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

JanuarySnowstor

Why do I get a feeling Kermit is also thinking red or at least Orange for a large part of the country? Indeed I notice a lot of other pro's on here that usually don't ramp have gone very quiet?? As if they know all the parameters are there for heavy snow on Thursday

Slashermcguirk

Noted, good steer

Cluedo Monopoly wrote: »

They said always to use a carrot for the nose.

Kermit.de.frog

Gaoth Laidir wrote: »

Remember the strong southeasterly winds Thursday, which will most likely push Leinster coastal areas and inland more towards marginal. Salt spray in the air should not be understimated.

No marginality here...:cool:

Speak Now

Slashermcguirk wrote: »

What did they say on weather after 9pm rte news?

Very vague, FI starts at T 48 :pac:

Kermit.de.frog

JanuarySnowstor wrote: »

Why do I get a feeling Kermit is also thinking red or at least Orange for a large part of the country? Indeed I notice a lot of other pro's on here that usually don't ramp have gone very quiet?? As if they know all the parameters are there for heavy snow on Thursday

I'd say orange but for the southeast for now.

Gaoth Laidir

JanuarySnowstor wrote: »

Why do I get a feeling Kermit is also thinking red or at least Orange for a large part of the country? Indeed I notice a lot of other pro's on here that usually don't ramp have gone very quiet?? As if they know all the parameters are there for heavy snow on Thursday

These are the criteria for Red. I don't see anything close to this happening.

Snow/Ice
10cm or greater in 6 hrs
15cm or greater in 12 hrs
30cm or greater in 24 hrs

Low Temperature/Ice
Air minima minus 10C (or below) for three consecutive nights or more.
Maxima of minus 2C.
Dangerous surfaces due to ice and/or lying snow/freezing rain.
Situation likely to worsen.

ZeroSum76

Kermit.de.frog wrote: »

I'd say orange but for the southeast for now.

Hi Kermit thanks would you consider Southeast to extend to South Dublin or more central Wicklow /North Wexford?

Fitzo123

Watching the charts the last few days and seeing the comments is confusing; from what I've seen, the chances for snow in Sligo have remained steady almost all week?

I'm expecting about 3-5cm; would that be right to those who know more than I?

Rougies

Gaoth Laidir wrote: »

Remember the strong southeasterly winds Thursday, which will most likely push Leinster coastal areas and inland more towards marginal. Salt spray in the air should not be understimated.

Oh we'll be fine here in south Dublin, the Wicklow mountains will soak up everything, including all the precip.

YanSno

Dry continental air will weaken the front considerably. 18z prep chart very unrealistic in my opinion. It will be a nowcast how does this affect the front we shall find out on Thursday

Meteorite58

SE looking good all right for possibly the highest totals but plenty of areas showing up as doing well enough.

JanuarySnowstor

So fun to watch anyway guys as it looks after this weekend that we might not see cold for the following week.
Ok red is a tall order but orange is certainly possible and indeed probable
Let's see what the morning brings. In the end of the day it's only a bit of fun and gives us a break from you know what

Kermit.de.frog

ZeroSum76 wrote: »

Hi Kermit thanks would you consider Southeast to extend to South Dublin or more central Wicklow /North Wexford?

In to Central Wicklow/North Wexford, yes.

Not yet for Dublin. Need to see how the models see things in the morning. It's a yellow for Dublin atm in my view.

Gaoth Laidir

JanuarySnowstor wrote: »

So fun to watch anyway guys as it looks after this weekend that we might not see cold for the following week.
Ok red is a tall order but orange is certainly possible and indeed probable
Let's see what the morning brings. In the end of the day it's only a bit of fun and gives us a break from you know what

Watching RTÉ Investigates right now and streamers and inversions matter little in the greater scheme of things. We must remember that.

ZeroSum76

JanuarySnowstor wrote: »

So fun to watch anyway guys as it looks after this weekend that we might not see cold for the following week.
Ok red is a tall order but orange is certainly possible and indeed probable
Let's see what the morning brings. In the end of the day it's only a bit of fun and gives us a break from you know what

I have to say the twists and turns, while they can be devastating at times are a very welcome distraction! Can't believe after all the ups and downs some actual snow might fall along the South East. Prepping for another huge letdown in the morning but that's how she goes - enjoy the ride!

JanuarySnowstor

JanuarySnowstor wrote: »

Why do I get a feeling Kermit is also thinking red or at least Orange for a large part of the country? Indeed I notice a lot of other pro's on here that usually don't ramp have gone very quiet?? As if they know all the parameters are there for heavy snow on Thursday

Whisth you!

M.T. Cranium

The argument between posters is mainly a proxy for the difference between models, so I won't hold it against anyone to be wrong in this situation. My own procedure is normally to try to blend model output into what I hope will be the actual outcome, that doesn't always work (especially if no model or average of any two is right), but to hold on to just one source every time invites problems too.

I'm surprised to learn (to be honest I learned this ten years ago but anyway) that UK and Irish met services ignore GFS output. The GFS is just about as likely to be right as the ECM and stats prove that out. Maybe they do take a peek, sometimes the uncertainty they indicate is a nod to the GFS/GEM camp.

In North America, the two main government weather agencies review all models and base forecasts on their considered opinion of what blend is likely to verify. The NWS does not hug the GFS or NAM and Environment Canada does not hug the GEM, they realistically rate the GFS and Euro higher. There is no similar home bias at work and the European model is highly rated although the word on the street is that it peaked in its advantage over the GFS a few years ago and nowadays performances are similar. The GEM is considered to be improving after some upgrades. We also have a rough and ready short range model known as NAM that will be given a serious look before major events. The UKMO has a fairly good reputation also but many think it will just reinforce the Euro (as the ECM is usually called on this side of the pond).

On equivalent weather forums, the Euro was called the "king" by many weenies but in this new era of equivalency it has lost that tag.

With North American snowstorms, the general rule of model performance is like this -- a lot of shifting, chopping and changing is expected after a first sighting around day seven (sometimes longer, not that often though). People don't take model output all that seriously until within 48 hours. A common model problem in general seems to be that heavy snow axes (axis plural not the kind you take to the computer during a downgrade) shift north, you can gain a bit of a forecast advantage by just assuming that the model consensus is 50-100 miles south of where it will actually end up. Why is that? Partly some faulty assumptions about frontogenesis, partly the law of climatology (snow will gravitate towards places where it most frequently falls). I've seen a number of cases where the model output was very well predicted in terms of pressure and thermals but the snow axis shifted anyway.

Since most of the snow we see in this forum is sea effect (a totally different set of rules might apply there) I can't really generalize about model performance and synoptic scale snowfall because I would be taking maybe ten events as my data base and many of them are fairly restricted as to how far off they could stray in geographical terms. A slider is going to be fairly easy to model. This coming event is part of a low frequency set that might hit once every five to ten years. It might be interesting to compare model performances but if we go back to Jan 1982 then the models were very rudimentary, and the forecasts were probably made "old school" where people drew up their own charts and prog maps partly based on guidance but mostly on experience.

In this coming event, if it materializes, the favoured areas at present appear to be something like Kilkenny-Carlow north then northwest towards central Connacht to south Ulster. But if Dublin ends up with a heavy fall, it may be an illustration of the northward shift principle at work.

As to colour code of alert required for this, I would be backing orange but "red" conditions might verify in a few spots. Will speculate on where closer to the time as it's rather pointless this early with the range of guidance we see before us.

Thewife

I apologise if this is the wrong thread to ask in , i am confused with all the different threads . Is Waterford likely to get some snow from this event on Thursday ?

weatherfiend

Been lashing graupel/snow last hour in D18. Love love watching the lamppost. It’s landing and not melting which is great. Love the wintry feel the last couple of days - always feel it clears a lot of illness (even if not bloody COVID) but fresh!!

Donegal Ken

The Met Eireann Harmonie model will be in a better time frame tomorrow that yellow warning today issued was only a early warning with a more updated warning expected on Wednesday. The latest Met Eireann Harmonie model brings the band up to Sligo and if you draw a line to Wicklow that's how far it gets so possibly more upgrades in the morning if the models are anything to go by tonight. The amounts showing on Thursday do not meet a Red Warning criteria there maybe a Orange warning in some areas of the south east but could change.

Oneiric 3

M.T. Cranium wrote: »

I'm surprised to learn (to be honest I learned this ten years ago but anyway) that UK and Irish met services ignore GFS output. The GFS is just about as likely to be right as the ECM and stats prove that out. Maybe they do take a peek, sometimes the uncertainty they indicate is a nod to the GFS/GEM camp.

The UK Met Office forecasts on their app and youtube occasionally refer to the GFS, or as they call it, 'the American model' especially when they are doing their longer range forecasts.

The ECMWF is a great model, but as you say, it is also highly overrated. And it is also incredibly mean. While the GFS, an American tax payer funded model, and all of its data is available not only to the American public free of charge, but to the entire world, the tax payer funded ECMWF data is not, and they charge unholy amounts for it. A reflection maybe of the long infamous technocratic nature of Europe and and its governing institutions.

M.T. Cranium

Thewife wrote: »

I apologise if this is the wrong thread to ask in , i am confused with all the different threads . Is Waterford likely to get some snow from this event on Thursday ?

Would ask in the other thread (chat) but the short answer is yes probably some snow, close to the coast it could change to sleet rather quickly, a few miles inland it might amount to anywhere from 3 to 20 cms depending on which guidance you like. And that's about the answer you might get for other locations in the general region of east Munster, south Leinster, inland Connacht, south Ulster. Much uncertainty involved in this at present.

bazlers

Cluedo Monopoly wrote: »

They said always to use a carrot for the nose.

Probably the best post of seen in a while:)

M.T. Cranium

Saw a report of lightning at Cork, what's that all about? Not much doing on radar.

In terms of that northwest France snow, interesting to note, it is occurring in a zone between 534 and 540 thicknesses and around -1 to -2 C 850s. Le Mans has 6 cm on the ground. 10 cm on Normandy coast. No doubt a heavy wet snow that is probably partly melting on paved surfaces. That's a very continental set of parameters for frontal snow that you might encounter in Tennessee or Kentucky.

Not saying that could ever verify in Ireland with the marine influence, but the 850s and thicknesses for Thursday are considerably better than those.

froog

there's some serious precipitation coming in waves starting thursday anyway, that much is certain. lasting all the way to sunday. what form it takes is the question, snow more likely on east coast. a mixture down south.

Danno

Cluedo Monopoly wrote: »

Slashermcguirk wrote: »

What did they say on weather after 9pm rte news?

They said always to use a carrot for the nose.

This should be banished to the "Chat" thread, but lets keep it here in case it all goes pear shaped and at least we'll have this to look back on.

Hat tip, sir! :cool:

Nqp15hhu

Think we had snow here with something similar on Tuesday.

Gaoth Laidir

M.T. Cranium wrote: »

Saw a report of lightning at Cork, what's that all about? Not much doing on radar.

In terms of that northwest France snow, interesting to note, it is occurring in a zone between 534 and 540 thicknesses and around -1 to -2 C 850s. Le Mans has 6 cm on the ground. 10 cm on Normandy coast. No doubt a heavy wet snow that is probably partly melting on paved surfaces. That's a very continental set of parameters for frontal snow that you might encounter in Tennessee or Kentucky.

Not saying that could ever verify in Ireland with the marine influence, but the 850s and thicknesses for Thursday are considerably better than those.

Soundings show a deep saturated layer just below zero, hence the high thickness. If it were here the surface layer would most likely be just too marginal.

M.T. Cranium

Posted a verbatim interpretation of 18z GFS model in the chat thread. The model is going for a lot of rain from Friday to Monday-Tuesday near the south coast, when that hits the snow packs that might develop over hilly terrain, flash flooding could result. That may be the biggest weather impact of this entire period.

Model implies 20-30 cm snow packs on high ground in southeast by mid-day Friday, slow then rapid melting expected weekend to Monday. Similar concerns further west if snow pack develops over those hills too (or even without it given the 100-150 mm rainfalls predicted).

Model output not a forecast (at this point).

Meteorite58

M.T. Cranium wrote: »

Posted a verbatim interpretation of 18z GFS model in the chat thread. The model is going for a lot of rain from Friday to Monday-Tuesday near the south coast, when that hits the snow packs that might develop over hilly terrain, flash flooding could result. That may be the biggest weather impact of this entire period.

Model implies 20-30 cm snow packs on high ground in southeast by mid-day Friday, slow then rapid melting expected weekend to Monday. Similar concerns further west if snow pack develops over those hills too (or even without it given the 100-150 mm rainfalls predicted).

Model output not a forecast (at this point).

ECM on it too and into the week coming.