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

Weathercheck

Weathercheck wrote: »

There is a risk right on the coast but maybe 20% but just a mile inland and full snow

Would that 2100 M2 buoy report not be of concern though? A DP of +2.5 C seems quite high.

Zzippy

gozunda wrote: »

The weathet Forecaster on the RTE six News said we were in for "



Now correct me if I'm wrong on my technical understanding of the Lee or Leeward side of mountains - which as far as I remember is the sheltered side away from the prevailing wind. It is the opposite Windward side which would normally get deposits of precipitation as the wind meets the elevated mountain topography.

So how is it that the Forecaster is suggesting that it is the other - Leeward side which will be getting the record breaking snow - when it is the windward side of those mountains which will be meeting the winds from an East and South Eastern direction?



Anyone else spot this tonight?

Just watched it and she definitely said windward side.

Gaoth Laidir

Wet-bulb temperatyures at 9 pm. Marginal now into the far southwest tip of England but elsewhere good.




Latest snow depths. Yeovilton (23 m) in sw England is getting pelted. Its snow depths have gone like this

Time...Reading
21:00...17cm
20:00...10cm
19:00...5cm
18:00...1cm

wakka12

gozunda wrote: »

The weathet Forecaster on the RTE six News said we were in for "



Now correct me if I'm wrong on my technical understanding of the Lee or Leeward side of mountains - which as far as I remember is the sheltered side away from the prevailing wind. It is the opposite Windward side which would normally get deposits of precipitation as the wind meets the elevated mountain topography.

So how is it that the Forecaster is suggesting that it is the other - Leeward side which will be getting the record breaking snow - when it is the windward side of those mountains which will be meeting the winds from an East and South Eastern direction?



Anyone else spot this tonight?

Very odd, MT also said in his report the opposite, that places to north and west of mountains would get less snow than places to east and south of them

ninebeanrows

Deleted User wrote: »

Would that 2100 M2 buoy report not be of concern though? A DP of +2.5 C seems quite high.

I usually check howthweather as an indicator of the most marginal parts of Dublin and it is still in snow territory at the moment. I am expecting it get get marginal (but the right side!) halting approx 0.5/0 as the snow pushes in later tonight.

M.T. Cranium

I posted this on the chat thread yesterday -- this will be like 1947 with internet.

Oneiric 3

Elmer Blooker wrote: »

but no one answered my post.
.

I did.

Rebelbrowser

Elmer Blooker wrote: »

There must be. I posted a chart earlier inquiring why the far southwest of England was much colder than northern England. My opinion was that it was a warm sector. I thought someone more knowledgable than me might have had an answer but no one answered my post.
I just pointed out a few mins ago that Valentia and Sherkin are colder than the Phoenix Park.

coldest temps last night were in Cork and all day Cork airport was the coldest reporting station so perhaps not such a surprise?

separately in terms of the ice particles falling, I wonder is there any similarity between this event and the event on 10 Jan 2010 when a front also moved north from Biscay and stalled over Cork. We got 10 hours of snow but it was this kind of tiny particles that appeared nothing but eventually caused a good 8cm or so to accumulate.

sdanseo

Deleted User wrote: »

Would that 2100 M2 buoy report not be of concern though? A DP of +2.5 C seems quite high.

Weathercheck wrote: »

I usually check howthweather as an indicator of the most marginal parts of Dublin and it is still in snow territory at the moment. I am expecting it get get marginal (but the right side!) halting approx 0.5/0 as the snow pushes in later tonight.

M2 buoy is 37km out to sea. Expect it to be considerably warmer than on the coast.

sean555

Updated Hirlam 18z has snow pushing further North and West

M.T. Cranium

County by county estimates of further snowfalls (on top of what is on the ground now) ...

Wicklow, Kildare ... 40 to 70 cm

Wexford ... 30 to 60 cm

Dublin ... 25 to 50 cm

Meath ... 20 to 40 cm

Louth ... 10 to 25 cm

eastern half NI ... 5 to 10 cm

Waterford, Carlow, Kilkenny, Laois ... 30 to 60 cm

Cork ... 20 to 50 cm

Kerry ... 5 to 30 cm

Limerick, Tipps, Clare ... 15 to 45 cm (generally heavier south)

Offaly, Westmeath, Longford, Roscommon, Galway ... 20 to 40 cm (generally heavier south Roscommon and east Galway)

Mayo, Sligo, Leitrim, Cavan, Monaghan ... 2 to 15 cm (15 more likely east and south)

Donegal ... 0 to 10 cm (higher amounts may be in sea effect bands northwest coast)

western Northern Ireland ... 2 to 15 cm (higher amounts towards south central NI)

______________________________________________

The ranges are large and maximum amounts will be on southeast facing slopes, in some cases a range north to south, this applies more to the northern counties, for Cork and Kerry a reduction in totals near sea level. Some of the other county variations more due to elevation than exposure to any particular direction, and of course a random factor always present with banding caused by upper level dynamics sometimes unrelated to the surface.

Could see 70 to 120 cm on top of higher summits. These estimates are for elevations where people are going to experience them.

Gaoth Laidir

The Cork TAF times the transition from snow to sleet at 10 am tomorro morning. Expect slightly earlier further east along that coast.

sdanseo

A solid WALL of heavy snow strectching the length of welsh coast heading across the Irish Sea.

All of it seems to have been whipped up from the sea itself as it didn't flow over Wales

Very intense blobs over Wales also.

gozunda

Zzippy wrote: »

Just watched it and she definitely said windward side.

Have the segment on record - and she says

Especially on the Lee side of mountains

There is no use of the phrase "Leeward" rather "Lee Side"

That's what caught my attention

The query there is the same - was it just a genuine mistake or other explanation?

sdanseo

Siobhan just specifically called out EPS (ECMWF) for its long term accuracy with this.

gozunda wrote: »

Have the segment on record - and she says

That's what caught my attention

The query there is the same - was it just a genuine mistake or other explanation?

Two elements to this.

The more obvious is that the side of a mountain facing into the wind gets hit harder. More drifting, much more exposed.

The lee side often suffers more snow because the air mass hits the mountain range, rises into colder air (1 degree per 500ft / 3 degrees per 500m) and condenses rapidly, dumping snowmageddon on the poor (lucky) souls below.

savj2

I'm familiar with ECMWF and other models but where can I find the harmonie model?

Gaoth Laidir

Casement depth has fallen 4 cm to 18 cm at 10 pm.

Donegal Storm

Coming up to 30 hours of non-stop snow here now and still no end in sight, even 30 hours of persistent rain would be remarkable never mind dry powder snow!

The radar is very messy at the moment but hopefully that heavier band in the Irish Sea have 'real' snow rather than the ice crystals of the past few hours. The crystals are actually adding further to accumulation here and coating everything in white but they're not much to look at

savj2 wrote: »

I'm familiar with ECMWF and other models but where can I find the harmonie model?

Harmonie isn't publicly available, I think Arome on meteociel is developed by the same team (ALADIN) so the closest thing we have

gozunda

sdanseo wrote: »

Siobhan just specifically called out EPS (ECMWF) for its long term accuracy with this.

Two elements to this.

The more obvious is that the side of a mountain facing into the wind gets hit harder. More drifting, much more exposed.

The lee side often suffers more snow because the air mass hits the mountain range, rises into colder air (1 degree per 500ft / 3 degrees per 500m) and condenses rapidly, dumping snowmageddon on the poor (lucky) souls below.

Ah ok thanks for this.

I am located close to the Galtee Mountains and depending on wind direction are sometimes sheltered from precipitation* being carried with wind hitting the other side of the mountain.

Notably we have had very little snow over the last two days.

I will report back tmrw as to whether the advancing front plus snow makes it across the mountain to this location

*Interestingly the wind speeds often become stronger on the Leeward side which make for some very interesting local weather conditions

Oneiric 3

It looks like at Claremorris at least, daily maxima records will be broken for the month of March (records go back to 1950) with the temp failing to get above freezing today.

I can only assume that similar records will be broken today in other places too.

IE 222

sdanseo wrote: »

Siobhan just specifically called out EPS (ECMWF) for its long term accuracy with this.



Two elements to this.

The more obvious is that the side of a mountain facing into the wind gets hit harder. More drifting, much more exposed.

The lee side often suffers more snow because the air mass hits the mountain range, rises into colder air (1 degree per 500ft / 3 degrees per 500m) and condenses rapidly, dumping snowmageddon on the poor (lucky) souls below.

I've notice the past while that radar suggest the Wicklow/Dublin mountain have been avoiding snow fall. Is this effect causing this to happen or is that event causing faultly readings.

Elmer Blooker

Advice please.
Chart for noon tomorrow, is that the front to the southwest of England thats meant to give us blizzards? Its nowhere near us and I don't like the look of that warm sector either but it doesn't surprise me, there would have to be one to complicate matters.

MJohnston

IE 222 wrote: »

I've notice the past while that radar suggest the Wicklow/Dublin mountain have been avoiding snow fall. Is this effect causing this to happen or is that event causing faultly readings.

Generally with these real-time radars, I'd say a good rule of thumb is - if it looks unusual, it's probably broken. They're not the most reliable!

Meteorite58

ECM 12Z

littlema

Hour long programme on BBC 4 about the Big Freeze of 1963. The explanation of how it started was interesting in light of what we now know.

Mods: please note this is of interest to anyone who loves charts, even if they are on cardboard!!

HighLine

Are the greens and blues trailing over the south west corner of England and towards us a worry? That would suggest the precipitation will turn wet earlier than expected?

sdanseo

GFS 18Z keeping temps and DPs good until tomorrow night

WHich particular feature in the FAX chart shows the warm sector (as opposed to the warm front)?

HighLine wrote: »

Are the greens and blues trailing over the south west corner of England and towards us a worry? That would suggest the precipitation will turn wet earlier than expected?

200km further south and predicted by UK services since this morning to be sleet or freezing rain.
The bulk of the green is over the sea which is completely expected also.

IE 222

MJohnston wrote: »

Generally with these real-time radars, I'd say a good rule of thumb is - if it looks unusual, it's probably broken. They're not the most reliable!

Yeah thats what i was thinking. Im sure their getting hammered up there.

Snow is definitely getting thicker here in Dublin 12 not by much but the dusty type seems to of passed for now. Its not been blown up of the ground as much.

Meteorite58

Are the greens and blues trailing over the south west corner of England and towards us a worry? That would suggest the precipitation will turn wet earlier than expected?

I wouldn't think so, I would think that is where the precipitation is heading into colder air and turning to snow.
as can be seen n the Gif below.

Gonzo

I've given up trying to measure the snow. This morning it was easy as it was an even 3 inches but now it's all over the place. Easily 6 to 8 inches in parts and over 12 in some drifts.Those dusty ice pellets have added to the snow depth here significantly.