Model Output Discussion; into 2015

[Johnp]

News from IF re latest UK Met: 

 

  fergieweather

New @metoffice data indicates no major Sudden Stratospheric Warming (SSW) is likely to occur "in the forseeable future". Moreover (cont'd)04/01/2015 19:51

 

  fergieweather

Cont'd... they note their monthly and seasonal modelling from back on Dec 27 dismissed the prospect. They add that a... (cont'd)04/01/2015 19:53

 

  fergieweather

Cont'd (3)...minor warming will be of minor significance, & resurgence of Polar Vortex/Polar Night Jet through nxt 2 weeks to 'near-normal'04/01/2015 19:57

 

  fergieweather

(4) Finally, they add "The model ouput of other reputable forecasting organisations is also in agreement with the Met Office model trends."04/01/2015 19:59

 

  fergieweather

(5) The @metoffice view re stratospheric situation was valid as of 1400hrs today. Clearly, the rest of winter cannot be forecast in detail.04/01/2015 20:03

 

 

I suppose that puts that to bed for this month.

First with the bad news as ever IDO!

Luckily history shows a SSW isn't always required for a cold spell.

[stratty]

First with the bad news as ever IDO!

Luckily history shows a SSW isn't always required for a cold spell.

 

Yeah - thank swearing is not big or cleveredy-doo-da!  :smiliz39:

[Frosty.]

News from IF re latest UK Met: 

 

  fergieweather

New @metoffice data indicates no major Sudden Stratospheric Warming (SSW) is likely to occur "in the forseeable future". Moreover (cont'd)04/01/2015 19:51

 

  fergieweather

Cont'd... they note their monthly and seasonal modelling from back on Dec 27 dismissed the prospect. They add that a... (cont'd)04/01/2015 19:53

 

  fergieweather

Cont'd (3)...minor warming will be of minor significance, & resurgence of Polar Vortex/Polar Night Jet through nxt 2 weeks to 'near-normal'04/01/2015 19:57

 

  fergieweather

(4) Finally, they add "The model ouput of other reputable forecasting organisations is also in agreement with the Met Office model trends."04/01/2015 19:59

 

  fergieweather

(5) The @metoffice view re stratospheric situation was valid as of 1400hrs today. Clearly, the rest of winter cannot be forecast in detail.04/01/2015 20:03

 

 

I suppose that puts that to bed for this month.

And the good news is ??

[swilliam]

First with the bad news as ever IDO!

Luckily history shows a SSW isn't always required for a cold spell.

Also it is a long term forecast and we know how reliable they are - it certainly does not put anything to bed.

Edited January 4, 2015 by swilliam

[Rocheydub]

Also it is a long term forecast and we know how reliable they are - it certainly does not put anything to bed.

Strat forecasts are usually very accurate, so startospherically speaking, it does. Not saying that the troposphere won't by the way.

[SMU]

Evening All-

 

A timely & handy post by Ian - Usually these types of posts are met with Sudden Swings to cold in the models- its called sods law.

 

 

At this point in Winter this particular point

fergieweather
Cont'd (3)...minor warming will be of minor significance, & resurgence of Polar Vortex/Polar Night Jet through nxt 2 weeks to 'near-normal'
04/01/2015 19:57

 

Is slightly contested in my own mind as it is my view the jet is pretty close to V max with this being reflected in the AO metrics-

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/ao.sprd2.gif

 

With a peak around the 8-9th, thereafter the GFS particularly paints a deceleration in the westerlies & some form of blocking to the West or North ( possibly toppling to the NE

 

A critical juncture in the next 15 days for the colder Jan / Winter forecasts V the Met office benign average one.....

 

All eyes on ECM in the next 2 or 3 days- whether it starts to signal the blocking touted by the GFS for the last 4 days, ( around the 16th)

S

[Frosty.]

I think the good news is we still have GEFS 12z perturbations showing this, and there are many more also showing cold and very unsettled weather with a risk of snow and ice days...keep the faith coldies, lots of polar maritime to come, and probably arctic air too, the gefs 12z mean continues to trend colder by mid month.

[fergieweather]

Hi all, as you might have gathered, UKMO felt it necessary to issue formal comment on the vexed SSW issue. As I noted some days back, any imminent/reliably-forecast SSW with likely implications for UK conditions would be signalled to public (as in early 2013). However, on this occasion it's a statement issued for opposite reasons, i.e. due to increased media interest and some very polarised forecasts grossly over-stating the likelihood of a major SSW in early-mid Jan. It must be noted this does NOT express view re other factors (MJO), NOR does it in any way rule-out colder conditions during the rest of winter. It is simply to clarify re stratospheric effects. Thanks, Ian

UKMO STATEMENT:

"(As of 1400 Z on Sunday 04th January 2015): The Met Office have new data that suggests that a major sudden stratospheric warming is not likely to occur in the foreseeable future. Monthly and seasonal probabilistic forecasting models used by the Met Office have shown no sign of any ‘major’ stratospheric warming events since as far back as 27th December. The model ouput of other reputable forecasting organisations is also in agreement with the Met Office model trends. The latest runs of these models all show that the decline in strength of the jet stream is about to stop and will be followed by a recovery of the polar vortex strength (and hence polar night jet) to near-normal conditions over the next week or two. This makes recent observations of a slight warming trend in the stratosphere a ‘minor’ SSW (i.e. temporary, and of only minor significance to weather conditions lower down in the atmosphere)."

[bluearmy]

Steve - I assume they are referring to the mid/upper strat zonal flow which is recovering back up to 45m/s by day 10.

Of course Ian, if there is a snow event mid month, joe public will believe the stuff which was predicated on the SSW in the media.

Edited January 4, 2015 by bluearmy

[Timmytour]

 NOR does it in any way rule-out colder conditions during the rest of winter.

 

 I've a feeling that comment will be construed by some (actually the Daily Express) to mean that Met Office now agrees with experts that Britain will become like Siberia bla bla bla  

Edited January 4, 2015 by Timmytour

[DAVID SNOW]

 I've a feeling that comment will be construed by some (actually the Daily Express) to mean that Met Office now agrees with experts that Britain will become like Siberia bla bla bla  

 

Maybe!   But what is does mean is that the UK does  NOT  'need' a SSW  for us to have a cold and snowy spell(all areas).

[Long haul to mild]

As far as strat forecasts are concerned, what kind of time period is the "foreseeable future"? Is it similar to the GFS i.e. about two weeks, or is it longer?

[Severe Siberian icy blast]

Maybe!   But what is does mean is that the UK does  NOT  'need' a SSW  for us to have a cold and snowy spell(all areas).

He just simply means to clarify the drama regarding "will we , won't we " see a SSW short term . I really don't see the need to analyse every single word and dissect it to the letter !

It's simply just a clarification of where we are stratospherically speaking , and not a weather forecast .

[Captain Shortwave]

As far as strat forecasts are concerned, what kind of time period is the "foreseeable future"? Is it similar to the GFS i.e. about two weeks, or is it longer?

Probably means no stratospheric driving force until February, but as others have said there are other drivers that can bring cold weather. To be honest it is nothing new as posts from the strat thread have pretty much said this (minor split followed by the polar vortex recovery with no real renewed warming). So it's up to other driving forces to do the business with the most interest in the MJO. Having a look at the day 10 charts, the GFS does something interesting over the Newfoundland (It's another cut off low and heights bridging from Canada into the Atlantic). A very similar set up to December, which perhaps re-enforces the notion of a similar cold snap to the last week of December.

GFS

Parallel

Similar low but no bridging ridge, the low dives south east into Iberia.

 

ECM

A weak low there, difficult to tell.

Edited January 4, 2015 by Captain shortwave
Added charts :)

[nick sussex]

As far as strat forecasts are concerned, what kind of time period is the "foreseeable future"? Is it similar to the GFS i.e. about two weeks, or is it longer?

I think the ship might have already sailed for January and theres no sign of any further strong warmings. We might just have to hope for other factors to become more favourable like the MJO.

[DAVID SNOW]

He just simply means to clarify the drama regarding "will we , won't we " see a SSW short term . I really don't see the need to analyse every single word and dissect it to the letter !

It's simply just a clarification of where we are stratospherically speaking , and not a weather forecast .

 

 

No drama from me, just stating a fact.

[Long haul to mild]

Thanks for the replies.

As recently as two weeks ago, an SSW was expected in early January, which turned out to be wrong. Is it unrealistic to hope that the forecasts of no SSW for the rest of the month could also be inaccurate?

Sorry, just how my rather unscientific mind is thinking!

Edited January 4, 2015 by Long haul to mild

[chionomaniac]

Hi all, as you might have gathered, UKMO felt it necessary to issue formal comment on the vexed SSW issue. As I noted some days back, any imminent/reliably-forecast SSW with likely implications for UK conditions would be signalled to public (as in early 2013). However, on this occasion it's a statement issued for opposite reasons, i.e. due to increased media interest and some very polarised forecasts grossly over-stating the likelihood of a major SSW in early-mid Jan. It must be noted this does NOT express view re other factors (MJO), NOR does it in any way rule-out colder conditions during the rest of winter. It is simply to clarify re stratospheric effects. Thanks, Ian

UKMO STATEMENT:

"(As of 1400 Z on Sunday 04th January 2015): The Met Office have new data that suggests that a major sudden stratospheric warming is not likely to occur in the foreseeable future. Monthly and seasonal probabilistic forecasting models used by the Met Office have shown no sign of any ‘major’ stratospheric warming events since as far back as 27th December. The model ouput of other reputable forecasting organisations is also in agreement with the Met Office model trends. The latest runs of these models all show that the decline in strength of the jet stream is about to stop and will be followed by a recovery of the polar vortex strength (and hence polar night jet) to near-normal conditions over the next week or two. This makes recent observations of a slight warming trend in the stratosphere a ‘minor’ SSW (i.e. temporary, and of only minor significance to weather conditions lower down in the atmosphere)."

I think that around the 27th December is the time that I realised that any early Jan SSW was not going to occur. At no point did we ever see the right 'warming' in any forecast that would completely destroy the vortex at 10hPA. However, we are seeing a trop based upwell split in the lower strat vortex over the coming days. This, in turn, has left two daughter vortices of which the Canadian daughter does get 'destroyed' by an upper warming at 10hPa - only for the Siberian daughter to regain strength and recover positionally over the pole.

 

I too, don't see any further significant upper strat warming over the next 3 weeks, but we should not lose hope because we have seen that this winter, the lower stratospheric vortex has been affected by upwelling tropospheric based splitting events. And, the vortex will come under strain again in the next couple of weeks and imo it is likely to split again before the end of the month (this is not to be confused with an SSW based split). It is at this time that we are likely to have our best shot of cold in the UK - note the stretching of the reformed Siberian daughter vortex by day 15 in the latest parallel output which is indicative of further increase in wave 2 based activity.

[ANYWEATHER]

 Please calm down

Edited January 4, 2015 by ANYWEATHER

[karlos1983]

Not much hope of something cold being given to us by the models or from an SSW then.

I might start buying the daily express as a source of hope to cling onto! :-)

Well fantasy is probably the best you'll get this winter, writing is on the wall and I'll eat my own hat if we end up with decent cold spell. Edited January 4, 2015 by karlos1983

[nick sussex]

ECM De Bilt ensembles still develop a colder cluster towards the end but not as yet a strong signal in terms of deeper cold for there.

 

http://www.weerplaza.nl/15daagseverwachting/?r=midden&type=eps_pluim

 

The wind directions only really begin to show some interest towards the 17th with a more nw element with a few breaking towards the ne and north.

 

I think anything of note for the UK  if it happens will show up around that time, before then some cooler conditions at times but generally nothing of note.

 

The will it or won't it MJO maybe that variable that could tip things either way.

[jellybaby1969]

Why are you looking at De bilt ensembles when the bias is to a nw polar maritime scenario..?

[bluearmy]

Extended ECM ens continue to show a scandi low anomoly and a med upper trough thereafter (smile john) ! The scandi low anomoly sustains. With the euro high anomoly gone, that leaves a decent envelope.

Also, developments with the vortex which stretches across from a weak centre Baffin over to ne Siberia ( note ed's post above). Coupled with the way the gefs dealt with the vortex late on and things are clearly afoot over the polar field.

going to see some weird and wonderful week 2 runs over the next few days.

Why are you looking at De bilt ensembles when the bias is to a nw polar maritime scenario..?

It's about the wind direction, not the temps. Point taken about a windward flow off the north sea

[nick sussex]

Why are you looking at De bilt ensembles when the bias is to a nw polar maritime scenario..?

I'm looking for signs that troughing will get sufficiently east and se also given the set up cyclonic colder there will likely be a bit colder especially for more northern areas of the UK.

 

De Bilt isn't only useful for easterlies, you get dew points and wind directions which as we know what the  set up could  be can be extrapolated as a guide for the UK.

 

The only thing the ECM offers for UK cities is  just rainfall and temperature, you can correlate wind clusters over there and dew points which can tell you whether the air is continental based or Atlantic based.

 

Hopefully that answers your question.

[Vorticity0123]

With 2015 having just started, we are approaching the heart of the winter. How will the weather evolve, and what are there any long term trends to be found? I will try to treat all these questions in this post. Furthermore, a possible storm system on Friday will also be briefly discussed.

 

For describing the current weather situation and for the forecasts up to 72 hours, I will use the GFS 12Z charts.

 

Current situation

 

The synoptic chart belonging to the current weather situation is given below:

GFS surface level pressure and 500 hPa heights (colours) 12Z run T+0

 

What can be seen is that there is a fairly amplified pattern currently present over Western Europe. Two troughs at 500 hPa can be distinguished, one being over the central Atlantic just south of Greenland (denoted by the black downward pointing curve, also indicated by the blue colours edging southward). Another 500 hPa trough can be seen over western Russia. Both troughs are associated with a low pressure at the surface.

 

On the other hand, a 500 hPa ridge can be found over Western Europe (denoted by the red line, also indicated by red/orange colours edging toward the north). This ridge causes a surface high pressure to be located over Western Europe and the UK, resulting in calm and settled weather there.

 

Short-term outlook

 

24 hours later, the 500 hPa ridge has moved slightly eastward, as can be seen in the link below:

 

http://www.wetterzentrale.de/pics/Rtavn241.gif (GFS surface level pressure and 500 hPa heights (colours) 12Z run T+24)

 

Two important things have happened as well. The trough located over the middle Atlantic has decreased somewhat in areal extent (it is pointing less far south), but on the other hand it has deepened slightly (as more purple colours are evident now). On the other side of the continent, the trough over Russia has dipped further south, which could result in wintry conditions being experienced as far south as Greece.

 

Another 24 hours later, the trends described previously have become more prevalent. This can be seen below:

 

GFS surface level pressure and 500 hPa heights (colours) 12Z run T+48

 

The 500 hPa trough over Eastern Europe (denoted in black) can be seen dipping as far south as northern Libya and Egypt. On the other hand, the 500 hPa ridge present over Western Europe (denoted in red) has moved further eastward and weakened slightly.

 

Prominent trough over Greenland

 

However, the most important feature is the massive 500 hPa trough gaining depth over Greenland and adjacent areas (encircled in black). Of the southern branch of the 500 hPa trough that was present over the central Atlantic, only a small dip can be observed over the UK. The northern arm, in contrast, has deepened significantly (indicated by the purple colours which become evident there). This is quite often a good indicator that a period of zonal weather will be experienced. To illustrate this, check the 850 hPa temperatures given below:

 

GFS 850 hPa temperatures (colours) 12Z run T+48

 

Focus mainly on the temperatures just off the west coast of the United States. What can be seen is that there is a very sharp gradient in temperatures there (very sharp change in temperatures over a relatively small distance). For example, a difference of more than 30*C in 850 hPa temperatures can be observed over about 1500 kilometres (rough estimate) just south of Nova Scotia.

 

Such temperature gradient is a perfect birth place for deep low pressure areas to form (at the surface). These low pressure areas will then move toward the UK as they are being steered by the huge 500 hPa trough over Greenland.

 

Regardless of the temperature contrasts, the deepening of the trough over Greenland remains remarkable, perhaps even puzzling to some extent. Perhaps this might have been helped by stratospheric downwelling of low heights, but I am unable to deduce this from stratospheric charts (100 hPa pressure charts, link). Does anybody have an explanation for the significant deepening of this trough?

Storm system

 

As a result of the huge temperature contrasts mentioned above, there is a possibility of a storm system to reach the UK on Friday. For comparison, the links to the ECMWF, UKMET and GFS (old) are given below for comparison. All models are valid for 12 UTC on Friday.

 

http://www.wetterzentrale.de/pics/Recm1201.gif (ECMWF)

 

http://www.wetterzentrale.de/topkarten/fsavneur.html (GFS)

 

http://www.wetterzentrale.de/pics/Rukm1201.gif (UKMET)

 

As can be seen from the charts, both the ECMWF and the GFS show a small low pressure system moving over Scotland in the 120 hour timeframe. However, given that the system is so small, and that we are looking at a small surface feature for 120 hours out, confidence is low at the moment.

 

Azores high dominance

 

Another interesting feature is the Azores high, of which the central pressure as forecasted by all models is expected to be as high as about 1045 hPa in about 5 days! This also enhances the pressure gradient over Western Europe, which will likely cause quite significant westerlies to be experienced in the UK at that timeframe.
 

The magnitude of the winds at the surface in general can also be seen at this timeframe:

 

http://www.wetterzentrale.de/pics/Rtavn1208.gif (GFS 10 m winds [in knots] 12Z run T+120)

 

Long term trends

 

For the long term trends, take a look at the spaghetti diagram of the GFS for 9 days out below:

 

GFS 500 hPa pressure spaghetti plot 12Z run T+224

 

The plot is slightly difficult to interpret, so here is some explanation.

Each colour represents one calculation of the GFS model (in this case the 12Z run). What all these lines indicate is the position of the 516, 552 and 572 hPa height. In simple terms, a higher height indicates a higher pressure. So each calculation represents three lines, all indicating the heights givin above. When many lines are close together, it means that there is high certainty in a certain synoptic pattern (being a trough, a ridge, or just plain zonality) at a certain position.

 

If one takes a look at the spaghetti diagram indicated above, it can be seen that many lines are very close together over the Atlantic, this being of all indicated heights (516, 552 and 572 hPa height). Moreover, all these lines are positioned about east-west (correcting for skewness caused by the projection). What this indicates, is that there is relatively high confidence that a zonal pattern will persist up to at least 9 days in advance, with mainly westerly winds and low pressure activity located near Iceland.

 

Another piece of evidence for the predictability of the pattern is the wind "pluim" of the Bilt ensembles from the ECMWF (This has also be mentioned by Nick Sussex). They can be viewed below:

 

Wind "pluim" of The Bilt by the ECMWF (12Z run).

 

In this "pluim" the y-axis represents the direction from which the wind comes. So 0 degrees is a northerly, 180 degrees is a southerly and so on. The green lines indicate 50 calculations (i.e. individual members of the ECMWF-model). The red line indicates the operational model.

 

I have rarely seen a wind direction "pluim" that is so consistent up to 14 days. Even at Friday next week (the 16th, about 12 days from now) all individual members show something between southerlies and west-northwesterlies. Therefore, there is little evidence of any change occurring in the westerly dominated pattern anytime soon.

 

Chances of a pattern change

 

In search for any other signals, there does seem to be something of a change possible. If one looks at the GFS ensembles for 12 days out, there does seem to be some ridging trying to form toward Greenland:

 

GFS Ensemble forecast, surface level pressure and 500 hPa heights 12Z run T+288

 

This feature has also been mentioned by some others above. Given that this is 12 days out, confidence is very low at the moment. Furthermore, the ensembles converge back to a more zonal pattern some days later. On the other hand, the predictability of the atmosphere does seem to be quite high, so the possibility of a Greenland/upward nosing Azores high is definitely not out of the question. Furthermore, the GFS ensembles do show the trend, which is supported by the operational forecast.

 

The 8-14 day 500 hPa heights and anomalies forecast from NOAA does not (yet) show anything that resembles a Greeenland/upward nosing Azores high. They can be found here. It will be interesting to see whether a trend toward a Greenland high pressure area will develop. For now, there is too much uncertainty regarding this feature, especially since the NOAA anomalies have not picked up this feature just yet, and given it is still 12 days away.

 

Conclusion

 

It seems that an extended period of very unsettled weather for the UK is on the way. Confidence is high that this general pattern (at 500 hPa, so not concerning surface features) will persist at least up to mid next week. Thereafter, there are weak signs that some high pressure activity will develop toward Greenland at about 13 days' time, but confidence is currently too low to draw any conclusions regarding that.

 

Sources:

http://www.wetterzentrale.de/topkarten/fsavneur.html

http://www.weerplaza.nl/15daagseverwachting/?r=midden&type=eps_pluim

http://www.cpc.ncep.noaa.gov/products/predictions/814day/500mb.php

http://www.geo.fu-berlin.de/en/met/ag/strat/produkte/winterdiagnostics/

 

EDIT: Added speculation about deepening 500 hPa trough over Greeland.

Edited January 4, 2015 by Vorticity0123