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

Nqp15hhu

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

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.

What are the models showing for Dublin tomorrow?

Meteorite58

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

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

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

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

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

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

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

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

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

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

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

pistolpetes11

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

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.

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

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

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

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

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

Video forecast done on Friday nights potential.

https://youtu.be/zCANHbebl6g

United road

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

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

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

Yes 2010 was a northerly..

Gaoth Laidir

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

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

Slashermcguirk

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

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.