South West/Central Southern England Regional Discussion 14/01/13, 12z onwards

[gottolovethisweather]

Just a few links or posts, which I feel are worthy of repeating for those who haven't had a chance to catch up on the latest.

http://m.facebook.co...pointswest&_rdr

The post replicated below by AWD is also worthy of mention re: the end of the week.

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UKMO predicting an ice day for many Somerset northwards and eastwards on Thursday;

With the -5c 850hpa line over Cornwall and the -8c 850hpa line nudging Bristol & East Somerset;

The airflow still moving west at this time too.

A quick look to Friday. The GFS version of events has already been covered by posts over the last few pages, so a quick glance at the ECM shows a band of heavy PPN over much of the West Country by 6am Friday Morning;

And 850hpa temperatures below -5c from Devon eastwards and northwards;

Suggestive of some heavy snowfall for many parts of the South West. The ECM shows the Atlantic trying to move eastwards, this shown by the -5c 850 line retreating to Wiltshire/Hampshire by Friday evening;

But unable to break through, and the cold edging west again, shown below by the -5c 850hpa line edging back into Somerset by Saturday morning:

By 18:00 Friday evening however, the PPN would have moved SE, away from the South West;

So the movement of the -5c 850hpa line is irrelevant to snowfall conditions anyway, as the PPN will of cleared through by the time the -5c 850hpa line moves east and back west again. The fact that the PPN heads South East, also suggests the ECM is modelling a slider front, and as such, Fridays band of PPN looks a reasonable bet to stay as snow for all east and north of Devon based purely on this run, with the limited data available to us.

However, without further detailed charts showing clear thickness boundaries, WBFL, Dewpoints etc, I cannot make a realistic forecast for snow potential for Friday from either the UKMO or ECM. All I can say is that they both look like delivering something.

Anyway, I stress that any snowfall will be marginal and is currently to a high degree of uncertainty. Until the NAE and NMM come into range, the high degree of uncertainty will remain, as with it being a knife edge event, a detailed view of each aspect will be needed to sway a forecast in either direction.

Friday has the potential for significant snowfall, but it also has the potential to go Pete Tong. Just keep an eye on the trends for now, and don't bother with detail until much nearer the time. All I can say however is I would rather have the upcoming week of weather and potential weather, than this;

Remember, we are the South West of England, not Siberia!

Short term is looking very cold, although surface temperatures may still be above freezing for some, the bitterly dry easterly air will make it feel bitter out. For midday Wednesday, the NAE has -7c 850hpa temperatures across the spine of the West Country;

Along with Dewpoints of -2/-3c and it will feel bitter outside;

Both the NAE and NMM also show some wintry PPN making it down over Somerset & Dorset tonight;

Which could give some elevated areas such as the Mendips a little surprise.

So to some up my thoughts;

- Tuesday - Thursday remaining cold/very cold across most of the South West, but predominantly dry after tonight's shower activity.

- Friday I think parts of the South West will see snowfall. Where and how much at this stage I don't know. I do believe that away from Cornwall and coastal areas, all PPN on Friday will fall as snow

- The Weekend I think will bring a less cold sector of air off the Atlantic and thus raising thickness' and 850hpa temperatures, turning any PPN to sleet and rain. The timing of this and extent of this at this stage I don't know. I do not believe any snowcover will be kept through the weekend though at this stage.

That's how I see things currently guys, but as ever, changes are likely and I will update on any changes in due course. It's an exciting period of model watching and a potentially exciting period of weather coming up. Things could be far worse for us down here, as we have seen many a year during the last couple of decades. Remember, winters like 2009/2010 are the exception rather than the rule for us.

Enjoy and let's all fight for the blue corner!

Edited January 15, 2013 by gottolovethisweather

[Bristawl Si]

Do you see a donwgrade coming?

.

Too early to tell - plus i ain't no expert.

Come to think of it, in these situs the 'experts' can only give a considered view of what's in front of them at this stage, for the next few days ahead.

[AWD]

After viewing pretty much most of the overnight model output, including the FAX charts, I've come to the conclusion....... God knows.

Considering the event is at T72, the differences between the models are startling.

You've got anything from a significant snowfall event, to a quick snow to rain event, to the continuation of dry, cold weather as the front doesn't make any inroads.

This is becoming increasingly likely to be a nowcast scenario as the models really haven't a clue.

[Mapantz]

Fingers crossed for anything! I include frost and ice in that because my lowest temp has only been 1.2°C a bit disappointing here to be honest.

[gottolovethisweather]

I will also replicate my thoughts below, just in case anybody may have missed that during the flurry of activity last night.

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Some top analysis tonight, so no point in me adding anything else other than what I gathered from my assessment of the GEFS 12z suite, when used in conjunction to previous output.

FI ranges from 17th January out West to the 18th January further East, so I suggest much uncertainty as to this weekend's surface feature.

Breaking down the details a little further.

Cornwall has the briefest chance of some SNOW on the Saturday 19th January after tonights possibilities. Thereafter it should eventually turn milder but never into the mild/very mild category. This to be taken with a pinch of salt too as FI is suggested as around the 17th.

Dorset ensembles show a good chance of SNOW from the Thursday 17th January right through to the Sunday 20th January, being the last date that the cold air would be holding on at this stage. Same caveats apply as above.

My patch, I would interpret Berkshire ensembles as showing the Friday 18th January right through to the Sunday 20th January as being the period to watch for SNOWFALL and again, the 20th being the last date for which the cold is likely to hold on. Smallest amounts of precipitation most likely within this region, when compared to the much more favourable areas out West, where there could be some substantial totals, more especially at elevation.

As an aside, should I look to London, the ensembles show FI being around the 18th January, again showing much uncertainity and the best chances of SNOW cover the period from Friday 18th January right through to the Sunday 20th January. Once again, the usual caveats apply and I would suggest some SNOW is possible but not looking like amounting to very much at this stage.

ALL IN ALL, NOT A LOT HAS CHANGED EXCEPT FOR THE FACT THAT FANTASY ISLAND IS SEEMINGLY CLOSER THAN PREVIOUSLY SUGGESTED. ADD TO THAT, THE ATLANTIC STILL HOPES TO PUSH ALL ITS WEATHER RIGHT ACROSS THE UK, BUT EVEN THEN, IT WON'T HAVE FULLY ACHIEVED THIS BY THE 20TH JANUARY AT THE EARLIEST.

ALL SYSTEMS GO AS WE'RE STILL VERY MUCH ON FOR BATTLEGROUND UK COME LATE ON THURSDAY 17TH JANUARY.

We will need to watch all subsequent runs, paying special attention to the afternoon set, because the above evolution may well be far removed from the reality.

[noonoo418]

As a newbie to this site I have followed the ups and downs on the MOD thread regarding the beginning of this cold spell for a few weeks now.

Having now created a user, it appears that this regional thread is much friendlier. It also strikes me that many on the MOD thread refuse to accept the idea of us in the South West of the country having some snow of our own. Fingers crossed we all see something more significant this weekend!!

[AWD]

Just to add the 06z GFS goes the same way as this mornings ECM run, with a mild sector coming into play and turning any snowfall quickly to rain on Friday.

I don't think this will be the case as I think the strength of the block is brig underestimated. However, it is something to ponder that has been picked up by models this morning now.

[Mapantz]

Just to add the 06z GFS goes the same way as this mornings ECM run, with a mild sector coming into play and turning any snowfall quickly to rain on Friday.

I don't think this will be the case as I think the strength of the block is brig underestimated. However, it is something to ponder that has been picked up by models this morning now.

The whole lot has been shunted east.

[gottolovethisweather]

Here are the set of ensembles used to back up my post from last night.

In each and every case, look at the precipitation spikes and the day on which they fall. Alongside this, you need to check the associated T850s on each occasion. To be fair, things are fairly marginal on certain occasions but other factors of course come into play when it comes to getting SNOW on the ground.

Cornwall

Dorset

Berkshire

London

As per usual, concentrate on where the mean (red line) on each member's run is expected to go as time goes forward. Then compare it against where it deviates sharply from the control (blue line). When the aforementioned occurs, you can safely say, that is when fantasy island begins.

Edited January 15, 2013 by gottolovethisweather

[latitude]

.

Too early to tell - plus i ain't no expert.

Come to think of it, in these situs the 'experts' can only give a considered view of what's in front of them at this stage, for the next few days ahead.

If the front on Friday stays in the Atlantic and slides into France, its an upgrade for longer lasting cold.

The 06z pushes the -5 850 line well out of the SW, and the undercut doesent seem to occur.

Interesting 12z coming up later.

[latitude]

Minimum temp last night +0.9.

Looking for below freezing tonight.

[latitude]

Oh and just to add, think this thread is the best place for discussing the model output for the SW from now on. The Mod thread is so IMBY right now.

[Beast of Plympton]

Oh and just to add, think this thread is the best place for discussing the model output for the SW from now on. The Mod thread is so IMBY right now.

Agreed. So in your far more expert opinion than mine, is devon still looking good for snow on Firday or is it hard to tell?

Edited January 15, 2013 by Beast of Dartmoor

[Karl83]

Oh and just to add, think this thread is the best place for discussing the model output for the SW from now on. The Mod thread is so IMBY right now.

Agreed. Prefer it in here. Much more relaxed.

[AWD]

Mmmmm...... The ECM, GEM and GFS all bring a wave of less cold uppers across the SW Friday afternoon;

We need to see this trend shift SW quickly. At the moment there is a reasonable signal from the models to suggest any snowfall turning to rain through Friday.

My confidence has dropped a bit compared to last night on a snowy Friday now. However, its a vet complex situation, and the latest FAX charts are favourable for us to stay colder. Things will probably change again by the 12z later.

This from Matt Hugo too;

Ireland and SW Eng in particular would likely be milder, but still for most it would *likely* be snow...

Going to be a tense few days guys. Never easy for us down here is it? :p

Edited January 15, 2013 by AWD

[gottolovethisweather]

Gibby's thoughts are always telling IMHO and I copy below his analysis from yesterday's 12z suite.

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Good evening. Here is the report on the 12z output from GFS, UKMO and ECM for Sunday January 13th 2013.

All models show a cold week to come. Early in the week troughs and a developing Low pressure slips SE over the UK and away to the SE midweek. This brings a mix of rain, sleet and snow for many with snow restricted but significant to the far East of the mainland. Elsewhere rain or sleet is far more likely with little disruption likely. In the second half of the week the pattern becomes more complex though still cold as the Atlantic moves up against the UK with the threat of heavy snow and/or milder weather knocking on the door by the weekend.

GFS shows a cold Easterly flow midweek quickly replaced by a cold SE flow to end as Low pressure approaches from the West. Some snow may well move into the West before dying out over the start of the weekend as the High to the NE rebuilds briefly. However, as the axis of the ridge sinks South the Jet rides over the top and the Atlantic cranks up a gear with the milder SSW flow taking shape quickly at the weekend. Thereafter, the pattern of Low to the North and High to the South with a strong West flow over the UK lasts for some time with some rain at times, especially in the North. There would be a few cooler intervals as cold fronts pass by but nothing remotely wintry at the surface felt for late January.

The GFS Ensembles are not so good for cold lovers tonight with a cold week being replaced by a trend towards more normal conditions later as the Atlantic takes control in week 2.

The Jet Stream shows the flow being directed under the northern High for the week to come before a strong turn North in the flow towards the North late in the week runs the risk of the flow riding over the top of the sinking or receding european High pressure at the weekend.

UKMO shows the midweek period dominated by High pressure to the NE with a ridge over England. The down side of this is that the stronger Easterly flow shown on the 00z is much lighter, hence less chance of penetrative snow showers inland from the East coast but on the plus side Low pressure slides SE close to SW Britain on Thursday with the risk of an area of snow in the SW causing problems here as more Northern areas stay cold, dry and frosty. By Friday a monster Low to the SW is a rare sight for UKMO with a strong to gale East or ESE flow blowing over the UK with an active front in the English Channel. With rain and sleet near the South Coast and Cornwall other areas of Southern Britain, Wales and the South Midlands would encounter potential blizzard conditions and major disruption should it verify.

ECM shows the midweek period as cold with an East flow and some snow showers in the East and SE for a time before the end of the week sees a complete difference to UKMO with a Scandi High holding solid with it's ridge over the UK maintaining frost and ice by night and little thaw of any lying snow in the East. Later in its run the High does give way slowly as the Atlantic pushes in to the UK with a band of snow followed by rain. However, with Europe remaining locked in cold, successive low pressure disrupts and continues to pull energy SE and although on this run it is too far East to mean anything other than rain for the UK away from the far East.

In Summary tonight there is a mixture of outcomes shown which make things no clearer on where we go forward from Thursday of this week. With blizzards (UKMO), cold and frosty weather, (ECM) and mild Westerly winds (GFS) are all on offer over the next few weeks. Much as I would like to see UKMO's evolution come to fruition I very much side with the ECM evolution with GFS far too progressive too quickly. Nevertheless, the GFS Ensembles are disappointing tonight and it looks like after a week or so more of cold we may have to confront the power of the Atlantic winning over early next week.

Edited January 15, 2013 by gottolovethisweather

[jethro]

Agreed. So in your far more expert opinion than mine, is devon still looking good for snow on Firday or is it hard to tell?

When it comes to Friday, there are no experts......It MAY happen but there again, it MAY not. This really is a keep everything crossed situation.

I do however seriously hope that people don't hang on every model run and think that it's gospel, the various options available from the current situation will change right up until the last minute - don't be despondent if the model runs say it isn't happening or you'll be up and down like a yoyo. To give you an example, only last night up here on the Mendips we were supposed to have snow, the forecast was changed at the last minute to reflect this happening - the weather was having none of it, slipped SW and missed us altogether.

[gottolovethisweather]

Mmmmm...... The ECM, GEM and GFS all bring a wave of less cold uppers across the SW Friday afternoon;

We need to see this trend shift SW quickly. At the moment there is a reasonable signal from the models to suggest any snowfall turning to rain through Friday.

My confidence has dropped a bit compared to last night on a snowy Friday now. However, its a vet complex situation, and the latest FAX charts are favourable for us to stay colder. Things will probably change again by the 12z later.

This from Matt Hugo too;

Ireland and SW Eng in particular would likely be milder, but still for most it would *likely* be snow...

Going to be a tense few days guys. Never easy for us down here is it?

I must say it is something that is irking me at the moment as well, but to be afair, how many times have we all overanalysed things in the past.

Patience is needed and to add, I haven't even looked at the pub run outlook, I never do when things are especially at the point of high shannon entrophy (to use a fergieweather reference)

Edited January 15, 2013 by gottolovethisweather

[weatherjay]

Looks like your gonna be trying to build a snowman with rain down in the south west! Last few runs have advanced the frontal system far enough east to allow warmer air to filter into! I wouldn't hold any hope for anything worthy of note anywhere In thr region! Looks like north/east midlands will be the sweet spot!

[gottolovethisweather]

On the topic of Gibby's posts.

The best thing to do in terms finding out where we may be heading is to compare Gibby's next 12z suite anlaysis, with the one I have shown above.

[Beast of Plympton]

When it comes to Friday, there are no experts......It MAY happen but there again, it MAY not. This really is a keep everything crossed situation.

I do however seriously hope that people don't hang on every model run and think that it's gospel, the various options available from the current situation will change right up until the last minute - don't be despondent if the model runs say it isn't happening or you'll be up and down like a yoyo. To give you an example, only last night up here on the Mendips we were supposed to have snow, the forecast was changed at the last minute to reflect this happening - the weather was having none of it, slipped SW and missed us altogether.

Thanks Jethro, tense times!! I know what you mean.... we had snow over night which I wasn't really expecting TBH. I guess the weather will do whatever it wants!!

[latitude]

Just got a feeling the block wont be strong enough for us in the SW with the colder uppers being mixed out giving us a wintry mix to start then to changing to rain. I would of liked to see the 06z match last nights 18z. As I said before the 12z will be interesting.

Taking the 06z alone, the East will do well again.

[gottolovethisweather]

Looks like your gonna be trying to build a snowman with rain down in the south west! Last few runs have advanced the frontal system far enough east to allow warmer air to filter into! I wouldn't hold any hope for anything worthy of note anywhere In thr region! Looks like north/east midlands will be the sweet spot!

Not sure which part of the southwest you are from, so can you please update your profile to show your location when you get a second.

And if it hasn't already been said, welcome aboard the madhouse that is neteather towers.

[AWD]

Another message from Matt Hugo;

Continued agreement from within the EC ENS for the colder to persist across most areas well into next week, especially away from the W/SW

[jethro]

Looks like your gonna be trying to build a snowman with rain down in the south west! Last few runs have advanced the frontal system far enough east to allow warmer air to filter into! I wouldn't hold any hope for anything worthy of note anywhere In thr region! Looks like north/east midlands will be the sweet spot!

And when the next model run comes out, it may be all change again. I can't be bothered to count how many model runs there are between now and Friday, but it's a lot - they'll all be different and considering we're talking of maybe 100-200 miles difference either way, I wish the best of luck to anyone trying to pin the tail on the Donkey when it comes to the boundary line. Your diagnosis is one option, there are countless others to choose from.