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

Robxxx7

Oneiric 3 wrote: »

Elmer Blooker wrote: »

-0.5c and rising too. There's ALWAYS a warm sector lurking somewhere.
These UK temperatures are quite odd? Compare Lancashire with Cornwall, and Belfast too. How the hell can the far south west of England be much colder than northern England? Answer: a small warm sector.
edit: -0.4c now. same old .................

I reckon with the low moving closer, that it would be pulling up colder air from the near continent, where temps are much lower than they are over the North Sea, up over SW England.

@17-PDR, a curious report alright. As Nacho said, it could be down to 'wet-blub' temps or something, which, as GL said before, (and if I remember correctly) need to be below 0.5c for snow. I have no idea what the wet blub temp would be in Valentia at the mo.

I can’t give an exact wet bulb temp but using the 1/3 rule and my current weather station data ( Mid Kerry) Current temp 0c Dew point -4.4c would give wet bulb approx -1.5c not exact science but general idea

ZX7R

nacho libre wrote: »

So is the sublimation process greater with wet snow than dry snow? Also what exactly happens when wet snow falls on dry snow?

It will stick to everything and could give higher accumulations, higher treat of downed power lines etc, it will also freeze quicker, and harder to clear, it is also a factor in avalanches layers of dry snow wet snow on top of causes a layer to slide ect

loughside

Deleted User wrote: »

Frontal edge almost to the IoM now, but theres still streamer development in the north Irish sea.

http://www.meteoradar.co.uk/

Yes, that band seems to be headed north west over the IOM and towards louth/down coasts?

Whats happening here?? Will it continue on that track?

Gaoth Laidir

nacho libre wrote: »

So is the sublimation process greater with wet snow than dry snow? Also what exactly happens when wet snow falls on dry snow?

With dry snow the dewpoints/relative humidity are lower, so the air is drier and water molecules will more easily sublimate into it. With wet snow, higher dewpoints/relative humidity means slower evaporation.

When wet snow falls on dry snow you get medium-wetness snow! :pac:

sdanseo

First few frames of ECM out now. Not a smidgeon of sleet to be seen. All snow, mostly moderate.

Gonzo

I've a feeling this may turn to sleet and rain in places by the morning, there is a relatively decent increase in temperatures over France heading our way, compared to what we have now. Emma is mostly rain over France and looks like its close to turning to sleet across southern english coastline.

Even with today's sub zero temperatures a thaw tried to get going. Small icicles on the car, roof and garden table. With temperatures likely above 0C tomorrow I reckon a thaw is definitely on the cards regardless of what is falling out of the sky.

BarryD2

Gonzo wrote: »

I've a feeling this may turn to sleet and rain in places by the morning, there is a relatively decent increase in temperatures over France heading our way, compared to what we have now. Emma is mostly rain over France and looks like its close to turning to sleet across southern english coastline.

Even with today's sub zero temperatures a thaw tried to get going. Small icicles on the car, roof and garden table. With temperatures likely above 0C tomorrow I reckon a thaw is definitely on the cards regardless of what is falling out of the sky.

Which will win out I suppose is the question. Just sleet here at 150m above sea level in Carlow/ Wexford area.

Still if the roads are wet & slushy and it freezes in due course, it'll be tricky.

Oneiric 3

On the topic of wet vs dry snow, while the snow over the last couple of days certainly has the high quality dry and dusty feel about it, it still lacks a certain quality from the snow that a true Arctic northerly brings.

sdanseo

BarryD2 wrote: »

Which will win out I suppose is the question. Just sleet here at 150m above sea level in Carlow/ Wexford area.

Still if the roads are wet & slushy and it freezes in due course, it'll be tricky.

You probably have very light snow rather than sleet, Temp -1 DP -4 in Oak Park Carlow, nearly 100m lower than you.

Casualsingby

Oneiric 3 wrote: »

On the topic of wet vs dry snow, while the snow over the last couple of days certainly has the high quality dry and dusty feel about it, it still lacks a certain quality from the snow that a true Arctic northerly brings.

Is it always wet snow from a potent Northerly like say from a Greenland high or does it depend? I know NW are always wet.

Gonzo

Gonzo wrote: »

I've a feeling this may turn to sleet and rain in places by the morning, there is a relatively decent increase in temperatures over France heading our way, compared to what we have now. Emma is mostly rain over France and looks like its close to turning to sleet across southern english coastline.

Even with today's sub zero temperatures a thaw tried to get going. Small icicles on the car, roof and garden table. With temperatures likely above 0C tomorrow I reckon a thaw is definitely on the cards regardless of what is falling out of the sky.

Afraid so. At Ploumanach on the north Brittany coast the current temp is +3.6 C, while the DP is +3.5 C.

Gaoth Laidir

Some timings for heavy snow (+SN) arrivals at the airports tonight, as per the 5 pm TAFs. Just to give an idea. Light and moderate snow are a given.

Waterford: Intermittent from now.
Cork: Intermittent from 8 pm to 10 am.
Dublin: Intermittent from 9 pm to 9 am.
Shannon: No heavy snow forecast
Knock: No heavy snow forecast.
Kerry: None before 9 pm (end of TAF).
Sligo:

MJohnston

Gaoth Laidir wrote: »

Some timings for heavy snow (+SN) arrivals at the airports tonight, as per the 5 pm TAFs. Just to give an idea. Light and moderate snow are a given.

Waterford: Intermittent from now.
Cork: Intermittent from 8 pm to 10 am.
Dublin: Intermittent from 9 pm to 9 am.
Shannon: No heavy snow forecast
Knock: No heavy snow forecast.
Kerry: None before 9 pm (end of TAF).
Sligo:

When it says "temporarily" in the TAF is that an indication of intermittent conditions then?

sdanseo

Deleted User wrote: »

Afraid so. At Ploumanach on the north Brittany coast the current temp is +3.6 C, while the DP is +3.5 C.

JUst for context though, current 850 temps there on HIRLAM are around +2 degrees.

They are not forecast to drop past -8 over any part of Ireland before late tomorrow night into Saturday AM. Staying below -10 until 10pm or so.

Gaoth Laidir wrote: »

Some timings for heavy snow (+SN) arrivals at the airports tonight, as per the 5 pm TAFs. Just to give an idea. Light and moderate snow are a given.

Waterford: Intermittent from now.
Cork: Intermittent from 8 pm to 10 am.
Dublin: Intermittent from 9 pm to 9 am.
Shannon: No heavy snow forecast
Knock: No heavy snow forecast.
Kerry: None before 9 pm (end of TAF).
Sligo:

Aren't the TEMPOs a sign of intermittent, and in the absence of a TEMPO condition is considered to be foreacast as constant?

HighLine

Temp 0.3c and DP -2.3 in Ashford, Wicklow but here in Wicklow Town, light precipitation is falling as sleet/rain.

Oneiric 3

Casualsingby wrote: »

Is it always wet snow from a potent Northerly like say from a Greenland high or does it depend? I know NW are always wet.

The last two Arctic spells I recall was 2010 and 2000, with the later being far above the former. In Dec 2000, like the current spell, it started off dry, and the snow, when it arrived, just piled up instantaneously. Never seen anything like it, so that defo was a dry snow event. I suppose the 'dryness' of snow depends on many factors, such as a dry air mass, low temps etc. One of the biggest snowfalls in Irish recorded history was back in April 1917, where snow accumulations where not measured in cm or inches, but in feet and metres, and all in a relatively short space of time, and that was an Arctic sourced event.

BarryD2

sdanseo wrote: »

You probably have very light snow rather than sleet, Temp -1 DP -4 in Oak Park Carlow, nearly 100m lower than you.

Ah, I know what sleet is. And I was just out walking in it a while back. But doubtless if ME are right, as temps fall overnight, it'll be thicker. It's -1.5 here at 150m AOD.

wakka12

So this will definitely be a snow event in Dublin ? Just getting a bit worried it'll turn to sleet .

Gaoth Laidir

TEMPO in a forecast means "for less than half of the stated time period".

nacho libre

Oneiric 3 wrote: »

On the topic of wet vs dry snow, while the snow over the last couple of days certainly has the high quality dry and dusty feel about it, it still lacks a certain quality from the snow that a true Arctic northerly brings.

What do you mean? What is it lacking?
I love the sound it makes when under foot. Also it's a sight to behold when it drifts too. As well as that it has accumulated fairly well.

Thanks ZX7R for the explanation about the impact of wet snow on dry snow.

Reati

HighLine wrote: »

Temp 0.3c and DP -2.3 in Ashford, Wicklow but here in Wicklow Town, light precipitation is falling as sleet/rain.

Outside Wicklow town here and Temp dropping again was up to-.5c down to -1.3 now. Dew point not moving.

-1.3 °C Feels Like -7 °C
19.8 km/h Wind from East
Gusts 24.1 km/h
Dew Point: -3 °C
Humidity: 86%

nacho libre

wakka12 wrote: »

So this will definitely be a snow event in Dublin ? Just getting a bit worried it'll turn to sleet .

Perhaps if you are at sea level on the coast and the warm air mixes out the colder air more than anticiptated to, but isn't currently forecast to

sdanseo

sdanseo wrote: »

JUst for context though, current 850 temps there on HIRLAM are around +2 degrees.

They are not forecast to drop past -8 over any part of Ireland before late tomorrow night into Saturday AM. Staying below -10 until 10pm or so.



Aren't the TEMPOs a sign of intermittent, and in the absence of a TEMPO condition is considered to be foreacast as constant?

There are relatively high uppers knocking on the east coast door at +18 hrs. Conditions could be marginal in the morning for those areas.

uck51js9zml2yt

Evelyn Cusack just said One Meter of snow for Dublin/Wicklow followed by flooding

nacho libre

Oneiric 3 wrote: »

The last two Arctic spells I recall was 2010 and 2000, with the later being far above the former. In Dec 2000, like the current spell, it started off dry, and the snow, when it arrived, just piled up instantaneously. Never seen anything like it, so that defo was a dry snow event. I suppose the 'dryness' of snow depends on many factors, such as a dry air mass, low temps etc. One of the biggest snowfalls in Irish recorded history was back in April 1917, where snow accumulations where not measured in cm or inches, but in feet and metres, and all in a relatively short space of time, and that was an Arctic sourced event.

Ah so you don't think it's accumulating well enough. I think it is but we are losing it even with freezing temperatures due to the time of year. However if we had this a month ago, we wouldn't have likely seen the level of showery convection that we had with this event. So you can't have everything. To me this has been an exceptional event just for the depth of cold it has given at this time of year. Some fairly impressive snowfall totals too- with hopefully a bit more to come tonight and tomorrow.

Oneiric 3

The Estonian Hirlam 12z run still seems quite positive about snow, even for eastern coastal fringes, all the way throughout:

http://www.ilmateenistus.ee/ilm/prognoosid/mudelprognoosid/euroopa/?lang=en#layers/temp2mv2,sadufaas

Winds will be blowing in from a very cold UK, so this, in itself, should help to keep temps at an acceptable level. (at least in theory)

Larbre34

Khalid Millions Grouch wrote: »

Evelyn Cusack just said One Meter of snow for Dublin/Wicklow followed by flooding

.......in areas subjected to orographic lift.

Danno

Khalid Millions Grouch wrote: »

Evelyn Cusack just said One Meter of snow for Dublin/Wicklow followed by flooding

At a later stage, Keelan was pushing her on flooding but Keelan wasn't able to seperate coastal flooding from snowfall melt flooding. Evelyn looked tired and never quite answered it wholesomely.

NAGDEFI

Larbre34 wrote: »

.......in areas subjected to orographic lift.

Would my area be subject to orographic lift? 340m asl south Laois?

Oneiric 3

Oneiric 3 wrote: »

The Estonian Hirlam 12z run still seems quite positive about snow, even for eastern coastal fringes, all the way throughout:

http://www.ilmateenistus.ee/ilm/prognoosid/mudelprognoosid/euroopa/?lang=en#layers/temp2mv2,sadufaas

Winds will be blowing in from a very cold UK, so this, in itself, should help to keep temps at an acceptable level. (at least in theory)

DPs even by the morning still seem ok apart from areas of the south coast. Hopefully that warmer air currently coming out of France as mentioned by Gaoth Laidir earlier will be modified by the colder air from the east.