on 4.5C.

Today may see another small rise to 4.6C then it should gradually start falling back.

[david16]

In recent times, normally we would have killed for a current CET of 4.5, but considering that the 1st half of December was the coldest start to a winter for 30 years, it's tinged with disappoinment especially considering the normal CET for the 2nd half of December is usually lower than what this 2nd half of December is going to end up by the looks of it now.

While considering how cold it was 1st half of December it was unrealistic to expect it see it fall further or even stay the same despite normal form 2nd half of December is usually lower than the 1st half, but you would have expected it to see it not rise by more than only just a few 10ths a degree, but a full 2C + 3/10ths of a degree rise nearly in less than 10 days it's quite a spectacular turnaround which is unreal considering the norm 2nd half of December CET is not usually as high as it has been since this mid December.

It always seems now that it's mild 1st half to a month with a colder 2nd half but not cold enough to get it average or below. Or it's extra cold 1st month as it's been this December, but record mild 2nd half to make up to put it around about average or just over average. Maybe one day we will hit our jackpot yet of a degree or more below average in the winter months. More than 1C below end of a month doesn't seem to be a impossible in the summer.

A southerly always appears form nowhere to totally spoil things when it seemed a certainty that it would end up significantly below normal to be classed as truly cold month, it suddenly it ends not quite as below to make it a significnatly cold monith.

Edited December 25, 2008 by david16

[david16]

This month looks like it the weather equivalent of trying to lose weight when on a diet, you look certain to lose it on this weeks official weigh in this Saturday compared to last Saturday (you were 2 or 3 lbs less on Thursday on the scales than you were last Saturday), but then a party night out on the Friday where you spoil yourself silly with food and drink (including 4 pints of beer or lager) ruins it completely and you have put weight on compared to last Saturday come the Saturday weigh in.

And it looked so promising for so long.

Edited December 25, 2008 by david16

[Optimus Prime]

In recent times, normally we would have killed for a current CET of 4.5, but considering that the 1st half of December was the coldest start to a winter for 30 years, it's tinged with disappoinment especially considering the normal CET for the 2nd half of December is usually lower than what this 2nd half of December is going to end up by the looks of it now.

Firstly the first half was the coldest since 1991, that's not thirty years and secondly, 2nd halfs of December being warmer then the first isn't all that uncommon, more common than you'd probably think.

The southerly probably isn't going to make a huge difference because it's going to be an inversion high meaning the CET land will be just as cold as if this easterly was to continue. Bearing in mind this easterly will be yet another disaster for cold!

A few years to chew on the idea of December being an ordinary month, look at this run in the 80s 

December 1991 finished on 4.6c despite averaging 2.1c for the first 15 days.

December 1990 finished on 4.3c despite the first half averaging 3.6c.

December 1987 finished on 5.5c despite the first half averaging 2.4c.

December 1983 finished on 5.5c despite the first half averaging 3.7c.

December 1982 finished on 4.4c despite the first half averaging 3.9c.

December 1980 finished on 5.6c despite the first half averaging 5.2c.

A few more examples in the 70s as well.

[Stratos Ferric]

Firstly the first half was the coldest since 1991, that's not thirty years and secondly, 2nd halfs of December being warmer then the first isn't all that uncommon, more common than you'd probably think.

The southerly probably isn't going to make a huge difference because it's going to be an inversion high meaning the CET land will be just as cold as if this easterly was to continue. Bearing in mind this easterly will be yet another disaster for cold!

A few years to chew on the idea of December being an ordinary month, look at this run in the 80s

December 1991 finished on 4.6c despite averaging 2.1c for the first 15 days.

December 1990 finished on 4.3c despite the first half averaging 3.6c.

December 1987 finished on 5.5c despite the first half averaging 2.4c.

December 1983 finished on 5.5c despite the first half averaging 3.7c.

December 1982 finished on 4.4c despite the first half averaging 3.9c.

December 1980 finished on 5.6c despite the first half averaging 5.2c.

A few more examples in the 70s as well.

I tend to agree. The real point is that sustained cold in December (i.e. month long) is exceedingly rare - the hemisphere isn't yet cold enough in enough places to ensure that the UK could import cold from more than one source - this latter would be a pre-requisite because you are not going to get a sustained quasi-stationary block this early in winter which means that acroiss the month we're going to pull in air from several directions; if those sources aren't all cold then the month will not be consistently and completely cold.

Given my opening sentence it follows that a cold start will often be followed by a relatively milder second half. We're also way past the peak rate of cooling now. In October the second half will usually be cooler than the first; In December the mean differential is far less, making the imbalance less unequal.

[Summer of 95]

In recent times, normally we would have killed for a current CET of 4.5, but considering that the 1st half of December was the coldest start to a winter for 30 years, it's tinged with disappoinment especially considering the normal CET for the 2nd half of December is usually lower than what this 2nd half of December is going to end up by the looks of it now.

While considering how cold it was 1st half of December it was unrealistic to expect it see it fall further or even stay the same despite normal form 2nd half of December is usually lower than the 1st half, but you would have expected it to see it not rise by more than only just a few 10ths a degree, but a full 2C + 3/10ths of a degree rise nearly in less than 10 days it's quite a spectacular turnaround which is unreal considering the norm 2nd half of December CET is not usually as high as it has been since this mid December.

It always seems now that it's mild 1st half to a month with a colder 2nd half but not cold enough to get it average or below. Or it's extra cold 1st month as it's been this December, but record mild 2nd half to make up to put it around about average or just over average. Maybe one day we will hit our jackpot yet of a degree or more below average in the winter months. More than 1C below end of a month doesn't seem to be a impossible in the summer.

A southerly always appears form nowhere to totally spoil things when it seemed a certainty that it would end up significantly below normal to be classed as truly cold month, it suddenly it ends not quite as below to make it a significnatly cold monith.

Why is it always the case post-1997ish, that 3 weeks of below average plus 1 week of above average equals average or above? Logically, since more of the month has been below average, therefore the CET should be that as well?

Take March 2006. This month was looking a dead cert for sub-4C, and a good bet for sub-3C, until about the 20th-22nd. A week of southerlies with temps into the low teens- not half as unusual for late March as is 3 weeks with nary a day topping 5C to start the month- came along. Yet it still only just squeezed under 5C, and went from being the coldest March for 30-something years to the coldest for only 10 due to an unremarkeable mild spell.

Summer half-year months that to me were mostly cold (and often dull and wet) have likewise recorded near average or even slightly above average CETs due to a few days of temps into the mid-20s in the SE corner of England only. July and August 2008, May and August 2005 (how on earth did those couple of days of heatwave in the Home Counties in May 2005 produce an average CET when here in Central England we had air frosts in the 3rd week of May) and the entire summer of 2002, take a bow.

[kold weather]

Looks like the models are slighly reducing the mins as we get into the actual easterly flow, looking quite possible that the CET zone will average around 2C from now on, which would be enough I suspect to drag us under 4C?

[The watcher]

3.9c here we come

[Kentish Man]

No increase yesterday - Hadley remains on 4.5C.

If the cold GFS 06z verifies we should edge back below 4.0C by month end and before any final adjustment.

[Guest North Sea Snow Convection]

I think that lowering dewpoints as the easterly kicks in from xmas will mean that clearer conditions come in from the continent by the weekend. This should assist some sharp night time frosts, especially in sheltered central and western areas along with the low daytime temps (assisted by that lovely 'refreshing' breeze! )

I think that sub 4 is very much on the cards

looks as though this is occuring as thought. GIN clear skies and that lovely bracing stiff easterly has arrived. Frost should verify and sub 4 very much probable with the cold sustaining through right into NY and beyond.

[reef]

looks as though this is occuring as thought. GIN clear skies and that lovely bracing stiff easterly has arrived. Frost should verify and sub 4 very much probable with the cold sustaining through right into NY and beyond.

I wouldnt be so sure, if anything that easterly wind will keep minima up. We need calmer conditions for frost in this airflow. Strong winds will just allow the air to mix and minima will stay above freezing. GFS shows this perfectly, as min temps are progged to only be below freezing if you're more than 40-50 miles inland. Only by the 30th when the winds slacken and move to a more southerly direction do we see widespread frosts.

Its telling when you look back through this thread though. Just 3-4 days ago the estimates were mid-3s by months end. Now we look like we'll be lucky to go sub-4C. To reach that we'll need a mean of 1.8C for the remaining 6 days. On Hadley's update, today's min was 2.3C, so today will miss out as temperatures in the CET zone at 11:00 were already 3-5C. So the odds lengthen further. It looks like our only chance will be if temperatures fall more than expected, or if there is a large correction at the end of the month.

[Snowly does it]

I wouldnt be so sure, if anything that easterly wind will keep minima up. We need calmer conditions for frost in this airflow. Strong winds will just allow the air to mix and minima will stay above freezing. GFS shows this perfectly, as min temps are progged to only be below freezing if you're more than 40-50 miles inland. Only by the 30th when the winds slacken and move to a more southerly direction do we see widespread frosts.

Its telling when you look back through this thread though. Just 3-4 days ago the estimates were mid-3s by months end. Now we look like we'll be lucky to go sub-4C. To reach that we'll need a mean of 1.8C for the remaining 6 days. On Hadley's update, today's min was 2.3C, so today will miss out as temperatures in the CET zone at 11:00 were already 3-5C. So the odds lengthen further. It looks like our only chance will be if temperatures fall more than expected, or if there is a large correction at the end of the month.

temps aren't forecast to increase much further today - if anything they will drop off after lunch.

I agree that 4 is hard from here - although worth remembering that GFS isn't really projecting temps to be below zero if you are '40-50 miles inland' - which is pretty much all of the UK apart from some parts of the Midlands, but more like 5 miles from the coast or 10 - the MetO are also keen on sub-zero minima form their forecasts.

It is still possible we will see 3.8, its more likely we will see 4.1 or thereabouts unadjusted and with manley 0.3 behind, we may see a traditional 0.2 correction - but I wouldn't count on it as Manley has adjusted upwards this month suggesting it was too low rather than Hadley too high early in the month.

[Guest North Sea Snow Convection]

I wouldnt be so sure, if anything that easterly wind will keep minima up. We need calmer conditions for frost in this airflow. Strong winds will just allow the air to mix and minima will stay above freezing. GFS shows this perfectly, as min temps are progged to only be below freezing if you're more than 40-50 miles inland. Only by the 30th when the winds slacken and move to a more southerly direction do we see widespread frosts.

Its telling when you look back through this thread though. Just 3-4 days ago the estimates were mid-3s by months end. Now we look like we'll be lucky to go sub-4C. To reach that we'll need a mean of 1.8C for the remaining 6 days. On Hadley's update, today's min was 2.3C, so today will miss out as temperatures in the CET zone at 11:00 were already 3-5C. So the odds lengthen further. It looks like our only chance will be if temperatures fall more than expected, or if there is a large correction at the end of the month.

I think that the majority would settle for the current position - below average is below average. There has been no high latitude blocking synoptics this month to set the bar low, and the initial very cold 30 yr record breaking first half of the month was achieved just on the back of an amplified jetstream and displaced atlantic block, as a subtle change to the flat jet trajectory keeping polar maritime north of most of the UK as we have often seen in recent years. The relatively modest (albeit extremely welcome change!) of synoptics to achieve this, is, on the contrary, much more telling IMO.

Turning to the month as a whole, and the correction since mid month - most months, historically, have had a milder interlude in a cold dominated month - and we should remember we are measuring against 30 - 40 yr averages, not against the expectations of a winter 62/63 or 1947, which are and always have been rare exceptions to the rule. I think it would only be if we were measuring against the outlier coldest months that any relative 'disappointment' could be expressed.

I noted that frost formed early here this morning just before daybreak as the cloud finally totally broke up - and I live in the windiest part of the country as is expected to continue in the coming few days. I think some central and western areas of the CET zone will see some keen frosts and that the breeze, being very dry, and in air with low dewpoints, will not inhibit some penetrating frosts. Indeed, I am suggesting it may accentuate them. Besides, black frost is actually a harder frost than the white variety - I have seen one of the beeb weather people referring to this re the current cold spell.

The cloudier skies will always be further north - much of the CET zone will be in the clearer zone. By months end, a slacker SE'erly slant (as you allude to) will assist the white frost variety more generally.

So lower mins look increasingly likely for the rest of the month, with chilly days -to assist the numbers needed to get below 4

Re GFS temp indicators - they are too unreliable IMO to take too much notice of.

Edited December 26, 2008 by North Sea Snow Convection

[Optimus Prime]

Almost gurantee below 4.0c now. Period 26th-31st averages 1.3c according to the latest GFS. With the current CET at 4.5c, should be around 3.8, final adjustment of around 0.2c brings it down to 3.6c.

1.0c below 61-90 average

1.5c below 71-2000 average.

The last few days do have some fairly hard frosts and low maxima. -4c by night and no higher then 2c by day, that would certainly knock of 0.3c during the last 2 days.

0.7c drop spread out over 6 days is only a drop of 0.11c per day. Very doable if you ask me.

Edited December 26, 2008 by Optimus Prime

[reef]

Almost gurantee below 4.0c now. Period 26th-31st averages 1.3c according to the latest GFS. With the current CET at 4.5c, should be around 3.8, final adjustment of around 0.2c brings it down to 3.6c.

1.0c below 61-90 average

1.5c below 71-2000 average.

The last few days do have some fairly hard frosts and low maxima. -4c by night and no higher then 2c by day, that would certainly knock of 0.3c during the last 2 days.

0.7c drop spread out over 6 days is only a drop of 0.11c per day. Very doable if you ask me.

I think that is extremely optimistic.

The GFS 12z has maxima of around 4C in the CET zone, with night frosts pretty light and patchy until Monday. Theres also the fact that the mean for today will be around 3C as the minima was recorded as 2.3C, with maxima of around 4C, with some areas higher, some lower.

Theres no guarantee the GFS will be right of course, but thats all we have to go on and the numbers pretty much tally with what the MetOffice have on their website.

[Nick F]

I think that is extremely optimistic.

The GFS 12z has maxima of around 4C in the CET zone, with night frosts pretty light and patchy until Monday. Theres also the fact that the mean for today will be around 3C as the minima was recorded as 2.3C, with maxima of around 4C, with some areas higher, some lower.

Theres no guarantee the GFS will be right of course, but thats all we have to go on and the numbers pretty much tally with what the MetOffice have on their website.

GFS tends to overdo the minima at night I find by 1-2C, should be a widespread air frost inland over England tonight given dew points are below freezing - air temp already close to or at freezing point over central England - mins of -3C inland expected by MetO generally a bit lower than GFS progs. Should be colder still Sat and Sun night.

Think 4C or just below is well achievable by end of next Weds.

[reef]

Hadley is still at 4.5C today, yesterday came in at 3.5C:

http://hadobs.metoffice.com/hadcet/cet_mean_est_2008

Today will see a fall, but cloud levels are high and as a result, the minimum last night failed to dip below zero. Metoffice has that at 0.2C:

http://hadobs.metoffice.com/hadcet/cet_info_min.html

Cloud levels look much higher than first thought, the chance of a widespread frost tonight is also very low.

http://www.metoffice.gov.uk/satpics/latest_uk_vis.html