Model Output Discussion - 05/01/2016 18z onwards

[phil nw.]

7 minutes ago, bluearmy said:

That's a bold statement Ali. I suspect that it wouldn't be too long until we arrived at a similar model evolution as we've been through the past week.  just have a retrogressive feeling. 

Not liking the trend in naefs anomalies after day 10 though Nick.

Signs of the High sinking into Europe.Maybe this will change but something to suggest the idea of westerlies returning may have some mileage.

Edited January 9, 2016 by phil nw.

[BLAST FROM THE PAST]

28 minutes ago, john mac said:

Well, I'm not pretending to be a weather expert but it was along the lines that cold weather will prevail through the second half of Jan, also the negative nao becoming less west based as we move forwards. Lost of fun and games to come. 

Indeed  John so potential for reload?  Sorry to put you on the spot but that is a nice summary re chances improving.

 

BFTP

Edited January 9, 2016 by BLAST FROM THE PAST

[karlos1983]

13 minutes ago, bluearmy said:

That's a bold statement Ali. I suspect that it wouldn't be too long until we arrived at a similar model evolution as we've been through the past week.  just have a retrogressive feeling. 

Well I'm glad Ali put it out there as I was thinking the same I must admit after your post. Last thing we want is a positive AO And NAO, although you didn't state that exactly, that's where my head was. 

I'm considering a cheeky PM to Stewart or Tamara. I'm in need of some urgent torpedoe reassurance 

Edited January 9, 2016 by karlos1983

[Nouska]

15 minutes ago, phil nw. said:

Not liking the trend in naefs anomalies after day 10 though Nick.

Signs of the High sinking into Europe.Maybe this will change but something to suggest the idea of westerlies returning may have some mileage.

Is this perhaps a response to the fact that the GEFS spend the fifteen day forecast period in an amplified state in MJO phase 8.

Looks very like the phase 8 January composite for our part of the world.

[supernova]

32 minutes ago, Vorticity0123 said:

After a record-crushing warm December month, January has so far delivered much more seasonable temperatures. In the Netherlands, some parts in the northeast have experienced a rather weird winter. Days of freezing rain made it possible to go ice skating on roads. Read more about it in my previous post here. Nevertheless, the southwest of the Netherlands, and most parts of the UK as well, have seen very little in the way of winter. Yet, changes may well be on their way, as possibly northerlies are going to set up shop. How does this look like, and what about possible uncertainty? Time to read on!

Here I mention the 500 hPa level. I assume this level is located about in the middle of the troposphere. I use this level here because the 500 hPa level is less influenced by surface features (like friction) than the surface level.

Troughing into Europe - High pressure towards the Atlantic?

Let's start with the current weather pattern.

GFS 500 hPa heights (colours) and surface pressure (white contours) as of today 12Z.

The chart shows little in the way of winter for the UK as of yet. Low pressure (and 500 hPa troughing, blue) in the Atlantic to the west of the UK is causing mostly unsettled weather there. Behind this low pressure area, we can see a ridge (yellow colours edging northward) buidling near Newfoundland. The ridge is forecast to move into the Atlantic, whereas the low pressure activity is expected to move into Europe towards Scandinavia.

If the ridge near Newfoundland would be able to amplify enough (that means that it is able to extend far enough northward), it may allow for cold air to flow from the north to the UK. Will this happen? That appears to be the main question for now. It should be stressed that the situation as described above is a severe simplification from reality, as many other minor developments are bound to change the details. For simplicity and clarity reasons, I will only focus on the large scale developments, and NOT on the small-scale features.

What about the differences and uncertainty?

Here we make a jump of 6 days. In order not to get a too messed pattern, I use an ensemble map instead of the operational run. Since the GFS run did not work on my computer, below are the ECMWF ensembles.

GFS 500 hPa heights (colours) and surface pressure (white contours) as of today 12Z.

At the large scale, we see a 500 hPa trough over Scandinavia, whereas some ridging at 500 hPa is evident over the Central Atlantic. The ridge is extending northwards all the way towards Greenland (yellow and green colours extending northward, red arrow). All models roughly agree on this pattern, but once again the devil is in the detail. Though we can also extract some more large-scale differences as well. Below are the ECMWF, UKMO and GFS operational runs for the very same timeframe as given above (for 6 days out):

ECMWF

UKMO

GFS

One clear difference in the models is the degree of amplification (northward extension) of the ridge over the Mid-Atlantic. The ECMWF and UKMO tend to amplify the ridge more than the GFS. The result of more northward-extension would be a higher likelihood of a more northerly base flow instead of northwest or west, with more chances on wintry weather.

Furthermore, we also see a myraid of solutions concerning the shape of the trough (blue colours) over Scandinavia. Nevertheless, the presence of this feature is quite certain. It is yet too early to talk about surface features, though, so to what extent a cold spell will develop or not over the UK is still in debate. A good guide for that are the ensemble forecasts as posted by Captain Shortwave.

Mid-Atlantic or Greenland ridging persisting?

In the long term, it seems that we will see a continuation of ridging over the Mid-Atlantic towards Greenland and beyond.

NOAA 500 hPa heights (green) and anomalies (red and blue) for 6 to 10 days out.

The map above shows a 'kink' in the green lines towards the north in the center of the Atlantic (also indicated by the red arrow). This 'kink' is indicative of the presence of ridging (high pressure activity). With this kind of ridging present, one could suggest that a northerly component is likely in the flow over the UK (see black arrow over the UK which runs parallel to the isobars). Therefore, I expect the temperatures during that period to be below average. This statement is in agreement with the ensemble forecast shown by Captain Shortwave. To what degree these below average temperatures will end up remains to be seen, but a somewhat more cool (fore some parts even wintry) spell appears to be quite likely in the medium-to long term.

I hope this post gives an understandable overview of the weather to expect in the coming days and also the uncertainties still present at large scales. If anything is unclear with respect to this post, just ask!

Sources:

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

http://www.cpc.ncep.noaa.gov/products/predictions/610day/500mb.php

 

 

 

Probably the post of the day for me. Informative, insightful, helpful, interesting and relevant. Thanks for taking the time to write this Vorticity, if I'm representative of the clueless enthusiasts on here, lots of us will have enjoyed reading this.

[karlos1983]

2 minutes ago, Nouska said:

Is this perhaps a response to the fact that the GEFS spend the fifteen day forecast period in an amplified state in MJO phase 8.

Looks very like the phase 8 January composite for our part of the world.

Blimey that's almost a carbon copy. 

[carinthian]

I think this graphic will now be close to a snow event nationwide on Wednesday night into Thursday, The short wave normal travels in the direction of the core of the jet , this being NWly. A warm sector is the usual case  south of the wave, the undercut of coldest air will be first felt in Ireland and Scotland and later on Thursday a deeper under cut to the east and south. Looking good for snowfall for many as the marginal event gradually diminishes. Like whats happening now.

 c

[Ali1977]

At T96 looks like another wave of WAA is just pushing up near East Newfoundland, this could be the GFS heading towards the ECM, prolonging the cold to Atleast late Sunday...early call but we'll see.

[chrisbell-nottheweatherman]

2 minutes ago, Lake District Blizzards said:

 

Surely we are still a long way off any agreed cold weather

bbc weather showing south westerly winds on Wednesday which is backed up by both the gfs and the ukmo 

after that on both models its looks as though Atlantic low pressure nudges through the door as the high sinks south

Apologies Mods, but I have to ask, not just for my own understanding but for others who may be confused - I haven't read any other posts here suggesting that the UKMO model shows the ridge sinking, allowing zonality as early as Wednesday?

Edited January 9, 2016 by chrisbell-nottheweatherman
Correcting typo.

[karlos1983]

2 minutes ago, Lake District Blizzards said:

 

Surely we are still a long way off any agreed cold weather

bbc weather showing south westerly winds on Wednesday which is backed up by both the gfs and the ukmo 

after that on both models its looks as though Atlantic low pressure nudges through the door as the high sinks south

The BBC nor any weather Model is showing s'westerlies next Wednesday as we know it.

[I remember Atlantic 252]

2 minutes ago, karlos1983 said:

The BBC nor any weather Model is showing s'westerlies next Wednesday as we know it.

technically they are, to me, this looks like a SW'ly, but no-one said a mild one, still looks cold

[carinthian]

7 minutes ago, carinthian said:

I think this graphic will now be close to a snow event nationwide on Wednesday night into Thursday, The short wave normal travels in the direction of the core of the jet , this being NWly. A warm sector is the usual case  south of the wave, the undercut of coldest air will be first felt in Ireland and Scotland and later on Thursday a deeper under cut to the east and south. Looking good for snowfall for many as the marginal event gradually diminishes. Like whats happening now.

 c

Looks like the channel low is going into Northern France, as we thought. This should help to keep the low upper temps in place over much of the UK as we head into next weekend. A good signal on this GFS run. Although I will like to see this on the UKMO fax when it next updates.

 C

[Captain Shortwave]

9 minutes ago, karlos1983 said:

The BBC nor any weather Model is showing s'westerlies next Wednesday as we know it.

Well technically we do see a south westerly flow as that secondary low approaches.

It isn't exactly something we would call mild though.

The pub run so far is still getting that low south of Greenland across, though it is very weak and shallow feature as opposed to the previous few runs, the Atlantic ridge as a result is a little better albeit it still doesn't look like other model output.

Moving ahead 12 hours that shallow low is now running through Wales and Central/Southern England. Producing snow too.

All conjecture though, especially as the GFS looks out of kilter with the rest of the model output, hence the solution is less likely than what we would usually rate it.

Edited January 9, 2016 by Captain Shortwave

[karlos1983]

6 minutes ago, I remember Atlantic 252 said:

technically they are, to me, this looks like a SW'ly, but no-one said a mild one, still looks cold

This is a southwesterly 

No further comments your honour 

Edited January 9, 2016 by karlos1983

[Lake District Blizzards]

bbc weather showing sw winds

met office westerly winds

and then the sinking high and atlantic breakthrough on gfs

[radiohead]

This is an improvement on the 12Z

[shaky]

Long may the gfs backdown continue!!much much better run more amplified!!

[Polar Maritime]

Lets just stick to what the 'Models' are showing please, Not what the BBC are, Thanks.

[stratty]

12 minutes ago, Captain Shortwave said:

Well technically we do see a south westerly flow as that secondary low approaches.

It isn't exactly something we would call mild though.

The pub run so far is still getting that low south of Greenland across, though it is very weak and shallow feature as opposed to the previous few runs, the Atlantic ridge as a result is a little better albeit it still doesn't look like other model output.

Moving ahead 12 hours that shallow low is now running through Wales and Central/Southern England. Producing snow too.

.........which was also hinted at on the BBC 9.55 weather for the week  (potential snow for some areas - beginning to be shown on the latest GFS)

Edited January 9, 2016 by stratty
latest

[igloo]

the GFS looks like its playing catch up once again to the euros the 18z run is a little better than the previous runs i can go back 5-6 years of model watching and i have seen this countless times before

[That ECM]

A small step in the right direction. Heights building north swinging the cold back from the continent.

[Ali1977]

Friday looks like another possible snow event...bigger down south than the Thurs one...I know these charts aren't accurate however.

[Lake District Blizzards]

13 minutes ago, chrisbell-nottheweatherman said:

Apologies Mods, but I have to ask, not just for my own understanding but for others who may be confused - I haven't read any other posts here suggesting that the UKMO model shows the ridge sinking, allowing zonality as early as Wednesday?

high pressure has sunk from greenland towards azores

and by the looks of it the next step in this chart (only goes up to 120) is the huge atlantic low to slip over the high towards the UK?

[TomDav]

Improvement on 12Z run I think with heights ridging up to Greenland

[carinthian]

This is a much colder run than the previous GFS forecast models. Could go along the lines of ECM and UKMO.

 C