Cold Spell Late Feb/ Early March Technical Discussion only MOD NOTE POST #1

Casualsingby

Oneiric 3 wrote: »

ECM ensemble spread for snow depth possibility from 'Emma' for my region (NE Co. Galway) which is in the lower risk area, but look at the amount of 'spread'. Really shows the high uncertainty regarding how far north the potential impacts of 'Emma' would be felt.

How do I check this out for my own location. Thanks.

Meteorite58

MOD NOTE

This thread is for Technical Discussion Only - for everything else use the event chat thread Off topic posts will be moved there.

Oneiric 3

Casualsingby wrote: »

How do I check this out for my own location. Thanks.

I posted the link on here in a following post but it ended up in a completely different thread?

Here Casualsingby:

https://weather.us/forecast/2961099-tuam/ensemble/euro/snow

You can check the spreads (and other cool stuff) of various parameters from a variety of models. Just put in your own location.

Oneiric 3

Oneiric 3 wrote: »

ECM ensemble spread for snow depth possibility from 'Emma' for my region (NE Co. Galway) which is in the lower risk area, but look at the amount of 'spread'. Really shows the high uncertainty regarding how far north the potential impacts of 'Emma' would be felt.

Absolutely. It appears the latest runs of the Euro 4 & the HIRLAM are diverging quite a bit over this.

Scubadevils

Although... if I read this correctly, looks like a lot of snow into Friday morning up the east coast into Dublin?

SleetAndSnow

Cork Airport has light snow showers, moving to snow, then Heavy Snow in its TAF : http://en.allmetsat.com/metar-taf/ireland.php?icao=EICK

Gaoth Laidir

Just flick through the different models on this chart and tell me how the northwestern half of the country should have a Red. The ECM ("EU") is the worst case scenario, but the high resolution show little or nothing there , e.g. the Euro4

https://weather.us/model-charts/gbr-hd/ireland/snow-depth/20180302-2100z.html

George Sunsnow

I’ll mention this here as it’s fascinating but the bbc shipping area forecast says for the Irish Sea


East 6 to gale 8. Moderate or rough. Snow showers. Good, occasionally poor. Occasional light icing later.

Not often you hear that !

Oneiric 3

Gaoth Laidir wrote: »

Just flick through the different models on this chart and tell me how the northwestern half of the country should have a Red. The ECM ("EU") is the worst case scenario, but the high resolution show little or nothing there , e.g. the Euro4

https://weather.us/model-charts/gbr-hd/ireland/snow-depth/20180302-2100z.html

If we took that chart provided in the link in isolation, I would be quite fearful about the wrath of Dubs.

Scubadevils

Gaoth Laidir wrote: »

Just flick through the different models on this chart and tell me how the northwestern half of the country should have a Red. The ECM ("EU") is the worst case scenario, but the high resolution show little or nothing there , e.g. the Euro4

https://weather.us/model-charts/gbr-hd/ireland/snow-depth/20180302-2100z.html

Looks encouraging for the south, east coast / midlands and up to about Drogheda. Certainly can't see how it would impact much of the Northwest. Presumably at this stage they still can't say for sure? I doubt they'd issue a countrywide red alert without serious consideration at this stage.

Hopefully the next set of model runs show some unity or we are heading for nowcast territory.

Scubadevils

Oneiric 3 wrote: »

If we took that chart provided in the link in isolation, I would be quite fearful about the wrath of Dubs.

That's why it's best to just quickly switch to ECMWF... :pac:

ascophyllum

Gaoth Laidir wrote: »

Just flick through the different models on this chart and tell me how the northwestern half of the country should have a Red. The ECM ("EU") is the worst case scenario, but the high resolution show little or nothing there , e.g. the Euro4

https://weather.us/model-charts/gbr-hd/ireland/snow-depth/20180302-2100z.html

I guess as North Donegal had lots of streamer activity today and whats lying on the ground will still be problematic tomorrow as a frozen mess. Sligo, Roscommon, Mayo had showers today (N17 was complete standstill at one point) and Mayo will get topped up tomorrow from Emma it seems. I agree some areas will remain bone dry but they can't give a red warning for half a county plus they just want people off the roads completely.

Donegal Storm

Oneiric 3 wrote: »

The last Met Éireann hourly weather report of Winter 2017-2018:

-5C and heavy snow in Cork, definitely one for the archives! I've been getting intermittent screenshots of the radar throughout the event as well just to keep a record as safe to say we won't be seeing a setup like this again any time soon.


Regarding the precipitation not reaching Dublin, considering the amount of spread between models its pointless looking at such minute track and positioning differences. No matter what the models show at this stage its going to come down to radar watching and likely evolve differently to any of the solutions currently being projected.

I'm still skeptical of much here for the simple but very unscientific reasoning that its so unlikely in Ireland for one huge snow event to go smoothly never mind two back to back. It'll do well to beat the past 24 hours here but looking forward to another memorable day ahead

Gonzo

concerned now about Emma not reaching here tomorrow especially after the beast under performing for much of the south Meath area.

BBC has Emma not reaching this area till nearly midnight tomorrow night and lasting into most of Friday.

Oneiric 3

Just looking at the various charts provided in GL's link above, and I can safely say that I have never come across a more pointless chart in all of my born days (from the 'US' model) Snow accumulation map:




You can view it in all its original glory here:

https://weather.us/model-charts/standard/ireland/snow-depth/20180302-2100z.html

MJohnston

ARPEGE from earlier seems to think that the Wicklow and Dublin mountains will absorb most of the oncoming snow for Dublin, but I'm not entirely sure why it sees it as then turning into rain over the city and north. Is there any reason that the precip being forced up at the mountains would cause that?



The same model does show Dublin getting a large amount of snow until Thursday/Friday midnight though.

Also - I can definitely see from that ARPEGE why the whole country is getting a red. Very few counties without significant snow.

piuswal

Oneiric 3 wrote: »

Just looking at the various charts provided in GL's link above, and I can safely say that I have never come across a more pointless chart in all of my born days (from the 'US' model) Snow accumulation map:




You can view it in all its original glory here:

https://weather.us/model-charts/standard/ireland/snow-depth/20180302-2100z.html

looks like they have some coastal exclusion zone , land/sea interface issue !

piuswal

LATEST IRISH WEATHER REPORTS
ON 1-MAR-2018 for 01:00

BALLYHAISE CAVAN(A) NE 09 Gust 22 FREEZING RAIN -5 92 0.1 1017

VALENTIA(A) NE 14 Gust 25 FREEZING RAIN -3 69 Trace 1011


Two freezing rain reports for the start of Spring! Never saw that before!

Anyone know how they distinguish between the various types of precip, I'm assuming they are all instrument recordings at this stage?,

M.T. Cranium

The only conclusion I am drawing about "Emma" is that one model will look good and most of the others won't, by Saturday.

The logical outcome given the strength of the cold easterly flow and the generally flabby look of Emma so far, is that this storm will be shunted west shortly after breaking through the 49N parallel, but the increasing gradient and frontal zone will allow heavy snow to develop over most of the southern half of the country. Further north, I think that despite stable low-level parameters, the sea effect process will continue at perhaps a reduced intensity and will keep a steady light to moderate snow coming inland on ESE winds across north Leinster into inland Connacht, and most of east Ulster also.

There are going to be pockets of low snowfall or even dry conditions perhaps, but too risky to fine tune this red warning, in any case its effect will be to deter people from making trips from some low-impact areas into the bad situation developing across most of the country, so in any case no nationwide red warning is ever likely to totally verify, that's not how weather actually works, they have to call it for the overall impact which could include some power outages because I think in some cases heavy wet snow combined with sleet in the south may bring down trees on transmission lines (maybe you have more of these buried than what I am used to here).

So in terms of detail, I am going to leave that to the morning update in my forecast, thinking generally a patchwork quilt of 20 to 40 cm amounts with the highest totals being around Wicklow and central inland southern counties, tapering to a general 10 to 20 inland northwest and 5 to 15 coastal northwest although a few near zero pockets won't surprise anyone. Some models show the track into Kerry, if that verified then northern totals would probably be higher.

I also think there is some chance of this snowfall event not really ending at all but continuing intermittently Friday night and resuming Saturday as a potential second low forms behind Emma and tries to duplicate the feat.

So it's a case of slowly diminishing sea effect snowfalls Dublin and north/west being overtaken by the gradual northward advance of frontal snows, probably a gap between these but in some cases perhaps just a merged non-stop snowfall (this more likely in central counties still getting the last dregs of sea effect when frontal snow moves in).

piuswal

MT

fyi (hope mod indulges this once)

No buried power lines and they do not support fallen trees as I have seen in B.C.

ThaitaniumM

00Z GFS rolling out. As suspected Emma looks a tad bit East but veers west as soon as she touches the south coast. ECM will be interesting. Best charts for now are the Harmonie and Arpege for precip charts.

M.T. Cranium

Arpege now more in line with GFS and GEM with no real northward push on low, the only difference now being that Arpege more or less loses the low by 48h in favour of the second low shown on all these models.

Without going into a lot of detail, would seem that these early models are backing mostly snow solutions with limited changeover near south coast.

A more detailed analysis of GFS convinces me that there would be low-level convergence between Wicklow (SE surface flow) and Dublin (ENE surface flow) during the snowfall event and that should overcome any shadowing effects for Dublin, think you'll be nicely included in the widespread heavy snowfall as a result. Even the shadowing west of Wicklow Mtns is probably not going to be an issue either.

Taking a rest now until ECM comes in, will be reading any and all thoughts with interest as we face this complex but important forecast.

Gaoth Laidir

Streamer intensity in the air Irish Sea has decreased overnight, but coverage is still widespread and accumulations are 1 cm per hour at both Dublin and Casement airports. Casement is now at 22 cm at 6 am and Dublin 11 cm.

Cork Airport is still 5 cm after no snow overnight.

Liffey4A

Gaoth Laidir wrote: »

Streamer intensity in the air Irish Sea has decreased overnight, but coverage is still widespread and accumulations are 1 cm per hour at both Dublin and Casement airports. Casement is now at 22 cm at 6 am and Dublin 11 cm.

Cork Airport is still 5 cm after no snow overnight.

Rain radar showing lots of activity over Louth but yet unusually nothing is falling here! How so?
Charts look like most snow should stay south of us today also

ThaitaniumM

A lot of cooler clouds over UK atm, not too sure if they will travel this direction. Will be fun to see if they do cross over.

M.T. Cranium

Anyone want to do a forecast? (ha ha)

ThaitaniumM

M.T. Cranium wrote: »

Anyone want to do a forecast? (ha ha)

Blizzards galore

Wrex

from all these models recently, dublin seems to be avoiding the worst of it over the next 24 hours?

ThaitaniumM

ECM out, looks like all snow until Saturday