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

Reckless Abandonment

Fridays low staying north. Could be rain by friday evening. But a week away wouldn't be surprised if it end up missing Ireland completely

snowstorm445

GFS following the ECM op in pushing cold air out by Friday. Feck.

Soccarboy11

Netweather posters seem confident its ok, with it being not as strong as previous runs and think the GFS is trying to work out the jet stream as its a rare event, and I kind of agree really the low seems weaker then before?

Soccarboy11

Almost certain this low will be gone in the coming runs, or else pushed further south. Not sure how it could push this strength of a easterly back so fast. I'm no expert at model reading though

sdanseo

If the ECM/GFS do verify it will be a very messy affair. Starting with heavy snow and turning to heavy rain, with potentially 20cm + of snow already on the ground.

Woudln't like to be in an area prone to flooding.

Kermit.de.frog

The 18z GFS brings a snowy breakdown on Thursday night in to Friday with significant falls. It may turn to rain in southern parts later but at this stage that is neither here nor there.

The evolution to this has to be worked out yet so treat very cautiously.

Snowbie

sdanseo wrote: »

No, I thought it had 2 types of chart, the "Précipiations" (not showing type) and the "Type Précip." (red and blue)

But the first chart with blue/green colour schemes also has the white hatch markings and corresponds with the red/blue "type precip" chart.

It's a bit odd. There is zero chance that anything falling out of the sky when it's -2 on the ground can be rain, surely?

For clarity, this is the ICON-EU as opposed to the ICON/DWD

Freezing rain. Regardless of what colour scheme these charts show and also take with pinch of salt, if an approaching low from the south meets the cold air with its advancing warm front, freezing rain can occur. A wedge of warm air rides over colder denser air and temps can be several degrees higher at height (just a couple hundred meters up) that when it rains it doesn’t have time to solidify or flake when falling into super cooler air and freeze upon impact....freezing rain.

Eg Christmas Day 2009 in Westmeath I had a temp of -3.4C and rain with some ice pellets but a layer of ice coated everything. Temp rose to 6C a few hours later as the advance warm front moved quickly up through the island. My min was -7.8C that morning so a decent diurnal range that day.
Maybe similar setup but it’s too far off to be certain yet and could well stall dumping snow if it’s slow moving if it does pan out at all.

JCX BXC

If that low stays about I'd be very concerned for the country as a whole, it will drop significant snowfall and I'm not convinced that it will turn to rain as the GFS suggests. It would be a crippling amount of snowfall.

MissMoc

What time is the next run at? My nerves are shot!

SeaBreezes

Soccarboy11 wrote: »

Almost certain this low will be gone in the coming runs, or else pushed further south. Not sure how it could push this strength of a easterly back so fast. I'm no expert at model reading though

There is the fact the snow shield may force freezing rain that day instead. Cause we don't have enough adjectives to describe rain in cork yet obviously.

Gaoth Laidir

Tuesday 12Z FAX, showing the cold front dissipating over Ireland. Showery trough getting into the east of the UK, followed by the 510 dam thickness line. Convergence line near the Channel Islands. Look at the strength of that Scandi high, 1055 hPa.

JCX BXC

SeaBreezes wrote: »

There is the fact the snow shield may force freezing rain that day instead. Cause we don't have enough adjectives to describe rain in cork yet obviously.

Previous to that rain thered be several hours of heavy snow, that chart is when the system moves up. That's why I'm not convinced that there'll be as much rain as it's forecasting as the temperatures will be very low.

Kermit.de.frog

And without further ado the fax chart for Wednesday



Sub 510 DAM and an active Irish sea.

Gaoth Laidir

Friday's low is just forming off the coast of New Foundland tonight and will rapidly deepen and move southeastwards over the next few days, cutting off and slowly meandering eastwards over the Azores Monday and Tuesday. By Wednesday it starts to fill and expand northeastwards, interacting with the coldest pool of easterly flow over NW Europe. It's this interaction that's still unresolved, so expect a few more model runs to iron out the details and see how the low forms south of New Foundland. In general, models tend to want to let cut-off lows rejoin the flow too early, so it could happen that in reality it will remain further south and catch the easterly flow later, meaning it would arrive here later or further east.

Soccarboy11

GEFS Ensamble looking better so hopefully

Gremlin

I would imagine that the models are not used to dealing with SSW and the associated complications that causes. So I think there might well be a wide margin for error this far out.

Gremlin

The other outcome, I can see is if the blocking high doesn't give up too easily, then the low could track northwards much farther west.

nacho libre

JCX BXC wrote: »

If that low stays about I'd be very concerned for the country as a whole, it will drop significant snowfall and I'm not convinced that it will turn to rain as the GFS suggests. It would be a crippling amount of snowfall.

The system in March 2013 was progged to come further north, but ended up further south and dumped a huge amount of snow in the channels island instead. With this in mind I'll be very surprised if the GFS is correct here. The low is riding on the jet stream but can't come that far north in my opinion. The GFS is notorious for being too progressive in these situations by underestimating the strength of blocks and just how hard they are to shift.

Donegal Storm

Yeah a small low pressure system like that won't be modelled correctly this far out, no point looking at run to run details. Give it to Wednesday I'd say before we have a good idea of how it'll behave


Also, nice to see you back Snowbie, this event seems to be getting everyone out of the woodwork

ninebeanrows

EC plumes show wide spread from Friday, still most supported cluster stays cold , 40% of eps members

highdef

nacho libre wrote: »

The system in March 2013 was progged to come further north, but ended up further south and dumped a huge amount of snow in the channels island instead. With this in mind I'll be very surprised if the GFS is correct here. The low is riding on the jet stream but can't come that far north in my opinion. The GFS is notorious for being to progressive in these situations by underestimating the strength of blocks and just how hard they are to shift.

Was this a different system that dumped massive amounts of snow to Ulster? You're mentioning the snow only got to the Channel Islands, hence my confusion.

Donegal Storm

Yeah the Channel Islands blizzard was on the 11th of March, delivered snow to large parts of the UK and Ireland though the main area of cold air was dragged down through the English Channel





Ulster blizzard was on the 22nd and 23rd, plenty of snow right across northern Ulster though the Antrim hills worst affected with snow lasting well into April






Nothing remotely close to that forecast in the semi-reliable timeframe this coming week, next Friday has potential but far to early to pin down details

Kermit.de.frog

ICON 00z, sub -16c 850 hpa temperatures not far off the southeast heading in to Thursday.



ICON also goes for pretty much the ideal outcome. The milder air does not advance to us at the end of the week. Heavy snow in the south and southeast.

ThaitaniumM

Kermit.de.frog wrote: »

ICON 00z, sub -16c 850 hpa temperatures not far off the southeast heading in to Thursday.

ICON also goes for pretty much the ideal outcome. The milder air does not advance to us at the end of the week. Heavy snow in the south and southeast.

ICON, the hero again!

Kermit.de.frog

GFS conducts the mild v cold battle over Ireland on Friday. A proper snow event. The mild air does get in eventually.





Some resolution here to come yet.

M.T. Cranium

GFS through 138h is marginally south with the Biscay low, it's having trouble reaching Ireland on this run although very close to Wexford. Verbatim would be pushing rain-snow line into south at low elevations, same up parts of east coast, but snow would hold on inland and north.

From there to 156h, low oozes north across Ireland, would not be bringing much mild air with it but verbatim would change over to cold rain in most places at some point. Biggest difference is that trailing second low is a lot weaker on this run.

GEM brings the Biscay low north at about 12W and loops it away from Ireland, still has the same result as GFS however, mild air slowly invading 2nd to 4th.

This is clearly a battleground scenario that is just in its opening phases and actual outcome may not be really sensed until 27th or 28th.

snowstorm445

Snow depths by midday Friday, before the thaw. :eek:

kod87

snowstorm445 wrote: »

Snow depths by midday Friday, before the thaw. :eek:

Not very impressive it has to be said (only a couple of cm for lowland dublin region), but i don't normally pay much heed to snow accumulation charts.

snowstorm445

kod87 wrote: »

Not very impressive it has to be said, but i don't normally pay much heed to snow accumulation cahrts

You’re right, still was more surprised by the fact that the whole country seems to get a covering briefly before a thaw sets in.

ThaitaniumM

GFS 00Z has it progged more southerly albeit very slightly, the next runs will be interesting how it all plays out