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

SleetAndSnow · 02-03-2018 8:36pm

Are we looking at sleet/rain moving into Cork City still on the latest HIRLAM model? Or will it (hopefully) remain as snow?

sdanseo · 02-03-2018 8:43pm

HONKEY TONK wrote: »

Can I ask someone here what was so special about Kildare's geography that it got hammered from Tuesday to today when towns between the coast and Kildare got SFA for a large part of the time.

https://en.wikipedia.org/wiki/Orographic_lift

Orographic lift occurs when an air mass is forced from a low elevation to a higher elevation as it moves over rising terrain. As the air mass gains altitude it quickly cools down adiabatically, which can raise the relative humidity to 100% and create clouds and, under the right conditions, precipitation.

irishfeen · 02-03-2018 8:47pm

At what height above sea level and distance inland are we expecting the incoming rain to be borderline sleet/snow over Munster tomorrow?

stooge · 02-03-2018 8:58pm

Neddyusa wrote: »

I'd imagine most of the epic snow from that area fell on Wednesday night and early Thursday

Certainly that's the case for here west of Athlone.
We had 1ft snow on the flat and 3-6ft in drifts....but it all came from continous Irish Sea steamers and nothing fell sincpm yesterday.... hence the yellow on that chart.

I'm in same area S roscommon. most fell on wednesday night, thursday morning and nothing of note since. In that respect it was very disappointing but still great nonetheless. Can anyone put forward an explanation? Is it to do wiht the orographic lift?

sdanseo · 02-03-2018 9:08pm

M.T. Cranium wrote: »

Some of the heavy appearance to the radar near Welsh coast is due to ice pellets or hail giving a stronger return. There is an elevated warm sector being mixed out as a result of compression of descending air from Welsh highlands.

Gaoth Laidir wrote: »

Regarding the precipitation band staying off the Welsh coast, I think it has something to do with mountain waves from the Welsh mountains. I noticed earlier on visible satellite stationary waves downwind of Wales and also Wicklow, so I think this has been the problem.

It's taken me this long to put 2 and 2 together and get 4 instead of 3.

I was looking at the precipitation west of Wales as a stalled approaching band, restrained somehow by nature. Where in fact these explanations make perfect sense and it's the same effect that I've been telling people in Kildare about since

policy75 · 02-03-2018 9:14pm

Is our friend from the east still in control. All the winds seem to be coming from the east at present. When is it likely/possible this will change or is there any such guidance obvious. This is not normal. What has happened to propogate this abnormal event and how does it correct itself?

Casualsingby · 02-03-2018 9:19pm

Gaoth Laidir wrote: »

How are they not higher with all the snow that fell? Considering there was a base of snow before Emma?

Artane2002 · 02-03-2018 9:21pm

Casualsingby wrote: »

How are they not higher with all the snow that fell? Considering there was a base of snow before Emma?

Blowing snow was a factor in Casement which cut down about 2cm, nothing substantial. I can't speak for Casement but Emma brought virtually nothing overnight here. Different story now though.

Casualsingby · 02-03-2018 9:22pm

[quote="[/quote]

Will that be used as an official record? As a volunteer recorded it and not met Éireann?

Neddyusa · 02-03-2018 9:22pm

stooge wrote: »

I'm in same area S roscommon. most fell on wednesday night, thursday morning and nothing of note since. In that respect it was very disappointing but still great nonetheless. Can anyone put forward an explanation? Is it to do wiht the orographic lift?

The simple answer is that the front from Emma didn't make it as far North as expected.

It made more northward progress along both east and west coasts but through the middle of the country it got no further North than Nenagh/Birr.

PMBC · 02-03-2018 9:31pm

policy75 wrote: »

Is our friend from the east still in control. All the winds seem to be coming from the east at present. When is it likely/possible this will change or is there any such guidance obvious. This is not normal. What has happened to propogate this abnormal event and how does it correct itself?

interesting programme on tv ?BBC earlier today showing how this process started about four weeks ago far south of here when some phenomenon occured eventually causing the air mass over the artic, ?artic vortex, to change direction from clockwise to anti clockwise thus sweeping cold winds from the East to Western Europe rather than the norm which is the opposite. According to the programme this happens about once every ten years.
Apologies for the poor summary

RobertKK · 02-03-2018 9:34pm

PMBC wrote: »

interesting programme on tv ?BBC earlier today showing how this process started about four weeks ago far south of here when some phenomenon occured eventually causing the air mass over the artic, ?artic vortex, to change direction from clockwise to anti clockwise thus sweeping cold winds from the East to Western Europe rather than the norm which is the opposite. According to the programme this happens about once every ten years.
Apologies for the poor summary

It is caused by a sudden stratospheric warming.

policy75 · 02-03-2018 9:39pm

RobertKK wrote: »

PMBC wrote: »

interesting programme on tv ?BBC earlier today showing how this process started about four weeks ago far south of here when some phenomenon occured eventually causing the air mass over the artic, ?artic vortex, to change direction from clockwise to anti clockwise thus sweeping cold winds from the East to Western Europe rather than the norm which is the opposite. According to the programme this happens about once every ten years.
Apologies for the poor summary

It is caused by a sudden stratospheric warming.

I guess the question is, when is it likely that things turn back to normal. What events must occur to make this happen and are these events anytime soon based on current weather models

wakka12 · 02-03-2018 9:48pm

No reason to believe this its just complete hope really but is climate change or anything possibly going to make events like (not as bad obviously ) this more common in ireland maybe? Solar minimums I heard somebody talking about..is sudden stratospheric warming becoming more common or is that an even that just randomly occurs with no pattern?

Meteorite58 · 02-03-2018 9:52pm

irishfeen wrote: »

At what height above sea level and distance inland are we expecting the incoming rain to be borderline sleet/snow over Munster tomorrow?

No Expert but what I am seeing is cold enough overnight for snow but upper air temperatures rise tomorrow as the Low remnants sweep across the country giving rain, sleet maybe early on and over high ground and possibly wet snow on mountain tops as the weather spreads Northwards. Away from Southern coasts temps remain fairly low although some differences in models, at a guess between 2 -5C but remaining much cooler in Northern counties. Will probably start to turn places fairly slushy. Just over 1C was enough to start a partial melt here today near Tralee .

Find the Iso 0° Couleur chart http://www.meteociel.fr/modeles/wrfnmm.php?ech=3&mode=37&map=334 handy for showing the 0° Isotherm ( freezing level ) in conjunction with the 850hPa charts. Helpful guide in determining height at which snow may fall.

Gaoth Laidir · 02-03-2018 9:55pm

Casualsingby wrote: »

How are they not higher with all the snow that fell? Considering there was a base of snow before Emma?

Blowing snow.was the main factor but also settling and daytime melt/sublimation. I notice that Casement have this evening changed their description of the snow cover from uneven loose dry snow to uneven wet or compacted snow. The constant snowfall today was light and just enough to keep the depth's head above water. I notice Casement hasn't any reports since 6 pm so I wonder if all is ok there.

Pa ElGrande · 02-03-2018 9:59pm

https://www.youtube.com/watch?v=7CHQRRPJK7s

Month-ahead look-ahead from Gavins Weather Videos taking us through the whole of March 2018 with the JMA and CFS V2 long range models seeing whether there's any sign of Spring following The Beast From The East.

MJohnston · 02-03-2018 10:03pm

Given the amount of thawing we got on Wednesday from direct sunlight (even though it was below freezing), the nebulosity (cloud cover) charts are probably worth tracking too, as it looks like the cloud layer will be thinning out a bit tomorrow in places, which should bolster any rise in temperatures and any rainfall in terms of removing snow:

ARPEGE:

GFS:

HIRLAM:

WRF:

pad199207 · 02-03-2018 10:34pm

Are winds beginning to turn more NE now?

Elmer Blooker · 02-03-2018 10:36pm

Fax chart, those who are looking forward to spring should look away now.
Northern blocking in control, a thaw is inevitable but I think snow drifts will still be around on St Patrick's Day.

fax72s.gif?0

Charles Babbage · 02-03-2018 10:41pm

Do I read this correctly that anywhere in inland Wicklow or in south Dublin on the higher side, say Sandyford will get another 30cm with most precipitation being snow until Sunday morning?

JCX BXC · 02-03-2018 11:21pm

Latest GFS suggests that the thaw has been delayed ever so slightly again. It has consistently overestimated how much Emma would succeed in battling the cold over Ireland.

Also hints of a northeasterly, let's see how this plays out.

Oneiric 3 · 02-03-2018 11:42pm

Here is the UK Met Office weather chart for 12pm today:

65541112

'Emma' proved to be a very ill-defined frontal system and it is quite possibly one of the strangest set ups I have seen on these charts.

Gaoth Laidir · 02-03-2018 11:49pm

And this was 18Z. Upper warm fronts all over the place. It's almost as if these are overrunning the cold surface layer, though it could also be something to do with orographic lift earlier over Northern Spain. Again, the reality was very different to the 24-hour forecast (2nd chart below).

Forecast from yesterday

hatrickpatrick · 03-03-2018 3:55am

Do we know yet (or indeed is it really possible to be sure) to what extent this winter's La Nina event in the Pacific may have contributed to the PV split and the resulting cold spell?

gabeeg · 03-03-2018 4:06am

I'd say it's impossible to untangle entirely from the SSW, but is a distant factor.

Gaoth Laidir · 03-03-2018 9:39am

I think whoever was doing the night shift at Casement lastnight couldn't come to work as reports are back on now since 7 am. Depth there 19 cm, Dublin 17, Cork 14, Knock 2, Shannon a patchy 1 cm.

Now is where it gets messy. Already a rapid thaw here this morning, and with rain later it's going to become treacherous.