Model Output Discussion - 1st February Onwards 12z--->

[igloo]

Yes it will feel spring like if the uppers get high enough like the ECM when it starts to sink it will more than likely

get more and more cloudy with drizzle starting to make head way in to the far NW the south of the uk will be colder and

more sunny but still should feel pleasant during the day

Edited February 1, 2015 by igloo
Removed quote as quoted post had been edited.

[Gibby]

Surely the clock is ticking now. The sun is now producing a tangible warmth (well we are the sunniest place in the UK) Do the models take this into account? It would appear that any snow is becoming increasingly unlikely in the far South based on the most recent outputs

I had to laugh at this post. It can snow in the South of England and has in many years right out to late April and is no more rare than snow in Winter months late years. Also dew points are less of an issue as Spring moves on with snowfall possible with temperatures of 8C or more in a cold showery North flow in April. Settling or disruptive April snow is a bit more rare but not unheard of. Sorry Mods OT.

[Dean E]

The 18z op drops the high over us even more quickly. Here we are Thursday:

 

Screen Shot 2015-02-01 at 22.26.44.png

 

Then it strengthens over the top:

 

Screen Shot 2015-02-01 at 22.29.11.png

 

This high on the current outputs isn't particularly cold either:

 

Screen Shot 2015-02-01 at 22.27.08.png

 

We may get inversion from that so that ironically with warmer uppers we have colder mean temps.

 

The biggest problem here is the danger of the high becoming static. However, as we have seen, things can change fast.

 

 

Temperatures for lunchtime the same day (8th February) under those uppers...

 

 

Remember, surface cold will be established by then. Overnight temperatures will be quite low as well!

[TEITS]

Well considering the very different GFS runs we have seen today I shall remain open minded to a possible very cold E,ly or a very cold N,ly or just HP sat over the UK. All 3 remain possible because it would not take much change in the placement of the HP for this to occur.

 

An example is the latest 18Z NAVGEM.

 

http://modeles.meteociel.fr/modeles/navgem/runs/2015020118/navgem-0-144.png?01-23

 

As you would agree it would not take much change for a very cold NE,ly to sweep across the UK.

[JOPRO]

It's not even as though we are currently enduring a prolonged zonal period with no end in sight. Quite the opposite in fact, which makes such whinges even more incomprehensible. For a start some of us have 5 or 6 days of very cold weather yet to come. Thereafter, plenty of options are on the table. Even if we end up with a uk high ( IMHO the most likely possibility right here, right now), what happens thereafter is very very much up for grabs and even THAT doesn't even take us to mid month!?

You make a very good point here, from what I remember the February 1991 cold spell started with a uk high, so many options on the table none of which can be ruled out be they cold or mild.

[Duane S.]

The 18z op drops the high over us even more quickly. Pretty much game, set and match unless there's an extraordinary turnaround. Here we are Thursday:

 

Screen Shot 2015-02-01 at 22.26.44.png

 

Then it strengthens slap over the top:

 

Screen Shot 2015-02-01 at 22.29.11.png

 

There's a lot of talk about cold but empirically speaking until tonight it hasn't been particularly cold (hence the gnashing of teeth over on the model moan thread) with January 1C above average and a faux-cold northerly bringing mostly sleety stuff to the south. This high on the current outputs isn't particularly cold either:

 

Screen Shot 2015-02-01 at 22.27.08.png

 

We may get inversion from that so that ironically with warmer uppers we have colder mean temps, although in the sun it will feel very pleasant by day.

 

The biggest problem here is the danger of the high becoming static. However, as we have seen and are now seeing with the end of this brief northerly with the toppling high, things can change fast.

Wib, you have been beating the drum for the cold spell to be a brief affair for over a week now, according to you we should be bathing in warm westerlies right now but instead the cold spell had been very good for many and indeed has many days left to run yet. A very decent cold spell by UK standards.

A UK high is the most likely next step and will likely lead to inversion with frigid temps at times. I for one will be more than happy to have that for a week and take my chances thereafter. Of course there remains a chance for sure it slips east and stagnates, drawing in TM air but retrogression has to also remain a viable option.

[Vorticity0123]

We have had an interesting period last week, with a brisk northerly delivering snow on several places across the UK. There seems to be a change in the pattern underway, with high pressure activity probably taking foothold over Western Europe. How does this pattern evolve, and how can high pressure activity still cause a lot of uncertainties? In this post, I will try to give an answer to these questions.

 

For the first 96 hours, I will use the GFS 12Z/18Z runs as a general guide.

 

Current synoptics

 

For the current situation, take a look at the GFS chart below:

 

GFS surface level pressure and 500 hPa heights (Colours) 18Z run T0

 

As can be seen from the image, a large 500 hPa trough (blue colours) extends over the center of Europe down to the Mediterranean. A complex area of low pressure at the surface is associated with this feature.

 

This trough has been influencing our weather over the past few days. Northerlies blew on the western side on the trough. Also, because the 500 hPa temperatures (not shown here) were very cold at the center of this trough, the air was very unstable (expressed by a big difference in temperature between the surface and aloft). This made formation of showers possible, which were carried southward by the northerly flow, bringing rain and snow toward the UK.

 

Aside from this trough, a 500 hPa ridge can be seen building over the Atlantic (orange colours edging northward), also visible by high pressure at the surface. This ridge will be important for our weather over the next week.

 

Transition to high pressure activity

 

Looking 48 hours later, the same general pattern as described above is maintained, but with a few crucial differences.  Check the GFS chart for 2 days ahead below:

 

GFS surface level pressure and 500 hPa heights (Colours) 18Z run T48

 

The 500 hPa trough located over central Europe is still there. However, there are two important things happening, being:

• The trough is weakening, as the dark blue colours (indicative for very low 500 hPa heights) are now longer visible.
• A piece of the trough is willing to dive southwestward (indicated by the black arrow). This movement will be very important for future developments.

Also, the 500 hPa ridge (orange colours edging northward) is still visible, but has moved some westward and is now located just to the west of the UK. Also note the orientation of the high has shifted some into a NE-SW orientation, basically pushing itself over the piece of the trough (over France) which is trying to move southwestward under the ridge.

 

Another 48 hours later, the developments mentioned above have continued, as can be seen below:

 

GFS surface level pressure and 500 hPa heights (Colours) 18Z run T96

 

The ridge which was located to the west of the UK 2 days before has now moved over the UK, yielding a strong area of high pressure at the surface (up to 1035 hPa).

 

Furthermore, the 500 hPa trough which was located over central Europe has been separated into a part that has shifted out of Europe, and another part which has become partially cut-off over Italy (blue colours). As a refresher, a cut-off low is a low pressure area that is separated from the mean flow by means of high pressure activity to the north of it.

 

The result is a high-over-low situation, which can be seen as a blocked pattern. This can also be seen on the Jetstream patterns as given by Netweather, which can be found in the following image:

Netweather Jetstream analysis from the 12Z GFS run valid for 96 hours out.

 

Note that the jet stream is very wavy and inactive, indicative of a blocked pattern.

 

(Un)certainties in future outlook

 

The situation described in the previous outlook is not expected to change much over the days to follow. However, small differences develop between the models, which may have significant implications for the weather across the UK. For example, compare the GFS and ECMWF MSLP forecasts for 7 days out:

 

http://www.wetterzentrale.de/pics/Recm1681.gif ECMWF

http://www.wetterzentrale.de/pics/Recm1681.gif GFS

 

As can be seen from the models, both agree that a strong 500 hPa ridge will be present over the UK (as indicated by the orange colours).  This provides enough certainty to conclude that high pressure activity will be likely by the end of next week.

 

However, there are small differences in the placement of the surface high pressure, with the GFS being much further east with the high pressure area than the ECMWF. Also, the 500 hPa ridge (and associated surface high) on the ECMWF is somewhat stronger  than on the GFS.

What makes these differences so important is that placement of the surface high to the east or west of the UK has major implications on the weather expected there. If the ridge would appear to be located to the east of the UK, a southerly flow will be present over the UK bringing mild weather. On the other hand, placement of the ridge to the west of the UK would result in a cool northerly. This uncertainty is reflected nicely in the wind distribution of the ECMWF ensemble for the Netherlands:

 

ECMWF wind distribution of 50 individual calculations 00Z run, 1 February.

 

The image indicates a set of wind vanes, each for a different time step. Each sector stands for a different wind direction. For example, the upper segment indicates northerlies, while the right-hand sector denotes easterlies, analogously for the lower and left sector. The distance from the center is the strength of the wind expected. The further away a run from the center is, the higher the wind speed will be. The green triangles denote a single ensemble run forecast for the wind speed and direction. The blue and red triangles are the Control and the OPER run, respectively.

 

When the triangles are very close together, it means there is a high certainty of the expected wind, while a large spread indicates uncertainty.

 

What can be seen is that from about 168 hours, a large disagreement between the various ensemble members develops regarding wind direction. Basically everything except a southeasterly is possible, with equal chances for each of the other wind directions. All models do agree, though, that the wind speed will not be high.

 

This spread can be linked to the synoptic situation discussed earlier by the high pressure area positioning near the UK. A very small deviation in the positioning of the center of the high may result in a complete turnaround of the wind direction to be expected, and the expected temperature.

 

Regardless of this spread, the fact that high pressure activity seems to be dominating our weather for a significant period of time is pretty certain. To illustrate this, take a look at the precipitation ensemble ‘pluim’ from the ECMWF:

 

ECMWF ‘pluim’ of precipitation for the Netherlands, showing 50 individual model calculations of the ECMWF model regarding precipitation (green lines). The red line is the operational run, while the blue line is the ‘control’ run.

 

Over the next 15 days, almost no model is calculating any precipitation to fall. It does take up to 13 February to see some members calculating a decent amount of precipitation. As high pressure is often accompanied by a lack of precipitation, this is good evidence that high pressure activity will dominate for the next several days.

 

Boundary-layer and high pressure activity

Of a final note, even if the location of the high pressure is certain, the weather over the UK can still be uncertain even up to the day itself (say, 12 hours out). This has to do with boundary layer dynamics, which are crucial in high pressure activity. The boundary layer, in general, comprises the lower 100m to 1 km of the atmosphere (the area where we ‘live in’).

 

Questions like: “What will be the height of the subsidence inversion caused by the high pressure area?†and “What will be the humidity of the surface air and?“ are of high importance. This can be the difference between a day full of sunshine, a day of cloudiness, or in the worst case a day of only fog. Therefore it has to be kept in mind that even if the general synoptic pattern is clear, the forecast for the actual weather being observed may not be that certain at all.

 

Conclusion

 

A pattern change is about to occur at the beginning of next week, with high pressure activity taking over. There seems to be a fairly high level of confidence that this will last for a week or even more. However, there are still small disagreements on the placement of the surface high, which will have major implications for the weather experienced across the UK; directly by means of wind direction and indirectly by boundary layer dynamics. Therefore, the models can be watched with interest.

 

Sources:

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

http://www.netweather.tv/index.cgi?action=jetstream;sess=

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

http://www.knmi.nl/exp/pluim/kansverwachtingen_staafdiagram.php?run=00&type=precip0618

Edited February 1, 2015 by Vorticity0123

[Yarmy]

Wherever the high ends up landing, surely the main story is the ever extending cold. The breakdown was progged for today just a few days ago. As Chiono has remarked, this is the slowest toppler in history.

[geordiekev]

https://forum.netweather.tv/topic/82300-model-output-discussion-16th-jan-12z-onwards-smile-while-you-post/?p=3136826

Copy of original post from Ian F:

Posted 22 January 2015 - 22:22

Well... good support in new EC Monthly by mid-Feb for GloSea5 signal re increased incidence of blocking. Indeed, by week 4, first output we've seen all winter with NO low MSLP anomalies anywhere on the NW Atlantic-European charts. However....where blocking sets-up, if it establishes, is another matter. This was stressed earlier re GloSea5 signal: it MAY lead to colder weather but equally may do opposite. Nonetheless, a growing (if still tentative) bi-model indicator of change eventually afoot.

Sorry as I don't know how to reply from a locked thread hence the copy and paste.

I'm just raising this again as Ian did mention that the monthly model they use referred to a possible blocking outcome come mid feb. If so then hopefully we should start to see some signs in the t240 charts in the next couple of days and looking at the current models I think there are definite signals beginning to loom.

As I have previously stated, with the Azores high displaced and now replaced with an Azores low it really is and has been fascinating model watching over the last six weeks. Personally I think the models struggle a bit with all of the stagnant highs and lows not being in their default homes and possibly the reason for the short term flips.

I could be wrong but I think quite a few members in here have had a chance at lamp post watching over the last few weeks myself included and I'm quite content at our lot so far, but I'm certainly not turning the lamp light off just yet.

Hopefully the next few days can firm up on this possible block and bring back some interest for us all.

[Geordiesnow]

Wherever the high ends up landing, surely the main story is the ever extending cold. The breakdown was progged for today just a few days ago. As Chiono has remarked, this is the slowest toppler in history.

 

I don't know what you mean, the cold feed will be cut off by Thursday, high pressure will be near/over the UK by the end of the week but temps will struggle to climb. That said, in terms of the length, we can't complain about this spell of weather, as for snow amounts, then that is a different story. 

 

I also suspect it will be an increasing cloudy high as Atlantic air with its cloud will topple in, best of the breaks will be for Southern areas for sure. 

[Cheshire Freeze]

The 0z GFS may turn out to be a better run for cold going forward (out to day 6 atm). Slightly better dig of the trough into Scandi, better Pacific amplification (marginally) and you'd think given the invite, the Atlantic/UK high would pull NW circa day 9/10. We'll see.

Edit: UKMO is Interesting even by day 6 as the vortex looks to be draining back to the Siberian side. Hmm.

Today we need to look for any trend which brings the vortex back across to the Siberian side or some northwestward extension of the Atlantic high (via vertical advection on western flank in the nearer timeframes ideally). The easterly (short term) is dead in the water bar a couple of days, what happens after is not.

Edited February 2, 2015 by CreweCold

[Snowman.]

GEFS shows considerable weakening of the Vortex

 

 

With a possibility of the Euro trough returning?

 

 

Rinse and Repeat perhaps? Some have called it.

 

CFS showing some interest for march as well been quite a strong signal for that over the past few weeks.

 

But as we see things a good 7-10 days under a rather robust high and it's likely to be cold.

Edited February 2, 2015 by SN0WM4N

[Captain Shortwave]

About the best we have on this mornings outputs

It would be nice if this is the evolution to back this west a little to increase the potency of any northerly.

 

For this week there is still the chance of a little snow in favoured windward spots and possibly further inland if disturbances develop. The showers tending to die away on Thursday as high pressure builds over the northern half of the UK.

Edited February 2, 2015 by Captain shortwave

[knocker]

A general short overview of this morning's GFS

 

After the middle of this week HP calls the tune, setting up over the UK before moving east only to be replaced with more HP evolving from the SW. Also generally speaking LP to the NW and NE much along the lines of last nights anomaly. This is limited to a general overview as the position of the HP is key to a more detailed analysis but the Anomalies are all suggesting a light westerly flow. This mornings anomaly is only out to T240 at the moment but you get the drift, so to speak.

Chart weatherbell

Edited February 2, 2015 by knocker

[West is Best]

All 3 main models now confirm the high pressure prognosis. Where it sits, and for how long, will determine much of the early February shape. After the initial hp build the T144 charts show slight variation.

 

GFS, right over the top:

 

UKMO has slight retrogression:

 

ECM shows retrogression:

 

None of the three have cold uppers, but the GFS would probably produce the colder initial conditions with night frost and sunny days. The other two are 'dirtier' with UKMO particularly having a mild draw from the south coming around the top. Both GFS and ECM eventually sink the high to produce zonal conditions. With a lot of upstream jet signal still in the mix you'd have to say that's the form horse.

 

Winter highs can stick around. Where and how this one does will determine much of the first half of February.

 

My feelings about all this, as opposed to clinical analysis, are over on here: https://forum.netweather.tv/topic/81281-model-banter-moans-and-ramps-autumnwinter-201415/page-157#entry3160224

 

Finally, it's good to see the GFS pulling the operationals in line with the control and mean. We all know why this has happened, but the constant yo-yoing between cold and mild members hasn't covered the model in glory. This is a much more sensible output:

 

[bluearmy]

Richard, the ECM op goes with yesterday's spread on the drop of colder uppers day 6. infact, day 7 has uppers of -9c around following day 6 where the range is -3 to -7c. Thats a cold recipe under high SLP? Not sure your statement re 'no cold uppers' at day 6 is correct?

[TEITS]

The outputs this morning are generally poor from a coldies perspective but at least the ECM gives us a glimmer of hope.

 

As Steve M suggested a few days ago a cold N,ly sets in on the right flank of the HP.

 

http://www.wetterzentrale.de/pics/Recm1682.gif

 

Sadly this doesn't last very long and is quickly toppled. However it is something to keep an eye on and alot depends on what happens upstream as to whether this HP can back further NW.

 

On a positive note the models continue to suggest snow showers from tonight onwards into tomorrow. Also some snow for N parts of Scotland.

 

http://expert-images.weatheronline.co.uk/daten/proficharts/en/euro4/2015/02/02/basis00/ukuk/prty/15020312_0200.gif

[knocker]

Richard, the ECM op goes with yesterday's spread on the drop of colder uppers day 6. infact, day 7 has uppers of -9c around following day 6 where the range is -3 to -7c. Thats a cold recipe under high SLP? Not sure your statement re 'no cold uppers' at day 6 is correct?

 Very true ba but thereafter that the transition to positive uppers which of course can be deceptive.

Edited February 2, 2015 by knocker

[West is Best]

Richard, the ECM op goes with yesterday's spread on the drop of colder uppers day 6. infact, day 7 has uppers of -9c around following day 6 where the range is -3 to -7c. Thats a cold recipe under high SLP? Not sure your statement re 'no cold uppers' at day 6 is correct?

 

The ECM T168 chart you mean, right? A slight bit of cherry picking there my friend   with milder uppers either side. You're right though that the ECM has slightly colder uppers than GFS in the reliable timeframe.

 Very true ba but thereafter that the transition to positive uppers which of course can be deceptive.

Yep, right on both counts. I wouldn't now mind a bit of inversion with cold nights and beautiful sunny days.

[nick sussex]

Morning all

 

It looks like the ECM made a good call with that deeper upstream coastal low and now that the UKMO has moved towards it then it would be a big surprise if both the ECM and UKMO are wrong at T96hrs.

 

The ECM does bring some colder air back in towards the UK between T144 and T168hrs so overnight we have seen a large westwards correction of that cold pool. Still too early to say whether that would verify, although the UKMO has moved towards the ECM its still not as amplified.

 

To get the best out of that possible set up we still need a further correction west and north with the high and more cutback of the jet in to the UK associated with that Scandi troughing so that the high aligns more ne/sw as low heights move east into Greenland.

 

Earlier the ECM does bring some -10 850's into the UK from the east and a window to develop some convective snow showers of the North Sea.

 

The further outlook is strongly behind high pressure close by to the UK but exactly where it sets up still uncertain and this will make a difference to the temperatures.

[IDO]

Again the well sign posted trend to move the Euro trough east and bring in the UK HP is strong on the GEFS. The consensus is very apparent with only one member defying the rank and file.

 

D7 mean:   D9 mean:  D11 mean: 

 

The uppers are generally just above average but temps may be just below as it looks like a cloudy high at times. Very dry on the GEFS to D16 with the current trend for the residue lower heights from the upper trough (cut off upper low) over Iberia/Bay of Biscay to remain in situ till D16 plus, so further wedges of HP from the west will ridge over the UK. Control is similar to the op and many of the GEFS:

 

T156 T312

 

This holding pattern looks quite reasonable, so my confidence is good for this going forward, it is a quasi blocked pattern that favours Eastern Europe for them to go into a prolonged colder spell. GEM is similar to the GEFS:

 

D5 D10

 

ECM and the UKMO ops continue to put a core High further west in this transition and the ECM mean from last night was a lot closer to the GEFS mean than the ECM op:

 

ECM and UK at D5:     

 

The difference is between D3-D5 with how the models handle a wedge of HP exiting the US. Both UKMO and ECM manage to break it through the trough to our west, where as the GFS is less successful. Hence the latter does not have the HP as far west as the Euros.

 

 

Maybe somewhere in the middle, though anything other than HP dominated charts up till around D10 is very unlikely IMO.

 

 

[West is Best]

 

The ECM does bring some colder air back in towards the UK between T144 and T168hrs so overnight we have seen a large westwards correction of that cold pool. Still too early to say whether that would verify, although the UKMO has moved towards the ECM its still not as amplified.

 

Earlier the ECM does bring some -10 850's into the UK from the east and a window to develop some convective snow showers of the North Sea.

 

 

 

Morning Nick,

 

Snow showers? Hmmm … not sure I'd start progging that too strongly on here at T168 given what has just happened and more importantly given the relatively milder uppers either side of T168:  

 

T120:

 

T216:

 

Even in a proper easterly you really need cold to dig in and it can take time coming off the relatively warm North Sea. Anyway, bit of a moot point as this isn't that kind of set up, at least not at the moment.

 

 It's lovely to see the sun out on a gorgeous crisp winter's day. Beautiful.

Edited February 2, 2015 by chionomaniac
edited to remove sarcasm

[Shunter]

Think this is whats known as Shannon Entropy - http://www.wetterzentrale.de/pics/MT8_Nuuk_ens.png     

[nick sussex]

Morning Nick,

 

Snow showers? Hmmm … not sure I'd start progging that too strongly on here at T168 given what has just happened and more importantly given the relatively milder uppers either side of T168:  

 

T120:

Screen Shot 2015-02-02 at 08.15.47.png

 

T216:

Screen Shot 2015-02-02 at 08.15.26.png

 

Even in a proper easterly you really need cold to dig in and it can take time coming off the relatively warm North Sea. Anyway, bit of a moot point as this isn't that kind of set up, at least not at the moment.

 

 It's lovely to see the sun out on a gorgeous crisp winter's day. Beautiful.

I wasn't talking about snow showers at T168hrs, that potential is mainly for Wednesday and Thursday of this week. I thought I made it clear that I wasn't sure about the renewed cold from the ECM. That could still go either way, just waiting to see the ECM ensembles and spreads if theres a cluster with a more favourably aligned high.

 

PS you look in a decent location for those snow showers, fingers crossed you get a decent covering.

 

PSS interesting ECM spread for T144 and T168hrs!

Edited February 2, 2015 by chionomaniac
Adjusted quote

[shaky]

Still a chance of snow showers into central and eastern england from late tonight till thursday!! So definitely some interest in the next 72 hours and then its all down to whether the ecm has got that northerly right or whether it will move east again!!