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

Gaoth Laidir · 11-02-2021 6:14pm

greenpilot wrote: »

Nope. Sitting here near Knock. Raining. No snow I'm afraid.

Really? Are you up near the airport? Currently air and dewpoint -0/-4.

PsMETAR KNOC 111700Z AUTO 13019G38KT //// // ////// M00/M04 1017 MSL=

greenpilot · 11-02-2021 6:17pm

Gaoth Laidir wrote: »

Really? Are you up near the airport? Currently air and dewpoint -0/-4.

PsMETAR KNOC 111700Z AUTO 13019G38KT //// // ////// M00/M04 1017 MSL=

I'm about 1km from the airport, on the Kilkelly side. Precipitation varying now between misty rain and an odd, tiny snow flake.. I'll drive up to EIKN in a sec

Lip Out · 11-02-2021 6:23pm

This chart posted earlier today shows a reinvigoration of precipitation later tonight for the south east. Is it just a howler or still in prospect?

https://twitter.com/MetEireann/status/1359761421752533000?s=20

11-02-2021 6:30pm

Lip Out wrote: »

This chart posted earlier today shows a reinvigoration of precipitation later tonight for the south east. Is it just a howler or still in prospect?

https://twitter.com/MetEireann/status/1359761421752533000?s=20

I'd say it will be completely wrong for the southeast as it was last night
Attached radar image has no precipitation at all I'm under it and can confirm that

lucernarian · 11-02-2021 6:30pm

I'd consider reports of rain/sleet 1km near Knock to be a fairly bad sign tbh for low level and coastal locations anywhere as this event continues.

Gonzo · 11-02-2021 6:41pm

latest GFS 12z is a downgrade for snow in the greater Dublin region, the snow shadow now even bigger than on previous runs. At this stage i'm expecting not much more than flakes in the air based on current model.

51-780UK.GIF?11-12

Once the mild air moves in we do get all the rain of course.

Icon very similar

Arpege has the front making it across on Saturday but it turns to rain over Dublin and the commuter belt.

arpegeuk-1-44-0.png?11-17

esposito · 11-02-2021 6:42pm

Gonzo wrote: »

latest GFS 12z is a downgrade for snow in the greater Dublin region, the snow shadow now even bigger than on previous runs. At this stage i'm expecting not much more than flakes in the air based on current model.

Once the mild air moves in we do get all the rain of course.

Icon very similar

Arpege has the front making it across on Saturday but it turns to rain over Dublin and the commuter belt.

What a joke this is. So hard to get decent snow in the east. I want one more cold blast before mid March with decent snow showers piling in.

Gonzo · 11-02-2021 6:45pm

esposito wrote: »

What a joke this is. So hard to get decent snow in the east. I want one more cold blast before mid March

This is rough stuff indeed, we got dealt the worst summer in all of Europe during 2020 and now it looks like this final chance of snow has a high probability of being a bust too.

We just have to hope the models have got this wrong, but based on today I wouldn't be surprised if this is correct. Hope i'm wrong but these models are far from inspiring.

11-02-2021 6:53pm

Gonzo wrote: »

This is rough stuff indeed, we got dealt the worst summer in all of Europe during 2020 and now it looks like this final chance of snow has a high probability of being a bust too.

We just have to hope the models have got this wrong, but based on today I wouldn't be surprised if this is correct. Hope i'm wrong but these models are far from inspiring.

I'm seeing Spanish friends in a Swiss ski resort in my insta feed having driven there from Madrid...its not helping!
If its any consolation those same models has tonnes of snow this evening in wickliw and wexford
12 hours of it
They were wrong
OK only supposed to start at 80m but not a hope of it
There should be a model tribunal

compsys · 11-02-2021 6:55pm

The irony that during an easterly it's the north, south and west that ends up with all the snow.

Billcarson · 11-02-2021 6:58pm

AuntySnow wrote: »

I'm seeing Spanish friends in a Swiss ski resort in my insta feed having driven there from Madrid...its not helping!
If its any consolation those same models has tonnes of snow this evening in wickliw and wexford
12 hours of it
They were wrong
OK only supposed to start at 80m but not a hope of it
There should be a model tribunal

And a cold spell tribunal. Wtf went so wrong this week?
Heights over Scandinavia not strong enough. ?
In future I will only really get sucked in when the heights are yellow on the charts not green .

Artane2002 · 11-02-2021 7:01pm

Billcarson wrote: »

And a cold spell tribunal. Wtf went so wrong this week?
Heights over Scandinavia not strong enough. ?
In future I will only really get sucked in when the heights are yellow on the charts not green .

the two main issues were that heights over us weren't low enough and thicknesses were too high.

greenpilot · 11-02-2021 7:01pm

lucernarian wrote: »

I'd consider reports of rain/sleet 1km near Knock to be a fairly bad sign tbh for low level and coastal locations anywhere as this event continues.

I took this just 40 mins ago. Passing the end of the runway. No snow at knock, despite reports.

Billcarson · 11-02-2021 7:05pm

Artane2002 wrote: »

the two main issues were that heights over us weren't low enough and thicknesses were too high.

I did think the fax charts from the uk met office looked strange given the wind from the east and the 528 dam line only partially over the country a number of days ago.

Brz555 · 11-02-2021 7:18pm

Ramping up in galway city again

Squidvicious · 11-02-2021 7:23pm

Billcarson wrote: »

I did think the fax charts from the uk met office looked strange given the wind from the east and the 528 dam line only partially over the country a number of days ago.

That's always been my rule of thumb for snow. If you're not on the right side of the 528 dam line, you won't generally get snow. I know that there are other factors and you may not get it even if you are on the right side, but it's a very good guide. That said, today, the biggest problem for most of us was a lack of rainfall intensity. Some areas did get snow, it's just that the front fragmented over most of the country. If the front had only been more active, we'd have been fine.

Daz_ · 11-02-2021 7:27pm

AuntySnow wrote: »

I'm seeing Spanish friends in a Swiss ski resort in my insta feed having driven there from Madrid...its not helping!
If its any consolation those same models has tonnes of snow this evening in wickliw and wexford
12 hours of it
They were wrong
OK only supposed to start at 80m but not a hope of it
There should be a model tribunal

Seems like a great idea travelling from spain to Switzerland in a pandemic for some skiing
Also why compare with Swiss Alps in the desire for snow ?!
The heavy snow build up / hype for this week has been fairly ridiculous

Nqp15hhu · 11-02-2021 7:28pm

Gonzo wrote: »

This is rough stuff indeed, we got dealt the worst summer in all of Europe during 2020 and now it looks like this final chance of snow has a high probability of being a bust too.

We just have to hope the models have got this wrong, but based on today I wouldn't be surprised if this is correct. Hope i'm wrong but these models are far from inspiring.

This won’t be the last snow, it always snows in March. Just stop looking to the east for snow, it’s not reliable. Look North.

Nqp15hhu · 11-02-2021 7:31pm

Billcarson wrote: »

And a cold spell tribunal. Wtf went so wrong this week?
Heights over Scandinavia not strong enough. ?
In future I will only really get sucked in when the heights are yellow on the charts not green .

- Convective cap limited the intensity of snow showers (warming with height above the 800mb level).
- Strong winds kept temperatures up at night limiting ice days and melting any light accumulations.
- Stratus clouds (sheet cloud) kept temps up at times.

So with the next cold spell look for lower heights, a more stable sounding (temp dropping with height to all levels) and limited wind.

Stop looking to warm fronts to deliver snow. It doesn’t usually work for us.

space2ground1 · 11-02-2021 7:32pm

I think despite my interest in meteorology, this will be my last time setting up followed threads for a weather event.
Through no fault of anyone here, yet another rollercoaster slows to a stop and falls over sideways. The models seem to have predicted 45 of the last 3 snow events.. rendering them less than useful.

I have learned a lot from the regular posters though so thank you! You deserve better from the models. I've always said there should be en element of mathematical probability built into them.

Nqp15hhu · 11-02-2021 7:33pm

Artane2002 wrote: »

the two main issues were that heights over us weren't low enough and thicknesses were too high.

The thickness values were under 520 decametres at times, which is low enough.

Nqp15hhu · 11-02-2021 7:35pm

Squidvicious wrote: »

That's always been my rule of thumb for snow. If you're not on the right side of the 528 dam line, you won't generally get snow. I know that there are other factors and you may not get it even if you are on the right side, but it's a very good guide. That said, today, the biggest problem for most of us was a lack of rainfall intensity. Some areas did get snow, it's just that the front fragmented over most of the country. If the front had only been more active, we'd have been fine.

It’s not a good guide. I have seen rain with 522 dam and we had snow last week with nearly 540 dam. The best thing is to look at your wet bulb temp AND the sounding for your area, with the air temp being below 0 right through the atmosphere.

Throughout this cold spell my wet bulb has been subzero and we have had no rain. So this is a very good approach to take.

11-02-2021 7:49pm

What are the models showing for Dublin tomorrow?

Meteorite58 · 11-02-2021 7:58pm

Latest ECM 12Z keeping it going in the West for a number of hours yet. Poor showing in Southern counties and the SE after the earlier promise. Looks to drift slightly in towards central counties but looks mostly light there. Heavier precipitation now moving up along the W coast.

yourdeadwright · 11-02-2021 8:00pm

Deleted User wrote: »

What are the models showing for Dublin tomorrow?

As far as i can see nothing for Dublin tomorrow but possibly get some. Snow about 10 or 11 am Saturday

Davaeo09 · 11-02-2021 8:02pm

The misery for the south east continues

When is the rain expected to be more widespread going by the latest models? (Bet they will be accurate for rain)

Meteorite58 · 11-02-2021 8:10pm

All the models showing frontal snow later Fri into Sat, blustery too. Rain set to follow Sat /Sun should make short change of snow on the ground.

pauldry · 11-02-2021 8:11pm

Cant understand the Net Weather map above. Granted the West is getting pummeled but Sligo is bone dry. Collooney has a few light snow grains.

Think Gerry Murphy had it spot on on the predictive. It showed snow fading as it reached Northwest. The snow depth chart will prob be accurate enough exclusive of Sligo but my kids keep asking me and I dont know...what time is it supposed to START snowing in Sligo?

Tomorrow night looks like another chance for Ulster and some of Leinster but Connaught will be 4 or 5c by then so just rain for Sligo or maybe sleet.

Neddyusa · 11-02-2021 8:13pm

Meteorite58 wrote: »

All the models showing frontal snow later Fri into Sat, blustery too. Rain set to follow Sat /Sun should make short change of snow on the ground.

Looks like any snow on the ground will only be seen by insomniacs

lucernarian · 11-02-2021 8:15pm

I don't have much faith in those charts if photos from beside Knock airport showed no snow. Somewhere like there would be assumed to have lying snow by now based on previous output.

Slashermcguirk · 11-02-2021 8:17pm

Have to disagree, the two biggest snow events for Ireland in 2010 and 2018 came from the east / north east. This one didn’t deliver as expected but doesn’t hide the fact the biggest quantities of snow / well known snow events in recent years came from easterlies. Besides despite the disappointment for us, lots in the west got great snow today

Nqp15hhu wrote: »

This won’t be the last snow, it always snows in March. Just stop looking to the east for snow, it’s not reliable. Look North.

200motels · 11-02-2021 8:19pm

Davaeo09 wrote: »

The misery for the south east continues

When is the rain expected to be more widespread going by the latest models? (Bet they will be accurate for rain)

A major disappointment, to say the least, the models even the short term ones were way off, nothing down here, roll on the summer.

Gaoth Laidir · 11-02-2021 8:20pm

It's the combination of temperature and moisture (virtual temperature) that determines thickness. Back at the start of March 2018 (below) we had as low as around 500 dam over Ireland, a result of the severe cold and dryness of all levels, not just below 700 hPa, like this week. The lowest thickness I saw this week was around 518 dam briefly in the extreme northeast of Ulster, but more typically 524-532 dam.

500-1000 hPa thickness is not a reliable guide for snow unless it's at 516 dam or below, which will pretty much guarantees snow to all levels. Above that then other factors come into play. You can have very cold low levels, supportive of snow, but warm and moist upper levels, and this would register as a high thickness, and vice versa. But never blindly take 528 dam as being an indication of snow without, as N said, looking at other much more important factors.

Nqp15hhu · 11-02-2021 8:22pm

Yes, i've had rain at 522dam many times from atlantic systems.

pistolpetes11 · 11-02-2021 8:24pm

Gaoth Laidir wrote: »

It's the combination of temperature and moisture (virtual temperature) that determines thickness. Back at the start of March 2018 (below) we had as low as around 500 dam over Ireland, a result of the severe cold and dryness of all levels, not just below 700 hPa, like this week. The lowest thickness I saw this week was around 518 dam briefly in the extreme northeast of Ulster, but more typically 524-532 dam.

500-1000 hPa thickness is not a reliable guide for snow unless it's at 516 dam or below, which will pretty much guarantees snow to all levels. Above that then other factors come into play. You can have very cold low levels, supportive of snow, but warm and moist upper levels, and this would register as a high thickness, and vice versa. But never blindly take 528 dam as being an indication of snow without, as N said, looking at other much more important factors.

Can I just say for anyone that is new to the forum or watches the forum regularly , GL is one of the most knowledgeable posters on here , you will learn a lot , look and listening to his muses on events and outcomes of events .

Over the last 12 years Ive been here , he is never too far off the mark , there is a lot of great posters here but if you want to learn , look and listen to what he says .

kerrycork13 · 11-02-2021 8:24pm

Lots of places saw snow today. North cork, limerick, north kerry, parts or tipp, galway and mayo and clare just to mention a few. Some places saw a couple of inches so I think saying it was a non event would be inaccurate.

11-02-2021 8:35pm

Theres a weather warning for wexford and wicklow and I don't see how it's going to come to fruition tbh
Same atmosphere here near Arklow all day and now
2.1c air
Dp -4.2
Wb -0.7

The phrase its too cold to snow isn't fictional, its there in black and no white in wexford and wicklow today

Nqp15hhu · 11-02-2021 8:49pm

AuntySnow wrote: »

Theres a weather warning for wexford and wicklow and I don't see how it's going to come to fruition tbh
Same atmosphere here near Arklow all day and now
2.1c air
Dp -4.2
Wb -0.7

The phrase its too cold to snow isn't fictional, its there in black and no white in wexford and wicklow today

As another poster referenced above, these events usually just produce virga often times.

TheMilkyPirate · 11-02-2021 9:00pm

AuntySnow wrote: »

Theres a weather warning for wexford and wicklow and I don't see how it's going to come to fruition tbh
Same atmosphere here near Arklow all day and now
2.1c air
Dp -4.2
Wb -0.7

The phrase its too cold to snow isn't fictional, its there in black and no white in wexford and wicklow today

Yeah wa surprised to see the warning myself. Be lucky to see a flake fall here overnight

YanSno · 11-02-2021 9:05pm

Today's front did as expected but was surprised how well some western counties, got more than was forecasted. I'm still confident that the eastern half of the country will get snow before it turns backs to rain early Saturday afternoon. There's a shadow that will affect Dublin and Kildare so precipitation will be light to moderate during Friday night into Saturday around those areas. I had a quick look at a few sounding for possibility of freezing rain which is unlikely for now. 1cm - 5cm for the eastern half of the country some hilly areas up to 10cm. It will all be washed away late morning early afternoon as the mild air will be bring showers of rain.

Nqp15hhu · 11-02-2021 9:18pm

Snow looking to stay as all snow here during Saturday warming up overnight.

But the front may be quite light by the time it reaches here.

Snowbie · 11-02-2021 9:59pm

Video forecast done on Friday nights potential.

https://youtu.be/zCANHbebl6g

United road · 11-02-2021 10:02pm

YanSno wrote: »

Today's front did as expected but was surprised how well some western counties, got more than was forecasted. I'm still confident that the eastern half of the country will get snow before it turns backs to rain early Saturday afternoon. There's a shadow that will affect Dublin and Kildare so precipitation will be light to moderate during Friday night into Saturday around those areas. I had a quick look at a few sounding for possibility of freezing rain which is unlikely for now. 1cm - 5cm for the eastern half of the country some hilly areas up to 10cm. It will all be washed away late morning early afternoon as the mild air will be bring showers of rain.

You have a great record on calling events, good work man!
You stuck in my mind with your comments back in 2018. Iv sat up when you post ever since.
You have called so much right over past 3 years!
Wish you were more active around here!
But im sure you have other stuff going on in your life!

Squidvicious · 11-02-2021 10:11pm

Nqp15hhu wrote: »

It’s not a good guide. I have seen rain with 522 dam and we had snow last week with nearly 540 dam. The best thing is to look at your wet bulb temp AND the sounding for your area, with the air temp being below 0 right through the atmosphere.

Throughout this cold spell my wet bulb has been subzero and we have had no rain. So this is a very good approach to take.

Thanks N and GL. Very disappointing day for me in South Co. Kilkenny from a snow point of view but at least I learned something. A question. Where do I find predictive charts for sounding and for wet bulb temperatures and what soundings levels am I looking for if I want another? Well, 2 questions!

Donegal Storm · 11-02-2021 10:14pm

Slashermcguirk wrote: »

Have to disagree, the two biggest snow events for Ireland in 2010 and 2018 came from the east / north east. This one didn’t deliver as expected but doesn’t hide the fact the biggest quantities of snow / well known snow events in recent years came from easterlies. Besides despite the disappointment for us, lots in the west got great snow today

December 2010 was a northerly, as was Dec '09. Once the cold air was in-situ in 2010 the winds turned NE'erly but the airmass itself came from Greenland. Though in general I'd agree that a north easterly gives the best chance of widespread snow.

Easterlies as I said last week I find highly over-hyped on here (bar the obvious exceptional events like 2018). Maybe that's partially an imby perspective in that they're utterly featureless here in Donegal but most of the easterlies I've seen have given coastal flurries and nothing much elsewhere. Give me an unstable polar northerly any day

Nqp15hhu · 11-02-2021 10:16pm

Yes 2010 was a northerly..

Gaoth Laidir · 11-02-2021 10:17pm

Squidvicious wrote: »

Thanks N and GL. Very disappointing day for me in South Co. Kilkenny from a snow point of view but at least I learned something. A question. Where do I find predictive charts for sounding and for wet bulb temperatures and what soundings levels am I looking for if I want another? Well, 2 questions!

Here is a good source. Click on the balloon icon to select sounding mode.

Click on the map at whatever time you want. The red line is the temperature, blue is dewpoint. Wet-bulb temperature is around 40% of the way between the temperature and dewpoint curve (closer to temperature) for temperatures near zero (that changes at higher temperatures).

If the blue and red curves are together in the lowest levels (below around 700 hPa) and are both below zero then that's a high-intensity snow setup. Even if the surface is a couple of degrees above zero, if the dewpoint is far enough below it to make the wbt below 0.5 C then snow should still prevail.

Slashermcguirk · 11-02-2021 10:34pm

I recall December 2010 all the snow for Dublin was coming from the Irish Sea, I remember just watching the constant showers coming from the east into Dublin day after day

Met Éireann forecast after the 9pm news showed plenty of snow for the east tomorrow night and Saturday morning. Hopefully one blast tomorrow and that will give Dublin some action before the milder air arrives as we approach Sunday

Donegal Storm wrote: »

December 2010 was a northerly, as was Dec '09. Once the cold air was in-situ in 2010 the winds turned NE'erly but the airmass itself came from Greenland. Though in general I'd agree that a north easterly gives the best chance of widespread snow.

Easterlies as I said last week I find highly over-hyped on here (bar the obvious exceptional events like 2018). Maybe that's partially an imby perspective in that they're utterly featureless here in Donegal but most of the easterlies I've seen have given coastal flurries and nothing much elsewhere. Give me an unstable polar northerly any day

11-02-2021 11:02pm

Slashermcguirk wrote: »

I recall December 2010 all the snow for Dublin was coming from the Irish Sea, I remember just watching the constant showers coming from the east into Dublin day after day

Met Éireann forecast after the 9pm news showed plenty of snow for the east tomorrow night and Saturday morning. Hopefully one blast tomorrow and that will give Dublin some action before the milder air arrives as we approach Sunday

Correct
There were 4 waves of cold in 2010
2 were artic continental sourced from Siberia via Scandinavia
1 was northwestern,the other a polar artic northerly
All of them were air sourced from the artic North
Its just the 3 most severe were the two artic continental and the polar continental in that order
Obviously people based in the north believe theirs are best as do the people in the East
The facts are as I remember them anyhow in my lifetime, most good snow events involve artic continental air as its less modified with less humidity and ergo much lower Dewpoints
Today's for example did deliver in the west
Without that artic sourced easterly ,today would have been wet and windy everywhere
The problem today and all week was it was too artic dry
Karl also illustrated how far away it's driving low was in his videos
That combined with high pressure dashed any hope further east
1022 in my location
Fronts don't like that

Anyhow enough said (by me)

John.Icy · 11-02-2021 11:07pm

Nqp15hhu wrote: »

Yes 2010 was a northerly..

The end of November/early December spell wasn't. Always seems to be a forgotten period despite it dumping 30cm-40cm in plenty of eastern areas. My biggest snow to date in my life.

Winter 10/11 did not start with the mid-December spell.

Aunty summed it up best while I was posting...all cold air comes from the pole. Just different routes at times.

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

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