General Model Output Discussion

[TEITS]

I think this only holds true for the southern half of England. 31 December, 1 and 2 January all look like they have significant potential to deliver a fair amount of convection for eastern Scotland and north-east England.

Yes but I did say a 24-36hr window of opportunity which covers 31st Dec, 1st Jan. As for Jan 2nd I did mention the SW that might bring a spell of prolonged snow.

[danm]

I would agree with Joe B/BFTP in respect that much of Jan will be cold. However I don't agree that it will be severe blizzards every day. This would be very unusual and apart from 1947 no other cold spell has ever delivered this. What you have to remember is even the cold winters of 1963 has spells of dry, very cold weather.

Based on the models I would say from tomorrow until the Weekend there is the risk of snow for everyone with the heaviest falls being W Midlands/N Wales. Beyond the weekend into next week remaining very cold and mainly dry but obviously some places might be at risk of snowfall due to disturbances that haven't been correctly modelled yet.

At the moment alot depends on whether the block over Greenland does back W or remain in situ.

I think thats the key thing - very often in these easterly airflows, small disturbances and convective showers sometimes appear at very short notice, giving some areas a good snowfall. I suppose we have to hope for that.

[Geordiesnow]

I disagree, this will be a very cold, but dry spell for most within the reliable time frame. Think it will be mid January before snow becomes more widespread, but that is way out in FI!

Since when has a polar airmass over a warmer north sea been "dry", not since i been living here thats for sure.

The only time when this happen is when instability is low and when upper air temps are quite mild. The only way i see this easterly being mostly dry IF the low and it weather front is too far north which leaves a legacy of cloud which stops convection out in the North Sea gets going. This might be the case in particular EA & the SE but even here i expect convection to get going eventually.

edit: I must admit, if the flow is too slack, we might see the showers not getting as far inland than say if the flow is stronger but we just have to wait and see.

Edited December 28, 2009 by Geordiesnow

[Defector]

Just posted by Ian F on the "South West" thread.

Evening guys and gals.

My (much learned and wholly inimitable) colleague Rob McElwee, who acted as our Durty Forecaster for much of today, would be correct to think I'm utterly bonkers still pondering weather issues at nearly 2000hrs when I should be shortly into bed, but my briefing conversation with him earlier this afternoon effectively told a similar story to my earlier notes: i.e., anticipate a largely (if not exclusively) rain event later tonight and tomorrow across the westcountry, with the key exception of..... yes, you've guessed it..... upland Gloucestershire.

So, the essence of tomorrow remains largely the same: possibly disruptive snowfall developing for the Cotswolds and Forest of Dean; perhaps to lower levels too, but for a 'best estimate' I've appended the sooper-dooper expert thoughts of our UKMO Chief Forecaster, who - having assimilated all the available data and not least the very consistent MOGREPS output (which served us so well in Feb 2009, especially) - has done a fab job in delineating the likely snow risk in the chart here. Note, crucially, this is not merely for Tuesday!! Wednesday too. The emphasis into parts of Wales and Engllish environs remains very evident; ditto the risk for Glos.... at least the higher areas, with WBFL's typically 250-450m.

Moving away from the snow hyperventilation expressed elsewhere on this wider forum (not this thread especially!), it's noticeable how the risk of heavy rain - and perhaps localised flooding - receives scant attention versus the prospects of 'white stuff'. In my view, this skews the likely outcome for much of southern England in the next 24hrs and I re-stress, the rainfall totals alone are more than worthy of note, let alone the snowfall into a rather focused area. But then I await to be proven wrong..... such is the nature of my job!

Oh - PS - also, don't dismiss the the ice risk from rain later tonight / tomorrow falling onto sub-zero surfaces. I just strolled through Bradley Stoke, S. Glos, and noticed some worrying signs this could become reality at points in the next 24hrs and especially further north.

Best

Ian

Attached thumbnail(s)

http://forumcache.netweather.tv/uploads/monthly_12_2009/post-8233-12620296814613_thumb.jpg

Edited December 28, 2009 by Defector

[Evening thunder]

We now have a very favourable solution in the longer term looking likely and people now turn to complaining about lack of precipitation!:wallbash: If we cant even nail details about this lows precipitation/track in the short term then how on earth are we going to be sure about the details for a week away?! Anyway there's always the risk of a low trying to approach from the SW and then being pushed back south but perhaps giving me a chance of some snow for once as I mainly missed out on the last cold spell.

There nearly always is at least a bit of precipitation around so it is likely some places will see some snowfall if similar to what is shown on the current charts verify. Also of course you have the added bonus that any snow on the ground from this week isn't going to be disappearing in a hurry!

Its a bit odd in a way after the majority dismiss the GFS output for days that they seem to assume ppn details for about a week away are correct on one evenings output.

A couple days ago I fell into the trap of getting a bit too hung up over the output at one stage when it seemed like I couldn't be more unlucky if I tried! But now when I look back at that it seems like it did no good but cause pointless upset/ disappointment on my behalf.

Anyway cold frosty weather with very cold nights and possible ice days is still pretty good IMO, even if we don't get any snow, which I think there will be some around.

Edit: I'd just like to throw in that if we had 'dry cold' but it was sustaining a nice covering of snow on the ground it wouldn't be too bad I'd have thought?

Although its very hard not to, (and im definitely guilty there!) I'd imagine that most times we get hung up over the model output it is overall pretty pointless as it doesn't actually turn out like that! but I guess that's what the rollercoaster is all about!

Edited December 28, 2009 by StormMad26

[TEITS]

Since when has a polar airmass over a warmer north sea been "dry", not since i been living here thats for sure.

Yes but you need the flow to bring the snow showers from the N Sea.

Like I said im not doubting the convective potential because there is a small window of opportunity. However you look at the ECM +120 to +168 charts and this would be mainly dry and cold with the exception of Scotland on Sat.

If you want the snowy pattern to persist into next week then we need to hope the block doesn't back W as suggested.

[LomondSnowstorm]

UKMO PPN charts can often tell a false story and always for whatever reason understrengths how much PPN is when it comes too North Sea shower clouds.

Too true. So often the prediction for occasional light showers for eastern Scotland has turned out to be about 5-10cm of snow!

[winter watcher]

I would agree with Joe B/BFTP in respect that much of Jan will be cold. However I don't agree that it will be severe blizzards every day. This would be very unusual and apart from 1947 no other cold spell has ever delivered this. What you have to remember is even the cold winters of 1963 has spells of dry, very cold weather.

Based on the models I would say from tomorrow until the Weekend there is the risk of snow for everyone with the heaviest falls being W Midlands/N Wales. Beyond the weekend into next week remaining very cold and mainly dry but obviously some places might be at risk of snowfall due to disturbances that haven't been correctly modelled yet.

At the moment alot depends on whether the block over Greenland does back W or remain in situ.

Yes I agree but i did not mention every day blizzards there mate. At the end off the day i am a bit off a non starter when viewing models know a bit but not a lot. And i am sure i speak for those as well who is on the same boat when we see very respected forecasters and members posting the evolution that we are discussing now regarding very cold weather with blizzards it makes us sit up and take note and maybe learn a bit more on the way. But equally when another well respected poster such as yourself disagrees or puts it in a different perspective then i/we really do struggle lol. Anyway sorry for rambling on and happy new year to all

[The PIT]

I guess model disscusion isn't this threads topic.

By the way anyone seen the huge breakdown on the ECM at T96????

[Duane S.]

At last an honest assumption, never expected any snow living on the south coast in Poole, and doubt to see any in the near future, 1cm in the last ten years has led to utter contempt of promising model outputs anyway good luck to those who do.

I can empathise with you Kent, I live 30 miles down the coast and snow is not common.

However, if you want potential then you simply could not ask for better than this. This setup will allow for the only way we will ever see proper snow and that is from an attack from the SW. Once we have the cold air over us, start to look to the SW next week, I'm not saying it is going to happen but unlike the vast majority of cold spells/snaps/blasts here in the UK we COULD profit from this one.

Edited December 28, 2009 by s4lancia

[Solar Cycles]

Yes but you need the flow to bring the snow showers from the N Sea.

Like I said im not doubting the convective potential because there is a small window of opportunity. However you look at the ECM +120 to +168 charts and this would be mainly dry and cold with the exception of Scotland on Sat.

If you want the snowy pattern to persist into next week then we need to hope the block doesn't back W as suggested.

Again another fine summary, from what I have seen Tetis is bang on the money here.

[West is Best]

Shades of the old SnowWatch on here tonight, but perhaps unsurprising.

Made me chuckle to see Ian claiming successful Met Office forecasting for February, when they really got it quite wrong with both the northerly extent and orientation of the lows, especially on February 06th. The resultant blizzards here in parts of Devon caught them out. They had forecast the low to move much further east and north, instead of which it stalled into the south-west.

And, rather than being a criticism, take that as a warning for everyone on here. There is considerable precipitation on this front, and it will abutt cold air. The result will indeed be substantial snowfall for some parts. However I don't believe anyone is clear at the moment where this will be. For what it's worth I remain unconvinced that this will be heading far north, but who knows.

Not long now to the 18z!

Edited December 28, 2009 by West is Best

[Buckster]

Clearly you didn't bother to properly hear their forecast and thought you would misinterprate their words? All the forecast I've seen show snow pretty much anywhere away from the coasts, and that's exactly what the models are showing.

er no ? this was the R. Mc forecast as of 15 mins ago

I was quite surprised at the positive mild spin, as he tends to favour the cold

I'll listen/watch more attentively at 20:28 and see if I misheard ....

Edited December 28, 2009 by Buckster

[Thundery wintry showers]

The window of opportunity for convection off the North Sea varies hugely depending on how far north you are.

For East Anglia and the southeast, OK, maybe 24-36 hours. But for NE England, the window looks like being between 48 and 72 hours- from 31 December to 2 January, and from north Yorkshire northwards, there will be some tomorrow as well. And for eastern Scotland, convection will be kicking in off the North Sea starting tomorrow and not finishing until at least Saturday, suggesting a window of 96-120 hours.

[TEITS]

Yes I agree but i did not mention every day blizzards there mate.

No mate but I was referring to Joe B and BFTP.

I forgot to add that I guarantee tomorrow that someone will get surprise snowfall whilst someone else who was expecting heavy snow will see far less than expected. Happens every single time. My early tip is the forecasts for tomorrow night around the E Midlands will be far more wintry than currently being suggested.

On a more positive note about next week is the backing W of the Greenland HP isn't certain yet due to the timeframe. Also because its generally going to be very cold the risk always remains for further snowfall.

[JoeShmoe]

The window of opportunity for convection off the North Sea varies hugely depending on how far north you are, and I think some southeast bias may be creeping in. For East Anglia and the southeast, OK, maybe 24-36 hours. But for NE England, the window looks like being between 48 and 72 hours- from 31 December to 2 January, and from north Yorkshire northwards, there will be some tomorrow as well. And for eastern Scotland, convection will be kicking in off the North Sea starting tomorrow and not finishing until at least Saturday, suggesting a window of 96-120 hours.

Yep and during the period before Xmas where forecasts suggested little or no snow we had 8 consecutive days of falling snow, 2 of which dropped over 3-4 inches on Edinburgh. The showers also came from the W giving Glasgow and the lowlands similar

Indeed the ppn forecasting up here (esp by the BBC) was little short of woeful

[casparjack]

I would agree with Joe B/BFTP in respect that much of Jan will be cold. However I don't agree that it will be severe blizzards every day. This would be very unusual and apart from 1947 no other cold spell has ever delivered this. What you have to remember is even the cold winters of 1963 has spells of dry, very cold weather.

Based on the models I would say from tomorrow until the Weekend there is the risk of snow for everyone with the heaviest falls being W Midlands/N Wales. Beyond the weekend into next week remaining very cold and mainly dry but obviously some places might be at risk of snowfall due to disturbances that haven't been correctly modelled yet.

At the moment alot depends on whether the block over Greenland does back W or remain in situ.

To be fair TEITS, even 1947 didn't deliver severe blizzards every day, I get the distinct impression that a sizeable majority on here don't actually understand what on earth is going on and simply want to know whether it's going to snow!!

Oh well, for the rest of us, let's just enjoy the development of the situation and try to get a hint of what might happen over the next 48 to 72 hours...

[Paul]

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[NorthNorfolkWeather]

Its not inaccurate, its just it isnt showing the temperature at 6pm. It is showing the maximum temperature for the three hours to 6pm. 'Bis zum termin' means 'to date' in German, hence it could be 4C at 3pm and 1C at 6pm and the GFS would be correct as the max temp during that period would be 4C.

Hi Reef,

Yes, you are right in what you say, but in the time from 12:00 to 18:00, the temperature here, 6 miles from the North Norfolk coast ( as the crow flies ) never got above 1.8C and was -0.1 at 15:55 and is now -2.3, so I think TEITS has a point, although that may not always be obvious.

It looks as though the trough is actually aligned slightly more to the WNW to ESE giving us an earlier shot at the real cold

[Frosty.]

Just been catching up.......a forecasters nightmare for the next couple of days with a wintry mixture of rain/sleet and wet snow in the southern half of the uk, no doubt there will be some disruption but at least we have had fair warning..no excuses. A very wintry set of charts from all the models, there looks to be a large window of opportunity for coastal snow showers to pepper northeastern scotland & ne england between now and early next week, even then it appears that winds may become Northerly or NW'ly, as shown on the gfs & ecm 12z so northern scotland seems to be most favoured in the longer range out to say the 7th Jan but a generally very cold spell looks like developing a vice-like grip until well into the new year.

[Geordiesnow]

The window of opportunity for convection off the North Sea varies hugely depending on how far north you are. For East Anglia and the southeast, OK, maybe 24-36 hours. But for NE England, the window looks like being between 48 and 72 hours- from 31 December to 2 January, and from north Yorkshire northwards, there will be some tomorrow as well. And for eastern Scotland, convection will be kicking in off the North Sea starting tomorrow and not finishing until at least Saturday, suggesting a window of 96-120 hours.

Yep and all the timings will vary depending how far North that front gets, obviously for my location, as far South will most certainly do.

As ever in these set ups, you have the weather front which brings the more persistent PPN, then you have the "dry" slow which is normally the legacy of cloud from the weather front and then you have the convective showers. These are heavier and more frequent as you head further away from the weather front hence why NE Scotland.

Regarding the longer term potential, it is still a little uncertain i feel but it would seem pressure would rise killing most of the showers and things drying up but staying cold.

[TEITS]

The window of opportunity for convection off the North Sea varies hugely depending on how far north you are. For East Anglia and the southeast, OK, maybe 24-36 hours. But for NE England, the window looks like being between 48 and 72 hours- from 31 December to 2 January, and from north Yorkshire northwards, there will be some tomorrow as well. And for eastern Scotland, convection will be kicking in off the North Sea starting tomorrow and not finishing until at least Saturday, suggesting a window of 96-120 hours.

Look for yourself.

http://en.vedur.is/w...ntic/#type=prec

Note pretty much what I said apart from on Saturday in E Scotland as I suggested.

However I do agree with you for tomorrow and Wed. However my post was referring to the ECM which starts at +72.

[SMU]

Anyone got the SHORT ensembles yet ECM-

Steve

[TEITS]

Anyone got the SHORT ensembles yet ECM-

Steve

Here we go mate.

http://www.knmi.nl/waarschuwingen_en_verwachtingen/ensemble_en.html

[Thundery wintry showers]

Indeed, 1947 was not a continuous snow fest. The reports I've seen for February 1947 suggest that there were frequent frontal snowfalls at the boundary between cold continental air and less cold air to the south during the first week, then a long dry cloudy spell in the middle associated with high pressure and south-easterly winds, and then frequent convective snowfalls in the last week as the high retreated to Greenland and winds backed north-easterly.

If we get another prolonged cold spell out of this, chances are it will become cold and dry at some stage, but the countrywide arrival of dry weather is out at T+144 or T+168 on all of the models, and before that there will be plenty of precipitation around in some parts of the country.