General Model Output Discussion

[Guest North Sea Snow Convection]

During the exceptional easterly outbreak of 11-14 January 1987, thicknesses nudged below 500 dam in parts of south-east England. There's no way we'll be able to sustain a pronounced enough easterly flow for long enough to bring thicknesses that low over to the British Isles- but usually, anything below about 522 dam gives a very high probability of falling and lying snow.

Thanks for that TWS - answers things nicely

And RRR - again that chart graphically illustrates the same point. I remember scraping the inside of my little car at lunchtime and the gearbox was frozen solid!

Edited December 28, 2009 by North Sea Snow Convection

[beng]

If anything the front on the +48hr fax chart is further S from my region. Although for SW its slightly further N.

http://www.meteociel.fr/ukmo/fax/fax48s.gif

I cannot really see much difference except the alignment of the front.

It's very similar to tonights GEM (front pushed south on the Eastern side of the UK) - rain to snow here on Wed perhaps

http://www.meteociel.fr/modeles/geme_cartes.php?&ech=54&mode=1

Edited December 28, 2009 by beng

[GoonerGregg]

There is going to be a lot of snow across the Midlands from this, record amounts I think, what with all the moisture and the cold air mixing in, a truly breathtaking snow event is upon them. For us in the SE, we have got a lot to look forward to in this excellent up and coming cold/very cold spell from Thursday evening onwards.

[Iceni]

you don't take it seriously it is a 'very rough' guideline - I've never seen a model which goes out that far either - it is 408 hours, probably turn out to be the opposite, but looking good in up to early next week (fingers crossed).

408 hrs = 17 days which would be around 13th January. Not unknown to have bitter Arctic conditions around then, so 'probably the opposite' in this case is possibly a more unrealistic statement than the chart itself.

For long-term forecasts it's wise to take note of whatever Glacier Point is posting — he's the chap for giving the background detail and underlying causes of the weather we see in the more reliable timeframe… and IMO he's been spot on so far.

[TEITS]

One thing I have just noticed with the GFS is how inaccurate it is with regards to the temps. Now considering we're looking at a front moving N then these inaccurate predictions don't help.

For example at 18.00 the GFS suggests 5-6C on the Norfolk coast and around 4C for my location.

http://www.wetterzentrale.de/pics/Rmgfs064.gif

However as of 17.30 its 1C on the Norfolk coast and between 1C & -1C inland.

Thats pretty poor to be honest and certainly doesn't help matters when deciding if it will rain or snow!

[Bolton67]

I know this is +240 BUT this is some very cold air .

http://www.meteociel...40&mode=1&map=0

[❄️❄️❄️❄️❄️❄️❄️❄️❄️]

Looking at the UKMO this evening at that suggestion of 515 dam air, how does that compare to the airstream of Jan 1987. Obviously it doesn't translate to as cold as that unique occasion - but what sort of level did we see then? Any technical expert know more on this subject?

Sub 510 dam air across the UK:

[Grimsby Snow Lover]

There is going to be a lot of snow across the Midlands from this, record amounts I think, what with all the moisture and the cold air mixing in, a truly breathtaking snow event is upon them. For us in the SE, we have got a lot to look forward to in this excellent up and coming cold/very cold spell from Thursday evening onwards.

Could someone please explain what is happening from Thursday onwards, I find model reading quite difficult at times, thanks

Edited December 28, 2009 by Grimsby Snow Lover

[beng]

One thing I have just noticed with the GFS is how inaccurate it is with regards to the temps. Now considering we're looking at a front moving N then these inaccurate predictions don't help.

For example at 18.00 the GFS suggests 5-6C on the Norfolk coast and around 4C for my location.

http://www.wetterzentrale.de/pics/Rmgfs064.gif

However as of 17.30 its 1C on the Norfolk coast and between 1C & -1C inland.

Thats pretty poor to be honest and certainly doesn't help matters when deciding if it will rain or snow!

Similar case here - around zero at 4pm - GFS predicted 5c. Aviemore was a stunning -14c at 4pm by the way (7c colder than GFS predicts for 6pm).

[Fozfoster]

One thing I have just noticed with the GFS is how inaccurate it is with regards to the temps. Now considering we're looking at a front moving N then these inaccurate predictions don't help.

For example at 18.00 the GFS suggests 5-6C on the Norfolk coast and around 4C for my location.

http://www.wetterzen...cs/Rmgfs064.gif

However as of 17.30 its 1C on the Norfolk coast and between 1C & -1C inland.

Thats pretty poor to be honest and certainly doesn't help matters when deciding if it will rain or snow!

One thing I have just noticed with the GFS is how inaccurate it is with regards to the temps. Now considering we're looking at a front moving N then these inaccurate predictions don't help.

Yes been watching that too its been 2 or 3c out all day.

[Tom D]

One thing I have just noticed with the GFS is how inaccurate it is with regards to the temps. Now considering we're looking at a front moving N then these inaccurate predictions don't help.

For example at 18.00 the GFS suggests 5-6C on the Norfolk coast and around 4C for my location.

http://www.wetterzentrale.de/pics/Rmgfs064.gif

However as of 17.30 its 1C on the Norfolk coast and between 1C & -1C inland.

Thats pretty poor to be honest and certainly doesn't help matters when deciding if it will rain or snow!

It's the same here, however that is the 'maximum' temperatures, minimum temperatures may be 3/4c but still as you say higher than reality.

[Thundery wintry showers]

GFS tends to overstate the moderating effects of the sea in some regions, particularly East Anglia and the southeast. It is quite common in winter for the GFS's temperature estimates for Norwich to be about 5C too high on a cold night. The inverse can also happen in summer though usually to less of an extreme.

On the other hand GFS temperature estimates tend to be near the mark for many inland parts of Britain.

[SMU]

http://www.meteociel.fr/modeles/nogapse_cartes.php?ech=6&code=0&mode=0&carte=1

Run of the day from the NOGAPs-- although we have the big gun ECM to come as well as the JMA-

Can any of the last 3 runs top that- ECM, JMA or the fabled pun run 18z-

S

[winter watcher]

There is going to be a lot of snow across the Midlands from this, record amounts I think, what with all the moisture and the cold air mixing in, a truly breathtaking snow event is upon them. For us in the SE, we have got a lot to look forward to in this excellent up and coming cold/very cold spell from Thursday evening onwards.

Yes Gregg that is what i can see very much so happening and to be honest i am not too biased towards my location so i wish a lot off good will and luck to our welsh and Midlands friends and hope they get a great snow event. As for us down south the euro models have been going for some time now that we could well be in for a very very severe cold spell and as Fred has stated he expects this from new years eve onwards and i expect the evolution to come true off course a severe easterly will put us right in the firing line expect upgrades too come thats what i have been told. :lol:

[NorthantsSnow]

GEM is stunning as far as tomorrow/Wednesday's event is concerned with the 0C isotherm sitting along the M4 corridor throughout.

I do hope it's correct- the GFS, while certainly improved, has it running from N Wales through to the Wash late Tuesday.

For here it could mean the difference between sleet/rain and snow.

[Snowyowl9]

Game set and match for this major snow event now the biggest snow/cold spell since the 80`s

it`s looking to me,what a fax chart for midweek.!!!!

http://91.121.93.17/pics/brack1.gif

GFS in deep FI shows something we havn`t seen since february 1986 a true cold high.

http://91.121.93.17/pics/Rtavn3001.png

http://91.121.93.17/pics/Rtavn3002.png

[SMU]

let the hypoerbole begin

S

[TEITS]

GEM is stunning as far as tomorrow/Wednesday's event is concerned with the 0C isotherm sitting along the M4 corridor throughout.

I do hope it's correct- the GFS, while certainly improved, has it running from N Wales through to the Wash late Tuesday.

For here it could mean the difference between sleet/rain and snow.

I tell you what mate i've given up looking at the models for tomorrow and this even includes the BBC forecasts.

For example on pg 402 the forecast for E Midlands tomorrow is persistant snow moving in later and yet if you look at 403 it differs. On pg 401 it just says rain, sleet, snow. The last BBC forecast I watched suggests heavy snow for N England on Wed and I can't see much evidence of this on the fax charts.

I can assure everyone that even at this late stage changes will occur and this includes the models/forecasts. If I was honest this is the most complicated situation I have ever known since following the models. A real blast to the past with these synoptics.

[bennytes]

let the hypoerbole begin

S

not the type of night to get bladdered and fall down drunk, Id say!

these charts are getting scary now.

In any experts opinion, any chance of this NOT happening now? where would the mild air come from to stop this anyway, realistically?

[SMU]

not the type of night to get bladdered and fall down drunk, Id say!

these charts are getting scary now.

In any experts opinion, any chance of this NOT happening now? where would the mild air come from to stop this anyway, realistically?

Not at 72 or 96-

Maybe a stumbling block at 120- with the scandi trough- thats the only block in the way of a CLEAN easterly-

S

[shuggee]

For anyone following us in the (still) frozen north (5th ice day here today in the last 11), you may have popped into the Scottish cold spell discussion and taken notice of the spectacular wins net weather's own model, that runs twice a day has scored - even against the big boys and the Meto/BBC forecasts...

In that spirit - here's the snow risk/snow level chart for 17h00 tomorrow from the netweather mesoscale model (NMM) 12Z run:

Note where the clear snow line is and how anything north of that has a good chance above 200ms of seeing lying snow

[TEITS]

not the type of night to get bladdered and fall down drunk, Id say!

these charts are getting scary now.

In any experts opinion, any chance of this NOT happening now? where would the mild air come from to stop this anyway, realistically?

Only way is if the LP moved much further N.

Looking at your location take my advice and buy a bloody big shovel!

[reef]

One thing I have just noticed with the GFS is how inaccurate it is with regards to the temps. Now considering we're looking at a front moving N then these inaccurate predictions don't help.

For example at 18.00 the GFS suggests 5-6C on the Norfolk coast and around 4C for my location.

http://www.wetterzentrale.de/pics/Rmgfs064.gif

However as of 17.30 its 1C on the Norfolk coast and between 1C & -1C inland.

Thats pretty poor to be honest and certainly doesn't help matters when deciding if it will rain or snow!

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.

[GoonerGregg]

I think there will be some suprises in this system, in that I mean there will probably be some heavy wet snow maybe in the SE. Wishfull thinking maybe before Thursday, but you never know do you. I wouldn't be suprised to see or hear of thunder snow in this system also with so much moisture involved mixing with this cold air.

Lovely to hear forecasts with Rob McKelwee on the BBC, he makes us cold lovers so optimistic and more often that not, he knows his stuff and doesn't really sit on the fence as much as other forecasters.

Looking forward to what unfolds in the coming days, even weeks judging by things at the minute.

[Snowyowl9]

Theres going to be huge drifts from these strong east/NE-lys,which carry on all week,turning more N-ly later.

http://91.121.93.17/pics/brack2.gif