Short range model discussion - into 2018

[knocker]

25 minutes ago, Sky Full said:

Looking at the detailed charts for the period out to about +65h there is a distinct wedge of less cold uppers shown forming across the SW and then making an arrowhead into south and west Wales.  The difference in temperature of this air is quite marked compared to the surrounding air and is modelled to considerably restrict the amount of snow falling over central Wales over the next three days.  This is the WRF but all high res models show this feature:

Is this the result of a geographical feature (Bristol channel, or Dartmoor perhaps?) or is it simply the dynamics of the low pressure system?  It stands out on the line of upper temperatures as they move north across the British Isles and it would be interesting to find out the reason for it.

 

The short answer, and the long come to that SF, is I have no idea but it will be wrapped up the complex movement of the depression and front(s).Just taking a step back for an overview you get these changes in six hours.

[matty40s]

2 hours ago, johnholmes said:

Quite agree, a RED warning is pretty unheard of, not sure if it has ever been issued. Some very clever folk about.

Doris had a red warning for a small area, for wind though,Crewe station lost it's roof.

[ptow]

2 hours ago, johnholmes said:

Quite agree, a RED warning is pretty unheard of, not sure if it has ever been issued. Some very clever folk about.

We had a Red warning in Reading on 5th Jan 2010. Got 36cm of lying snow out of it.

[Sky Full]

21 minutes ago, knocker said:

The short answer, and the long come to that SF, is I have no idea but it will be wrapped up the complex movement of the depression and front(s).Just taking a step back for an overview you get these changes in six hours.

 

Very interesting progressions and especially the chart above which clearly shows the kink above the Bristol Channel in an otherwise quite circular and unblemished system!  Fascinating how the atmosphere works - will we ever be able to model all its complexity....

[bbtablet]

14 minutes ago, Sky Full said:

Very interesting progressions and especially the chart above which clearly shows the kink above the Bristol Channel in an otherwise quite circular and unblemished system!  Fascinating how the atmosphere works - will we ever be able to model all its complexity....

No - we have as much chance as managing to model personality - too many variables.

[lassie23]

Over on TWO they are pretty bullish about milder weather come Sunday for the south

Edited February 28, 2018 by lassie23

[knocker]

Current satellite. Moderate snow here now

[JoeShmoe]

Red warning now for Central Belt ...

 

Snow showers already affecting the area will become heavier and more prolonged later on Wednesday afternoon and at times through the evening and overnight period, with 5 cm of snow falling within an hour in some places and lying snow reaching 20-30 cm and possibly 40 cm in a few places by mid morning on Thursday. Strong easterly winds will lead to significant drifting of lying sno

 

[Man With Beard]

Coldest March day tomorrow looks a bit of a push but not out of the question:

 

[Interitus]

2 hours ago, Sky Full said:

Looking at the detailed charts for the period out to about +65h there is a distinct wedge of less cold uppers shown forming across the SW and then making an arrowhead into south and west Wales.  The difference in temperature of this air is quite marked compared to the surrounding air and is modelled to considerably restrict the amount of snow falling over central Wales over the next three days.  This is the WRF but all high res models show this feature:

Is this the result of a geographical feature (Bristol channel, or Dartmoor perhaps?) or is it simply the dynamics of the low pressure system?  It stands out on the line of upper temperatures as they move north across the British Isles and it would be interesting to find out the reason for it.

 

Yes, this is because of topography though is does get complicated by fronts and comparison with some of the other charts helps to show what's going on.

Taking the +61h 850 temperature rising over mountains lowers the temperatures, descending air in the lee of the mountains warms it

The best indicator is from the 700mb omega chart, with uplift shown in orange and reds, sinking air in blue, the mountain ranges show as vertical motions perpendicular to the wind flow, the Welsh mountains, Pennines and Cumbrian fells stand out sharply

There are other areas though which don't correspond to topography, such as the band of more gentle vertical motions from Ireland, across Wales and the south east and into France and Belgium. This is a warm front, as can be seen from the precipitation chart, which is enhanced by the flow over the higher regions and reduced in the subsidence zone in the lee of the Welsh mountains

Finally, the 850mb theta-e chart often shows fronts more clearly than the 850 temperature as it better shows the different airmasses. In this case it is not particularly distinct, but the 850 wind shows it veering from south easterly to south westerly in the frontal zone -

Edited February 28, 2018 by Interitus

[beatpete]

4 hours ago, johnholmes said:

Quite agree, a RED warning is pretty unheard of, not sure if it has ever been issued. Some very clever folk about.

One out for scotland now.

 

[johnholmes]

18 minutes ago, beatpete said:

One out for scotland now.

 

I should have not said anything about them being rare should I, please stop commenting, I think you have made the point.

Sure is a white world outside.Currently not snowing or blowing it around, temperature on -2.3 C. I might venture out of the back patio door and measure it again.

[Buzz]

45 minutes ago, Interitus said:

Yes, this is because of topography though is does get complicated by fronts and comparison with some of the other charts helps to show what's going on.

Taking the +61h 850 temperature rising over mountains lowers the temperatures, descending air in the lee of the mountains warms it

Thanks very much for that explanation, I wondered why Carmarthenshire etc was in the "bugger all snow" zone from the forthcoming frontal systems. In that case I'll pop my snow shovel back into storage.

However, on the back of that, ISTR some major dumpings on south Wales from warm fronts that DID result in copious amounts of snow for the aforementioned "bugger all snow" regions, or was that because those fronts approached from a slightly different direction?

Edited February 28, 2018 by Buzz

[knocker]

A westerly view from the midday MODIS and although these are low helicity readings I think indicative of the instability within this cold pool

[knocker]

The Channel convergence zone come upper front has just given a couple of hours of moderate snow here but now cleared

Edited February 28, 2018 by knocker

[chrisbell-nottheweatherman]

2 hours ago, knocker said:

A westerly view from the midday MODIS and although these are low helicity readings I think indicative of the instability within this cold pool

Remarkable how far south the 528 DAM line is.

[West is Best]

7 hours ago, knocker said:

It never ceases to amaze me that that some on this forum feel qualified enough to advise the professionals at Exeter on what they should, or not, be doing regarding warnings, particularly as the current system was initiated by the latter. I'm sure they will issue the appropriate warnings when, and if, they think it necessary.

Because of course they always get it right

Having lived in those parts I've twice seen extremely heavy falls that were entirely overlooked by the mandarins at the MetO.

Anyway, this is a great forum and it's fun to outwit them. As Alan Hansen has found out, sometimes well informed punters know best

[West is Best]

For the sceptics ... the setup that had produced the Red for Scotland is nowhere near as severe as that for Devon, Cornwall and to which I would now add Somerset and south Wales. The ppn charts show conditions tomorrow could be horrendous. 

 

Reminds me of 1978/9 actually when Devon and Cornwall were cut off by 20 foot snowdrifts on the M5.

[johnholmes]

1 hour ago, knocker said:

The Channel convergence zone come upper front has just given a couple of hours of moderate snow here but now cleared

How is Sidney with all that white stuff, best make sure doors and windows are tight shut or he may appear at your dinner table!

 

Edited February 28, 2018 by johnholmes
mis spelling sindey well alright Sidney

[knocker]

5 minutes ago, johnholmes said:

How is Sidney with all that white stuff, best make sure doors and windows are tight shut or he may appear at your dinner table!

 

Blasphemy!- away and stand in the corner for two hours.

[knocker]

Anyone for a convergence zone? The 1200 Geostationary

Edited February 28, 2018 by knocker

[swebby]

29 minutes ago, West is Best said:

For the sceptics ... the setup that had produced the Red for Scotland is nowhere near as severe as that for Devon, Cornwall and to which I would now add Somerset and south Wales. The ppn charts show conditions tomorrow could be horrendous. 

 

Reminds me of 1978/9 actually when Devon and Cornwall were cut off by 20 foot snowdrifts on the M5.

The red warning for Scotland appeared this morning as a localised upgrade of an amber based on conditions current to that time.  If we were consistent, a red for the SW would only be likely tomorrow lunch time.  That would not surprise me as there is significant variance in the model outputs (i trawled through them all on Meteociel) handling on the precipitation bands for Thu/Fri  = Snow, no snow, blizzard, freezing rain.  It seems the latest ICON has gone and moved things yet again.

I do get what you are saying WIB and I'd imagine the MetO are strongly considering a red warning(s) for parts of the SW but probably want to know exactly where to apply them and what they need to be for, suspect its still a bit of a game of pin the tail on the donkey until tomorrow morning?  I would say this is the sensible approach, better than flagging then removing, or worse relocating, red warnings issued too early and we have had an amber for over a day now, so its not as if we've not been warned.

Edited February 28, 2018 by swebby

[knocker]

Current 700mb wind field

https://earth.nullschool.net/#current/wind/isobaric/700hPa/orthographic=-4.00,53.89,2223/loc=-10.519,61.361

 

[Woollymummy]

8 hours ago, The Enforcer said:

January 2010, Central Southern England.

My partner was away in Europe in a tour bus where the cold was so deep the inboard toilet tank froze when they got to Berlin, -22 or something. I was at home with two toddlers, we ran out of proper firewood and had to break up some old fence panels from the garden piles to burn in the log fire. Not comfy weather. Much better now as we have a stove which warms the room properly.

[jethro]

1 hour ago, West is Best said:

For the sceptics ... the setup that had produced the Red for Scotland is nowhere near as severe as that for Devon, Cornwall and to which I would now add Somerset and south Wales. The ppn charts show conditions tomorrow could be horrendous. 

 

Reminds me of 1978/9 actually when Devon and Cornwall were cut off by 20 foot snowdrifts on the M5.

One persons horrendous is another persons wondrous.

My fingers have been crossed so long now I don't think I'll be able to get my gloves on when it comes.