Model output discussion - 1st December onwards

[phil nw.]

Just now, MPG said:

Indeed but the main clustering is above the +5 degrees mark. Therefore more likely mild to cool until the end of the month....but there is a clear split but not in colds favour.

You have to watch the trend in the number of members going cold/mild too.

I don't think we can take too much from them at face value because of such a large spread.As NS said the mean will mask a number of different clusters cold and mild and i think today the number of colder ones have increased,for what it's worth.

The main point is there is not a clear way forward compared to a few runs ago when it was mild zonal all the way.

[Cheshire Freeze]

Of more pressing concern in the closer time frame is the forecast for more slow moving, heavy rain over Cumbria. Could get very, very bad there once again

 

There looks to be the potential for over 24 hours of heavy rain in the area once again on the 12z GFS

 

Edited December 7, 2015 by CreweCold

[nick sussex]

The UKMO has now flipped at T120hrs and separated that nuisance low to the sw from low heights near the UK. At T144hrs it builds high pressure north.

The complexities of the pattern get even more complicated because whats likely to happen is a lobe of lower heights will be pushed south to meet the nuisance low which has now amplified in response to the upstream pattern.

Its possible depending on the amplification of the new low formed that you might see a ridge thrown towards Scandi:

 

 

In terms of trend it looks to be moving towards the ECM 00hrs run. The GFS cuts a shortwave east across the north of the UK, unfortunately this would bring a lot more rain to those regions already badly effected. There could also be some snow on the northern flank of that more especially for higher ground.

Edited December 7, 2015 by nick sussex

[Nick L]

ECM also going with further heavy rainfall targeting Cumbria over the next few days, cumulative precip charts showing 70mm+ quite widely, which will mean in excess of 100mm possible over the mountains. The last thing they need.

[knocker]

I mentioned this morning that the gfs has been consistently modeling the low next weekend to move NE over the UK with the upper trough stretching away down to the SW providing a useful gateway. This continues but at the moment the follow up low nips into France but this analysis will obviously change.

Charts weatherbell

 

[Ali1977]

Nothing of interest on the GFS 12Z, other than unfortunately more rain in Cumbria!! Going to be V hard to break down this PV I think!! 

[Summer Sun]

A chiller day on Saturday looking at UKMO before things settle down on Sunday

[feb1991blizzard]

6 minutes ago, Greenland1080 said:

This seems to be a further update from Cohen's blog..

http://www.aer.com/science-research/climate-weather/arctic-oscillation

 

Longer-term weather prediction will likely require a correct forecast of the strength of the stratospheric polar vortex. Currently the polar vortex is strong and as predicted to strengthen further.  As long as the polar vortex remains strong, the overall hemispheric pattern will likely remain mild.  A favorite diagnostic of ours to analyze and anticipate troposphere-stratosphere coupling is the polar cap geopotential height (PCH) anomaly plot.  Consistent with the predicted positive AO, the models predict that over the next two weeks the polar cap geopotential height anomalies will remain mostly normal to below normal for much of the troposphere and well below normal for the stratosphere (Figure 7).  Consistent with below normal PCH the vertical transfer of energy from the troposphere to the stratosphere or vertical wave activity flux (WAFz) is predicted to be relatively quiet. (Figure 8).  However the operational GFS form this morning is predicting the tropospheric PCH to increase as well as the WAFz end of week two.  This is a low confidence forecast at this point but consistent with our thinking.

[Ali1977]

GFS Control at day 10 looks very different, quite a bit of WAA within the ensembles at day 10 also.

[cheshire snow]

^^^

So Basically is above implying in short what we have now is what

We will endure in the foreseeable future?

C.S

Edit in reply to Feb 1991 post

Edited December 7, 2015 by cheshire snow

[Captain Shortwave]

The output still continues to resemble an absolute mess with deviation continuing from Friday onwards.  A lot of potential solutions still available for the coming weekend ranging from bone dry to an absolute washout.

Ridiculous chart of the day courtesy of the GFS control

Snow to low levels in Scotland for a time, temperatures in the south for next week would end up even higher than they are forecast to be this week. Oh and a lot of rain on the dividing line which happens to be northern England 

 

Please note that there is no effort to actually making a sensible forecast in the post because simply I don't have a clue.

Edited December 7, 2015 by Captain Shortwave

[Ali1977]

Really good GFS with around 14 showing ridging or blocking at day 11...by far the best looking this year.

sadly the WAA eventually gets bowled over by the relentless PV...good effort at a swing though!!

Edited December 7, 2015 by Ali1977
Amend

[TSNWK]

Please can someone advise what the difference is between the GFS operational and control ? And should any value be placed over one or the other.

many thanks.

[chrisbell-nottheweatherman]

21 minutes ago, feb1991blizzard said:

Longer-term weather prediction will likely require a correct forecast of the strength of the stratospheric polar vortex. Currently the polar vortex is strong and as predicted to strengthen further.  As long as the polar vortex remains strong, the overall hemispheric pattern will likely remain mild.  A favorite diagnostic of ours to analyze and anticipate troposphere-stratosphere coupling is the polar cap geopotential height (PCH) anomaly plot.  Consistent with the predicted positive AO, the models predict that over the next two weeks the polar cap geopotential height anomalies will remain mostly normal to below normal for much of the troposphere and well below normal for the stratosphere (Figure 7).  Consistent with below normal PCH the vertical transfer of energy from the troposphere to the stratosphere or vertical wave activity flux (WAFz) is predicted to be relatively quiet. (Figure 8).  However the operational GFS form this morning is predicting the tropospheric PCH to increase as well as the WAFz end of week two.  This is a low confidence forecast at this point but consistent with our thinking.

Given the way that much of Cumbria is underwater, I shudder to think what will happen should the vortex strengthen still further.

[Frosty.]

The Gfs 12z shows a decent window of fine weather developing next week as high pressure builds NE across the uk for a time, this would be welcome relief for the areas hardest hit by the severe flooding....fingers crossed for them!

Edited December 7, 2015 by Frosty.

[Cloud 10]

34 minutes ago, Greenland1080 said:

This seems to be a further update from Cohen's blog..Friday...can't remember when he last updated so apologies if repost

http://www.aer.com/science-research/climate-weather/arctic-oscillation

 

 

I'm liking the look of their winter temperature anomaly forecast.

 

[Nick L]

6 minutes ago, TSNWK said:

Please can someone advise what the difference is between the GFS operational and control ? And should any value be placed over one or the other.

many thanks.

The GFS operational is the main, "high resolution" run.

The control is a part of the ensemble suite. It is run at the same starting conditions as the operational, but at a lower resolution, along side dozens of other ensemble members at slightly different starting conditions than the control.

[Daniel*]

Not a good run at all for Cumbria in particular flood stricken by exceptional rainfall from Storm Desmond with the ground absolutely waterlogged there will be little to no infiltration just further flooding a rather bleak time for this part of the world with inevitably more flooding to come in the week ahead. A ghastly prospect for those who are trying to salvage what they can; fingers crossed this unsettled weather abates and fizzles out.

Edited December 7, 2015 by Daniel*

[damianslaw]

Another messy picture being shown by the models, with lots of various output, hard knowing how things will pan out come the weekend, but interesting to note UKMO has backed away from its zonal SW fest, and moved more in line with ECM output, both hinting at height rises to the NE. I always think ECM does best with developments to our east, and is the first model to latch onto height rise development in that vicinity.

In the short term - staying very unsettled and I'm keeping my fingers crossed we don't see too much troublesome rain.

I'm quietly optimistic that later in the month we will see a much drier theme and quite possibly colder one (nothing severe), but seasonal all the same - it will be 2 months with hardly a break from heavy rain and cloud.. I'm a strong believer mother nature balances herself out, extreme wet spells coming to abrupt endings and vice versa very dry spells coming to abrupt endings. I remember the hosepipe ban being announced in March 2012 and then the taps were turned on... Very wet autumns in 2000 and 2009 were followed by lengthy drier periods, conversely the wet winter of 94/95 was followed by a 2 year very dry period.. I've done a thread on this observation in the past.

[feb1991blizzard]

15 minutes ago, chrisbell-nottheweatherman said:

Given the way that much of Cumbria is underwater, I shudder to think what will happen should the vortex strengthen still further.

As I understand it, he is saying that he expects it to weaken AT SOME POINT as WAF (wave activity flux) is set to increase (please someone with more expertise correct me if I'm wrong) which should start to weaken the strat vortex but for the time being you only have to look at short - medium range charts and met office warnings to realise it could get worse (the flooding) before it gets better, you only need moderate amounts of rain when so much has already fallen to cause problems.

[chrisbell-nottheweatherman]

Just now, feb1991blizzard said:

As I understand it, he is saying that he expects it to weaken AT SOME POINT as WAF (wave activity flux) is set to increase (please someone with more expertise correct me if I'm wrong) which should start to weaken the strat vortex but for the time being you only have to look at short - medium range charts and met office warnings to realise it could get worse (the flooding) before it gets better, you only need moderate amounts of rain when so much has already fallen to cause problems.

Indeed - the first possibility of weaking of the strat vortex is (according to the post in question) 2 weeks away at minumum, and that the far side of a vortx strengthening.

[chionomaniac]

4 hours ago, nick sussex said:

Trying to piece together the NWP puzzle is proving difficult. As you saw from those USA discussions on the previous page there is a lot of uncertainty upstream. However in the updated state forecasts the ECM is the preferred solution for the pattern in the east Pacific.

Interestingly todays ECM 00hrs builds pressure north of Svalbard, this does actually have some strat support. You'll note that we see a reversal of zonal winds from around 70N, you'll also see the strong zonal winds further south:

You can see below that build of pressure near Svalbard:

If the strat forecast is correct then some height rises are likely in that area. A brief note about the strat, in case people haven't been following that thread, the forecast is for some waning of the PV. If we add this to the upstream changes its understandable that the models are inconsistent at the moment.

Hi Nick,

 

The bit you highlight is the trop forecast from yesterdays 12Z ECM mean zonal winds mean chart. Effectively the charts are based on the full ECM computation from that run. The strat forecast is all the bit above the blue (above 100hPA) - yes the monstrous red orange bit as you highlight regarding the jet further south. What is interesting is that arctic high can present itself with that existing strat strength and forecast. If we could get the strat to weaken and then the Arctic presents itself again then mid latitudes could get very interesting as ba pointed out earlier.

[nick sussex]

5 minutes ago, chionomaniac said:

Hi Nick,

 

The bit you highlight is the trop forecast from yesterdays 12Z ECM mean zonal winds mean chart. Effectively the charts are based on the full ECM computation from that run. The strat forecast is all the bit above the blue (above 100hPA) - yes the monstrous red orange bit as you highlight regarding the jet further south. What is interesting is that arctic high can present itself with that existing strat strength and forecast. If we could get the strat to weaken and then the Arctic presents itself again then mid latitudes could get very interesting as ba pointed out earlier.

So something weird is going on? You wouldn't normally expect to see this. We await the ECM with interest especially tomorrows Berlin update.

[BLAST FROM THE PAST]

3 hours ago, Ed Stone said:

But it's the not-knowing that makes model-watching such fun? Anything after 16/12, maybe sooner, looks like a dog's breakfast?

Indeed Pete, its all still in the mix up for grabs.   I'm just quietly watching, and quietly liking this indecision

 

 

BFTP

Edited December 7, 2015 by BLAST FROM THE PAST

[knocker]

A quick glance at NH temp anomalies and the trough dragging some wet weather our way