Further Cold Spell In February? 0-180 Charts Only

ninebeanrows

Su Campu wrote: »

If a chart like the one I posted above produces a "Classic snow event" - or any snow for that matter, then I will eat my hat!

Seriously guys, has the place gone mad from the lack of snow???!!!

I think your underestimating it slightly, although it is miles away at this stage so a bit pointless discussing it.

But the 18z pushes the cold that bit further north than seems apparent on the UKM and has a snow event for a good part of Ulster and the northwest.

BEASTERLY

darkman2 wrote: »

This is a crude drawing so forgive me for that but this should be close enough to what that chart implies.

I think it's a bit more complicated than that!

Su Campu

Weathercheck wrote: »

I think your underestimating it slightly, although it is miles away at this stage so a bit pointless discussing it.

But the 18z pushes the cold that bit further north than seems apparent on the UKM and has a snow event for a good part of Ulster and the northwest.

Ah now hang on, we were only talking about that 144 hr UKMO chart posted! Don't care what the others say, THAT one didn't have snow on it (for Ireland anyway!).

It could well turn out to be snowy, but only if something NOT resembling that chart verifies!

I'm honestly sitting here with my mouth open at some of the optimism I'm seeing here.....

ninebeanrows

Su Campu wrote: »

Ah now hang on, we were only talking about that 144 hr UKMO chart posted! Don't care what the others say, THAT one didn't have snow on it (for Ireland anyway!).

It could well turn out to be snowy, but only if something NOT resembling that chart verifies!

I'm honestly sitting here with my mouth open at some of the optimism I'm seeing here.....

GFS Operational is a bit of a kicker

Although ECM is fairly negative all around so my hopes for nothing bar a 36 hour cold northwesterly are quite low yet.

darkman2

BEASTERLY wrote: »

I think it's a bit more complicated than that!

Don't patronise me.


Su Campu - your not interpreting it correctly IMO. I am astonished you don't see the snow potential on that chart. It is a classic frontal snow situation for Ireland. It's very hard to get anything much more favourable on a synoptic chart. If that came off tomorrow I have to say you would be completely wrong. There is nothing more I can say. Hopefully it's not academic and we see similar output tomorrow is all I will say.

Sponge Bob

I believe it will be close so I carefully said close earlier. For a 144hr it is not unpromising or fantastical.

The same model run you show below, however, models the southward marching 850hpa -8 Isotherm thus at its maximum southern extent on Sunday after which it is modelled to fade away northeastwards .

Problem is that it is rather dry on Sunday. By the time the moisture pushes in from the Atlantic on Monday the -8 850hpa Isotherm is lurking north of us.






This is all subject to change like any dacint 144hr ish model but we are as ever looking at moisture colliding with -8 or lower over Ireland if we are to expect snow. It ain't in the 18z but like any good bus service there will be another one along any minute. :cool:




You are showing the moisture ingress below BUT after the -8 @ 850hpa has departed our shores.

Weathercheck wrote: »

I think your underestimating it slightly, although it is miles away at this stage so a bit pointless discussing it.

But the 18z pushes the cold that bit further north than seems apparent on the UKM and has a snow event for a good part of Ulster and the northwest.

lucernarian

I reckon the 18z GFS has some small amount of potential for Ireland. If it weren't for the fact it was a forecast for 6 days away! It's certainly one to look at.

If I may offer an alternative view to the ones above - this link shows the 850hPa thickness value and I feel it's a more useful predictor of snow/rain probabilities. This is in my experience over the past two years. The 130dam line is key. It's slightly optimistic in general but still gives a better account of what happens on the ground than the 528 dam line which can be either too pessimistic or optimistic depending on source of polar air.

http://expert-images.weatheronline.co.uk/daten/proficharts/en/2012/02/13/basis18/nweu/th85/12022000_1318.gif


Given how the air is firmly Polar Maritime and not Polar Continental (meaning it's mad to even hope for snow in >528dam air), the time away from verification of the forecast, the experience I have with what usually comes from the NW in the line of cold air and the likelihood that a shortwave would run by Ireland and give enough moisture to make it fall as snow and not also sweep the cold away means that I would be confident of snow in central and northern connacht along with inland Ulster. And even then less than 10cm. But those are my own reading of the charts, which will inevitably change. I remember seeing better charts for the Atlantic battle on 30th December 2009 and that ended up as 2 inches of snow for Galway and Roscommon and the rest on hills!

As sponge bob highlighted, the -8 850hPa area will be important.. Extensive modification of the existing airmasses will be guaranteed. Though interestingly it closely follows the 130dam line.

darkman2

Morning all,

UKMO on track with it's snow event. This is a brilliant chart for Ulster, North Leinster and Connaught if you want snow. If you don't it's great for the South. P.S the -8 850hpa line is not important at all in this situation.

Su Campu

darkman2 wrote: »

Don't patronise me.


Su Campu - your not interpreting it correctly IMO. I am astonished you don't see the snow potential on that chart. It is a classic frontal snow situation for Ireland. It's very hard to get anything much more favourable on a synoptic chart. If that came off tomorrow I have to say you would be completely wrong. There is nothing more I can say. Hopefully it's not academic and we see similar output tomorrow is all I will say.

I'm sorry darkman but I don't see the snow potential because it's not there. I've already shown that your forecast of sub-528 dam over the northern half of the country was wrong, and I fail to see where the airmass in place will be cold enough, even allowing for some evaporational cooling. It's a classic frontal precipitation setup alright, but the precipitation in this case will be rain (sleet on higher ground).

Now as i said it may well turn out to snow by then (MT says rain though), but it will NOT snow with the chart posted yesterday! Let's leave it at that.

Regarding 850-1000 thicknesses, 1300 m is not enough. We'd need below 1290 m. And again I warn against using the hirlam thickness charts on weatheronline when it comes nearer the time as they are grossly incorrect (as are the theta-e values).

Sponge Bob

Gfs 06z develops a more propulsive southward push of cold uppers than the last 2 runs did. It may be harder for the Atlantic to push the -8 Isotherm northwards away from Ireland if this pattern is the outcome.

I'll change from close to very close now.

Rebelbrowser

To my uneducated eye the 6z GFS would produce snow for NI and North West on Saturday night. Wouldn't need much to change for rest of us to see some. That said everytime we need a change in the models the change ultimately goes the other way. Also I'm sure someone will show in a minute that that this this is an outlier amongst the 6z ensembles.

See extracts below......

Redsunset

http://matthugo.wordpress.com/2012/02/14/cold-weekend-ahead-thoughts-analysis-18-19th-feb-12/
Above link is Matts thought on how things are shaping up.
I'm skeptical myself at this range but it is an evolving situation and looks like improving to an all snow event for northern regions as the low could dive further. Can go either way.

snowstorm445

Hope we see some snow this Saturday, or at least something cold.

Not sure about the rest of Feb though! I'd say we'll see intermittent cold, but not sustained cold. There isn't much sign of it anyway.

Sponge Bob

redsunset wrote: »

http://matthugo.wordpress.com/2012/02/14/cold-weekend-ahead-thoughts-analysis-18-19th-feb-12/
Above link is Matts thought on how things are shaping up.
I'm skeptical myself at this range but it is an evolving situation and looks like improving to an all snow event for northern regions as thev low could dive further. Can go either way.

What does he see in -5 @ 850 I thought that was a sleet indicator

darkman2

Su Campu we will have to agree to disagree.


We need to keep a really close eye on developments. If you take a UKMO/GFS/GEM blend there is a real risk of a snow event in Ireland towards the end of the weekend or Monday. Nothing is nailed but the signs are there. If the trough maintains a track of taking the center just to the South of Ireland and does not deepen too dramatically then there is a very good chance of snow. If, however, it deepens and tracks further North all bets are off. So far the model not playing the ball is the ECM. Be interesting to see how that developes later. The signs are there and it's right to be aware of it but not go mad and exaggerate at the same time as it's still 5 or 6 days away.

So in summary turning much colder with wintry showers, inc snow showers, in the West and North on Friday continuing over the weekend. Frost and ice becoming widespread. Then toward the end of the weekend a risk of a period of frontal snow for some parts of the country.

Rebelbrowser

darkman2 wrote: »

Su Campu we will have to agree to disagree.


We need to keep a really close eye on developments. If you take a UKMO/GFS/GEM blend there is a real risk of a snow event in Ireland towards the end of the weekend or Monday. Nothing is nailed but the signs are there. If the trough maintains a track of taking the center just to the South of Ireland and does not deepen too dramatically then there is a very good chance of snow. If, however, it deepens and tracks further North all bets are off. So far the model not playing the ball is the ECM. Be interesting to see how that developes later. The signs are there and it's right to be aware of it but not go mad and exaggerate at the same time as it's still 5 or 6 days away.

So in summary turning much colder with wintry showers, inc snow showers, in the West and North on Friday continuing over the weekend. Frost and ice becoming widespread. Then toward the end of the weekend a risk of a period of frontal snow for some parts of the country.

GFS at 12z is an upgrade again in terms of temps and thickness on Sat night / Sun morning but not sure how much precipitation is around. Most of the country under -8's and sub 528 DAM. UKMO not as good but not too far away either.

Su Campu

It looks like darkman's famous chart will not materialise now anyway so he will get away with his error in thicknesses! :P

For me it's looking like some wintry showers in the northern and northeastern parts of the country for a time during Saturday, but it's a fast-moving trough and will be moving quickly to the east as the high builds in from the west, putting a dampener on the activity of showers. Still some disagreement between the models regarding exactly how far the cold air will reach, with the GFS up to its usual antics. We could see some snow showers at all levels in the north Saturday, but still too early for any detail. A cold night Saturday night, though, with a harsh frost looking likely.

My forecast for the rest of the month still remains unchanged, with a positive NAO and Atlantic systems becoming more frequent during the last decade. We may see the odd brief flirt with cold like this weekend's but overall I would say average to slightly above average temperatures, around average to slightly below average precipitation.

darkman2

No errors in any charts I have been looking at. Don't know what charts you have been looking at.

Slight upgrade in the short term in terms of snow showers and a generally colder couple of days. We have lost the potential more significant snow from the models on Monday this afternoon so a downgrade from that point of view.

Won't only be the North having snow showers (allbeit lighter) at all levels btw;)

Su Campu

It wasn't the chart that was wrong, it was your interpretation of the thicknesses on it, which you don't seem to accept.

darkman2

Su Campu wrote: »

It wasn't the chart that was wrong, it was your interpretation of the thicknesses on it, which you don't seem to accept.

I don't accept that. You have to use a bit of intuition aswell. I saw that chart and my eyes lit up like a Christmas tree (well, not really but you know what I mean) whereas you go straight to the thickness values which are not all that relevant in that situation. I don't really want to go back over this because it's probably not going to happen now anyway but where it a situation where a cold front was moving south with cold air rushing in behind then there is more validity to your obsession with thickness values. In the case highlighted it's a warm front moving into a cold air mass. There is always an element of compensation for some criteria that may be marginal in a situation like that. That's where I differ with you on that. But we won't know because it probably ain't gonna happen now.

Su Campu

darkman2 wrote: »

I don't accept that. You have to use a bit of intuition aswell. I saw that chart and my eyes lit up like a Christmas tree (well, not really but you know what I mean) whereas you go straight to the thickness values which are not all that relevant in that situation. I don't really want to go back over this because it's probably not going to happen now anyway but where it a situation where a cold front was moving south with cold air rushing in behind then there is more validity to your obsession with thickness values. In the case highlighted it's a warm front moving into a cold air mass. There is always an element of compensation for some criteria that may be marginal in a situation like that. That's where I differ with you on that. But we won't know because it probably ain't gonna happen now.

But you didn't say it was marginal, you said a certain classic snow event if it came off, and said there were sub-528 over the northern half of the country when in fact there were not. And you still don't accept that.

Anyway, this is hijacking the thread.

Sponge Bob

That was fun but the 18z has arrived.

Model shows a waft of -8 over the country Sunday but not for the first time this winter I must ask...where is that pesky Moisture when the cold is around???? Not that different from the 12z I must say.

Over to Darkman.

Nabber

A case of snow today gone tomorrow.
Febuary has been great for potential that never was. This one is still 120hrs away, any one have the stats on accuracy this winter on cold for ireland on the models past 72hrs? 120 has been all but consistently wrong on predicting cold for Ireland


GFS 120hrs

lucernarian

Su Campu wrote: »

Regarding 850-1000 thicknesses, 1300 m is not enough. We'd need below 1290 m. And again I warn against using the hirlam thickness charts on weatheronline when it comes nearer the time as they are grossly incorrect (as are the theta-e values).

Although they were empirical observations, 130dm is the crucial number when I've looked at potential rain/snow situations. E.g. the December 2009 event. I can accept there's differences in the airmasses involved but certainly, 130dm has brought snow in the past. Whether it sticks to the ground or not is another matter:p

I'm not sure if the hirlam comment was for me but I don't really use that model. NAE and GFS are my preferred ones for short term modelling.