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South West and Central Southern England Regional Weather Discussion 03/03/2018 Onwards


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Nothing here now. Wish I could join in (even though its better for the plants to not have this). Overnight will see changes to our conditions locally. Looking convective for our near futures..

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And it's 'eyes down' for the full house......Tonight's bingo card!  

BINGO!    Full House.....  ;-)   Oh my goodness, my giddy aunt What is this, spring with a new slant? I said I didn't want you, go away snow But I'm here again, eyes all aglow

To help pass the time, lets play a game....Netweather South West Thread Bingo.....no prizes for the winner apart from the accolade of being a bit of a smarty pants

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7 minutes ago, Bring Back1962-63 said:

TONIGHT'S AND TOMORROW'S SNOW

At last the snow has reached Exmouth :)  0.5c fairly light (1200) and medium flakes. After my bullish forecast earlier I was beginning to doubt myself - no I wasn't :D  I must keep an eye on the live charts, radar and satelitte etc while I write this post! The fronts chart does not auto update - I'm not aware of one that does. The old Met O site used do update them regularly but dropped that extremely useful feature 2 years ago.

lastsnowradar_uk.gif  anim_ir_color.gif  analyse-2018-03-17-06.png  temp_eur2.png pression2_uk.png 

temp_uk.png  pointrosee_uk.png  windchill_uk.png  vent_uk.png  arpege-9-7-0.png?17-11

I'll start with the good news before I move on to the very good news! The narrow line of snow over our region is the cold front clearing south-south-westwards. There are still a few slightly heavier burst on it but it's mostly light to moderate snow. The very cold air is undercutting so quickly and almost all the snow is the dry powdery stuff. The ground surface (down to 10 cm below) is still 4c to 5c - hence the melting and only slight settling. This will change as the surface (not the lower 9 cm) cools to nearer zero later today. Then almost all the snow will readily settle and start to accumulate. There will be very little sunshine to melt it today and especially tomorrow which will be an ice day for many of us. The snow showers further north are spreading out slightly (with small gaps between them) but have been intensifying with white echos showing up. It's the snow showers pushing into East Anglia and down the M4 corridor that we need to keep an eye on. Once the cold front clears just to our south (more or less stalling in the English Channel) more snow showers will develop over the south-east with a Thames streamer likely this afternoon. As the flow backs slightly from east to east -north-east and with a strong wind - it's these showers that should spread right across our region later this afternoon. Some are likely to be pretty heavy and many parts should see some accumulations by this evening. Now let's move on to the very good news!

Met O Fax Charts:   0600 Sat Mar 17th                                    0000 Sun Mar 18th                                1200 Sun Mar 18th                                 0000 Mon Mar 19th                                  1200 Mon Mar 19th       

               20180317.0650.PPVA89.png  20180317.0442.PPVE89.png  20180317.0514.PPVG89.png  20180317.0514.PPVI89.png  20180317.0514.PPVJ89.png

We can see all the fronts that cleared through our region this morning. By midnight the main cold front (the last one in the queue that brought in the sub zero temps) has stalled in the Channel. They show a Thames streamer and a Lincs streamer (the toothed quasi stationery black trough lines). Now this is where it gets trickier. Various models have (or "had") very slightly different solutions. I'll look at some of those in a minute after I've gone through the Met O thinking. They develop a wriggle in the cold front and then a minor LP on it. They show this developing in the eastern Channel over the far north-western French coast and near to the Kent and Sussex coasts. There would already be more continuous snow around and to the north of the front and the snow shower activity slightly further north and north-westwards (say south of the M4 for a change!) is also likely to intensify. By midday tomorrow they show this feature in the south-west approaches and moving westwards. The trailing occluded front remains in the Channel and much of southern England and more especially the south-west is likely to have seen some "at least" quite heavy snow. Much will depend on the exact track of the minor LP, whether it deepens at all and how far the fronts push northwards. The south Midlands and south Wales "may" also see some of this continuous snow or at least enhanced snow shower activity. By midnight Sunday into Monday they show the front well clear of the south-west but stretching west-north-westwards from the Brest Peninsular through the Channel with the easterly flow right across our region again. That flow is still over much of  southern England during Monday - already lasting longer than predicted until yesterday. Let's look at the excellent Arpege pressure charts for some greater detail and their take on this from their 6z run. 

(Exmouth UPDATE: 1300 now and moderate "dry powder" snow with larger flakes and starting to settle - I am right under the cold front and it's down to 0c - many of you should be below zero by now).

         0000 GMT Sun Mar 18th                            0060 GMT Sun Mar 18th                         0900 GMT Sun Mar 18th                         1200 GMT Sun Mar 18th                           1500 GMT Sun Mar 18th

arpege-53-18-0.png?17-11  arpege-53-24-0.png?17-11  arpege-53-27-0.png?17-11  arpege-53-30-0.png?17-11  arpege-53-33-0.png?17-11

        1800 GMT Sun Mar 18th                             2100 GMT Sun Mar 18th                       0000 GMT Mon Mar 19th                          0300 GMT Mon Mar 19th                        0600 GMT Mon Mar 19th

arpege-53-36-0.png?17-11  arpege-53-39-0.png?17-11  arpege-53-42-0.png?17-11  arpege-53-45-0.png?17-11  arpege-53-48-0.png?17-11 

The main fairly slack LP is centred over much of central and southern France by midnight tonight. Arpege show a minor LP cell developing just west of the Cherbourg peninsular. This deepens slightly during Sunday and pushes slightly north-westwards. to lie about 50 miles south of the Lizard by 1500. It slowly pushes westwards and then south-westwards to end up just west of the Brest Peninsular by midnight Sunday/Monday. It then drifts slowly southwards into Biscay during Monday. There are signs of "possible" further disturbances showing up later on Monday near the Channel but that's already too far ahead with all this uncertainty on the micro detail. I'll pick up on that tomorrow morning.

I've had a look at the other models and the GFS 0.25 Hr is very similar to Arpege. In fact I feel that there is pretty good agreement on the 6z runs for the next 24 hours or so.  Things could change on the 12z output but it looks like the minor LP will skirt along the Channel just off the south coast. How much the old front reinvigorates is difficult to tell. The extreme temp contrast with the sub zero surface temps, very low dew point temps and sub -8c (or lower) uppers over southern England (and all of the UK) will engage with the warmer air to our south. Unlike two weeks ago, when we had storm Emma doing battle with the Beast, this time we have a minor LP feature and the deep cold will win this initial battle. There is even a possiblilty of some extremely heavy snow with a full on blizzard and I will not be surprised to see the already expanded amber warning area being further enlarged and possibly a red area from roughly the IOW westwards through to Cornwall and uo to about 50 to 100 miles inland. There is no point in my showing any snow charts, which many of you will do anyway. Just watch it all develop. This may well be an all nighter :)  

I'll be back with another (briefer) update this evening.  I've now got a slight covering here but still melting on the roads and pavements - just below zero now too, which is not bad for the south coast in mid March at 1400!   David

Hi David 

 In your post you mention starting with the good news and then you say you will move on to the very good news but I didn’t see where that very good news started ?

 

Why are you talking very good news just for Devon and Cornwall as it does look like that small low pressure is going to hit them quite hard but what about the rest of us further north in Somerset and Wiltshire are we likely to see any snow from this small feature tomorrow? 

 

Thanks 

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Just now, Georgie said:

I'm wondering weather I will get any its sunny here.:wallbash:

your under the amber warning from midnight  be patient your time will come!

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2 minutes ago, offerman said:

Hi David 

 In your post you mention starting with the good news and then you say you will move on to the very good news but I didn’t see where that very good news started ?

 

Why are you talking very good news just for Devon and Cornwall as it does look like that small low pressure is going to hit them quite hard but what about the rest of us further north in Somerset and Wiltshire are we likely to see any snow from this small feature tomorrow? 

 

Thanks 

I do actually pick up on that halfway through. I also say that the snow will affect the whole of the south from Kent to Cornwall and up to 50 to even 100 miles inland. The very heavy snow is likely to be further west (perhaps IOW westwards) as the feature tracks westwards and deepens slightly. If you want me to stick my neck out - I would say 5-10 cm in the south-east and well over 20 cm further west close to the coast. Perhaps 25 cm + over the moors and locally even more than that. Some huge drifting too. Keep an eye on that radar. The initial snow in the south-east will be the Thames streamer with more organised  and heavier snow showers. Then early this evening we should see the main snow area start to develop. I need a break now for lunch and to recharge my batteries for the main event.  :) 

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9 minutes ago, offerman said:

Hi David 

 In your post you mention starting with the good news and then you say you will move on to the very good news but I didn’t see where that very good news started ?

 

Why are you talking very good news just for Devon and Cornwall as it does look like that small low pressure is going to hit them quite hard but what about the rest of us further north in Somerset and Wiltshire are we likely to see any snow from this small feature tomorrow? 

 

Thanks 

unless modelling has got it wrong, not much snow for wilts/M4 corridor IMHO....rather frustrating to see areas along the south coast expected to get battered whilst traditionally better favoured areas miss out, but hey ho at least this thread has bragging rights to most snow as a whole

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The temperature contrast to this time yesterday is unreal! Anyway the odd flake of snow popping up in a biting wind.

You can tell the humidity has dropped because the ground is dry now despite the heavy snow earlier.

Will be interesting to see what happens to this streamer when it hits land

image.thumb.png.2eef52e0edcf410e800bf85518022a14.png

Edited by Quicksilver1989
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It actually hasn’t stopped snowing here all day, apart from the heavy stuff this morning it’s been light but now the temps at 0c the lighter stuff is laying 

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1 minute ago, tomjwlx said:

0.4C DP -3.0C snow but light and fine flakes its struggling to settle

Ground is cooling, got drizle snow here which is just starting to settle on surfaces. If we get some real snow later it will have no problem.

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1 minute ago, karlos1983 said:

I have snow falling nicely, and this time it is not struggling to settle/not melting. Cushty 

Still no real idea what to expect this evening but its moving in right direction.

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Light snow on and off for a while now, heavier burts every now and again. 

I know one thing, looking at the radar makes those few in the mod thread,  who over the build up to this event kept saying it looked like a dry easterly, well they look a little foolish! lol

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Temp 1.5 and dp -1.4 

 

Some stuff lightly blowing in the wind but nothing at all has settled after the lunchtime pour down of snow. It's going to be a long night. And I'm still badly suffering with this burst ear drum. 

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