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

munsterlegend

Kermit.de.frog wrote: »

Dublin is exposed to the southeasterly wind so should be fine but Kildare is definitely in a shadow to some extent. Most models actually show that with either light precip or even none at all at times.

Was wondering if soundings looked positive in the south west away from the coast. Atlantic usually not good for snow down here.

Bejubby

Looks good for us in the sunny South East.

Kermit.de.frog

munsterlegend wrote: »

Was wondering if soundings looked positive in the south west away from the coast. Atlantic usually not good for snow down here.

Looks ok for a while tomorrow evening inland Cork/Kerry, even close enough to coasts. It might not last long though.

This will be a nowcast. We can dump the models tomorrow and what happens, happens.

munsterlegend

Kermit.de.frog wrote: »

Looks ok for a while tomorrow evening inland Cork/Kerry, even close enough to coasts. It might not last long though.

This will be a nowcast. We can dump the models tomorrow and what happens, happens.

Cheers Kermit. Am hoping for some stalling down here by that front.

R.F.

Im learning a lot here. Green = Good ??

igCorcaigh

R.F. wrote: »

Im learning a lot here. Green = Good ??

I think green is heavier precipitation. White hatched lines equal snow. I think!

Daniel2590

igCorcaigh wrote: »

I think green is heavier precipitation. White hatched lines equal snow. I think!

Yeah if you look at the scale at the bottom green is better than blue (from a more precipitation point of view), increasing in precipitation as you go further right on the scale.

Edit: And yes, the white lines = snow, rather than rain.

Kermit.de.frog

R.F. wrote: »

Im learning a lot here. Green = Good ??

Aye, the darker greens, yellows etc indicate more preciptation amounts over an hour mostly. But sometimes over 3 or 6 hours... depending on the model and resolution.

For example..


ICON chart above is preciptation over 1 hour.


However, the GFS chart above is precipitation over 3 hours.

Thus the latter on the face of it will always look like more "impressive". It's really not, it's just the different periods.

igCorcaigh

Daniel2590 wrote: »

Yeah if you look at the scale at the bottom green is better than blue (from a more precipitation point of view), increasing in precipitation as you go further right on the scale.

Edit: And yes, the white lines = snow, rather than rain.

My French is also improving.
Verglas = ice.

munsterlegend

Met Éireann update for tomorrow. Positive for snow.

Sleet and snow in the southwest tomorrow morning will gradually extend northeastwards across Munster, Connacht and south Leinster through the day, with snow accumulations leading to some hazardous conditions. Snow will turn to rain or sleet in southern and southwestern coastal districts. Remaining mostly dry elsewhere with sunny spells, although cloud will increase later. It will be windy and very cold with highest temperatures of 1 to 3 degrees, with an added wind chill factor due to fresh to strong and gusty southeasterly winds. Winds will be strongest in the west and southwest.

Kermit.de.frog

Kermit.de.frog wrote: »

Dublin is exposed to the southeasterly wind so should be fine but Kildare is definitely in a shadow to some extent. Most models actually show that with either light precip or even none at all at times.

See here, this is a shadow

Anti snow is up half the night watching cows calving at the moment, is that chart suggesting I bring my new shovel with me?

Kermit.de.frog

AuntySnow wrote: »

Anti snow is up half the night watching cows calving at the moment, is that chart suggesting I bring my new shovel with me?

Not sure about a shovel but you area is probably among the most well primed for this one.

Cluedo Monopoly

R.F. wrote: »

Im learning a lot here. Green = Good ??

justy182

FRIDAY NIGHT: A wet and windy night as rain spreads countrywide, falling as sleet or snow in Ulster and parts of north and east Leinster. Rain will be heavy in southern coastal counties with a risk of some flooding. Lowest temperatures of 0 to 4 degrees generally, but less cold in the southwest with lows of 5 to 9 degrees. Southeasterly winds will be fresh to strong and gusty.
Update from Met E.

I'm holding on for this in SE Ulster. Are the models still supporting this period of snow?

Nqp15hhu

I’m very confused. Very mixed messages on this forum. Some saying Ulster will see nothing.

So I check Xc weather and I am down for no higher than 4c from now to next Thursday.

But the Met Office says 9c from Sunday. Which is right?

Nqp15hhu

Nqp15hhu wrote: »

I’m very confused. Very mixed messages on this forum. Some saying Ulster will see nothing.

So I check Xc weather and I am down for no higher than 4c from now to next Thursday.

But the Met Office says 9c from Sunday. Which is right?

Neither

Kermit.de.frog

Nqp15hhu wrote: »

I’m very confused. Very mixed messages on this forum. Some saying Ulster will see nothing.

So I check Xc weather and I am down for no higher than 4c from now to next Thursday.

But the Met Office says 9c from Sunday. Which is right?

It will be milder, wetter and windier from Sunday for everyone.

How long that lasts is impossible to know. Most of next week looks a write off. Some models show signs high pressure will begin to reassert itself to the east or northeast later in the week.

Nqp15hhu

So why does xc weather say 3c for Sunday?

Tyrone212

Nqp15hhu wrote: »

I’m very confused. Very mixed messages on this forum. Some saying Ulster will see nothing.

So I check Xc weather and I am down for no higher than 4c from now to next Thursday.

But the Met Office says 9c from Sunday. Which is right?

Ulster won't tomorrow(maybe cavan area). Ulster should Friday night/Saturday.

DOCARCH

Nqp15hhu wrote: »

So why does xc weather say 3c for Sunday?

Thats based on GFS.

Says same (3c and snow) for me in Dublin on Sunday, whereas Met Eireann app, based on ECM, says 10c and rain.

I know which I would prefer!

Nqp15hhu

DOCARCH wrote: »

Thats based on GFS.

Says same (3c and snow) for me in Dublin on Sunday, whereas Met Eireann app, based on ECM, says 10c and rain.

I know which I would prefer!

Yes, would prefer the cold held on a bit longer.

Donegal Ken

Ulster and north Leinster looks like it will see disruptive snowfall on Friday night and Saturday morning in particular with good cross model agreement now. As for Xc I never ground it to be a great app.

Nqp15hhu

Donegal Ken wrote: »

Ulster and north Leinster looks like it will see disruptive snowfall on Friday night and Saturday morning in particular with good cross model agreement now. As for Xc I never ground it to be a great app.

It’s reflective of what the gfs shows though which is a continuation of the cold.

Humberto Salazar

Nqp15hhu wrote: »

It’s reflective of what the gfs shows though which is a continuation of the cold.

I use the Weather Channel app, it's a useful tool but like most apps, flawed in some respects. I think they use GFS too, and after Saturday it's a mild wet week ahead according to that. Temps 9 to 11 each day up to following weekend. Take that with a pinch of salt but more likely to happen than a return to cold in my opinion.

MJohnston

ECM 06z is a touch less generous with the snow on the Thursday/Friday wave, but a little bit more generous with it on the Saturday morning:

nacho libre

Nqp15hhu wrote: »

It’s reflective of what the gfs shows though which is a continuation of the cold.

Until Sunday at the latest it looks like. Flooding could be the big issue by the end of the weekend. It's a great pity just as everything has dried out. If cold does return after mid month, i hope we can get more days like today out of it.

MJohnston

Humberto Salazar wrote: »

I use the Weather Channel app, it's a useful tool but like most apps, flawed in some respects. I think they use GFS too, and after Saturday it's a mild wet week ahead according to that. Temps 9 to 11 each day up to following weekend. Take that with a pinch of salt but more likely to happen than a return to cold in my opinion.

Apps take a model run and programatically turn that into an auto-generated forecast for a given location. It's essentially the same as looking at a model and taking it as absolute gospel.

The app coder could have added some algorithmic adjustments on top of a model, but these will be very generalised (and in the case of the Weather Channel, US-specific). The whole point of these apps is to require zero human intervention in the forecast generation.

In short, I think they're usually rubbish. Met Eireann's app I want to give the benefit of the doubt and say that (a) they're using their own model which is better tuned for Irish meteorological conditions and (b) they might possibly be hand-tuning the model generated forecasts for parts of the country anyway, and they can feed that into their app.

nacho libre

Humberto Salazar wrote: »

I use the Weather Channel app, it's a useful tool but like most apps, flawed in some respects. I think they use GFS too, and after Saturday it's a mild wet week ahead according to that. Temps 9 to 11 each day up to following weekend. Take that with a pinch of salt but more likely to happen than a return to cold in my opinion.

Yes, it looks like we'll pay for this cold spell with several mild and wet days, but there are tentative signs the cold could return sometime after mid month. It will be interesting to see if we see a change in the UKMO long range for the worst, as per recent ECM runs, or if they will stick to ebbing and flowing theme.

Nqp15hhu

nacho libre wrote: »

Yes, it looks like we'll pay for this cold spell with several mild and wet days, but there are tentative signs the cold could return sometime after mid month. It will be interesting to see if we see a change in the UKMO long range for the worst, as per recent ECM runs, or if they will stick to ebbing and flowing theme.

I just hope it’s more of a NE when it does return, with intense instability.

Kermit.de.frog

MJohnston wrote: »

ECM 06z is a touch less generous with the snow on the Thursday/Friday wave, but a little bit more generous with it on the Saturday morning:

Precip extended further north though so better for Dubs for Thursday night/Friday.