Model Output Discussion - Cold spell ending - what next?

[WYorksWeather]

Going to do my usual post on ensembles etc. later on. But first I'd like to do a more detailed explainer on influences on temperature. In the UK we have two main influences on our temperature that vary depending on the time of year.

The first and most obvious one is solar energy. This one is pretty straightforward. As we move on from the winter solstice, the strength of the sun increases. This process is not linear - initially the change is very slow. At my location, days have lengthened by around 45 minutes since the winter solstice. Of course the peak angle of the sun above the horizon, and hence its strength, has also increased slightly.

We're about four weeks out from the solstice. If we look at where we'll be in another four weeks, so by mid-February, day length will have increased by another 65 minutes. Four weeks after that, by mid-March, the four-weekly increase compared to mid-February is 120 minutes.

Naturally, this process leads a lot of people to think that winter is on its way out by mid-February. However, the second major factor is the temperature of the oceans. Oceans hold an enormous amount of heat, and so they have significant thermal inertia. In other words, sea surface temperatures are at their coldest in March, as they are still responding to colder weather. The same is true over the summer - peak sea surface temperatures in the Northern Hemisphere are typically reached in September.

You can see this clearly in the charts below.  The first chart shows Northern Hemisphere sea surface temperatures today, and the second chart is the projection at day 15. You can still see the advance of the colder colours down the chart, albeit slower than earlier in the winter.

So, how does the change in the sign of temperature work? The answer is that at this time of year we have two competing forces. Sea surface temperatures are still dropping slowly, and solar insolation is increasing slowly. These forces are currently roughly balanced, and hence January and February are relatively similar in temperature.

Towards the middle of February, you see the mean temperature curve begin to bend upwards, and then more sharply in early March. It is at this point that sea surface temperatures are bottoming out, so that counteracting force disappears, and solar insolation begins a more rapid climb.

Summary

Overall, the main point to make is that early to mid-February is still the heart of winter. The four week period from e.g. December 22nd to 19th January probably has a similar, or even slightly lower chance of producing a major cold spell, compared to the upcoming four week period from today, the 19th January, to 16th February.

Beyond that, while severe cold in late February or early March is not unheard of in recent years, most notably the BFTE in 2018, it does become less likely. That following four-week period, from 17th February to 16th March, is a period of much more rapid change.

So, my take on this is that we continue to observe the modelling through to mid-February. If we get to mid-February and there is no evidence of an upcoming cold spell, then only at that stage is the clock running out on winter.

For more experienced posters on here, probably very little of this is new, but I thought it was worth a more detailed explanation.

 

 

[AO-]

Chart of day 10 EC. After the first failed attempt a second one on the way? Great chart for people in Greece that like winter. The southerly current on our side of the continent is not very mild, but still everything should be more West in order to get the next attempt of a cold spell. The Euro high as predicted...

[Anthony Burden]

Evening all,a stormy unsettled week coming up feeling mild after a very cold period then all eyes on high pressure and position along with orientation.ECM 240 hrs looks promising but at that range will change of course but Scandinavian high still on the cards so good watching to see if February could turn into a cold month as met office has frequently pointed in that direction with an easterly feed.

[WYorksWeather]

GFS seems to have binned what looked like an emerging cold or at least average signal on tonight's GFS 12z ensembles, when you compare to yesterday.

There is a lot of scatter in the extended, but I'm really not seeing a cold signal here. Exceptionally mild from Sunday night through to the 26th, then something nearer average, but likely still a little above given the mild nights. There is a cluster of colder ensemble runs, but this doesn't look like anything more than the usual scatter you'd expect to see at this range.

Of course, it will still feel cold, but I think people are in danger of losing perspective here. Even looking at very warm London stations such as Kew Gardens, the late January means on the GFS chart above of 6-7C are at least 1C above average. I've checked charts for elsewhere, and whilst the numbers differ, the general trend is very similar.

Overall, the smart money for at least the current horizon of the model runs is that temperatures will be milder than average, and at times very substantially so.

This is emphatically not a winter is over post, though. All of February is still well outside the reliable.

ECM to compare and contrast later, of course...

[BLAST FROM THE PAST]

BLAST FROM THE PAST

Posted Sunday at 17:35

Location: Redhill, Surrey

I’ve got a feeling that a HP for mainly the south and near continent is looking  to set up shop after the weekend….and dig it’s heels in.
 Going to wait until Wednesday and see where we are then….as there can be adjustments …but Kaprun for 20-27 is looking HP dominated with chilly nights but mildish sunny days.  Still there’s a lovely snowbase in place and a Glacier

BFTP

 

 

So we are at Friday, and to me the HP looks like it will ‘generally’ be in situ as suggested.  I suspect we’ll be in a similar place on my return on 27th.  Be nice to return to something far more juicy looking, but for now have a good week….I think I might.

 

ECM for 29/1….be interesting to see what it looks like at t48.

 

regards

 

BFTP

Edited January 19 by BLAST FROM THE PAST

[Frosty.]

The CFS is looking nae bad in F1! …so much for global warming eh!  

Edited January 19 by Frosty.

[Cambrian]

A confounding feature of this winter so far has been the extent of the tropospheric forcing and the spiritless stratosphere. It’s also been a winter of quite violent bursts of mobility followed by profound periods of stasis, typically signalled by an initial phase of retrogression.

For the former, we have storm Isha and its followers for the coming week, and for the latter, it’s a waiting game. 

Out in week 2 with the 12z GEM ensemble mean what we’re really looking at is a splitting of the southern European heights, one pulse north into Scandinavia, but it’s all very longitudinal and has little traction for an easterly due to the lack of a proper clear out from the south, and ultimately little staying power over Scandinavia. 

 

The other slightly later pulse of heights is west from the Mediterranean into the Atlantic, its passage assisting in scuppering any potential easterly flow through Western Europe, but ultimately this retrogression leads to the prospect of an Atlantic ridge. Notice that the heights in Europe are slowly falling away. 

Looking north, I like the look of the way the PV is being handled, drawn first north away from eastern Canada, then east along the north of Greenland to north of Svalbard. 

The jet stream responds by its exit from the eastern seaboard being pulled a long way south between day 8 and day 16 beginning to split around the forming Atlantic high, here on the 12z GEPS.

 

Most of all I like this evolution as it’s the most reasonable roadmap that I’ve seen so far with good potential to lead to the destination mapped out by the CanSIPS and CFS monthly anomalies (run dates Dec 31st and Jan 15th respectively) for February…

 

…both with the European low anomaly, and strong heights to the west or northwest, and much scope to deliver a highly seasonal month. 

Despite the wait, plenty of opportunity for interesting developments to emerge along these lines (and potentially no doubt many others too!) in the next couple of weeks, as we move towards what could be a fascinating February. 

[Northernlights]

38 minutes ago, WYorksWeather said:

Going to do my usual post on ensembles etc. later on. But first I'd like to do a more detailed explainer on influences on temperature. In the UK we have two main influences on our temperature that vary depending on the time of year.

The first and most obvious one is solar energy. This one is pretty straightforward. As we move on from the winter solstice, the strength of the sun increases. This process is not linear - initially the change is very slow. At my location, days have lengthened by around 45 minutes since the winter solstice. Of course the peak angle of the sun above the horizon, and hence its strength, has also increased slightly.

We're about four weeks out from the solstice. If we look at where we'll be in another four weeks, so by mid-February, day length will have increased by another 65 minutes. Four weeks after that, by mid-March, the four-weekly increase compared to mid-February is 120 minutes.

Naturally, this process leads a lot of people to think that winter is on its way out by mid-February. However, the second major factor is the temperature of the oceans. Oceans hold an enormous amount of heat, and so they have significant thermal inertia. In other words, sea surface temperatures are at their coldest in March, as they are still responding to colder weather. The same is true over the summer - peak sea surface temperatures in the Northern Hemisphere are typically reached in September.

You can see this clearly in the charts below.  The first chart shows Northern Hemisphere sea surface temperatures today, and the second chart is the projection at day 15. You can still see the advance of the colder colours down the chart, albeit slower than earlier in the winter.

So, how does the change in the sign of temperature work? The answer is that at this time of year we have two competing forces. Sea surface temperatures are still dropping slowly, and solar insolation is increasing slowly. These forces are currently roughly balanced, and hence January and February are relatively similar in temperature.

Towards the middle of February, you see the mean temperature curve begin to bend upwards, and then more sharply in early March. It is at this point that sea surface temperatures are bottoming out, so that counteracting force disappears, and solar insolation begins a more rapid climb.

Summary

Overall, the main point to make is that early to mid-February is still the heart of winter. The four week period from e.g. December 22nd to 19th January probably has a similar, or even slightly lower chance of producing a major cold spell, compared to the upcoming four week period from today, the 19th January, to 16th February.

Beyond that, while severe cold in late February or early March is not unheard of in recent years, most notably the BFTE in 2018, it does become less likely. That following four-week period, from 17th February to 16th March, is a period of much more rapid change.

So, my take on this is that we continue to observe the modelling through to mid-February. If we get to mid-February and there is no evidence of an upcoming cold spell, then only at that stage is the clock running out on winter.

For more experienced posters on here, probably very little of this is new, but I thought it was worth a more detailed explanation.

 

 

Just to add have always treated March as  winter up here on the farm. Since we are closer to the Arctic North and East winds in spring are always colder and their frequency also increases in spring.

[Mike Poole]

ECM clusters T192-T240:

Cluster 2 (14 members) has a proper go at a Scandi high.  Cluster 4 has a strong high but ends up to the east of the UK.  Cluster 1 (contains the op) has a less strong build of heights, and cluster 3 weaker still, remains +NAO regime.

T264+:

Clear retrogression signal shown on cluster 1 - even makes the Atlantic ridge regime (purple border) at the end - this has been hinted at previously, but this looks a stronger signal.  Cluster 2 has a high in the vicinity of the UK, to the east.  Cluster 3 has a strong then weakening Scandi high (some members surely in the previous cluster 2).  So still plenty in the mix there, from which something colder could develop…

[AO-]

A small downgrade of EC tonight in the EPS after the 27th. Only one Member going for the full hit. I will check later which one this is. In fact it is a bit disappointing, but both the models (EC and GFS) are backtracking for the end of January. Nothing is set in stone yet of course, but patience is needed for sure. 

Wind probability

 

It looks like the number of southerlies has increased and the number of easterlies has decreased. Mike will probably post the cluster scenarios later on. Curious about the scenarios with a Westerly it southwesterly flow.

Edited January 19 by AO-

[Rain All Night]

10 hours ago, RainAllNight said:

A summary of this morning's model runs.

Deterministic runs up to day 7 (Fri 26th)

Now we can see that Wednesday won't be the end of our succession of Atlantic misfortunes, with another arriving by Friday morning.

Ensemble means at days 10 & 13 (Mon 29th & Thu 1st)

Though the differences are small, these charts look just that little bit less promising to me for a spell of dry weather than yesterday's 12z outputs in my quoted post. Perhaps still OK for the south of England.

A summary of this afternoon's global model runs.

Deterministic runs from days 1 to 7 (Sat 20th to Fri 26th)

I'll be honest, these are disappointing. I'd thought, up to now, that we might see a wholly dry second half to next week for southern Britain.

Ensemble means from days 8 to 14 (Sat 27th to Fri 2nd)

ECM seems to be offering southern Britain a dry week, so I'll take that. Not so sure about the other two. Not much sign of high-latitude blocking.

Edited January 19 by RainAllNight

[northwestsnow]

EC 46 looks very dry.

The model is not really seeing retrogression at this point...

Sad thing about tonight's EC 46 is it looks very sparce on snow which would mean some people remaining snowless out to late Feb , hopefully not ...

Edited January 19 by northwestsnow

[Singularity]

3 hours ago, Mike Poole said:

February composites for 6 and 7 El Niño, amplitude >1.

6 looks rubbish, I’m sure someone was ramping it slightly on here the other day, can’t remember who.  7 looks good but that’s where the question mark over amplitude on the model output is at the moment.

These composites are for all MJO amplitudes however. The ones I’ve referred to are for at least 0.5, maybe even 1.0 amplitude & were produced more recently making them a bit more relevant to the current climate.

Not that MJO composites tell all. The AAM cycle adds its own twist, as does the stratospheric polar vortex state if it’s usually strong or weak.

I continue to view the week 2 modelling with only slight interest for the time being. The first major opportunity to disrupt the Atlantic trough enough to start migrating high pressure appreciably toward Scandinavia is next Fri so I’m hoping for a clearer picture by Mon on whichever way things will go.

3 hours ago, Mike Poole said:

February composites for 6 and 7 El Niño, amplitude >1.

6 looks rubbish, I’m sure someone was ramping it slightly on here the other day, can’t remember who.  7 looks good but that’s where the question mark over amplitude on the model output is at the moment.

These composites are for all MJO amplitudes however. The ones I’ve referred to are for at least 0.5, maybe even 1.0 amplitude & were produced more recently making them a bit more relevant to the current climate.

Not that MJO composites tell all. The AAM cycle adds its own twist, as does the stratospheric polar vortex state if it’s usually strong or weak.

I continue to view the week 2 modelling with only slight interest for the time being. The first major opportunity to disrupt the Atlantic trough enough to start migrating high pressure appreciably toward Scandinavia is next Fri so I’m hoping for a clearer picture by Mon on whichever way things will go.

[northwestsnow]

Ec 46 - MJO forecast - I don't think the MJO has done much to help at all..

[Daniel*]

Appears the El Niño is in terminal decline after peaking in late December as strong El Niño, it is the 2nd strongest El Niño of 21st century, will this have implications for late winter and early spring? I’m not sure over next few weeks, but a weakened El Niño is better for winter prospects in general. Our last strong El Niño being 2015/16 the mildest winter on record in London.

[suxer]

22 minutes ago, northwestsnow said:

EC 46 looks very dry.

The model is not really seeing retrogression at this point...

Sad thing about tonight's EC 46 is it looks very sparce on snow which would mean some people remaining snowless out to late Feb , hopefully not ...

Wouldn't bank to much on this model,wasn't long ago it had high level blocking galore 

[AO-]

Apparently it is member 39 going for the full blast with uppers below-10 at day 12 with a full blown easterly and a Genua low. From the text book I would say. High pressure over Lapland. 

Edited January 19 by AO-

[mulzy]

43 minutes ago, northwestsnow said:

EC 46 looks very dry.

The model is not really seeing retrogression at this point...

Sad thing about tonight's EC 46 is it looks very sparce on snow which would mean some people remaining snowless out to late Feb , hopefully not ...

Indeed nws - it's looking ominous.  Another snowless winter is possible in London to add to the many in recent history.  What makes this winter different is the ridiculous level of ramping by experts and amateurs alike.  Anyway, we have 5 or so weeks of winter left so who knows but the signs are not good (see chart below).

 

[Don]

41 minutes ago, northwestsnow said:

Ec 46 - MJO forecast - I don't think the MJO has done much to help at all..

It won't if that forecast comes off, although it does look to miss out phase 7 as Joe B said yesterday?  However, there's not many ensembles taking it into phase 8.

Edited January 19 by Don

[WYorksWeather]

1 hour ago, Northernlights said:

Just to add have always treated March as  winter up here on the farm. Since we are closer to the Arctic North and East winds in spring are always colder and their frequency also increases in spring.

Certainly - at your location there's still a substantial chance of cold, snowy weather into March. The chance is still firmly decreasing by that point, though from a higher base. You've probably got more chance of ice and snow in March than most of us have in February!

I was being partially tongue in cheek with the above, but turns out it's actually true! For example, daily mean at Kew Gardens for February is 5-6C. Lossiemouth has the same average for March.

Anyway, I'll leave it at that as I don't want to derail the model thread.

 

 

[mulzy]

58 minutes ago, Singularity said:

These composites are for all MJO amplitudes however. The ones I’ve referred to are for at least 0.5, maybe even 1.0 amplitude & were produced more recently making them a bit more relevant to the current climate.

Not that MJO composites tell all. The AAM cycle adds its own twist, as does the stratospheric polar vortex state if it’s usually strong or weak.

I continue to view the week 2 modelling with only slight interest for the time being. The first major opportunity to disrupt the Atlantic trough enough to start migrating high pressure appreciably toward Scandinavia is next Fri so I’m hoping for a clearer picture by Mon on whichever way things will go.

These composites are for all MJO amplitudes however. The ones I’ve referred to are for at least 0.5, maybe even 1.0 amplitude & were produced more recently making them a bit more relevant to the current climate.

Not that MJO composites tell all. The AAM cycle adds its own twist, as does the stratospheric polar vortex state if it’s usually strong or weak.

I continue to view the week 2 modelling with only slight interest for the time being. The first major opportunity to disrupt the Atlantic trough enough to start migrating high pressure appreciably toward Scandinavia is next Fri so I’m hoping for a clearer picture by Mon on whichever way things will go.

Serious question - are MJO analogues flakey at the best of times and not worth the paper they are printed on in a world that is warming very fast?

Edited January 19 by mulzy

[WYorksWeather]

ECM seems much the same as GFS earlier. The signal for anything cold is really very weak bar a couple of outliers. Unfortunately the mean is signalling the dominance of heights mainly in southern Europe, possibly into central and eastern Europe at times. We seem to have periods of very mild south-westerlies alternating with slightly cooler westerly or north-westerly winds as the most likely outcome. Probably some chances of frost and fog at times when the high ridges closer to us.

Here are the ECM means at days 3, 6 and 9:

  

There's nothing cold about those I'm afraid.

If we add in the extended at days 12 and 15:

 

That is at least an improvement in some respects, with less of a tendency for extremely mild south-westerlies, strong winds and rain. However, the orientation of the high ridging in is just all wrong for anything truly cold. You're probably looking at temperatures still above average, with milder air coming over the top of the high. The mildest areas relative to average will be further north.

ECM meteograms for Reading, Leeds, Newcastle and Glasgow below:

All in all, this just looks like a pattern that after the next week of exceptionally mild weather, will just use up another week of winter without delivering anything.

We still have February to go at though, as discussed earlier. I still think we'll get at least one more throw of the dice. But equally, I see no point in ramping anything up at this stage given the relatively poor ensemble suites.

[Ladyofthestorm]

2 hours ago, Frosty. said:

The CFS is looking nae bad in F1! …so much for global warming eh!  

I hope Mr Frosty you do know the difference between weather and climate. Lol

[bluearmy]

33 minutes ago, Don said:

It won't if that forecast comes off, although it does look to miss out phase 7 as Joe B said yesterday?  However, there's not many ensembles taking it into phase 8.

I assume phase 8 would be post day 16 so won’t show on the three ens suites 

but the 46 also goes to day 20 so it would seem that phase 8 isn’t before feb 8th at the earliest 

[pinball wizard]

Models probably not showing anything conclusive at the moment either way for cold, need to see where we stand in three or four days time after these incoming deep lows pass through IMO.

I've been following the AI Graphcast model a lot recently too and that has been struggling to show anything remotely cold friendly.

Looking back through the archives of snow watch and it appears we're rapidly approaching the cut off date, time to call for the grebes. 

 

Graphcast for 29th Jan