Cold Spell - Feb 7th to 13th 2021 - Technical Discussion

Danno

Technical Discussion for the current spell of cold with potential for snow...

Any non-technical chat can be posted here: https://www.boards.ie/vbulletin/showthread.php?t=2058155857

Apologies for locking the wrong thread for a few moments, a big oops!

The Up to 120hrs Thread has been locked.

Rebelbrowser

The Euro 04 precipitation charts for the next 48 hours make no sense. Showers coming from the east but it seems skipping over the east and south coasts and causing accumulations inland in the likes of Kerry and Galway. Current model run is at https://www.weatheronline.co.uk/cgi-bin/expertcharts?LANG=en&MENU=0000000000&CONT=ukuk&MODELL=euro4-high&MODELLTYP=1&BASE=-&VAR=prty&HH=12&ZOOM=0&WMO=&ARCHIV=0&LOOP=1&RES=0

Gonzo

tonights GFS 18z is turning out to be very much a mild outlier from the 12th. Most members keeping it cold. The mean shows an even smaller mild blip compared to the 12z.



Thursday into Friday is now looking rather snowy across all the country except for coastal parts of the far south-west.

Gaoth Laidir

Cloud has really broken up overnight but cloud top heights have not increased at all. Soundings from the UK show them ranging from 850 - 750 hPa. Watching for any signs of increases during the day.

Gaoth Laidir

Nottingham sounding from 06Z.

Villain

HARMONIE showing some more shower activity tomorrow:

https://twitter.com/MetEireann/status/1358675740590567425?s=20

Rebelbrowser

Gonzo wrote: »

tonights GFS 18z is turning out to be very much a mild outlier from the 12th. Most members keeping it cold. The mean shows an even smaller mild blip compared to the 12z.

Thursday into Friday is now looking rather snowy across all the country except for coastal parts of the south west]

For us south coasters to cling to, I see the GEM has Thursdays front stalling over the southern half and retreating. Very different outcome if that happened!

munsterlegend

Rebelbrowser wrote: »

For us south coasters to cling to, I see the GEM has Thursdays front stalling over the southern half and retreating. Very different outcome if that happened!

Yep ECM looking quite snowy for a while down here as well..

Villain

Met Eireann update on Morning Ireland:

Monday to Wednesday showery setup, mainly in East, 1-2cms in Ulster and Leinster, tomorrow more widespread with 1-2cms anywhere most likely in Leinster. Thursday could see significant snowfall and significant accumulations, looking at up to 5cm widely. Milder weather from Friday so snowfall Thursday may not stick around.

Kermit.de.frog

GFS has two snow events - one on Thursday/Friday and the other Sunday/Monday...

Gaoth Laidir

Met.ie Harmonie shows a very broken band of precip over the country Thursday.

https://www.met.ie/

Rebelbrowser

Gaoth Laidir wrote: »

Met.ie Harmonie shows a very broken band of precip over the country Thursday.

https://www.met.ie/

That would tally with the 5cm Villain says was referenced on Morning Ireland. You'd expect more from an intact front surely?

nacho libre

Rebelbrowser wrote: »

That would tally with the 5cm Villain says was referenced on Morning Ireland. You'd expect more from an intact front surely?

Yes you would. Is 5 cm considered significant by them? Surely the ground will be cold enough inland for the snow to stick from the get go. I would prefer this Harmonie scenario even if it means we only get a modest covering before it all fizzles out. Rather than a quick snow to rain event.

Donegal Ken

Gaoth Laidir wrote: »

Met.ie Harmonie shows a very broken band of precip over the country Thursday.

https://www.met.ie/

That timeframe for Thursday is the output from the ECMWF model. Harmonie only runs up until 12:00hrs Wednesday 54hrs. If you look at the bottom right you will see this.

arctictree

Latest GFS has snow all day Thursday and into Friday for east. Total amounts seem to be fairly light though for a frontal event. Sunday/Monday seems to be the one to watch, not out yet though as I type...

Reckless Abandonment

arctictree wrote: »

Latest GFS has snow all day Thursday and into Friday for east. Total amounts seem to be fairly light though for a frontal event. Sunday/Monday seems to be the one to watch, not out yet though as I type...

It looks snowy on Saturday too.

Reckless Abandonment

Reckless Abandonment wrote: »

It looks snowy on Saturday too.

Friday morning very snowy in SE Wicklow and north wexford



Saturday 6pm after a lull back at it with Gusto :eek:
If these two were to verify,that would be a fair pile of snow in South Leinster

bazlers

The energy will more than likely get zapped (very techical term) out of that front as it moves across the country rubbing shoulders with that high.

Davaeo09

bazlers wrote: »

The energy will more than likely get zapped (very techical term) out of that front as it moves across the country rubbing shoulders with that high.

and the counties that happens over are in for a treat

piplip87

I see GFS precipitation type chart makes multiple attempts of fronts coming up from the south from Thursday. Northern half of the country looks like just snow until it the rain finally comes on Tuesday.

If that where to verify thay could mean rather disruptive snow from the Dublin to Galway line and above. Cavan,Monaghan North Meath look like the sweet spots here.

Whooohoooo my first post commenting on charts lol

Kermit.de.frog

bazlers wrote: »

The energy will more than likely get zapped (very techical term) out of that front as it moves across the country rubbing shoulders with that high.

Under pressure alight but if it does it mean colder air has won out and probably another front with snow risk following behind.

Kermit.de.frog

TheMilkyPirate

That would be a fair dumping for the south/East

Danno

TheMilkyPirate wrote: »

That would be a fair dumping for the south/East

Excellent setup for keeping the cold locked in for another front, with the snow fields keeping the air frigid as it comes up from the southeast.

nacho libre

Yes, if the front on Thursday has too much oomph, it could mean a quicker transition to rain. The best case scenario as has been mentioned is for it slowly to run out of juice. From an imby perspective, I just wish it was all a bit further west. Still if the cold air does win out there maybe further opportunities over the weekend.

Rebelbrowser

TheMilkyPirate wrote: »

That would be a fair dumping for the south/East

If this trend this morning continues, by Thursday I'm not sure we will even see rain down here in Cork..... Up til two days ago this was an all rain affair in Cork on the models, then it was a few hours snow followed by lots of rain. Now that's flipped completely. In fairness, all tallies with Met E's attitude as far back as late last week. Its almost as if the professional meteorologists knew better than us keyboard warriors (with the obvious exceptions to that description!)

Villain

The Met Eireann meteorologist commentary has been updated:

https://www.met.ie/forecasts/meteorologists-commentary

Shower risk:


Thursday into Friday:

nacho libre

Rebelbrowser wrote: »

If this trend this morning continues, by Thursday I'm not sure we will even see rain down here in Cork..... Up til two days ago this was an all rain affair in Cork on the models, then it was a few hours snow followed by lots of rain. Now that's flipped completely. In fairness, all tallies with Met E's attitude as far back as late last week. Its almost as if the professional meteorologists knew better than us keyboard warriors (with the obvious exceptions to that description!)

As Auntysnow mentioned previously they have access to data we don't see. The Chief forecaster seemed confident something would happen on Thursday, but obviously would not commit to anything until she had to. I imagine Met Eireann also share data with the UKMO. Bear it mind it was mogreps (UKMO'S own model) ,afterall, that indicated that this cold period would be extended, and that the other models would start to back that scenario. It now looks like that will happen.

Rebelbrowser

Very interesting Met E update indeed. Their take on Thurs / Fri as of now is "...current projections indicate a spell of sleet and snow spreading north-eastwards over Ireland on Thursday and into Friday bringing accumulations of snow to many areas. However, the snow may transition to rain in some southern and western parts as milder air attempts to move in from the Atlantic...". The word "may" in the final sentence is a big change and has me very interested in the end of the week all of a sudden....

Danno

Rebelbrowser wrote: »

Very interesting Met E update indeed. Their take on Thurs / Fri as of now is "...current projections indicate a spell of sleet and snow spreading north-eastwards over Ireland on Thursday and into Friday bringing accumulations of snow to many areas. However, the snow may transition to rain in some southern and western parts as milder air attempts to move in from the Atlantic...". The word "may" in the final sentence is a big change and has me very interested in the end of the week all of a sudden....

Updated by Matthew Martin on 08/02/2021

Our old friend Weathercheck has clearly been browsing this forum recently!

Quite an upbeat read and very well written. I do wonder if the first front stalls/fizzles out before getting over to the east?

snowgal

Danno wrote: »

Updated by Matthew Martin on 08/02/2021

Our old friend Weathercheck has clearly been browsing this forum recently!

Quite an upbeat read and very well written. I do wonder if the first front stalls/fizzles out before getting over to the east?

yes thats my concern too. It may change before Thursday and the East may not actually get the front at all...

nacho libre

Well, i hope our old friend Weathercheck is right with the "may" and that the transition would be in parts of the west and south, rather than all of the west and south.


I certainly don't relish it being 3 or 4 degrees with cold rain on Thursday night. I'd sooner it all fizzled out in that case.

Gaoth Laidir

Cloudtops are still low over the UK, showing at around 2900 m at Albermarle 12Z sounding. Still that very strong 700 hPa inversion. Steering flow there roughly ESE. Snow depth at that station is 3 cm, but fairly respectable 20 cm in SE England from that frontal event and 28 cm at Aboyne, Scotland.

Rebelbrowser

Big difference in DPs from North East to South West

D9Male

I am intrigued with Thursday -> Friday event. If the front is struggling to make its way up from the south west, I suspect that will compound the rain shadow effect on Dublin city from the Dublin mountains. Or do I have that wrong?

snowgal

yes thats my understanding too, hence the East actually might not fair well at all.....but it seems to be knife edge situation..

Steopo

nacho libre wrote: »

As Auntysnow mentioned previously they have access to data we don't see. The Chief forecaster seemed confident something would happen on Thursday, but obviously would not commit to anything until she had to. I imagine Met Eireann also share data with the UKMO. Bear it mind it was mogreps (UKMO'S own model) ,afterall, that indicated that this cold period would be extended, and that the other models would start to back that scenario. It now looks like that will happen.

Be interested to know if they do. Know they’ve collaborated with UK on storm names & weather observations (wow.met.ie) but have never indicated they use UKMO model for forecasting. Public info indicates they use HIRLAM for short term & ECM for forecasts up to 10days with obviously professional versions of those & advanced visualisation (met.ie/science/forecasting-centre www.iblsoft.com ). ECM has consistently indicated a snow event on Thurs since MetE mentioned the risk so would have thought that’s where they’ve picked it up?

nacho libre

Steopo wrote: »

Be interested to know if they do. Know they’ve collaborated with UK on storm names & weather observations (wow.met.ie) but have never indicated they use UKMO model for forecasting. Public info indicates they use HIRLAM for short term & ECM for forecasts up to 10days with obviously professional versions of those & advanced visualisation (met.ie/science/forecasting-centre www.iblsoft.com ). ECM has consistently indicated a snow event on Thurs since MetE mentioned the risk so would have thought that’s where they’ve picked it up?

I could imagine a scenario whereby the UKMO would share model info' with them for potentially impactful events for Ireland the UK, but they don't rely on the UKMO for guidance, as you say they use the ECM and Hirlam for that.

Oneiric 3

ECM 6z struggles to bring the 'snow line' below (Edit: actually above) 200m away from very SW during Thursday.



Any potential snowfall from this front looks light to moderate at best and on this run at least, it struggles to make it into Ulster.

munsterlegend

Oneiric 3 wrote: »

ECM 6z struggles to bring the 'snow line' below 200m away from very SW during Thursday.



Any potential snowfall from this front looks light to moderate at best and on this run at least, it struggles to make it into Ulster.

It’s always looks promising until the models get a firmer grip of the higher uppers coming in with an Atlantic front. I am expecting a sleety mess in most of Cork except very high ground as that what happens 9/10.

Oneiric 3

munsterlegend wrote: »

It’s always looks promising until the models get a firmer grip of the higher uppers coming in with an Atlantic front. I am expecting a sleety mess in most of Cork except very high ground as that what happens 9/10.

I agree. This is all just speculation for now and no doubt models will chop and change big time up till (and during) Thursday. Would instinctively expect a ****ty sleety transition here at best as well. Nacho and those further north of here tend to do better in these set ups by and large.

nacho libre

Oneiric 3 wrote: »

I agree. This is all just speculation for now and no doubt models will chop and change big time up till (and during) Thursday. Would instinctively expect a ****ty sleety transition here at best as well. Nacho and those further north of here tend to do better in these set ups by and large.

Well yes, its subject to change, but if it were to pan out as the current Met Eireann guidance suggests, i would sooner it decays before reaching here. I love snow, but a quick transition to several hours of cold rain, no thanks. Nacho in refusing snow shocker:eek:

Calibos

Does that chart mean its game over for decent snow on Thursday even further north and east for the Wexford to Galway line?

TheMilkyPirate

GFS better than ICON keeping the front intact over much of the country. Turning to rain in the south west.





Second front on Saturday and has it snowing until Valentines day in the inland south east. Large pinch of salt needed with that at this stage.

Longing

GFS Saturday and Sunday looks fun.

Donegal Ken

Calibos wrote: »

Does that chart mean its game over for decent snow on Thursday even further north and east for the Wexford to Galway line?

No it doesn't mean game over. There still is good potential for some areas to see snow on Thursday into Friday. Long time between now and Thursday.

arctictree

Christ almighty the latest GFS has pretty much constant snow for Leinster from Thursday to Sunday. The Atlantic just not getting through with each push.

squarecircles

if that transpired that would almost be a red alert for Leinster.
72 hours of continuous snowfall.

Gonzo

latest charts are looking very snowy for Leinster over the weekend. If these chart verify some places could be in trouble. Very unlikely to verify but teh GFS 12z is predicting between 18 and 80cm of snow in Leinster by Monday. (30 to 80cm more for the wicklow mountains)



But a huge pinch of salt to bear in mind as the fronts may break up on their way to Leinster depending on how well the cold block remains. On the other hand the Atlantic and it's warmer uppers could make this all very marginal. However right now it looks some parts of Leinster could be in for serious dumpings of snow over the weekend.

TonyMaloney

The Icon sees it as a pretty marginal event for most

Cloudio9

squarecircles wrote: »

if that transpired that would almost be a red alert for Leinster.
72 hours of continuous snowfall.

No six nations match on Sunday then.