Model Output Discussion

[kold weather]

Some very interesting models this morning, the GFS ensembles look most interesting simply because some now track the main low so far SW that it helps to drag in a cold SE airflow and then actually helps to lift a depression up from the south, which would give another decent snow event...

I'd feel very happy if I was in the north today, his does look rather win win, though the LP right over us or just to the west probably is the worst solution, the further SW this one goes, the better the chances for a more lengthy snow window so to speak.

[Lewis]

Some very interesting models this morning, the GFS ensembles look most interesting simply because some now track the main low so far SW that it helps to drag in a cold SE airflow and then actually helps to lift a depression up from the south, which would give another decent snow event...

I'd feel very happy if I was in the north today, his does look rather win win, though the LP right over us or just to the west probably is the worst solution, the further SW this one goes, the better the chances for a more lengthy snow window so to speak.

Im very happy mate, after reading the charts i think i should be happy shouldn't I?

Coldest air sticks around me much longer, at the time of the precipitation, isotherm and dews are fine.

Over-all good models this morning.

lewis

Edited February 11, 2010 by Storm Force Lewis

[Matty M]

A poor run from Irelands perspective.

We need the low to shoot really far southwest or to our east, with preference to the latter.

6z is Maritime cool, sleet/rainy muck.

[kold weather]

Yeah I think your not in a bad position Lewis though obviously the longer the evolution goes on the more your location and others down the cast coast wil lbecome marginal, esp if the solution that I outlined occured and we get an easterly drag come in with milder air getting pumped in...

However even then I'd have thought that would have to lead to some pretty good falls before hand.

Still its a very fluid evolution and it could evolve in various way yet...but I'd imagine the north, esp on high ground could see some very big falls early next week but we shall see.

[SP1986]

I'm not entirely sure where people are getting ideas of significant snowfall from, unless I'm reading different charts.

The biggest oppurtunity for snow lies around 114 to 120 hours, even then by the west coast it will be of rain if that chart comes off. There are other light rain/sleet/snow events on the charts but nothing serious.

hmm!

[BLAST FROM THE PAST]

Also worth mentioning too that is the LP stays west like 06z the cold air over the SE cannot get shunted away and so temps would be favourable. Any initial southerly would not bring mild air in as sub -10c air gets sent into France as the HP retrogrades so N,E,S of the UK is cold air as the LP dives southward.

BFTP

Edited February 11, 2010 by BLAST FROM THE PAST

[kold weather]

Yep BFTP, I think the 06z isn't a bad solution and also really raises the risk of another depression feature being swang up from France, the key is the Lp keeps a closed circulatuion the whole way SSW, as long as that happens then we may well have some fun and games...

[Snowyowl9]

Interestingly very snowy GFS 6z even into deep FI.

http://www.wzkarten3.de/pics/Rtavn1441.png

http://www.wzkarten3.de/pics/Rtavn1681.png

http://www.wzkarten3.de/pics/Rtavn2881.png

http://www.wzkarten3.de/pics/Rtavn3001.png

[Tom D]

Interestingly very snowy GFS 6z even into deep FI.

http://www.wzkarten3.de/pics/Rtavn1441.png

http://www.wzkarten3.de/pics/Rtavn1681.png

http://www.wzkarten3.de/pics/Rtavn2881.png

http://www.wzkarten3.de/pics/Rtavn3001.png

And how we'd like to see those charts at +96. At that range it's trends that need to be looked for. On those charts there's a interesting HP building near Scandinavia and if this trend is upheld then it looks good for cold conditions in the medium term.

Over the weekend into next week, the low tracking south it will be cold (below average) everywhere, however pinpointing snow/sleet/rain is not something that can be done until the day before earliest. It may not even be possible to forecast what will fall from the sky a few hours in advance, but that's the nature of marginal events. For some people there could be pleasant surprises, for others disappointment.

[Hammer]

although looking at thease they look goooooooodddddd,

but next weeks event does not look good apart from the north.

perhapes a little more time for us to wait yet.

I think you perhaps need to be a little more open minded although can understand the caution in your exact location, certainly Meto Update seems to not rule out snow even in the south. Very much at this range, no certainty about risk.

I would say I am quite pleased with the 6z charts and latest Meto update, certainly some interesting days ahead of us and I look forward to seeing more detail on this over the weekend.

Edited February 11, 2010 by Hammer

[snowmadchrisuk]

Hardly worth bothering with then.

The 6z GFS shows Mon/Tue A front coming from the North and falling as Snow anywhere with the exception of far western coasts . It then goes on to show Heavy Snow moving up from the South during Wed/Thur and falling as snow across much of SE/Eastern and Central England.

These apart from the North , Sleety / rain and wrong side of marginal comments are just plainly WRONG , If they are being based on the 6z GFS run .

Edited February 11, 2010 by snowmadchrisuk

[MKN]

The 6z GFS shows Mon/Tue A front coming from the North and falling as Snow anywhere with the exception of far western coasts . It then goes on to show Heavy Snow moving up from the South during Wed/Thur and falling as snow across much of SE/Eastern and Central England.

These apart from the North , Sleety / rain and wrong side of marginal comments are just plainly WRONG , If they are being based on the 6z GFS run .

Completely agree if it turned out exactly how the 6z gfs showed it to then many parts would have the heaviest snow of the winter so far. It will probably end up so finely balanced there will be people expecting rain and some snow right up until the day. Maybe if the bbc forecasts start showing heavy snow on the countryfile/tracks forecasts members who are sceptical will jump on board.

[locneverstop]

Small question,

Does the zero degree isotherm have any bearing on the precipitation? For example the GFS is showing heavy snow for my area on tuesday, but the isotherm is sitting at 300 or so metres.

Would that mean that snow will fall to 300m before turning back to sleet/rain?

thanks...

[Optimus Prime]

Small question,

Does the zero degree isotherm have any bearing on the precipitation? For example the GFS is showing heavy snow for my area on tuesday, but the isotherm is sitting at 300 or so metres.

Would that mean that snow will fall to 300m before turning back to sleet/rain?

thanks...

The 0c Isothern should drop level as the precipitation falls.

Hold on going to post the most awful, mild and rainy chart of the season.;

[karyo]

The 6z GFS shows Mon/Tue A front coming from the North and falling as Snow anywhere with the exception of far western coasts . It then goes on to show Heavy Snow moving up from the South during Wed/Thur and falling as snow across much of SE/Eastern and Central England.

These apart from the North , Sleety / rain and wrong side of marginal comments are just plainly WRONG , If they are being based on the 6z GFS run .

Based on the 6z GFS, I agree. However, are we just considering the most favourable output and choose to ignore the ECM and UKMO? The euros don't look anywhere near as good!

Karyo

[MKN]

Based on the 6z GFS, I agree. However, are we just considering the most favourable output and choose to ignore the ECM and UKMO? The euros don't look anywhere near as good!

Karyo

Then you can argue that being based on just the run currently shown as the ecm has had some decent looking runs over the past couple of days. the ukmo seems to be the mildest outcome but then the fax charts dont seem to back it up, which would suggest the metoffice going for something between the gfs and ecm. Eitherway its not going to be decided to sat/sun. The all important bbc forecast sunday morning could be a classic or one of dissapointment. Think we all deserve an american style winter snow storm to finish things of with

[locneverstop]

The 0c Isothern should drop level as the precipitation falls.

Hold on going to post the most awful, mild and rainy chart of the season.;

Ha! bullseye for me if that came off, which it probably won't.

I do fall in line with the coldies at this point. Although I know nothing compared to a lot of members here at the moment, I do feel that the GFS has got things slightly wrong. Watching that low complete a lap of honour round the UK doesn't seem to be normal behaviour. Do other models support that track (I only have experience with GFS!)

[TEITS]

I'm not entirely sure where people are getting ideas of significant snowfall from, unless I'm reading different charts.

The biggest oppurtunity for snow lies around 114 to 120 hours, even then by the west coast it will be of rain if that chart comes off. There are other light rain/sleet/snow events on the charts but nothing serious.

hmm!

At the moment Stephen it depends on your location. In recent days the favoured locations have been further N & W with Ireland being very much favoured. However if the LP verified the risk is towards N & E areas.

For example Thurs is a fairly big snow event for E parts according to the 06Z. Look at the link below for Feb 5th 2009 and this gave 8 inches of snow for Cambs, Northants.

http://www.wetterzentrale.de/archive/ra/2009/Rrea00120090205.gif

Also note the upper temps were only around -4C.

http://www.wetterzentrale.de/archive/ra/2009/Rrea00220090205.gif

Members opinions on the track of this LP is going to depend on their locations. So what might be favourable for me might not be the case for others.

Edited February 11, 2010 by THE EYE IN THE SKY

[Optimus Prime]

The UKMET has the low further towards the north. GFS has it towards the west and ECM has it towards the east. All very close but the UK is a small country. If this way America they probably wouldn't bother pinpointing on these sort of details.

As seen in December low pressure can sit over the UK with developing shortwaves within the area of energy. This is what happened in December and so it gradually turned milder for the south while the north got cold and snowier.

Many cold winters have these slow moving setups. Hence the cold and snowy winters of the past. An easterly generally gives 5-10 days of very intense cold for England before the pattern resets and the weather turns milder. The scenarios shown give the UK as a whole a longer prospect for cold.

The winter of 1990/1991 was cold for the easterly in February

1995/1996 for the low pressure acting the way it has in December and probably this month

[karyo]

Then you can argue that being based on just the run currently shown as the ecm has had some decent looking runs over the past couple of days. the ukmo seems to be the mildest outcome but then the fax charts dont seem to back it up, which would suggest the metoffice going for something between the gfs and ecm. Eitherway its not going to be decided to sat/sun. The all important bbc forecast sunday morning could be a classic or one of dissapointment. Think we all deserve an american style winter snow storm to finish things of with

Actually, this is the only thing that is missing from this winter for me! I've had loads of snow already but no snow storm/blizzard! You can tell how much the bar has been raised by such a fab winter!

Let's hope the 12z is similar to the 6z! I doubt it but you never know...

Karyo

[Bolton67]

for Feb 5th 2009 and this gave 8 inches of snow for Cambs, Northants.

http://www.wetterzen...00120090205.gif

Also note the upper temps were only around -4C.

http://www.wetterzen...00220090205.gif

What memories !!! and how similar the GFS 06z is to Feb 09.

[TEITS]

The UKMET has the low further towards the north. GFS has it towards the west and ECM has

Many cold winters have these slow moving setups. Hence the cold and snowy winters of the past. An easterly generally gives 5-10 days of very intense cold for England before the pattern resets and the weather turns milder. The scenarios shown give the UK as a whole a longer prospect for cold.

Im not sure I agree.

If what we're seeing in the model output is going to bring a prolonged cold spell then we're going to need to see pressure rise over Scandi bringing an E,ly. If not slowly becoming milder is the likely outcome.

[Geordiesnow]

Still some good potential in the models for next week, we don't want the low to get too far west otherwise places that will have the cold air over them will be fairly dry and places that have got PPN will be too marginal for snow, as i said yesterday its all very fine balances.

What the GFS 12Z shown yesterday would appears to be a one off and the low won't get that far east but weirder things have happened in the model output so who knows.

Some areas will get alot of snow next week i feel, i think those further east will be more likely to get snowfall as they are closer to the colder air but they are also in a risk they could miss the PPN all together if the low gets too far west. For those in the West, if the low is to far West, the cold air will be more modified as it has to travel over yet more Atlantic waters therefore alot more marginal even though there should be quite a bit of PPN falling. I think if the low is further east, western areas can get the convective showers which have more chance of being of snow as you will get the colder air with those showers.

All in all, an interesting output but one that could easily just end up as being cold and wet if we don't want the low where we want it!

[johnholmes]

Small question,

Does the zero degree isotherm have any bearing on the precipitation? For example the GFS is showing heavy snow for my area on tuesday, but the isotherm is sitting at 300 or so metres.

Would that mean that snow will fall to 300m before turning back to sleet/rain?

thanks...

the zero isotherm is just one of the various factors forecasters have to take into consideration when trying to predict whether it will rain, sleet or snow.

Intensity of precip is quite important, as is the 850mb temp, and the 1000-850mb 'thickness' as its called.

Generally a zero isotherm of 300m and MODERATE or more rate of precip would give fairly wet snow. This could be further complicated by what is called evaporative cooling=when precip at sufficient intensity falls over several hours it 'lowers' the zero isotherm, and MIGHT end up in the case quoted with drier type snow.

hope that helps

its very complex which is why so many snow/rain forecasts even at T+12 are not all that accurate!

even so hope it helps-keep asking questions there are plenty of people on here happy to answer them.

[locneverstop]

the zero isotherm is just one of the various factors forecasters have to take into consideration when trying to predict whether it will rain, sleet or snow.

Intensity of precip is quite important, as is the 850mb temp, and the 1000-850mb 'thickness' as its called.

Generally a zero isotherm of 300m and MODERATE or more rate of precip would give fairly wet snow. This could be further complicated by what is called evaporative cooling=when precip at sufficient intensity falls over several hours it 'lowers' the zero isotherm, and MIGHT end up in the case quoted with drier type snow.

hope that helps

its very complex which is why so many snow/rain forecasts even at T+12 are not all that accurate!

even so hope it helps-keep asking questions there are plenty of people on here happy to answer them.

Thanks for that, it was actually your forecast that inspired me to ask the question!

I'm beginning to see how this all fits together. I think I may wait till the 12Z on Monday to give my first ever snow prediction, because at the moment it's way out of my comfort zone with the way the GFS has a habit of going off on a tangent within 72 hours