Cold Spell - Snow & Ice Possible Thursday 8th / Friday 9th

Kermit.de.frog · 02-02-2018 7:53pm

munsterlegend wrote: »

So Monday night/ Tuesday morning nationwide risk of snow?

Trending the right direction and currently looks that way for most particularly the eastern half of the island for Monday night. When I said nationwide I don't mean all of us simultaneously of course:pac:

George Sunsnow · 02-02-2018 7:59pm

Ecm 12Z accumulated snow for 9am wenesday morning

gabeeg · 02-02-2018 8:04pm

How do you think it looks for a bit of lake effect snow from the Irish sea on Monday afternoon?

No reading from the M2 on met.ie

Rougies · 02-02-2018 8:19pm

gabeeg wrote: »

How do you think it looks for a bit of lake effect snow from the Irish sea on Monday afternoon?

No reading from the M2 on met.ie

Unlikely, the wind directions look like being all over the place. You need a fairly straight fetch across the sea for lake effect.

giveitholly · 02-02-2018 8:23pm

Kermit the snow potential that you are talking about for the west and north Tues night,would that be widespread showers or a front

Gaoth Laidir · 02-02-2018 8:56pm

I want to believe that this will be like Feb '91, but there are a few flies in the ointment.

The easterly cold doesn't quite make it to us. It's like a brief lapping wave on your toes as you stand near the sea shore, but it doesn't become entrenched over us. On a good note, dewpoints will be lower.

The actual event will be another Atlantic northwesterly, and you know my views on them. From around midday Monday winds swing west-northwesterly, so we're really now talking about the chance of wetter snow from the Atlantic.

850 hPa temperatures look good at first glance, but as this level is 300-400 metres higher than the recent Atlantic westerlies (>1500 m versus as low as 1100 m recently in the north) caution must be advised. Temperature at the 925 hPa level about -3 to -4 at around 850 metres, but this level is rising into Tuesday as high pressure moves in. Higher levels (700 and 500 hPa) show coldest in the north, but geopotential heights will be very high.

It's a fast-moving system, so the precipitation should pass in 3-6 hours. Maybe some front-edge snow in the midlands and east as the drier low levels will keep wet-bulbs down, but with the Atlantic airmass following we should see wbt rising and precip turing more mixed and rising to higher ground.

That's all on current guidance, but it could of course change (one way or the other). I do think any corrections will be eastwards, though, as there is no real easterly flow of cold to put up a fight against an increasingly strong westerly jet and increasing pressure.

gabeeg · 02-02-2018 9:13pm

I think this has been asked a few times, but does anyone know of a precedent for two such cold fronts meeting over our heads?

I guess I'm hoping beyond hope that the models are out of their depth, and that we'll all be following suit soon enough.

Meteorite58 · 02-02-2018 9:36pm

The Front looks to arrive later then the earlier runs which would favour snowfall more I would imagine by the time it moves across the country in to increasingly cold and night time air. Temps and Dew Points look promising for the Eastern half of the country. Thinking looking like there could be a fair amount of snow on the ground Tues morning from somewhere around the midlands to the E/ NE /SE and perhaps parts of the S . Early days yes but the models been fairly consistent and steady with this now for a couple of days.

EDIT: Looking through the charts more as regards accumulations of snow and perhaps seeing 2-5cm by Tues morning.

Kermit.de.frog · 02-02-2018 9:54pm

giveitholly wrote: »

Kermit the snow potential that you are talking about for the west and north Tues night,would that be widespread showers or a front

Occluding and weakening fronts from the north. Likely to remain somewhat intact upon reaching the north, northwest and down along the west coast. More showery and lighter activity elsewhere.

For now...

Meteorite58 · 02-02-2018 10:06pm

Very cold uppers on Tues and looking like wintry showers along Atlantic coasts. Feeling very cold along the coasts in a fresh NW wind, blustery in the showers.

George Sunsnow · 02-02-2018 10:53pm

Oooooooooooooooh

kittyn · 02-02-2018 11:04pm

Good to see your interest has been peaked WB

munsterlegend · 02-02-2018 11:09pm

George Sunsnow wrote: »

Oooooooooooooooh

You'll have to set up your own Arklow streamer thread!

Kermit.de.frog · 02-02-2018 11:12pm

18z GFS is more or less the same as the afternoon run regarding Monday night and Tuesday. No real progress toward the UKMO/ECM with that initial eastern air having more of a foothold in to the country on the other two models.

gfs-1-66.png?18

If anything the GFS signals possibly snow - rain - snow through Monday night.

Still a lot to happen for next week yet on the models.

Kermit.de.frog · 02-02-2018 11:35pm

George Sunsnow wrote: »

Oooooooooooooooh

Donegal Storm · 02-02-2018 11:44pm

gabeeg wrote: »

I think this has been asked a few times, but does anyone know of a precedent for two such cold fronts meeting over our heads?

I guess I'm hoping beyond hope that the models are out of their depth, and that we'll all be following suit soon enough.

The precedent is unfortunately that the Atlantic wins out with snow falling over the UK. I've never seen a worthwhile frontal snow event in my 30 odd years living here.

I hate to always be the pessimistic one in these threads but I just can't get excited by marginal Atlantic snow. Arpege is currently the most optimistic model with light snow across the east overnight Monday but temps rise to 5C on Tuesday so it'll immediately turn to a slushy mess.

Kermit.de.frog · 02-02-2018 11:49pm

Donegal Storm wrote: »

Arpege is currently the most optimistic model

Have to disagree there. UKMO and ECM are the most "optimistic" models regarding Monday night at the moment.

Boredwithit · 03-02-2018 12:03am

Gaoth Laidir wrote: »

850 hPa temperatures look good at first glance, but as this level is 300-400 metres higher than the recent Atlantic westerlies (>1500 m versus as low as 1100 m recently in the north) caution must be advised. Temperature at the 925 hPa level about -3 to -4 at around 850 metres, but this level is rising into Tuesday as high pressure moves in. Higher levels (700 and 500 hPa) show coldest in the north, but geopotential heights will be very high. .

Could you explain this please. 850 temps are what the temperature is at 1500m. When I look at gfs ECM UKMO etc 850 temps are what it is at 1500M. Could you explain it better. Because it makes no sense to me. Thanks

Meteorite58 · 03-02-2018 12:12am

Boredwithit wrote: »

You're talking absolute ****e here

Mod Note: Boredwithit before making anymore posts read the forum charter.

This is an unacceptable post and not to be repeated.

Donegal Storm · 03-02-2018 12:12am

Boredwithit wrote: »

You're talking absolute ****e here

Interesting, could you look back through my memory and let me know when I've experienced one?

Boredwithit wrote: »

Could you explain this please. 850 temps are what the temperature is at 1500m. When I look at gfs ECM UKMO etc 850 temps are what it is at 1500M. Could you explain it better. Because it makes no sense to me. Thanks

850hPa charts show temperature at whatever height the pressure reading is 850hPa. When sea level pressure is higher, the 850hPa level will be higher

Gaoth Laidir · 03-02-2018 12:20am

Boredwithit wrote: »

Could you explain this please. 850 temps are what the temperature is at 1500m. When I look at gfs ECM UKMO etc 850 temps are what it is at 1500M. Could you explain it better. Because it makes no sense to me. Thanks

The 850 hPa level on any given day can be anywhere from 1100 to 1550 metres over Ireland, depending on the season, temperature, surface pressure, etc. It's the same way surface isobars vary from day to day. The standard atmosphere height is 1450 metres, and this is roughly what gets loosely quoted, but many times it's not correct.

This is the GFS 850 hPa forecast for next Tuesday morning. The black lines show the height of this pressure level above sea level, in decametres (dam), so the 152 line (1520 metres) is right down the country.

This was a few weeks ago. The same pressure level was at only 1160 metres in the north, some 350 metres lower down.

If you're looking for the -8 °C temperature, you must also look at the height of this level too. A -8 °C at 1520 metres would equate to around -4 or -5 °C at 1160 metres, given a rough lapse rate of around 1 degree/km in a well mixed layer, such as a showery northwesterly. In reality, it's the temperature and humidity profile well below this layer that's most important for snow. Cold and dry best prevents melting.

pauldry · 03-02-2018 1:01am

Gettin a bit stressed

This Monday / Tuesday event is avoiding Sligo

Dont tell me its hail the next night for us....again.

Ah well. Dublin is due some snow.

Is there anyone here who could say what counties will n will not see anow Monday/ Tuesday?

It doesnt matter if your wrong. I just want to see opinions

ninebeanrows · 03-02-2018 1:09am

EC showing pure snow gold for decent stretch of country with front. Not much on it mind but going for 2-4cm widely.

fraxinus1 · 03-02-2018 1:37am

If it looks like Dublin rather than Donegal is going to get this snow event, then I'll jump in the car and head there. I can stay with my son and his wife and it would be lovely to bring the grandchildren to the park with the sled. Does anyone have any idea when the counties to be affected are likely to be pinned down?

Donegal Storm · 03-02-2018 2:38am

Gaoth Laidir wrote: »

This is the GFS 850 hPa forecast for next Tuesday morning. The black lines show the height of this pressure level above sea level, in decametres (dam), so the 152 line (1520 metres) is right down the country.

Just out of interest do you know why dam is used as the measurement for thickness? It's a fairly unorthodox measurement that I've never comes across other than a couple of obscure fluid dynamics measurements. Would it be simply just to save space on the charts?

Gaoth Laidir · 03-02-2018 3:01am

Donegal Storm wrote: »

Just out of interest do you know why dam is used as the measurement for thickness? It's a fairly unorthodox measurement that I've never comes across other than a couple of obscure fluid dynamics measurements. Would it be simply just to save space on the charts?

Dam is usually used for larger numbers (e.g. 500 hPa heights or 500-1000 hPa thickness) as the final digit is insignificant and can be left out to save space on charts. For lower levels (700, 850, 950 hPa) metres should be used as the last digit is now becoming significant. For example, a 850-1000 thickness of 1280 m pretty much guarantees us snow all the time, whereas even 1290-1300 m is much more marginal.

ninebeanrows · 03-02-2018 8:29am

EC certainly much watered down compared to yesterday's 0z in terms of longevity of this cold snap.....

However, with regards to Monday night, still very similar with 2-5cm accumulated snow progged widely across Ulster, Leinster, east Connacht and parts of east Munster.

esposito · 03-02-2018 9:17am

Weathercheck wrote: »

EC certainly much watered down compared to yesterday's 0z in terms of longevity of this cold snap.....

That was always going to happen wasn’t it. Still, room for improvements too.

I personally wouldn’t call it a “snap”. More like a cold spell to me.

Can see lots of cold coming our way from the east, the problem is that fronts with less cold air keep coming in from the damn Atlantic to spoil the party. Frustrating is the word.
Interesting times for the month of February though, keeping us all on the edge of our seat.

squarecircles · 03-02-2018 9:18am

I'm glad I didn't get my hopes up.
Turning into a Watery mess as usual.

RobertKK · 03-02-2018 10:12am

Met Eireann updated the forecast last hour and it is a more wintry outlook. They do say confidence in the forecast is low for later next week but now instead of rain, mention rain, sleet and snow as possible.

Cold Spell - Snow & Ice Possible Thursday 8th / Friday 9th

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