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Jane Louise

Southwest & Central Southern England Regional Discussion 9th January 2013>

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Please carry on here. Good luck everyone biggrin.png

Thanks Jane.

SNOW SNOW SNOW SNOW SNOW SNOW SNOW SNOW :)

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Trying not to get to excited just yet will be interesting over the next few days when the higher res models come in to play for the weekend and then in to next week subscribed to net weather extra the other day for NMM and radar looks like it could well come in handy!

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I'm no good at reading charts can someone plz tell me if it will fall as rain or snow on th iow? Thanks

Well after sunday with the lastest charts iow and most of south coast will see snow! Im now pretty sure this will happen now, its now coming accross now in the latest tv forecasts!

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Still waiting for ians forecast to get uploaded to bbc weather... good.gif

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With the lastest ECM just gone we really are now looking at quite disruptive snow for much of the UK, Just wait on what gsf says tonight though but im sure we will now see an upgrade again tonight for the gsm after todays poor runs. This is very hard to forecast just yet as there is still alot of uncertainty. But i wouldnt be suprised too see some big totals coming our way next week!

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Coastal towns like Plymouth still look good for snow? Get the feeling it could be quite damp :<

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Coastal towns like Plymouth still look good for snow? Get the feeling it could be quite damp :<

Turning to sleet saturday night, then snow from sunday onwards! Very promising i have to say!

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updated meto forecast on my iphone has snow for me now saturday night !.....I still think it will turn to snow more readily than meto are saying atm so am very happy, NAE tomorrow !!!

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Well things are looking promising, and I'm going into the MOD to see what's going on!!!

Good luck with that.

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Can't see how many are viewing the model thread - mods can you see??? smiliz19.gif

Will it be over 1300???

Can't see how many either qg, I expect there's probably more then 1300 Lolsmile.png

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I never see any snow here in Torpoint just off Plymouth :-(

I never see any snow here in Torpoint just off Plymouth :-(

Being born and bred from Plymouth, I only ever remember seeing snow on Dartmoor it's now 13 years since I left there. Good luck though you never know.wink.png

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There were 1530+ plus just before it crashed last night. There were 1414 this afternoon and it was only 4:45pm!!!

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Being born and bred from Plymouth, I only ever remember seeing snow on Dartmoor it's now 13 years since I left there. Good luck though you never know.wink.png

Apparently the last big snow event was the winter of 85 ish I think!!! According to mum that is

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updated meto forecast on my iphone has snow for me now saturday night !.....I still think it will turn to snow more readily than meto are saying atm so am very happy, NAE tomorrow !!!

Agreed - from tomorrow evening we move into NAE mode and the first stages of nowcasting begin.

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Right guys, lets see where we stand tonight on the weekend especially.

All models are in agreement of colder air arriving into the UK on Friday, getting down to our part of the world on Saturday. Below you can see the last frame of the latest high res NAE output suggesting temperatures at the 850hpa heights, roughly 1500m above sea level, are already into negative values for much of the West Country, with very cold values further east to come;

post-12721-0-97893600-1357761886_thumb.j

One of the core ingredients when determining the type of precipitation falling from the sky, is the upper air temperature, the 850hpa. As a rule of the thumb, when the 850hpa temperature is -5c of below, there is an increased risk of snowfall. However, its not as simple as that solely. You also have to look at thickness, which as you can see below, according to the NAE, become progressively colder from the east through Friday

post-12721-0-39535000-1357761895_thumb.j

Other factors such as the Wet Bulb freezing level, which is the height above sea level that snow will fall at before turning to sleet & rain, also have to be taken into account.

Onto the weekend then. On Saturday, the four main models agree on a low pressure system sliding SE across southern parts of the UK.

post-12721-0-51832200-1357761903_thumb.jpost-12721-0-80477000-1357761912_thumb.j

post-12721-0-00352600-1357761921_thumb.jpost-12721-0-20130300-1357761932_thumb.j

The air flows anti clockwise around low pressure systems, so its on the northern flank of this system that easterly winds are generated as wind flows east to west. Therefore the further south and west this system is before it heads SE, the better, as this would mean more snow and less rain due to the quicker arrival if colder air. As things stand currently, and this is still subject to change at this relatively short timeframe, the centre of the low pressure system is expected to be somewhere on the southern channel coast, with the colder air filtering roughly from Reading to Worcester. This can be seen below;

post-12721-0-58931900-1357761944_thumb.jpost-12721-0-51632300-1357761951_thumb.j

This is at 13:00 Saturday afternoon. At the same time we have a band of rain moving in from the W/SW. At this timeframe, this will fall as rain across most of the South & South West.

post-12721-0-93718800-1357761963_thumb.jpost-12721-0-23910400-1357761974_thumb.j

Moving on a few hours to Saturday evening and things start getting interesting. The GFS model stalls the rainband over the Southern Midlands as it comes up against the surge of cold air from the east. The cold air, shown below ( the blue colours );

post-12721-0-82068400-1357761998_thumb.j

begins to undercut the rainband, and as it does this the rain starts turning to sleet & snow. Shown below again by the GFS;

post-12721-0-86524800-1357761982_thumb.jpost-12721-0-37546400-1357761990_thumb.j

By Saturday evening, if the GFS verifies, snow will start falling across Gloucesteshire, northern Wiltshire. The band of precipitation then slowly starts sinking south/south eastwards, and still with the cold air undercutting the band, snow starts falling more widespread across the region as shown here, at midnight;

post-12721-0-13847600-1357762013_thumb.j

The GEM suggests the rainband doesn't make it as far north as the GFS, as the surge of colder air is quicker to push west than what the GFS shows.

This would mean less snowfall for northern areas of our region, but more snowfall for southern areas as there is less rain initially due to the colder air undercutting more quickly. The other models side better with the GEM than the GFS, so its a possible scenario too.

Detail such as how much snow, will it settle etc is not worth answering currently until we get much nearer the time, and the exact track of the precipitation is more or less nailed.

Below are the GFS temperature ensembles at both 850hpa and at surface level, for Cornwall;

post-12721-0-95166500-1357762018_thumb.jpost-12721-0-46370900-1357762024_thumb.j

Somerset;

post-12721-0-64902600-1357762031_thumb.jpost-12721-0-54901500-1357762037_thumb.j

And Wiltshire;

post-12721-0-27699000-1357762044_thumb.jpost-12721-0-85385200-1357762049_thumb.j

The green line is the Operational GFS run. The run most talked about in the model output thread. The blue line is the Control GFS run and the red line is the mean solution. All other coloured lines are ensemble members, ran at a lower resolution to the Operational.

As you can see, there is strong agreement now for a cold spell this weekend. All members agree on this. Throughout next week, the lines start to diverge, suggestive of lower confidence and a variable of outcomes. Note the green line, the Operational run, is at the very top of the suite at times, this suggests it has little support from its ensemble members for such a mild outcome. The red line, the mean, stays cold throughout the suite, albeit at times moderated. The Operational run therefore is a low possibility solution currently for next week, but can't be totally ignored due to its higher resolution.

The mean line for the surface temperature is below 5c throughout, so a reasonable chance of cold conditions continuing for the foreseeable.

I could go on in more detail, but to be honest, uncertainty is higher than normal currently, and a lot could still change so there is little point. In summary;

- Light Rain on Friday across the region in association with a trough ahead of the main band on Saturday. Temperatures cooler, but not cold yet!

- Tricky one still on Saturday, but a period of rain quickly turning to snow is likely across inland areas of the region. I don't think the snow will cause too much disruption currently, and won't be anything to significant, but one too keep an eye on.

- Saturday night into Sunday could give a covering of snow in places as the PPN leaves us to the south.

- A possible Ice Day for some. Cold but looking dry with Ice in places.

- Monday onward. Some models bring a notable snow event across the West Country on Monday, this could be something quite significant. For now however, its just one too watch. Due to the GFS Operationak being on its milder options, and only supported by the JMA model, I would have to say colder rather than milder conditions are more favoured currently, however by no means whatsoever a cert.

Things need watching carefully but some models, most notably the ECM, bring a severe snowfall risk with them next week.

Exciting times ahead. It really doesn't get no better than this for us down here. Good luck all and keep your fingers crossed.

Thanks.

post-12721-0-94218900-1357762004_thumb.j

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I havent seen any snow forecast, what did points west forecast say? Bbc only have sleet sat night then dry sunday.

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I havent seen any snow forecast, what did points west forecast say? Bbc only have sleet sat night then dry sunday.

to cover themselves!

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Meant to on the symbols forecast on website. Yet charts paint a different picture bit of course as we all know saturday is long way off and lots can change in that time. Hope we do get snow though aftet decembers letdown.

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