Cold Spell Late Feb/ Early March Technical Discussion only MOD NOTE POST #1

Gaoth Laidir

Tuesday 12Z FAX, showing the cold front dissipating over Ireland. Showery trough getting into the east of the UK, followed by the 510 dam thickness line. Convergence line near the Channel Islands. Look at the strength of that Scandi high, 1055 hPa.

JCX BXC

SeaBreezes wrote: »

There is the fact the snow shield may force freezing rain that day instead. Cause we don't have enough adjectives to describe rain in cork yet obviously.

Previous to that rain thered be several hours of heavy snow, that chart is when the system moves up. That's why I'm not convinced that there'll be as much rain as it's forecasting as the temperatures will be very low.

Kermit.de.frog

And without further ado the fax chart for Wednesday



Sub 510 DAM and an active Irish sea.

Gaoth Laidir

Friday's low is just forming off the coast of New Foundland tonight and will rapidly deepen and move southeastwards over the next few days, cutting off and slowly meandering eastwards over the Azores Monday and Tuesday. By Wednesday it starts to fill and expand northeastwards, interacting with the coldest pool of easterly flow over NW Europe. It's this interaction that's still unresolved, so expect a few more model runs to iron out the details and see how the low forms south of New Foundland. In general, models tend to want to let cut-off lows rejoin the flow too early, so it could happen that in reality it will remain further south and catch the easterly flow later, meaning it would arrive here later or further east.

Soccarboy11

GEFS Ensamble looking better so hopefully

Gremlin

I would imagine that the models are not used to dealing with SSW and the associated complications that causes. So I think there might well be a wide margin for error this far out.

Gremlin

The other outcome, I can see is if the blocking high doesn't give up too easily, then the low could track northwards much farther west.

nacho libre

JCX BXC wrote: »

If that low stays about I'd be very concerned for the country as a whole, it will drop significant snowfall and I'm not convinced that it will turn to rain as the GFS suggests. It would be a crippling amount of snowfall.

The system in March 2013 was progged to come further north, but ended up further south and dumped a huge amount of snow in the channels island instead. With this in mind I'll be very surprised if the GFS is correct here. The low is riding on the jet stream but can't come that far north in my opinion. The GFS is notorious for being too progressive in these situations by underestimating the strength of blocks and just how hard they are to shift.

Donegal Storm

Yeah a small low pressure system like that won't be modelled correctly this far out, no point looking at run to run details. Give it to Wednesday I'd say before we have a good idea of how it'll behave


Also, nice to see you back Snowbie, this event seems to be getting everyone out of the woodwork

ninebeanrows

EC plumes show wide spread from Friday, still most supported cluster stays cold , 40% of eps members

highdef

nacho libre wrote: »

The system in March 2013 was progged to come further north, but ended up further south and dumped a huge amount of snow in the channels island instead. With this in mind I'll be very surprised if the GFS is correct here. The low is riding on the jet stream but can't come that far north in my opinion. The GFS is notorious for being to progressive in these situations by underestimating the strength of blocks and just how hard they are to shift.

Was this a different system that dumped massive amounts of snow to Ulster? You're mentioning the snow only got to the Channel Islands, hence my confusion.

Donegal Storm

Yeah the Channel Islands blizzard was on the 11th of March, delivered snow to large parts of the UK and Ireland though the main area of cold air was dragged down through the English Channel





Ulster blizzard was on the 22nd and 23rd, plenty of snow right across northern Ulster though the Antrim hills worst affected with snow lasting well into April






Nothing remotely close to that forecast in the semi-reliable timeframe this coming week, next Friday has potential but far to early to pin down details

Kermit.de.frog

ICON 00z, sub -16c 850 hpa temperatures not far off the southeast heading in to Thursday.



ICON also goes for pretty much the ideal outcome. The milder air does not advance to us at the end of the week. Heavy snow in the south and southeast.

ThaitaniumM

Kermit.de.frog wrote: »

ICON 00z, sub -16c 850 hpa temperatures not far off the southeast heading in to Thursday.

ICON also goes for pretty much the ideal outcome. The milder air does not advance to us at the end of the week. Heavy snow in the south and southeast.

ICON, the hero again!

Kermit.de.frog

GFS conducts the mild v cold battle over Ireland on Friday. A proper snow event. The mild air does get in eventually.





Some resolution here to come yet.

M.T. Cranium

GFS through 138h is marginally south with the Biscay low, it's having trouble reaching Ireland on this run although very close to Wexford. Verbatim would be pushing rain-snow line into south at low elevations, same up parts of east coast, but snow would hold on inland and north.

From there to 156h, low oozes north across Ireland, would not be bringing much mild air with it but verbatim would change over to cold rain in most places at some point. Biggest difference is that trailing second low is a lot weaker on this run.

GEM brings the Biscay low north at about 12W and loops it away from Ireland, still has the same result as GFS however, mild air slowly invading 2nd to 4th.

This is clearly a battleground scenario that is just in its opening phases and actual outcome may not be really sensed until 27th or 28th.

snowstorm445

Snow depths by midday Friday, before the thaw. :eek:

kod87

snowstorm445 wrote: »

Snow depths by midday Friday, before the thaw. :eek:

Not very impressive it has to be said (only a couple of cm for lowland dublin region), but i don't normally pay much heed to snow accumulation charts.

snowstorm445

kod87 wrote: »

Not very impressive it has to be said, but i don't normally pay much heed to snow accumulation cahrts

You’re right, still was more surprised by the fact that the whole country seems to get a covering briefly before a thaw sets in.

ThaitaniumM

GFS 00Z has it progged more southerly albeit very slightly, the next runs will be interesting how it all plays out

kod87

GFS has it all over by saturday morning, any precipitation will be rain by then, disapointing considering that this time yesterday the models were showing a more prolonged cold spell. If the GFS is correct (a big if) then this will be short and sweet.

Kermit.de.frog

UKMO going all out snow event

nacho libre

kod87 wrote: »

Not very impressive it has to be said, but i don't normally pay much heed to snow accumulation cahrts

Neither do i- especially when streamers are involved. Places like Norfolk and parts of Kent could see 15- 20 cm by the end of the week due to them. Maybe parts of Ireland too;)

patneve2

Time to start looking at next week more closely. Late Tuesday/Wednesday holds enormous potential for the E Coast. -12 to -15 uppers, long ENE fetch and most importantly the wind doesn't look excessively strong. If current charts were to verify I should get my 10cm on Wednesday, with larger amounts about 10 to 30 km inland. Snowfall occurring at a temp of -2 at times. Thursday doesn't look as favourable due to a stronger wind, but this might change. Not even thinking about the Friday low yet.

Kermit.de.frog

The temperatures in the Irish sea on Wednesday night.

Kermit.de.frog

patneve2 wrote: »

Thursday doesn't look as favourable due to a stronger wind, but this might change. Not even thinking about the Friday low yet.

Why do you think that?

If the Irish sea temperatures were 4 or 5c maybe.

Not so.



The wind could be the same speed as on Neptune and anything that comes off the Irish sea would be snow.

patneve2

Kermit.de.frog wrote: »

Why do you think that?

If the Irish sea temperatures were 4 or 5c maybe.

Not so.



The wind could be the same speed as on Neptune and anything that comes off the Irish sea would be snow.

I agree, it would snow at -200 meters with these uppers. What I am trying to say is that at times a very strong wind isn't good for convection. Showers find it hard to form over sea and tend to blow over quickly. The north easterly with -13 uppers in 2013 is an example of this...and yes obviously that was a much smaller event. I may be completely wrong about this and anyways in any case we are going to get plastered over the next few days. Major major event incoming.

M.T. Cranium

With the stronger winds though you could have double streamer action that starts in the North Sea, partially unloads across a narrow part of northern England then enters the Irish Sea ready to reload, moderate to strong winds are not known to be a hindrance to lake effect snowfall but just organize the streamers into narrower bands sometimes.

I agree the pre-Friday period has lots of potential and then it seems almost 50-50 that snow on Thursday night into Friday morning could hold on against this first mild wave. I think we all know this spell will likely break down either this way or through some sort of long slow relaxation of the block (2013 never really broke down if I recall, it just slowly transitioned to average through April).

Anyway, lots of questions for the "king" to address at 0600-0700h. Arpege has gone its full 102h and only brought the low to northwest Spain with no real indications of a northward trend, looks more like it's heading for France on the last two panels.

M.T. Cranium

It strikes me that a solution not shown on any particular model but which could be a weighted average would be a tight loop of this low south of Ireland around 50 N and then for it to head east into the Channel. That could be a best case scenario for snowfall (or worst case scenario for snowfall impacts).

Worth noting -- good streamer formation over Baltic Sea in parcel of air mass roughly equivalent to Tuesday Irish Sea, streamers are nearly continuous and making plenty of progress inland in northern Germany tonight.

Kermit.de.frog

M.T. Cranium wrote: »

With the stronger winds though you could have double streamer action that starts in the North Sea, partially unloads across a narrow part of northern England then enters the Irish Sea ready to reload, moderate to strong winds are not known to be a hindrance to lake effect snowfall but just organize the streamers into narrower bands sometimes.

I agree the pre-Friday period has lots of potential and then it seems almost 50-50 that snow on Thursday night into Friday morning could hold on against this first mild wave. I think we all know this spell will likely break down either this way or through some sort of long slow relaxation of the block (2013 never really broke down if I recall, it just slowly transitioned to average through April).

Anyway, lots of questions for the "king" to address at 0600-0700h. Arpege has gone its full 102h and only brought the low to northwest Spain with no real indications of a northward trend, looks more like it's heading for France on the last two panels.

Going for some decent shower activity off the Irish sea too

Kermit.de.frog

GFS control run has up to 36 hours of continuous snowfall pretty much nationwide away from south facing coasts on Thursday night and Friday/night.

M.T. Cranium

We are writing an exam that only nature can grade, and the only reward for passing is to write another one.

igCorcaigh

Kermit.de.frog wrote: »

GFS control run has up to 36 hours of continuous snowfall pretty much nationwide away from south facing coasts on Thursday night and Friday/night.

Kermit, can I please ask you, from that same GFS run, how long before than snowfall turns to rain? I'm thinking of the southern counties; are we looking at a slushy mess or a more gradual thaw?

Strictly a literal interpretation of this run that is, not a projection.

Kermit.de.frog

igCorcaigh wrote: »

Kermit, can I please ask you, from that same GFS run, how long before than snowfall turns to rain? I'm thinking of the southern counties; are we looking at a slushy mess or a more gradual thaw?

Strictly a literal interpretation of this run that is, not a projection.

The operational GFS run currently would give quite a few hours of heavy snowfall to southern coastal counties on Friday but is progged to turn back to rain here briefly before the main band of snow moves north.

Rain follows for Saturday night.


That's the shortest interpretation for your location. All subject to change.

kod87

The ECM brings the low pressure right over the country at 144 hrs but crucially the uppers remain at -4 to -6, cold air winning that battle

Kermit.de.frog

ECM has, what seems to me, to be a major snow event for the end of the week. Similar to UKMO and better than GFS in that respect.

To paraphrase - "the kettle is on the boil"

kod87

I like the ECM run for next weekend, lots and lots of potential

M.T. Cranium

All of these solutions can only be taken as approximate at this point, but the ECM scenario looks like a prolonged snow event that just tapers off to drizzle and near freezing temperatures rather than a heavy rain and thaw.

munsterlegend

M.T. Cranium wrote: »

All of these solutions can only be taken as approximate at this point, but the ECM scenario looks like a prolonged snow event that just tapers off to drizzle and near freezing temperatures rather than a heavy rain and thaw.

Does that not tie in with Met office uk thinking as well?

Villain

ECMWF OP on milder side

JCX BXC

kod87 wrote: »

GFS has it all over by saturday morning, any precipitation will be rain by then, disapointing considering that this time yesterday the models were showing a more prolonged cold spell. If the GFS is correct (a big if) then this will be short and sweet.

Not completely, has another reload with another countrywide band of snow Wednesday week.

Artane2002

This is what the ICON 06Z is showing for Friday.

downwiththatsor

Artane2002 wrote: »

This is what the ICON 06Z is showing for Friday. Credit to radiohead on Netweather. Sorry about the link, I'm not sure how to post the picture directly on phone

ThaitaniumM

GFS 06Z just rolling out now. It seems we have slightly cooler uppers and hint of that low just a slight fraction to the E. Also a reload of the cold into FI too.

Artane2002

Looks like the low is further southeast on the GFS 06Z.

dacogawa

Looking at the GFS if there is some sort of thaw from that low that could push up on Friday/Saturday there could be another issue with the very high Spring Tide (4.51m in Dublin on Sat, Friday 4.48m) and winds.

Very unlikely but I've said before it would just take 3 things timed together to turn Grand Canal Dock into Venice (spring tide, big low & lots of rain before) I've seen it over the edge of the Liffey with less going on.

Something worth keeping in mind, we don't need a big thaw and a spring tide at the same time...



I still don't trust the GFS above the ECM so probably nothing to see here

JCX BXC

Current GFS would be a very slow thaw if anything, although how much will a foot of snow thaw in a temperature of 1c

JanuarySnowstor

dacogawa wrote: »

Looking at the GFS if there is some sort of thaw from that low that could push up on Friday/Saturday there could be another issue with the very high Spring Tide (4.51m in Dublin on Sat, Friday 4.48m) and winds.

Very unlikely but I've said before it would just take 3 things timed together to turn Grand Canal Dock into Venice (spring tide, big low & lots of rain before) I've seen it over the edge of the Liffey with less going on.

Something worth keeping in mind, we don't need a big thaw and a spring tide at the same time...



I still don't trust the GFS above the ECM so probably nothing to see here

Glad you mentioned this.
Cork always suffers with high tide and Easterly winds. Could become a secondary issue

Artane2002

Here is what is shown for Saturday morning by the GFS 06Z. Correct me if I'm wrong but this looks like an all snow event in Ireland to me? The South is in -4c uppers while the far north has -6c uppers.

LEIN

Artane2002 wrote: »

Here is what is shown for Saturday morning by the GFS 06Z. Correct me if I'm wrong but this looks like an all snow event in Ireland to me?

Hopefully, it will not drag air up from the med or it cloud be curtains for some.