Model Output Discussion - 21st - 28th November

[Gavin Hannah]

At present yes MSB, just take a look at this chart from last year to see what conditions we need over the pole for such a link up to happen.

http://www.wetterzen...00120101120.png

See what your saying there. That makes it a lot clearer how the different highs and lows interact now I've seen that chart.

[nick sussex]

What at first hand looks like the GFS and ECM in agreement is altogether different as we approach the 240hrs range. The GFS is most certainly going to run the jet over the top pushing the ridge well into Europe but centreing this to the south.

The ECM is not so clear cut, it holds the troughing more over Europe, begins to retrogress the pattern and has more amplification upstream, it also begins to move the PV away from southern Greenland.

I'd be surprised if there weren't some colder options in the extended range of the ECM De Bilt ensembles for Holland, I think we're likely to see a high ridging ne towards the UK.

The question is how far north will any high get?

Edited November 27, 2011 by nick sussex

[clark3r]

looking at the ECM at 240 FI i no! but high building from the south west and high building in the north east although things will prob change maybe a cold blast 2nd/3rd week december!

lol is this the blocking James madden forecasts!!!

Edited November 27, 2011 by clark3r

[Summer Sun]

ECM looking very seasonal tonight with Gales possible for the North on Saturday and Sunday whilst the Southern half of the UK remains less windy.

[damianslaw]

What at first hand looks like the GFS and ECM in agreement is altogether different as we approach the 240hrs range. The GFS is most certainly going to run the jet over the top pushing the ridge well into Europe but centreing this to the south.

The ECM is not so clear cut, it holds the troughing more over Europe, begins to retrogress the pattern and has more amplification upstream, it also begins to move the PV away from southern Greenland.

I'd be surprised if there weren't some colder options in the extended range of the ECM De Bilt ensembles for Holland, I think we're likely to see a high ridging ne towards the UK.

The question is how far north will any high get?

Yes there are tentative signs of heights building eventually near and over the country as we head towards middle of december - these will most likely build from the south. High ridging NE can quickly transfer into scandi leaving us under what some people term 'faux cold' conditions a term i dislike. Such conditions deliver much surface cold and light winds, temps do struggle especially under fog, frosts and fogs are the name of the game and it certainly isn't 'mild weather'.

Back to the models and I am expecting them to firm up on strong heights building in from the SW after the 5th dec, where they go anyones guess - could be a mid atlantic high, could just sit over southern england, could ridge over most of the country and into scandi - all three scenarios would deliver vey different weather -

mid atlantic high (weak variety) - would see fronts move into scotland from the NW, eastern parts dry and possibly frosty, but generally very benign conditions for all with the ridge quickly topplingsouth again and renewed westerly/southwesterly attack.

heights building into s england - jet contines to sweep fronts across northern half of the country - here mild wet and windy, the south foggy and damp possibly frosty if skies cleared but very grey miserable conditions.

heights ridging NE across country and into scandi - cold frosty foggy nights, milder sunny days but colder under any fog.

[Gibby]

Good evening. Here's a resumee of the 12zs from GFS, UKMO and ECM tonight.

GFS shows a freshening SW airflow over the UK tomorrow and Tuesday pushing the existing ridge of High pressure over England and Wales away eastwards. Troughs moving across Western and Northern areas will bring extensive rain for those areas which extends East across the rest of the UK later on Tuesday. Thereafter the weather remains disturbed with further spells of rain and gales with cooler, showery weather inbetween. In the cooler weather the air could be cold enough for snow over higher ground in the North. Through FI tonight high pressure slowly builds back from the South pushing Atlantic Lows and the Jet stream further North again and leaving the UK under High pressure and settled chilly conditions at the end of the run.

The GFS Ensembles shows the operational as a mild outlier at the end while the mean for the run stays close to or just a bit below the long term average for London. Aberdeen ensembles show a similar pattern in general through the run.

UKMO tonight shows an increasingly unsettled and wet week to come with some welcome rain for some of the rain starved areas as well as for all other areas too. The rain may be heavy at times and with deep low pressures moving in close to the North at times gales will be commonplace too with temperatures falling from reasonable levels to values a litlle below normal by next weekend, the chill accentuated in the strong winds.

ECM too looks much the same with a very unsettled spell up and coming through the coming week before in a move similar to GFS High pressure builds up from the SW at the end of the run.

In Summary there will be plenty of wind and rain to talk about for many this week. Things will feel distinctly colder than recently especially in the South where it's been so mild recently. In the north snow is possible on the hills at times as well while in about 10 days time both GFS and ECM show a good signal in their operationals of a return of High pressure from the South.

[nick sussex]

Yes there are tentative signs of heights building eventually near and over the country as we head towards middle of december - these will most likely build from the south. High ridging NE can quickly transfer into scandi leaving us under what some people term 'faux cold' conditions a term i dislike. Such conditions deliver much surface cold and light winds, temps do struggle especially under fog, frosts and fogs are the name of the game and it certainly isn't 'mild weather'.

Back to the models and I am expecting them to firm up on strong heights building in from the SW after the 5th dec, where they go anyones guess - could be a mid atlantic high, could just sit over southern england, could ridge over most of the country and into scandi - all three scenarios would deliver vey different weather -

mid atlantic high (weak variety) - would see fronts move into scotland from the NW, eastern parts dry and possibly frosty, but generally very benign conditions for all with the ridge quickly topplingsouth again and renewed westerly/southwesterly attack.

heights building into s england - jet contines to sweep fronts across northern half of the country - here mild wet and windy, the south foggy and damp possibly frosty if skies cleared but very grey miserable conditions.

heights ridging NE across country and into scandi - cold frosty foggy nights, milder sunny days but colder under any fog.

This mornings ECM ensembles control run looks like it went for the high further north and a continental flow over in Holland eventually.

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

Given tonights operational run I would be surprised if theres not a few more colder options showing in the ensembles.

Of course Euro highs can bring different conditions across mainland Europe to the UK, what might bring coldish temps here in sw France could depending where the high centred bring mild sw'erlies into the UK.

I think I'd agree though that high pressure moving ne looks a good bet, we'll just have to wait and see what the models do over the coming days.

[jonnybradley]

Thanks for the reply Nick F.

There there does seem to be a high building in the Atlantic again (Azores?). As MSB said the current models do have it tracking more SW but as others have said this is in FI and where it ends up no body knows.

[Gavin Hannah]

Thanks for the reply Nick F.

There there does seem to be a high building in the Atlantic again (Azores?). As MSB said the current models do have it tracking more SW but as others have said this is in FI and where it ends up no body knows.

Could be the key to the start of our winter is where this high ends up. North into greenland would be much welcome, but as mentioned by folks on here, that has almost 0% chance of happening. I think the best we could hope for is for the HP to track well south of the UK.

Edited November 27, 2011 by MadSnowboarder

[jonnybradley]

Thanks for the reply Nick F.

There there does seem to be a high building in the Atlantic again (Azores?). As MSB said the current models do have it tracking more SW but as others have said this is in FI and where it ends up no body knows.

Sorry meant to say SE!

Edited November 27, 2011 by jonnybradley

[feb1991blizzard]

For once the GFS FI is the most realistic option, drier spell for the Southern half of UK mid december but after that the high will end up to the south and south east of us again with the jet firing up again giving us mild, wet and windy for Xmas IMO.

[Frosty.]

We are still on track for a possible cold snap from next weekend through to the middle of the following week with snow showers to northern and eastern coasts and frosty nights, the north of scotland probably worst affected by this if it happens. For the coming week it starts very mild with temps up to 13-14c again in southern britain but slowly turning less mild later in the week. Scotland and N.Ireland turning milder for a time but with heavy rain and gales and then colder by midweek with wintry showers and strong westerly winds but then the 528 dam line will be forced north by another deepening low spreading into nw scotland on thursday with snow for the mountains as cold air lingers in the far north, then next weekend there is a chance of cold air sweeping southeast with snow to the far north and down the east coast.

[Gavin Hannah]

A light difference between the GFS chart for 3 Dec, and the NOAA chart.

http://hw.nwstatic.co.uk/gfsimages/gfs.20111127/12/138/h500slp.png

http://www.cpc.ncep.noaa.gov/products/predictions/610day/610day.03.gif

Noaa have the low to the north of the UK tracking further south so far as I can tell. The NOAA charts aren't the easiest to read.

[Grimsby Snow Lover]

A light difference between the GFS chart for 3 Dec, and the NOAA chart.

http://hw.nwstatic.c...138/h500slp.png

http://www.cpc.ncep....y/610day.03.gif

Noaa have the low to the north of the UK tracking further south so far as I can tell. The NOAA charts aren't the easiest to read.

I know what you mean there, I find these charts the hardest ones to read, maybe because they focus on American and use dashed lines. Would love a few tips on what to look for etc.

[johnholmes]

re the posts from Ms and GSL.

The first chart is the GFS 500mb temperature chart with the isobars in white on it.

The second chart if the 500mb anomaly chart which you often see me discuss. The dashed lines, in red show the areas where the predicted 500mb height is above the average for the time of year. The blue dashed lines show those -ve area, heights below average.

You cannot, without a fair amount of practice relate the two charts together. The 500mb anomaly chart is also the expected mean values over the dates quoted at the bottom of the chart, in this case for 3-7 December; the GFS chart is for one fixed time=Sat 3 December at 0600Z.

I'm happy to carry on a chat with either/both of you via pm if you wish so as not to clog up the model current discussion thread?

this link may help regarding what you can use the basic GFS output for trying to forecast for your own area-

http://forum.netweat...d-and-use-them/

this link to a pdf explanation may help understand what they 500mb anomaly charts are and how we can use them to predict what the atmosphere at 500mb may look like in 6-15 days time-remember its at 500mb NOT the surface, hence my comment about ittakes some practive to be able to relate one to the other.

ask via pm if you need further help-anyone is welcome.

found it!

500mb teach in 28 nov11.pdf

Edited November 27, 2011 by johnholmes

[Jhonny Peter Carson]

If you watch the current BBC forecast you can see the snow falling in the Atlantic West and North of Ireland. These nw winds are going to be a headache this week for the Met Office. I think that end of week snow over parts of the UK.

[lorenzo]

Great post JH

Also would add that the NOAA forecasters dont add input over weekends - unless exceptional circumstance.

Another page here for bookmarking , recently on Fbook which is good, holds the vital upstream discussions http://www.hpc.ncep.noaa.gov/html/discuss.shtml

[legritter]

evening all ,iv looked at charts and read some of the talk on other forums etc ,and i have a hunch that next weekend could throw up some surprises . good events can develope from just little features popping up , tonights fax should be interesting and by tuesday night we could be looking at some interesting ,charts for sat/ following tues . i am by no means forecasting a snow fest but there could be some lucky fellow members with a SMILE on their faces . warm seas /colder air . we have certainly moved on since last weekend , im certainly getting more confident of some good things coming out of this winter . regards legritter .

[Matty M]

Let's be avin' it! Heavy wet snow for many. Severe storm for Channel

[Robbie Garrett]

evening all ,iv looked at charts and read some of the talk on other forums etc ,and i have a hunch that next weekend could throw up some surprises . good events can develope from just little features popping up , tonights fax should be interesting and by tuesday night we could be looking at some interesting ,charts for sat/ following tues . i am by no means forecasting a snow fest but there could be some lucky fellow members with a SMILE on their faces . warm seas /colder air . we have certainly moved on since last weekend , im certainly getting more confident of some good things coming out of this winter . regards legritter .

Are we talking about blizzards? and an inversion etc providing colder temperatures for the UK.

[Cheshire Freeze]

A lovely marginal snow event at 192 hours on the GFS 18z. If only.

[Robbie Garrett]

Let's be avin' it! Heavy wet snow for many. Severe storm for Channel

Isn't that a secondary low forming of the 3rd December one?

[mountain shadow]

Wow!, a very exciting 18z so far. A disturbed week, getting colder and windier with an extremely intense low pressure system tracking north of Scotland. One to keep an eye on. Following this system the air is polar in source and with a trough moving up the channel, severe flooding for parts of the south with heavy snow on its northern edge.

We all couldn't wait for the euro high to disappear, hopefully not a case of be careful what you wish for.

[Matty M]

Wow!, a very exciting 18z so far. A disturbed week, getting colder and windier with an extremely intense low pressure system tracking north of Scotland. One to keep an eye on. Following this system the air is polar in source and with a trough moving up the channel, severe flooding for parts of the south with heavy snow on its northern edge.

We all couldn't wait for the euro high to disappear, hopefully not a case of be careful what you wish for.

Yes, duck at dat. An extreme low south of Iceland.

[Grimsby Snow Lover]

Just out of interest how does the NAO or AO turn negative from its current positive state?