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South West and Central Southern England Regional Weather Discussion 01/12/2018 Onwards

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You can see how tricky this is going to be by just looking at the frontal structure on this morning's fax. One suspects a fair chance of snow behind the cold front but this is essentially a nowcast I feel.

PPVK89.thumb.gif.f91f692c46f2046f7d97a0a822900ab6.gif

Edited by knocker
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ICON north of M4? ?

iconeu_uk1-42-57-0.png?27-10

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20 minutes ago, knocker said:

You can see how tricky this is going to be by just looking at the frontal structure on this morning's fax. One suspects a fair chance of snow behind the cold front but this is essentially a nowcast I feel.

PPVK89.thumb.gif.f91f692c46f2046f7d97a0a822900ab6.gif

Indeed a very complex set up really, not the "classic" channel low's we see every now and again. Not long until EURO4 starts coming into range.

Edited by Zephyr

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8 minutes ago, Zephyr said:

ICON north of M4? ?

iconeu_uk1-42-57-0.png?27-10

Haha the ICON can f**k off. Always the same for Wales and the South West, it all looks good until a day or two away.

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Having had chance to wake up properly now and digest a rather scrumptious Avocado, Smoked Salmon & Poached eggs with Benedict sauce on toast, I can now see an evolving trend on this mornings model output.

I've picked out the French, ARW model, an advanced research weather model derived from the NMM.  I'm using this model as it looks a good cross fit between all the other usual model output this morning, essentially a mean evolution.

What looks apparent, is the core of the low will head into France now, along with the core of the PPN.  Could be some blizzard like conditions through Central parts of France.

For our region, we are reliant on a trailing front above the main spawn low.  Most models do show a front crossing Southern England from west - east some time between Tuesday evening and Wednesday morning.  

It's a complex situation regarding what falls from this front, ie wet or white.  Timing and intensity will play a huge part in this.  Initally, we could see a drag of less cold upper air and thus, less cold dewpoints ahead of this front, meaning an intial period of rain or sleet for the region. This scenario becomes more likely the further South and West you are in the region;

arw-42-63-0.thumb.png.33bad5577ad45f9c5a68d0f52a2ee7f0.png

You can see on this chart a signal for hill snow only in our region initially, with a more coherent signal for snowfall over the Cotswolds, Forest of Dean and Brecon Beacons.  Like any PPN chart, don't take this too literally, it just shows the complexity and marginality of this situation.

As night falls however, and temps drop a little, we see a more coherent risk of snowfall down to lower levels across the region, away from Devon, Cornwall and southern coastal districts (ie south of the A303 again);

arw-42-64-0.thumb.png.120a3934204ac5041393d8745996296c.png

Worth noting, the moors of Devon are likely to see mostly snow all the way through here, could be a nice covering over Dartmoor for example.

The heavier PPN now over the West Country, evaporative cooling should aid the transition to snowfall further, so by Tuesday evening, we *could* be hearing reports of snow falling in Yeovil, Bristol, Bath, Swindon and Warminster for example.

The front then rattles through our region, turning increasingly more to snow as it does;

arw-42-67-0.thumb.png.d7dcdfef05a5f3a2ae9f45b480f77fa0.png

As you can see there, once it hits Central Southern England and into SE England, it's now snow for many.  I suspect areas like Reading, Guildford and Aldershot could see a decent snow event from this.

For us though, it all depends on timing and PPN intensity. With a good chance of many of us, away from the highest ground, seeing a brief period of rain or sleet first, it maybe difficult to envisage seeing any notable accumulations, with perhaps the eastern.extremities of our region being the exception.

For areas west of Hampshire and Wiltshire, expect nothing but hope for something.  I think personally, there isn't enough snowfall being modelled to provide any degree of confidence in any accumulative snowfall.  

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light snow shower here nr Colyton -encouraging.?

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3 minutes ago, Jayfromcardiff said:

Oh well warnings for only the SE by the looks of it.

Still time between now and Tuesday night for that to move West.

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Just now, bathweatherwatcher said:

Still time between now and Tuesday night for that to move West.

They must be 80% certain as they didn't even mention any uncertainty in the track of the snow in their warning description.

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3 minutes ago, bathweatherwatcher said:

Well the ballon has gone up with the Met issuing their first yellow warning though for most of our region it’s not good news.

https://www.metoffice.gov.uk/public/weather/warnings#?date=2019-01-30

Being just outside the edge of the warning area, I'd take that. Still plenty of time for change too!

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I'm sure the warning area will change. When any new models come out.

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Personally I’d be more nervous if I were under the warning now! As they have a habit of moving in these setups...

but yeah it’s not ideal.

Edited by karlos1983

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5 minutes ago, karlos1983 said:

Personally I’d be more nervous if I were under the warning now! As they have a habit of moving in these setups...

but yeah it’s not ideal.

Not sure it'll move west, more like further east of anything. When are the next model runs?

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So close!! Hopefully it will adjust west a bit 

F7F8576A-3182-40B8-9359-4BF5EC8DB3AA.png

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9 minutes ago, Jayfromcardiff said:

Not sure it'll move west, more like further east of anything. When are the next model runs?

Well..... as I was saying Jay ? it’s not impossible or improbable 

720829A6-8AFB-44C6-8785-9AA6C94DFF81.thumb.png.544dc601871f7779d88d908a5951c164.png

 

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They’ve revised warnings many times before so no reason why not again following models runs as it gets closer to the time for when the warning was issued.

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Screenshot_4.thumb.png.a1a3ee6b4a5fa34aba497d78c15589a5.png

Heavy snow at Midnight Tuesday into Wednesday 

 

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My view, on Tuesday/Wednesday hasnt changed. Not enough entrenched cold in situ before the front arrives on Tues to give decent snow for our neck of woods. And it is not a classic channel low either imho.

Edited by Bristle boy

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I expect nothing but watch nowcasts these days. So many times these channel lows skip the south and snow stays in the channel or it gets mixed out with warm uppers. Even with all charts high, medium, or low resolution and forecasts lol predicting snow. That said, when they pay off (very rare) they really pay off and we get a good dumping. I've seen this scenario many, many times but I can count on one hand how many notable events we've had in recent times. Simply, the odds aren't in our favour. We do have hope though lol

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2 minutes ago, snowysouth said:

I expect nothing but watch nowcasts these days. So many times these channel lows skip the south and snow stays in the channel or it gets mixed out with warm uppers. Even with all charts high, medium, or low resolution and forecasts lol predicting snow. That said, when they pay off (very rare) they really pay off and we get a good dumping. I've seen this scenario many, many times but I can count on one hand how many notable events we've had in recent times. Simply, the odds aren't in our favour. We do have hope though lol

You're correct, better off not pinning hopes too much and just wait and see!

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Good morning all, I'm just inside the warning area for Tuesday Wednesday.  I'm really trying not to get excited as I know from past experiance it can all change at the last minute.  Haven't  even mentioned it to the kids. Starting to struggle now lol I don't care how much falls as long as I see it fall. Here's hopi g it changes so more get in on the action ❄❄❄

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