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

pistolpetes11

This is the Technical Scientific thread for discussion on tonight and tomorrows possible snow event, will it snow in my back garden at such and such a time will just be deleted or merged into the other thread which will be linked below



https://www.boards.ie/vbulletin/showthread.php?t=2057817783

Rebelbrowser

I wonder could I ask again a question I posed in the other thread, namely what is different about this set up from normal that gives the big snow risk? I thought you would need deep imbedded cold for such a battleground scenario to occur but I dont see that in the upper temps. What am I missing?

ZX7R

Technical question, as mentioned in the other thread about heavy perception, would met eairann take into account, evaporation snow fall into account when making there forecast for snow fall tonight, as well as the low temperatures

Neddyusa

Anyone care to make lying snow max predictions for ME stations tomorrow and Monday morning?

Sun - Mt Dillon 16 cm

Mon - Gurteen 21 cm

6Z Hirlam for +24 hrs. Indicates the maximum northward position of the front before it starts pulling away to the south and east again.

ninebeanrows

It is important to note- that whilst i don't know the actual parameters behind the above snow chart. In general rain/snow type charts will shade in snow even if there is only a small amount of the precip falling as snow.

Indeed as of yesterday - the EC was showing 50-50 rain and snow in the precipitation for Dublin region. Inland it was 90%+ snow.

Gaoth Laidir

Dublin TAF shows light rain from midnight, tempo sleet from 3 am as light variable winds increase easterly 15 gusting 25 knots from 2 am. The airport may be about the extent of the marine layer, further inland should see more of a snowy nature.

Knock is hell for leather snow...

TAF EIKN 091100Z 0912/1012 VRB03KT 9999 FEW010 SCT025
PROB30 TEMPO 0916/0921 3000 BR BKN005
BECMG 0921/0924 11012KT 3000 -SN SCT003 BKN007
TEMPO 0923/1012 1200 SN OVC002
BECMG 1001/1003 08015KT
TEMPO 1003/1006 09016G26KT BECMG 1010/1012 05013KT=

Rebelbrowser wrote: »

I wonder could I ask again a question I posed in the other thread, namely what is different about this set up from normal that gives the big snow risk? I thought you would need deep imbedded cold for such a battleground scenario to occur but I dont see that in the upper temps. What am I missing?

You won't see that in the upper charts. Looking at 850 hPa temperatures is useless in this setup as we're not talking about convective snow in normal lapse rates. The sounding below shows how temperature is actually fairly constant with height through the bottom few thousand metres, and is at or below zero. 850 hPa temp is only -2 °C, which would not normally hint at anything other than rain.

ZX7R wrote: »

Technical question, as mentioned in the other thread about heavy perception, would met eairann take into account, evaporation snow fall into account when making there forecast for snow fall tonight, as well as the low temperatures

As the whole lower atmosphere is completely saturated there is no scope for evaporative cooling.

Meteorite58

Raining lightly now near Tralee at 5.1C ( could see the mountains get a bit whiter before they became obscured by cloud ). Will be interesting watch the front move into the colder air as it moves up the country later this evening.













No doubt driving conditions Sunday/ Monday going to be testing for a lot of people,

JCX BXC

Temperature quite low here, while Clare is on a yellow rainfall warning I wonder could heavy precip drop the temperature enough to have a flurry?

Gaoth Laidir

The ECM Extreme Weather Index is high for total precipitation by tomorrow night.

Meteorite58

Frontal rain bearing cloud off the SW

Gaoth Laidir

The fact that we have a pair of low centres by morning - one off Wexford but another in Galway Bay - could lead to some subtle variations in the exact extent of that easterly marine layer in the east.



The 12Z ICON has the main bulk of precip back further south, in line with the other models. Note that this model has a known drizzle bias, so it may be overdoing the precip slightly.



Lastest forecast soundings are still showing heavy (wet) snow for many low-lying areas of the midlands and west during the morning.

nagdefy

I feel this event is going to be very much a nowcast.

There'll be surprise falls for some, and others who appeared to be in more favourable areas prior to the event may face disappointment.

That low off Rosslare could drag some colder air further south east possibly?

I'm down with flu symptoms and stuck in Portlaoise Was looking forward to getting some pics at home as i'd rate our chances of a decent fall at 70% or so.

JCX BXC

Almost forgot about the TAF's!

Knock:

BECMG 0921/0924 11012KT 3000 -SN SCT003 BKN007
TEMPO 0923/1012 1200 SN OVC002

Light Snow from 9pm, temporarily moderate from 11pm. Gonna be a white out there!

Shannon:

TEMPO 1009/1014 3000 -RASN

Periods of sleet from 9am-2pm tomorrow.

Dublin

TEMPO 1002/1009 11015G25KT 3000 RASN

Periods of sleet betwen 2am-9am

That's it, nothing for Casement or Cork in the 5pm TAF's other than rain.

Gaoth Laidir

I'm a bit worried about the extent of cloud cover across the country this evening. With that in place there won't be much cooling in that central slab of the country where snow could fall. Almost everywhere us still above zero at the moment. With cloud on the increase its an uphill battle to hold onto our cold layer. It could swing the wrong side of marginal for low levels, or at least a wet mix. Need it to clear a bit.

Gaoth Laidir

Snow warning for Knock airport

EIKN AD WRNG 02 VALID 092200/101000 SNOW MOD 5 TO 10CM FCST =

Only frost warnings for the Dublin and Casement, and crucially only until 1 am. Nowt after that.

EIDW AD WRNG 01 VALID 091700/100100 FROST MOD GND AND FBL AIR DEPOSITIONS LIKELY FCST =
EIME AD WRNG 01 VALID 091600/100300 FROST MOD GND AND FBL AIR DEPOSITIONS LIKELY FCST =

Meteorite58

The rain proper arriving into the SW now.

5.8C now in Tralee RH 86% , SE wind avg 29 km/h ,Bar 997.2 hPa Falling Rapidly






The charts for the next 24hrs.

Meteorite58

High cloud moving up the country with a slight rise in Temps in places

ninebeanrows

HIRLAM accumulations by midday tomorrow

Meteorite58

A lot of water falling in one form or another, lucky Monday is set to be mainly dry.

gimpotronitus

Weathercheck wrote: »

HIRLAM accumulations by midday tomorrow

This shows south dublin around the rathfarnham, ballinteer, tallaght area with a possible covering.

But goes against what MT was saying in his update.

Meteorite58

The Zoom facility on the ARPEGE. That is as much as you can open the page .Not too sure how accurate this is going to be, follow the link below to zoom in closer.

http://www.meteociel.fr/modeles/arpegezoom.php?mode=45&x=384&y=384&ech=26&zoom=2.1

arctictree

The map of Wicklow does not seem to take local topography into account. For example, there is high ground to the east of roundwood (where I live). Also there are valleys with huge differences in elevation across only a few linear miles e.g Glendalough.

Donegal Storm

That's because of the resolution of the model, it's only got 10km grid squares, no model has high enough resolution to take individual valleys into account. I'm not sure how they model height, if they take the average across a grid square or the highest point.

Speak Now

Meteorite58 wrote: »

Almost laughable in that sequence the reluctance of the rain to turn into snow when it hits Waterford at KilkennyWexford boundary. Is it snow or Liam McCarthy!!!!!

arctictree

Donegal Storm wrote: »

That's because of the resolution of the model, it's only got 10km grid squares, no model has high enough resolution to take individual valleys into account. I'm not sure how they model height, if they take the average across a grid square or the highest point.

Sounds about right. Although take Glendalough for example. Average height would probably be much higher than the places where people live.

MJohnston

The WRF NMM is the best resolution model I think we have for Ireland, but the 18z is taking forever to roll out, here's the current latest frame available:

Donegal Storm

Arome is 1.3km, no idea how reliable or accurate it is but this is what it's showing for the morning. A patchy and fairly light covering for most at lower levels, a few favoured areas getting a good dumping though

MetLuver

Gaoth Laidir wrote: »

I'm a bit worried about the extent of cloud cover across the country this evening. With that in place there won't be much cooling in that central slab of the country where snow could fall. Almost everywhere us still above zero at the moment. With cloud on the increase its an uphill battle to hold onto our cold layer. It could swing the wrong side of marginal for low levels, or at least a wet mix. Need it to clear a bit.

I was thinking the same thing since this morning, it's nice to hear someone else mention it. The models cannot take these details onto account and so it may be a good idea to take snow depth charts less seriously with this in mind.

MJohnston

WRF run is a bit more complete now:

Rougies

MJohnston wrote: »

WRF run is a bit more complete now:

It's very bullish on the shadow effect of the Blackstairs and Slieve Bloom mountains!

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.