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chionomaniac

Winter Model Discussion 18Z 16/1/13 onwards.

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Good evening all.

Well, slowly but surely, we are getting closer to a potential snowy spell. This type of slider has not been seen for many years. So how much snow will we get and what lays beyond - more sliders I suspect!

Please discuss here.

Remember to use the regional threads when discussing snow amounts for particular areas. No moaning or trolling and please try to back up your posts with relevent charts/links where appropriate.

Thanks and good luck all!

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I am so on the border of the pink stuff on that chart haha. Whats the pro thoughts on south wales as a whole on friday smile.png How far with the mild push inwards

Possible snow totals Sat morning: post-14819-0-69642600-1358367892_thumb.g

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Quite impressed with how well the UKMO GM has handled the evolution of this cold spell so far, which makes a change.

6 day 500mb verification stats shows that UKMO is top of its game atm: http://www.emc.ncep.noaa.gov/gmb/STATS/html/acz6.html

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Question, last week we were being shown similar but not as extensive snow albeit it further out but it came to nowt down south due to a mild sector that got wrapped in the low.

Isn't there a risk the same could happen again or is there less / no mild air around for the low to pick up?

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@ Manutdmatt

Look at the NAE image again and look at the bracketed area at the bottom, 12+48. I know where you are looking to suggest it is only 6z but that never tallies up.

13011812_1612.gif

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Here's the BBC weather map for the main snow areas on Fri, amber area is the where the heaviest falls are expected.

post-6751-0-52617900-1358368226_thumb.jp

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Timmy,

I don't mean to put out your fire so to speak but the GFS isn't the best model. It's the best model at being 3rd best and has been for a long long time. The verification stats say it all. I know your a fan but the fact is it's not the best performing model.

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Question, last week we were being shown similar but not as extensive snow albeit it further out but it came to nowt down south due to a mild sector that got wrapped in the low.

Isn't there a risk the same could happen again or is there less / no mild air around for the low to pick up?

There is no mild sector in this depression - at least not one that will cross away from the extreme SW. The risk is entirely from lack of precip. However if this system fades quicker than expected then it is likely that there will be another on Monday which possibly would be a little further north.

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Summary of the models today using the GFS, ECM, UKMO, GEM, JMA and NOGAPS.

96 hours Sunday - All models show a low travel across the South of the Atlantic and deepen once it leaves the jet stream, the GFS however is the only one to send this low up towards the South of Greenland and it has done this for the past three runs,

Here's a comparison to what most models show and the GFS,

post-6686-0-27804400-1358367755_thumb.pn

I've gone through the ECM to see if it's been consistent with the other idea of sending the low South like what the other models say and it has here is the 12z and 00z runs side by side,

post-6686-0-56660100-1358367768_thumb.pn

To be fair to the GFS here is the same type of comparison for it,

With this sort of disagreement at 96 hours this is why it's difficult to really know what may happen next.

120 hours Monday - Four of the six models show a low to the South West of England like this,

The likes of the ECM and GEM would bring plenty of cold weather to many parts of the UK.

Back to the GFS it's weakened the deep low by this point the Atlantic still has a bit more power and the blocking to our North is a bit weaker than what the other models show,

144 hours Tuesday - Most of the models show what the ECM has a low near the English Channel again this would bring further cold weather,

The GFS seems to be the odd one out here and continues to show the blocking to our North weaken and the Atlantic weather looks stronger,

Overall - All the models do agree on a cold set up in the short time range but it's where we go from Monday onwards is where the big question mark is, most of the models do show a low travel along and down across the far South of the UK bringing more cold weather to much of the UK next week, the GFS is the only one to show something different and doesn't send the low down South it has big disagreement at the moment from the other models but that doesn't mean it is wrong it could be right but lets hope it's wrong and moves over to what the other models show.

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@ Manutdmatt

Look at the NAE image again and look at the bracketed area at the bottom, 12+48. I know where you are looking to suggest it is only 6z but that never tallies up.

13011812_1612.gif

I expect emphasis for this precip to shift 50-80 miles further west going by latest EC OP and EC mean.

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Here's the BBC weather map for the main snow areas on Fri, amber area is the where the heaviest falls are expected.

There seems to be thought that this front could basically stall or move very slowely over the UK due to the jet stream (lack of). This alone increases risks and the SE winds increases blizzard like conditions. Can`t wait for this time tomorrow when speculation should be over and either a huge downgrade or a met upgrade stretching the amber region.

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@ Manutdmatt

Look at the NAE image again and look at the bracketed area at the bottom, 12+48. I know where you are looking to suggest it is only 6z but that never tallies up.

13011812_1612.gif

The band of precipitation isn't forecast to reach eastern areas until around 3pm. The snow shown in eastern areas on that chart is not part of the main band. The NAE always throws light precipitation that isn't really there ahead of the main band. If that run of the NAE had gone on another couple of frames we would have been able to see how much precipitation it is actually showing for eastern areas.

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The date at the bottom says "Fri 18/01/2013 06"

06... then 12. 06 being the last chart.

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06... then 12. 06 being the last chart.

If i could just put this one to bed.Look at the bottom right of the chart-it says wed 12+48 meaning it`s weds chart at 12z looking 48hrs ahead.

Hope that clears it up.

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I can't see how the Met Office can't upgrade widely in the East Midlands/Home Counties/London area. The verbatim of the yellow warning is based on uncertainity; just needing to firm up facts before committing themselves. The models have remained consistent and there haven't been vast changes since this time yesterday.

Could be a hell of a lot of problems come rush hour Friday afternoon,

I guess there is still massive uncertainty on whether the snow will reach far enough East and produce "disruptive" amounts of snow.

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There seems to be thought that this front could basically stall or move very slowely over the UK due to the jet stream (lack of). This alone increases risks and the SE winds increases blizzard like conditions. Can`t wait for this time tomorrow when speculation should be over and either a huge downgrade or a met upgrade stretching the amber region.

it could be that the met increases the current amber areas to red and the extends the amber to a more extensive areas probably covering the whole of central northern england if the gfs precipitation charts are to be believed.....

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I guess there is still massive uncertainty on whether the snow will reach far enough East and produce "disruptive" amounts of snow.

there yellow warning on the met site

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Copied from London & South East

--------------------------------------------------

Something quite not right, I'd say we are not just on the cusp of something special, but more so something quite serious...

uksnowrisk.png

A lot of it depends on the snowfall this weekend, going by the MetOffice warning it could have a very significant impact. At this stage a very low possibility, but I await the upgrade. Winds will strengthen and blizzard conditions are a possibility,with the potential for some severe disruption, though currently there is a good deal of uncertainty about intensity of snow. Icy conditions and low temperatures throughout. Snow accumulations expected Monday and Tuesday with snow showers later. Strengthening winds later exacerbating the cold feel.

If ECM is to believed then come Wednesday, we are ****ed!! GFS got this one correct last week by showing a severely deep low heading into the UK sometime early next week.

ecm500.120.png

ecm500.144.png

Something quite not right, seeing temperatures that low for London next week. Minimum of -8*C could be reported. But I suspect with accumulations as much as they could be Wednesday Morning, the temperatures could start to fall quite a bit for London & South East. I wouldn't be surprised if this weekend and early next week dumps a good bit of accumulation and temperature plummet that a Red Warning wouldn't be issued as the threshold for the home counties is quite less than most of the rest of the country.

301nb08.jpg

Red — National Emergency

Reached when a period of cold weather is so severe and/or prolonged that its effects extend outside the health and social care system. A level 4 warning would be issued on advice from, or in collaboration with, our Government partners. At this level, the health effects may occur among the fit and healthy, and not just in high-risk groups.

http://www.metoffice...oldWeatherAlert

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Excellent post Robbie. I think the excitement of the last few days has started to turn into shocked silence. Worrying times ahead methinks!

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18z nae is bit slower than the 12z with eastward push of precip. 18 z totals

London 2mm

Brum. 7 - 8 mm

Bristol 8 - 11 mm

Manc. 2-4 mm

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NAE 18z precip accumulations show another westward shift for Friday, btw before anyone says, precip accum is out before the main NAE output so it is 18z

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UKMO continues to show a very cold outlook for the foreseeable future. It has been performing excellently in recent days, much better than GFS and ECM which have had there wobbles, but not the UKMO.

Once again GFS wants to throw in a different scenario than UKMO and ECM and perhaps more notably GEM, by weakening heights to the north and powering up the atlantic as we move into middle of next week. I do think there is greater room for error in the GFS output simply because it puts out 4 outputs each day, it often gets it right on one run, then drops the idea in the next one, then yo-yos around on the next only to return back to what it was showing 2/3 or sometimes more than 4 runs ago.

If the ECM/UKMO output verifies then the UK is certainly about to go into a deep snow freeze, with two very notable widespread snow events on Friday and Monday followed by frigid air from the NE and the threat of further heavy snow showers from the NE. Its a classic locked in cold snowy synoptical output, the likes we haven't seen for many many years. The winters of 08/09, 09/10,10/11 never produced classic renewed battleground situations resulting in widespread snowfalls.

The charts right now for Friday have an air of 5 Feb 96 about them. BBC are anticipating rainfall totals in N Ireland of 20-40mms, indicative of the very heavy precip associated with the front. Could anyone tell me what the equivalent of 1mm of rain is in terms of snowfall amounts is 1cm?

In terms of overall output perhaps we need to go back to some of the cold winters of the 80's for similiar charts, and these charts are not in fantasy land there are just within the reliable timeframe.

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Be interesting to see whether the snow reaches beyond west midlands soon! Nae def slowing rate of passage of front, with it seemingly disintegrating a bit like the 12 z gfs showed!

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