North West England Cold Spell Discussion

[Osbourne One-Nil]

I can't work it out for Cumbria (on top of trying to work out whether I'm north-west, north-east or Pennines), but I think I'd be due a fair dumping wouldn't I...being right next to the Pennine's western flanks and 600ft up?

[Bartlett Low]

hmmmm i watched the bbc too, they seem very reluctant to go past wednesday, infact they only showed a 23 hour forecast, and to be honest i think they're uncertain. Im at the coast and in easterlies we never get laying snow, but it DOES snow very often, I also expect the weather to be a lot more positive for us over the weekend, and just out of curiousitywhy does a breakdown of a weather system cause frontal snow? and would it be a cold front?

Hi, it's not the breakdown of the system as such but a breakdown of the cold conditions, often from a weather system approaching from the South West.

When this system moves into the colder surface air then often frontal snow occurs. The problem (especially in the North West) is in recent years when this has happened the warm air has encroached too rapidly meaning only very brief snowfall before the precipitation turns to rain or in some cases falling totally as rain only. Basically the cold air has been readily swept aside by the Atlantic system. In some more memorable breakdown snow events the cold air has "stood its ground" resulting in the "background" synoptics you will have heard mention of.

[wysiwyg]

hmmmm i watched the bbc too, they seem very reluctant to go past wednesday, infact they only showed a 23 hour forecast, and to be honest i think they're uncertain. Im at the coast and in easterlies we never get laying snow, but it DOES snow very often, I also expect the weather to be a lot more positive for us over the weekend, and just out of curiousitywhy does a breakdown of a weather system cause frontal snow? and would it be a cold front?

No it would initially be effectively a warm front. If the cold air over the UK was stubborn enough and the warm sector was moving slowly enough, the warm air would rise over the cold air. As that happened the warm air would cool and so would be less able to hold water vapour. The vapour condenses out, falls through the cold air where it readily turns to snow. A further effect that sometimes occurs is that the (now cooler) warm air that is shedding its moisture cools enough to begin to push the cold air under he warm sector. This speeds up the occlusion of the front and can sometimes lead to prolonged snowfall as the whole system becomes slow moving. This may be a little simplistic but I think it gives you the guist of what can happen as the atlantic tries to break down an entrenched cold spell.

[k19]

No it would initially be effectively a warm front. If the cold air over the UK was stubborn enough and the warm sector was moving slowly enough, the warm air would rise over the cold air. As that happened the warm air would cool and so would be less able to hold water vapour. The vapour condenses out, falls through the cold air where it readily turns to snow. A further effect that sometimes occurs is that the (now cooler) warm air that is shedding its moisture cools enough to begin to push the cold air under he warm sector. This speeds up the occlusion of the front and can sometimes lead to prolonged snowfall as the whole system becomes slow moving. This may be a little simplistic but I think it gives you the guist of what can happen as the atlantic tries to break down an entrenched cold spell.

But surely any snow falling then would thaw VERY quickly?

[wysiwyg]

But surely any snow falling then would thaw VERY quickly?

Yes it usually does unless you get the latter scenario where the warm sector is completely undercut by the cold sector and lifted totally off the ground. Its all down to the relative energy levels (positive and negative) in the cold block (high pressure) and the approaching low pressure system.

I'm probably not anywhere near the best person to try and explain this as my knowledge of metorology is fairly basic. Worth having a look at some of the links and guides in the learning area - that's where I got most of my basic knowledge from.

[k19]

Yes it usually does unless you get the latter scenario where the warm sector is completely undercut by the cold sector and lifted totally off the ground. Its all down to the relative energy levels (positive and negative) in the cold block (high pressure) and the approaching low pressure system.

I'm probably not anywhere near the best person to try and explain this as my knowledge of metorology is fairly basic. Worth having a look at some of the links and guides in the learning area - that's where I got most of my basic knowledge from.

Also could convection occur near the coast when the northerly is in progress? Would the coast see any snow at all

[iand61]

If the definition of sleet was one rain droplet in every 100 on your windscreen containing a tiny piece of 90% melted ice then i can catagorically state that.

It was definately sleeting 1300ft up on the Lancs Yorks border at 8pm.

Although if only one flake on the London weather centre can make a white Christmas then what i drove through was close to a full blown whiteout.

Current temperature is 2'c so maybe something approaching winter weather is just around the corner.

Ian

[wysiwyg]

Also could convection occur near the coast when the northerly is in progress? Would the coast see any snow at all

I think I'm right in saying that convective snow can and does occur due to the Irish sea, however the big problems for the Lancashire coastal fringe in a true Northerly flow are a ) we are sheltered by the Lake District and southern Scottish uplands and, b ) we dont actually have very much coast facing north. I think convective snow for the coastal plains either side of the Ribble Estuary is pretty unlikely in a true northerly. We would be relying on something backing round more to a NNWrly direction to stand a chance of convective snow showers. In a true Nrly we would stand more of a chance from the small troughs that often form at fairly short notice in this type of airflow.

The North Wales coast I think does quite well from a Northerly - I can remember when I used to live on the Wirral seeing Deeside and Westwards getting a good pasting in a Nrly but it was dry down by the estuary side at Thurstaston - Maybe Steve P can shed some more light on that?

[Thundery wintry showers]

The winds are likely to back west of due north at some stage (indeed almost immediately if the ECMWF is right) so convective snow showers should occur near the west coast. Temperatures will, as usual, be pretty marginal along the coastal fringes due to the warming effects of the sea, so the snow may struggle to settle there, but upwards of a few miles inland you should see settling snow.

For example if you take the Lancaster area (one which I'm quite familiar with as I used to live there), I expect that Lancaster will have lying snow from the NW'ly, but at Morecambe and Blackpool it may not stick around for long.

[k19]

I think I'm right in saying that convective snow can and does occur due to the Irish sea, however the big problems for the Lancashire coastal fringe in a true Northerly flow are a ) we are sheltered by the Lake District and southern Scottish uplands and, b ) we dont actually have very much coast facing north. I think convective snow for the coastal plains either side of the Ribble Estuary is pretty unlikely in a true northerly. We would be relying on something backing round more to a NNWrly direction to stand a chance of convective snow showers. In a true Nrly we would stand more of a chance from the small troughs that often form at fairly short notice in this type of airflow.

The North Wales coast I think does quite well from a Northerly - I can remember when I used to live on the Wirral seeing Deeside and Westwards getting a good pasting in a Nrly but it was dry down by the estuary side at Thurstaston - Maybe Steve P can shed some more light on that?

Net weather is saying i have snow thurday friday and saturday, all above 80% BBC says possibly some on thursday night only. I don't think being at the coast will allow ANY snow on thursday and friday surely?

[wysiwyg]

Net weather is saying i have snow thurday friday and saturday, all above 80% BBC says possibly some on thursday night only. I don't think being at the coast will allow ANY snow on thursday and friday surely?

See TWS's post above

Also could depend on where you are in Preston. I've seen the back end of Preston (i.e longridge, ribchester etc) get pasted with snow whilst town centre and out towards the west is just rain and he odd bit of sleet. It's a very marginal area in virtually any possible setup.

[Snow free zone]

Net weather is saying i have snow thurday friday and saturday, all above 80% BBC says possibly some on thursday night only. I don't think being at the coast will allow ANY snow on thursday and friday surely?

Where about's are you ? i live in Preston and we are 15 miles inland ? so certainly would not class myself as on the coast. I also would not pay much attention to the BBC 5 day forecasts they can and will change

Edited December 15, 2009 by Snow free zone

[k19]

Where about's are you ? i live in Preston and we are 15 miles inland ? so certainly would not class myself as on the coast. I also would not pay much attention to the BBC 5 day forecasts they can and will change

Well, im a good few miles south of preston and am about 5-7 miles from the coast the strange thing here is that we can get some incredible snowfall but the second it hits the ground it melts, infact in the february cold spell last year, we saw little over a centimetre and it thawed by 10:30am

Edited December 15, 2009 by K.1000

[Thundery wintry showers]

I expect sleet or rain from Saturday's event in western parts of this region I'm afraid. I've seen it happen many times before in that kind of setup- snow to the east of the Pennines & parts of east Lancashire/Cumbria, but rain near the west coast due to the warmer pool of air out west. Still, see my post above re. snow from Sunday through Tuesday!

[k19]

I expect sleet or rain from Saturday's event in western parts of this region I'm afraid. I've seen it happen many times before in that kind of setup- snow to the east of the Pennines & parts of east Lancashire/Cumbria, but rain near the west coast due to the warmer pool of air out west. Still, see my post above re. snow from Sunday through Tuesday!

Your probably right. what was the setup last year? In february, because we managed at least some from that

[Snow free zone]

Well, im a good few miles south of preston and am about 5-7 miles from the coast the strange thing here is that we can get some incredible snowfall but the second it hits the ground it melts, infact in the february cold spell last year, we saw little over a centimetre and it thawed by 10:30am

Well it was the same here. I am almost on the M6 not far from the football ground. The M6 is quite often the line where the sleet stops and the snow begins, as someone has said Longridge often gets snow when we don't and its only 5 miles away.

[Snow free zone]

TWS is quite right, and if you look at the latest predicted chart for Sunday it shows the wind has more of a Westerly element and we get some good snow showers in the NW.

Add: If this run comes off we will be digging ourselves out on Tuesday !! LP moving down over Ireland and giving us plenty of the white stuff. Nice charts to look at, but in reality I fear it will be well wide of the mark.

Edited December 15, 2009 by Snow free zone

[Spurry]

The GFS 18z is offering some hope , so far it keeps things colder and snowier for the NW longer than any run so far , i know it's only 1 run but out to 144z it is painting a wonderful snowy scene

[Guest]

Has anyone phoned the Fat Controller to tell him that he'll have to dig Thomas out on Monday morning???

OK, this is the last time I'm going to make this joke, three times is two times too many...:lol:

[cheshire snow]

The GFS 18z is offering some hope , so far it keeps things colder and snowier for the NW longer than any run so far , i know it's only 1 run but out to 144z it is painting a wonderful snowy scene

Beat me to it LOL

Was just going to say the same thing

The local weather tonight just did not want to know understand they have to be carefull

Whay they say but these charts are painting a different picture to waht they are saying

C.S

[Snow free zone]

Good old GFS we even get a white Christmas one of the best runs for snow i have ever seen for the NW. If the winds turn more W then its game on for us i reckon.

[swainclubber]

Beat me to it LOL

Was just going to say the same thing

The local weather tonight just did not want to know understand they have to be carefull

Whay they say but these charts are painting a different picture to waht they are saying

C.S

well in 24 hrs the dew points will turn to our favour, so its game on from then

[Bartlett Low]

The 18z is truly a monsterous run for the North West.

Plenty of potential for decent lasting lying snow for the whole region going of that (admittedly "pub") run.

If it verifies anything like the 18z we are in business!

[cheshire snow]

Well what a pub run that was OMG

Just checked my snow risk for my area obviously wont pan out that way but

Next Monday it stating 11cm of Snow and an overnight low of -12c

A bit to extreme me thinks

C.S

[SP1986]

I reckon the 18z is way over the top, it's just showing a bizarre run, against all others, it'll be changed by tomorrow.