Snow and Ice Warning : Saturday(PM)/Sunday 9th/10th Dec - TECHNICAL ANALYSIS ONLY

Meteorite58

Very heavy rain now in Tralee. Rain Rate 13mm/h atm, 7.2mm in the last couple of hours, 6.5C, Bar 990.8hPa Falling Rapidly, Windy 10 min avg 32 km/h SSE



The leading edge showing sleet and the beginnings of Snow in Galway

MJohnston

WRF is toying with some snow up in the north of the island late tomorrow, but frustratingly the 18z has no frames beyond this point:



The 12z run was very bullish about that possibility earlier though:

Meteorite58

Gaoth Laidir

I'm calling time on this. Temperatures around the country are just too high for snow to low level. We needed a few degrees less than we have now. Even Mullingar has risen from -4.2 at 7 pm to +0.6 now at 11 pm. Gurteen is 3.2, dewpoint +0.2. I fear the depth of cold may not be enough to give more than cold rain.

Met Office Sigwx chart for 6 am gives sleet, with some freezing rain and some isolated heavy snow, in area B1. Not the widespread SN we hoped.

nagdefy

Gaoth Laidir wrote: »

I'm calling time on this.]

A little dramatic. It's your opinion. A very valid and well backed up one, and respected may i add. But stating 'i'm calling time on this' suggests an inflated sense of one's importance:D

Gaoth Laidir

nagdefy wrote: »

A little dramatic. It's your opinion. A very valid and well backed up one, and respected may i add. But stating 'i'm calling time on this' suggests an inflated sense of one's importance:D

I mean I'm going to bed!! :cool:

nagdefy

Gaoth Laidir wrote: »

I mean I'm going to bed!! :cool:

Ha ha ha! Fair enough!

The phraseology i thought you meant with one wave of your hand you were calling off the event:D

Lol!!

Liffey4A

I search for your posts Gaoth Laidir as I think they help balance out the wide range of opinion on this board.
Looking forward to see what the outcome of these models will be tomorrow.

Gaoth Laidir

00Z reports. Still no sign of widespread sub-zero.

PsMETAR BALD 100000Z 09009KT 9999 FEW015 SCT030 BKN050 03/M02 0995 MSL=
PsMETAR BELM 100000Z AUTO 10011KT 9999NDV FEW023/// SCT031/// BKN100/// 02/M01 0993 MSL=
PsMETAR BYHE 100000Z AUTO 12004KT 9000NDV BR BKN040/// M01/M01 0996 MSL=
PsMETAR CLAR 100000Z AUTO 10010KT //// // ////// 02/00 0994 MSL=
PsMETAR CORK 100000Z 12014KT 5000 +RA SCT002 BKN003 07/07 0991 MSL=
PsMETAR DUBL 100000Z 10008KT 9999 FEW017 BKN035 01/M01 0996 MSL=
PsMETAR FINN 100000Z AUTO 11007KT 9000NDV BR BKN044/// BKN220/// M00/M01 0996 MSL=
PsMETAR GURT 100000Z AUTO 11012KT 9999NDV -RA FEW033/// BKN041/// OVC049/// 03/02 0993 MSL=
PsMETAR JOHN 100000Z AUTO 12010KT 6000NDV -RA OVC003/// 06/05 0994 MSL=
PsMETAR KNOC 100000Z AUTO 11010KT //// // ////// M00/M02 0995 MSL=
PsMETAR MACE 100000Z AUTO 09019KT 2600NDV -RASN OVC015/// 03/02 0990 MSL=
PsMETAR MALI 100000Z AUTO 14009KT 9999NDV BKN050/// 01/M01 0996 MSL=
PsMETAR MULL 100000Z AUTO 10006KT 9999NDV BKN024/// OVC030/// 01/M02 0995 MSL=
PsMETAR OKPK 100000Z AUTO 12007KT 9999NDV DZ FEW016/// BKN039/// OVC044/// 03/02 0995 MSL=
PsMETAR ROCH 100000Z AUTO 13019KT 4000NDV RA BKN006/// 08/07 0991 MSL=
PsMETAR SHAN 100000Z 10012KT 6000 RA FEW007 BKN013 04/04 0992 MSL=
PsMETAR SHER 100000Z AUTO 08010G28KT 7000NDV -RA BKN005/// 09/08 0989 MSL=
PsMETAR VALE 100000Z AUTO 13011G21KT 9999NDV -SHRA BKN031/// 10/07 0988 MSL=

Donegal Storm

Gaoth Laidir wrote: »

00Z reports. Still no sign of widespread sub-zero.

Forecast on hi res models has been for 0-2C generally at ground level for the past couple of days, freezing level around 100-250m

I've been skeptical all along of widespread low level snow but don't think anything is necessarily different at the moment to what was forecast

Billcarson

nagdefy wrote: »

A little dramatic. It's your opinion. A very valid and well backed up one, and respected may i add. But stating 'i'm calling time on this' suggests an inflated sense of one's importance:D

Perhaps but the guy knows his stuff and I would take what he says seriously. Anyway time will tell.

nagdefy

Billcarson wrote: »

Perhaps but the guy knows his stuff and I would take what he says seriously. Anyway time will tell.

Not saying he doesn't.

Gaoth Laidir is going for UK Met and it's that v Met Eireann. We'll see.

Billcarson

nagdefy wrote: »

Not saying he doesn't.

I know sorry, but if there is one guy in here who I look to regards snow chances it's him (not giving him a big head) . I think I know a reasonable amount about weather but I wish I had his knowledge. Although I hope he is wrong on this occasion but what he is saying makes sense.

Danno

Gone to +4.1c here in south Laois now and dewpoints have rallied up to +3.1c. Quite a breeze blowing too, averaging 11mph with gusting into the mid 20s. It seems this front has marched further north than expected allowing milder/modified air to flood in across the south east and east.

Gaoth Laidir

The HiRLAM says this is what we should be seeing right now. Widespread snow through much of Connaught and into the midlands. It's not turned out this way yet.

The other models shows much less for this time, mostly just a small spot up around Knock area. So we can say that so far, the HiRLAM is not doing well with this situation.



Right, now bed!

nagdefy

Billcarson wrote: »

nagdefy wrote: »

Not saying he doesn't.

I know sorry, but if there is one guy in here who I look to regards snow chances it's him (not giving him a big head) . I think I know a reasonable amount about weather but I wish I had his knowledge. Although I hope he is wrong on this occasion but what he is saying makes sense.

It's heavy weight stuff..

Met Eireann and MT v Gaoth Laidir and Met UK

Pay per view!:D

Neddyusa

Gaoth Laidir wrote: »

The HiRLAM says this is what we should be seeing right now. Widespread snow through much of Connaught and into the midlands. It's not turned out this way yet.

The other models shows much less for this time, mostly just a small spot up around Knock area. So we can say that so far, the HiRLAM is not doing well with this situation.



Right, now bed!

You might have hit the hay slightly too soon GL.
That Hirlam looks very similar to the radar right now:

Gaoth Laidir

Neddyusa wrote: »

You might have hit the hay slightly too soon GL.
That Hirlam looks very similar to the radar right now:

Oh good, so maybe it's getting its act together now. Game on!

Donegal Storm

Does anyone know how the netweather radar actually works? How does it pick up sleet and snow and is it actually accurate?

M.T. Cranium

I'm guessing it's a computer program designed to interpret existing radars and match observations of any kind with precip type.

As such it is estimating, not reporting.

JCX BXC

Donegal Storm wrote: »

Does anyone know how the netweather radar actually works? How does it pick up sleet and snow and is it actually accurate?

As above, it's an estimation game. They use temperatures reported by met stations and estimate temperatures for other areas.

M.T. Cranium

The thing that often swings the outcome in these knife-edge situations is the last minute effects of latent heat of condensation. The column cools that extra half degree and sleet can turn over to moderate snow. Time of day is on your side, most marginal situations profit between midnight and noon, lose ground noon to midnight.

The factors working in the wrong direction would be increased inflow from Irish Sea (surface temps raised and heat distributed into the air mass on land), urban heat island (stop driving now) and feedback from recently saturated ground where it's raining hard now.

The models have tried to parse all of the above and come up with their scenarios, the consensus seems to be snow slowly winning the battle against rain with a faster advance once the first low of the two has moved well past Wexford. The second low will lose all contact with Atlantic warmth around 09z coming inland and this may accelerate the push of snow to the south and even southwest for a time.

Rougies

M.T. Cranium wrote: »

I'm guessing it's a computer program designed to interpret existing radars and match observations of any kind with precip type.

As such it is estimating, not reporting.

It uses observations, model output, and radar. I don't know what model/models they use or what observation stations but it's actually surprisingly accurate. Still an estimation of course but I would say it's a good guide from experience.

Donegal Storm

M.T. Cranium wrote: »

I'm guessing it's a computer program designed to interpret existing radars and match observations of any kind with precip type.

As such it is estimating, not reporting.

Yeah just wondering it it takes atmospheric profile into account or if it's a more simplistic feature based on surface reports

Seems reasonably accurate so far going by reports in the other thread

Gaoth Laidir

Met Éireann's aviation chart for 12Z shows an area south of a line Wesport-Dublin. A front lies Limerick-Rosslare, moving southeastwards at 10 knots. The freezing height is 2000 ft from Limerick to Wexford and 1000 ft just north of that, from Ennis to say Gorey.

For this area they give light, occasional moderate rain or sleet, with occasional moderate snow north of the front. Isolated heavy rain.

Gaoth Laidir

Warnings out for severe ground and moderate air frosts at some of the airports overnight tonight.

Cork EICK AD WRNG 01 VALID 101930/110900 FROST MOD GND AND FBL AIR DEPOSITIONS LIKELY FCST =

Dublin EIDW AD WRNG 02 VALID 101830/111000 FROST MOD GND AND FBL AIR DEPOSITIONS LIKELY BECMG 1022/1101 SEV GND and MOD Air FCST =

Shannon EINN AD WRNG 01 VALID 101815/110930 FROST MOD GND AND MOD AIR DEPOSITIONS LIKELY FCST =

Casement EIME AD WRNG 01 VALID 101815/111000 FROST MOD GND AND FBL AIR DEPOSITIONS LIKELY BECMG 1022/1101 SEV GND and MOD Air FCST =

Knock EIKN AD WRNG 01 VALID 101400/110930 FROST FBL GND AND FBL AIR DEPOSITIONS LIKELY BECMG 1017/1019 SEV GND and MOD Air FCST =

MJohnston

So I thought it'd be interesting to do a bit of model quality comparison, seeing how various forecasts fared from a day and a bit out. I took the live Netweather precip-type radar for 12pm today and created a graphic comparing it to the 0z runs from yesterday of a range of models:



You can view a full size version here.

The ECM unfortunately doesn't seem to have a Precip Type chart, but if anyone has one, I can slot that in.

Other than that, here's my overly simplified grades for each model:

• ECM - C: Hard to fully judge this one without the precip types showing up, but it looks to have gotten the positioning of the heaviest precip correct.
• ARPEGE - B: Positioning looks great, and the distribution of snow to rain looks close to reality, overall intensity seems to be about right too. Slight marks off for missing some of the southern snowfall, and over-estimating the east a little.
• WRF - E: Terrible positioning, especially as the snow never reached that far north at any point that I can see. Far too intense. Slight plus points for correctly calling the Irish sea effect on the Dublin area.
• ICON - E: About the same as the WRF, but slightly less intense.
• GFS - E: Poor resolution doesn't tell us much, but looks about the same as the two above.
• HIRLAM - Although it showed snow much further north than it reached, it did indicate only very light amounts in that area. Otherwise seems to have performed decently at showing the higher intensity areas, and again spots that Irish sea effect (no model seemed to miss this, which is good).

So the ARPEGE would be the winner here for me. I'd like to do one of these for the snow accumulation charts, but I don't have any live data on what the actual snow accumulation is, would anyone be able to supply that? Hopefully this is useful!

Meteorite58

Cloud covering much of Ireland but the snow fields in Western and Northern counties are showing up well.

MJohnston

Meteorite, did the cloud clear enough before sunset to get a better snapshot of the snow coverage across more of the island?

Villain

MJohnston wrote: »

So I thought it'd be interesting to do a bit of model quality comparison, seeing how various forecasts fared from a day and a bit out. I took the live Netweather precip-type radar for 12pm today and created a graphic comparing it to the 0z runs from yesterday of a range of models:



You can view a full size version here.

The ECM unfortunately doesn't seem to have a Precip Type chart, but if anyone has one, I can slot that in.

Other than that, here's my overly simplified grades for each model:

• ECM - C: Hard to fully judge this one without the precip types showing up, but it looks to have gotten the positioning of the heaviest precip correct.
• ARPEGE - B: Positioning looks great, and the distribution of snow to rain looks close to reality, overall intensity seems to be about right too. Slight marks off for missing some of the southern snowfall, and over-estimating the east a little.
• WRF - E: Terrible positioning, especially as the snow never reached that far north at any point that I can see. Far too intense. Slight plus points for correctly calling the Irish sea effect on the Dublin area.
• ICON - E: About the same as the WRF, but slightly less intense.
• GFS - E: Poor resolution doesn't tell us much, but looks about the same as the two above.
• HIRLAM - Although it showed snow much further north than it reached, it did indicate only very light amounts in that area. Otherwise seems to have performed decently at showing the higher intensity areas, and again spots that Irish sea effect (no model seemed to miss this, which is good).

So the ARPEGE would be the winner here for me. I'd like to do one of these for the snow accumulation charts, but I don't have any live data on what the actual snow accumulation is, would anyone be able to supply that? Hopefully this is useful!

Harmonie was on the money, like really really accurate 24 hrs out.