Model Output Discussion

[cooling climate]

Andy- I suggest you keep an eye on the blog by Ian F-he has insight into how the UK Met see events unfolding, believe me, whatever some on here may think, they are much much better placed than anyone on here to give a reasonable idea of how things may pan out. When I had access into the senior man's comments I found it highly illuminating-okay of course its wrong at times but it was always a balanced unbiased and highly professional view-so as I suggest keep an eye on Ian's blog-well worth reading when he does it and expands beyond the more localised area he does forecasts for.

This is not a go at you Andy-just a suggestion for others as well.

The Met forcasts fluctuate just like the models and once you are more than three or four days out

then they are out of their comfort zone. In this set up I would suggest the time frame to be

even less than this.

Just to add although I know it is only one run and anything past t72 is definitely FI at the moment

but the ECM evolution from t216 -240 onwards suggest anything but mild weather.

[Guest North Sea Snow Convection]

i think reality will soon set in Matt

http://www.meteogrou...e_forecast.html

the latter part of the week certainly on the cool side but unlikely to be cold for anything notable.

The clearest thing that sticks out from those London ECM ensembles is what it suggests about the midweek low as depicted by the ECM operational.

It is way way above the mean for temps, wind (most especially) and ppn

Edited February 20, 2010 by North Sea Snow Convection

[nick sussex]

The models unfortunately look reluctant to drive the pattern eastwards and because of this hopes for a much colder end to the month seem to be receding. Although some places have seen snow with some more to come over the next few days it looks unlikely now that the UK will benefit from any of that very cold upper air to the ne. Theres always the danger with the western based negative NAO that eventually pressure will rise to the se and the trough edged too far west.

Here the mean height comparisons show the trend to a slow warm up as low pressure will with time come ne too far west.

http://www.meteo.psu.edu/~gadomski/ECMWF_0z/hgtcomp.html

Unless theres a big change upstream to shunt the pattern eastwards then less cold conditions are likely later next week as the colder air gets backed further west into the Atlantic, the far north looks likely however to hang onto the colder conditions for a while longer.

Theres only so long you can sustain these marginal conditions with the current set up and so the odds on less cold to average conditions have shortened.

[Guest FireStorm]

I was under the impression its usually GFS FI that totally overcooks low pressure systems, A quick flick through the ECM 00z made me chuckle, SW not only due for potentially heavy rains but in simple terms a hurricane equivalent system

http://charts.netweather.tv/ecmimages/20100220/00/ecm500.192.png

[Nick F]

I see some disappointment rife on here from southern quarters! But we are making the best of what is mostly an Atlantic driven pattern now, and we should be grateful that cold air is still close by and we still have the potential for lowland snowfall for some parts of the UK. but I guess our expectations have been raised considerably by events earlier on this winter.

We will see over the coming days an increasingly familiar pattern of shortwaves developing over the Atlantic and moving NE on the forward side of a cold upper trough continuing to extend SW from the Norwegian Sea to our NW. I think those south of central areas will have to accept that snow potential will be rather low next week and perhaps the snowline beginning to drift a little more north with time too - with the jet to our south tending to buckle NE towards the UK - as the trough continues to amplify SW-wards over the N Atlantic, allowing milder air to flood NE across mainland Europe. Signs of a return to bitter cold with -10C T850s with none of this marginality look low now, with troughing developing to our N and NW.

Have updated my blog this afternoon for the weather this weekend and coming days:

http://forum.netweather.tv/topic/61574-snow-potential-week-commencing-15th-feb/

[Cheese Rice]

It does look like the main risk has shifted further north, which is great for me but for those further south I can see why you are disappointed. But you have to remember this winter is better than any of the other ones (not including last winter) so to complain when most places have seen a fair few number of snow events is been too negative. Anyway I'm pretty confident the south will see a widespread snow event. Some will be further south and some further north so hopefully we will all benefit in the end.

Edited February 20, 2010 by 10123

[johnholmes]

Here the mean height comparisons show the trend to a slow warm up as low pressure will with time come ne too far west.

http://www.meteo.psu...0z/hgtcomp.html

Unless theres a big change upstream to shunt the pattern eastwards then less cold conditions are likely later next week as the colder air gets backed further west into the Atlantic, the far north looks likely however to hang onto the colder conditions for a while longer.

Theres only so long you can sustain these marginal conditions with the current set up and so the odds on less cold to average conditions have shortened.

that pattern shown by Nick above is repeated, on the NOAA 500mb anomaly charts; they have been showing a similar set up for almost a week now.

Thus there are conflicting signals, 30mb temp has been well above normal until very recently, AO is -ve, NAO also; neither quite as -ve as a month ago, although AO is about the same.

GFS and ECMWF in the T+240 time scale have, it seems, increasingly been suggesting that there is unlikely to be any real deep cold return to the UK. GFS in its outer FI reaches has, most of the time, agreed with this. Sometimes its shown the current 'cold' likely to continue, at other times its shown a much milder outcome.

The comment from Nick F regarding the upper trough-jet stream etc, are all relevant to what I've just quoted and the post from Nick S.

The next few days are likely to see some largish snowfalls (on relatively low ground) from anywhere from the Midlands north-exact areas will NOT be known until no further than 24 possibly 12 hours ahead. Again as Nick F has posted the snow threat is most likely to edge north through the week.

Its not certain by any means that my comments or the others from both Nicks' and 1 or 2 others will be correct but for those still believing in a return to deep cold its time, in my view, to accept that its less rather than more likely. For newcomers to the daily discussion on will it get colder-will the cold remain-then best you take the last couple of posts on board.

Mushy will be delighted if it turns into spring after this next week-some others of us will also be quite relieved although when I post I do try very hard to stop my winter prejudice showing or my preference for spring and summer weather to occur in the months with those titles!

sorry just a quick ps

It has been for many areas probably not only the coldest but wintriest winter for many parts of the country-see the relevant thread with data to show this.

Edited February 20, 2010 by johnholmes

[grab my graupel]

Hi everyone, the Moderating team has had to move a number of posts into the Model Moods thread

Can we try to keep the 'North v South bias' comments out of this thread please?

Thank you

Brian

[full_frontal_occlusion]

Wherever it happens over the next week, somewhere in this motley collection of islands will get pasted and as is always the case, the higher up one is the better the chances.

As others have stated numerous times before, the positioning of the lows and their trajectories are all important. The tolerance errors for this kind of set up dictate even mesoscale models will struggle to define the actual lowland snow areas until 18 hrs or less before the event.

ffO.

Edited February 20, 2010 by full_frontal_occlusion

[Thundery wintry showers]

Just a thought- this pattern is starting to remind me of a less cold version of March 1947 with this succession of Atlantic lows gradually tracking further and further north. There could well be problems with flooding, particularly in the Midlands and south, and a considerable shortage of sunshine in the same areas. The areas that get large amounts of snow are particularly at risk if the lows continue to track further north causing the snow to be washed away by rain.

For Scotland sunshine and snow showers, the latter initially mainly in the west but then transferring mainly to the east, looks likely for the foreseeable future.

[LomondSnowstorm]

Just a thought- this pattern is starting to remind me of a less cold version of March 1947 with this succession of Atlantic lows gradually tracking further and further north. There could well be problems with flooding, particularly in the Midlands and south, and a considerable shortage of sunshine in the same areas. The areas that get large amounts of snow are particularly at risk if the lows continue to track further north causing the snow to be washed away by rain.

For Scotland sunshine and snow showers, the latter initially mainly in the west but then transferring mainly to the east, looks likely for the foreseeable future.

Predominantly yes but there is the possibility of the low on Wednesday making its way far enough north to give some frontal snowfall to southern Scotland as shown by the Met Office advisory for over 15cm from northern England to Fife. The slight difference perhaps being the track and position of the lows? http://www.wetterzentrale.de/pics/archive/slp/1947/Rslp19470313.gif .

[StewieEatWorld]

Predominantly yes but there is the possibility of the low on Wednesday making its way far enough north to give some frontal snowfall to southern Scotland as shown by the Met Office advisory for over 15cm from northern England to Fife. The slight difference perhaps being the track and position of the lows? http://www.wetterzen...slp19470313.gif .

I could see the potential for a lot more than 15cm! Just been out and its bitterly cold, grass frost surviving in the shade as well.

But back to the models... hopefully the 12Z's are good, if we still have a low tracking across Central/Southern Scotland and Northern England for wednesday maybe by Sunday or Monday, i'll be one happy bunny!

Edited February 20, 2010 by Mr Stewie

[Thundersquall]

The 06Z run from GFS shows a Low pressure system moving in from the SW at T+48, then becoming progressively more elongated roughly NEbE-SWbW up to T+72. By T+108 is has resolved itself into a more rounded centre, centered over The Wash. Finally clearing away by T+138, but hot on its heels is another Low Pressure winding itself up off the SW Approaches. That takes a similar path (across the Bristol area?) but zips through and is gone by T+174 by which time it's already just to the East of Denmark.

I think Bristol for example is right on the boundary between colder winds coming in from the ENE and slightly less cold winds coming in from the WSW. Any slight shift south of the predicted track (which often happens in these situations) and we stay in the colder air and are more likely to get snow (I am referring to the T+48 to T+90-ish time-scale).

The strong Jet Stream core is, I think, too far south over the Straits of Gibraltar to have any oomph to push the track of these successive Low pressure systems a lot further north.

And the upper air steering at 200hpa is generally blowing stright along the Low pressure's elongation, and not across it, further preventing any real push northwards.

Edited February 20, 2010 by Thundersquall

[LomondSnowstorm]

I could see the potential for a lot more than 15cm! Just been out and its bitterly cold, grass frost surviving in the shade as well.

But back to the models... hopefully the 12Z's are good, if we still have a low tracking across Central/Southern Scotland and Northern England maybe by Sunday or Monday, i'll be one happy bunny!

I'd say that's unlikely but probably by Wednesday the lows will have pushed that bit further north. http://www.meteociel.fr/ukmo/run/UW48-21.GIF?20-06 http://www.meteociel.fr/ukmo/run/UW120-21.GIF?20-06

http://www.meteociel.fr/modeles/ecmwf/run/ECM1-96.GIF?20-12

[StewieEatWorld]

I'd say that's unlikely but probably by Wednesday the lows will have pushed that bit further north. http://www.meteociel...48-21.GIF?20-06 http://www.meteociel...20-21.GIF?20-06

http://www.meteociel...M1-96.GIF?20-12

Yeah, i meant wednesday, but didn't word my post well. I am right in thinking, if they push too far north, milder conditions will spread over the majority of the UK sooner rather than later? So the path they are taking the now, by gradually moving further and further north will let the cold air persist for that little longer, which in turn increases snow chances further on the week?

[LomondSnowstorm]

Yeah, i meant wednesday, but didn't word my post well. I am right in thinking, if they push too far north, milder conditions will spread over the majority of the UK sooner rather than later? So the path they are taking the now, by gradually moving further and further north will let the cold air persist for that little longer, which in turn increases snow chances further on the week?

Yep. Ideally for cold in the long run you want the lows tracking further south and east, but this looks fairly unlikely to happen, so the best that can happen is the lows slowly edging a bit further north, gradually decreasing the snow risk from the Midlands northwards while keeping Scotland in generally -6 - -8 uppers for a week, and probably more, to come. But of course in the short term for Scotland the snow risk would increase greatly with lows exiting the UK a little further north than on the 6Z, though convection showers are likely to affect eastern areas at times anyway with the low further south.

[Thundersquall]

Could we be talking about damaging winds over Southern England and South Wales if this chart turns out to be accurate?

[LomondSnowstorm]

Could we be talking about damaging winds over Southern England and South Wales if this chart turns out to be accurate?

Could well be, even pretty gusty here with not inconsiderable drifting but for your area it would be very windy with (I think) some squally showers through the Bristol Channel.

[Harsh Climate]

For us in northern england the charts are perfect! But nothings set in stone yet... As the lows tracking further north could mean sleet instead of snow and if they track further south we could miss the precipitation all together ...

I think there will be plenty of UPGRADES/DOWNGRADES to come at the same time, depending on whether your in the midlands/northern england/scotland

[Thundersquall]

For us in northern england the charts are perfect! But nothings set in stone yet... As the lows tracking further north could mean sleet instead of snow and if they track further south we could miss the precipitation all together ...

I think there will be plenty of UPGRADES/DOWNGRADES to come at the same time, depending on whether your in the midlands/northern england/scotland

On the subject of upgrades or downgrades, the 12Z charts are coming through. The charts are up to T+42, and yes, the track is a little further south and Low pressure is 5mbs higher at 980mb.

Looks like a downgrade in terms of the Low pressure being much more filled and much further south and really only just grazing the Bristol Channel.

Edited February 20, 2010 by Thundersquall

[03jtrickey]

On the subject of upgrades or downgrades, the 12Z charts are coming through. The charts are up to T+42, and yes, the track is a little further south and Low pressure is 5mbs higher at 980mb.

Looks like a downgrade in terms of the Low pressure being much more filled and much further south and really only just grazing the Bristol Channel.

NAE is showing plenty of precipitation around on Sunday and Monday, but what will it be?

[Joe Bloggs]

Tomorrow's snow now appearing on the 12z GFS

http://www.wetterzentrale.de/pics/Rtavn184.png

http://www.wetterzentrale.de/pics/Rtavn244.png

Northern limit appears to be North Lancs/South Cumbria area

Judging by the projected dewpoints, Wales looks set to have a snow turning to rain setup, best chance of snow towards the NE towards Ruthin etc, by midday snow only likely Manchester northwards, anywhere south probably seeing rain.

By 18z tomorrow however there is some residual stuff left across the South Midlands/Eastern England, could be some snow on the back edge of the front.

Into Monday, precipitation only reaches Southern England now, not even reaching South Wales. Risk of temp snow is again aligned up with the northerly limit of the front, possibly the M4 corridor type of area, however by midday it looks like rain for just about everywhere as sub zero projected dewpoints become reserved for Wales, Northern England and Scotland...

It's only the GFS, so given the current disagreement amongst the output, possibly best to wait for the NAE and the UM before making too much judgement.

[conor123]

I think the GFS has got it right now with Monday's low roughly, they always end up more southerly tracking than forecast, should hopefully mean a better snow risk for Tuesdays front.

In the short term tonight's low is a bit stronger and a tad further north to actually.

[Thundersquall]

NAE is showing plenty of precipitation around on Sunday and Monday, but what will it be?

I would hazard a guess that the boundary between rain and snow will be the area in the 30's millimetres. Anywhere north of this maximum accumulation would in my opinion be more likely to get snow.

Bristol's roughly 2cm rainfall equivalent would get a decent 20cms snow assuming it all falls as snow and the temperature stays close to freezing.

[conor123]

http://www.wetterzentrale.de/pics/Rtavn962.png

Oh dear, thankfully that looks very unrealistic but low is to far west so ends up to far North stopping cold air returning before the next low..