Severe Frost countrywide + Occasional Snow Showers in the East from Thursday 9th Feb

squarecircles

Checks thread,ohhh dear, backs away* na nite.

Gaoth Laidir

lucernarian wrote: »

"there was also cloud cover and therefore no cold surface layer built up to advect over here"

Some nice observations there, but it seems to hang off the line I quoted above. I don't get what this whole cloud cover = less snow idea is based on. What of inversions which led to higher cloud cover and extremely cold temperatures? Or of the oft-observed effects of northerly outbreaks in early March, where sunlight warmed the ground and prevented snow from sticking?

At this time of the year there is a net loss of heat through radiation to Space. Clear skies at night time maximise this loss, overcast layers of stratocumulus - which we've had - reduces it. These layers often do form beneath inversions, which was the case this week. The inversion eroded and elevated a bit in the past 24 hours as cloud thickened, as in the Albermarle soundings (the direct upwind source of our air today) below show. Note also the 4-degree increase in 850-hPa temperature, from -10 to -6.




March is a different story to February, so it has no bearing on today's analysis.

Again, not sure what the relevance is of snow *falling* at 1c. It's when it sticks that counts to the public at large in terms of disruption, and to me as a weather nerd I guess.

What I do know is that a wet bulb temperature can be positive (slightly) even if the dewpoint is negative. Going by nothing more than experience, such a scenario results in snow (perhaps wet snow) falling and sticking but would inevitably melt, and there's my "brush test" where sweeping snow away would leave traces of slush behind rather than just wet ground or ice.

For snow to stick it must first fall. Forecasting whether it will fall is the first step. Today it rained at low levels. No amount of rain will accumulate as snow. As I said, we can have either rain or snow at 1 degree, depending on wet-bulb temperature, which is around about 1/3 of the dewpoint depression below the temperature (e.g. temperature 1, dewpoint -2 => wet bub =0 C). So with temperature of +1 C, if the dewpoint is 0, the wbt is above 0, and snow will most likely melt. If dewpoint is -3, wbt is below zero, so it will most likely remain frozen. Once we've determined that snow is reaching the ground then it's up to a combination of ground temperature and snowfall rate that will affect if and how fast it will melt or accumulate. After a few nights of clear skies and frost the ground will be a lot colder than after a few nights of cloud cover and air temperatures staying above zero.

M.T. Cranium

Currently below marginal parameters for snow (other than very high summits) but a colder bubble is indicated over Britain now, that will drift west across Ireland with somewhat better conditions mid-day. Probable effect will be to intensify shower cells and keep temperatures from rising very much, mixed wintry showers and maybe a bit of thunder too. This moves off to the west by tonight and much milder air will dominate for the next week, in fact, model output looks very mild for next weekend (mid-teens possible). Aside from hills, best bet for seeing any hail or snow showers today would be inland north-central counties like Cavan, Monaghan and later into parts of west Ulster.

Graces7

Sudden strange loud gusts of wind.. not been outside yet but moonlight...West Galway...

kingshankly

Jordan Quiet Comma wrote: »

Raining heavy in Drogheda. Mournes / Wicklow Mts should do well overnight despite the naysayers.

Looking out my window at the Mourne's not a pick of snow on them

Graces7

May I please as a long term poster here thank and congratulate all the forecasters and posters of positive input for a sterling work in our uncertain and changeable weather?

THANK YOU!

Oneiric 3

According to the 'Indo' :rolleyes: we are currently in the grip of a 'Scandinavian Shiver'.

http://www.msn.com/en-ie/news/national/scandinavian-shiver-sweeps-across-country/ar-AAmPaxU?li=AAmb2oK&ocid=spartandhp

They helpfully warn us that this 'Scandinavian Shiver' could bring temps to a bone chilling, mind numbing 3 to 6c later today.

Christ on a bike.. :rolleyes:

sjb25

Oneiric 3 wrote: »

According to the 'Indo' :rolleyes: we are currently in the grip of a 'Scandinavian Shiver'.

http://www.msn.com/en-ie/news/national/scandinavian-shiver-sweeps-across-country/ar-AAmPaxU?li=AAmb2oK&ocid=spartandhp

They helpfully warn us that this 'Scandinavian Shiver' could bring temps to a bone chilling, mind numbing 3 to 6c later today.

Christ on a bike.. :rolleyes:

Oh Jesus I better get extra coal in :eek: does anyone on here no exactly what time it may rain at my house today and mite it turn to hail or snow if so what time I need to know I NEED to know

lucernarian

Gaoth Laidir wrote: »

At this time of the year there is a net loss of heat through radiation to Space. Clear skies at night time maximise this loss, overcast layers of stratocumulus - which we've had - reduces it. These layers often do form beneath inversions, which was the case this week. The inversion eroded and elevated a bit in the past 24 hours as cloud thickened, as in the Albermarle soundings (the direct upwind source of our air today) below show. Note also the 4-degree increase in 850-hPa temperature, from -10 to -6.




March is a different story to February, so it has no bearing on today's analysis.



For snow to stick it must first fall. Forecasting whether it will fall is the first step. Today it rained at low levels. No amount of rain will accumulate as snow. As I said, we can have either rain or snow at 1 degree, depending on wet-bulb temperature, which is around about 1/3 of the dewpoint depression below the temperature (e.g. temperature 1, dewpoint -2 => wet bub =0 C). So with temperature of +1 C, if the dewpoint is 0, the wbt is above 0, and snow will most likely melt. If dewpoint is -3, wbt is below zero, so it will most likely remain frozen. Once we've determined that snow is reaching the ground then it's up to a combination of ground temperature and snowfall rate that will affect if and how fast it will melt or accumulate. After a few nights of clear skies and frost the ground will be a lot colder than after a few nights of cloud cover and air temperatures staying above zero.

There is nothing in the soundings to show clear skies or the lack thereof had any impact on the upper level air mass itself. Air temperatures are what determine if snow will stick for the most part in any source I've read and in various cases I've lived through. You said earlier that wet bulb temps would be negative when dewpoints hit 0, and then you've clarified/backtracked on that.

What follows about snow sticking is what I'm skeptical about. Ground temperatures play a part, accumulation rate plays a tiny part, but air temperatures and the temperature of the snow itself is the overwhelming factor.

Back in Nov 30th 2010, from about 12pm to 3pm, snow wasn't sticking in Dublin city centre and roads were extremely slushy. Why? It wasn't because it had snowed that morning - which would cool the underlying ground far more than a surface frost because water and ice have such high heat capacity - but because air temperatures were hitting 1.5/2 degrees Celsius (in hindsight probably the temperature where wet bulb temp turned positive).

The melted ice and surface water that afternoon on the roads in inner city Dublin had little bearing on subsequent hours, as history shows us.

Oops69

"mid- teens" this week according to MT, one of the most depressing terms in forecasting imo, its either annoyingly warm in januraty or feburary or too cool in summer , The Romans really got the name wrong for this country , not Hibernia , should be 'Mid- teenia' , god , please give us some decent weather.

Clonmel1000

No severe frost nationwide and practically. I snow anywhere. Is that about the size of it?

Gonzo

Clonmel1000 wrote: »

No severe frost nationwide and practically. I snow anywhere. Is that about the size of it?

there was a dusting on mountain tops but no lying snow or frost in lower lying areas. But we are officially in a severe Scandinavian shiver according to the Indo so it must be true!

I've seen more wintry looking frosty scenes here during normal weather that doesn't even make the headlines or cause a topic of conversation here!

Graces7

Oneiric 3 wrote: »

According to the 'Indo' :rolleyes: we are currently in the grip of a 'Scandinavian Shiver'.

http://www.msn.com/en-ie/news/national/scandinavian-shiver-sweeps-across-country/ar-AAmPaxU?li=AAmb2oK&ocid=spartandhp

They helpfully warn us that this 'Scandinavian Shiver' could bring temps to a bone chilling, mind numbing 3 to 6c later today.

Christ on a bike.. :rolleyes:

Actually relieved to read this as I am unable to get anywhere near warm and thought it was my illness.

Met for Galway say 4 degrees right now and that east wind is an iced knife.

Small craft warning says force 6-7, easterly. A howling one.

West Galway

Macy0161

Just had a bit of graupel here near Roundwood.

LEIN

Icy mix falling here atm.

Periscal

Precip forming of east Wicklow,once it hits us it will be snow here west wicklow

DOCARCH

Light graupel shower here in Dublin 16. 4.1c DP -0.1c atm.

Gonzo

shower of ice/graupel here too

q85dw7osi4lebg

Graupel shower here at Meath coast. Winds seem to have picked up a bit in the last while.

pad199207

Snow Grains here in Kildare now

Snowbiee21

It won't last long most showers will be rain during the day

JCX BXC

I'm rarely this negative, but god this has been the worst failure of a weather event in a long time. Minimum temperature here in West Clare was -0.7c over the whole cold spell! There was barely ice on the car. Even the UK had bitter disappointment, with the forecasts being even more certain than here just for most areas to get sleet or rain with maybe 5 minutes of snow. Looks like we were the wrong side of marginal. Oh well, we can't expect every easterly to be the deep freeze we're looking for.

Anyway, look ahead. Any nice storms on the way?

average_runner

Just back from watching the kids play hockey. It got cancel after 30 mins, just too cold.

Baltic out there.

average_runner

JCX BXC wrote: »

I'm rarely this negative, but god this has been the worst failure of a weather event in a long time. Minimum temperature here in West Clare was -0.7c over the whole cold spell! There was barely ice on the car. Even the UK had bitter disappointment, with the forecasts being even more certain than here just for most areas to get sleet or rain with maybe 5 minutes of snow. Looks like we were the wrong side of marginal. Oh well, we can't expect every easterly to be the deep freeze we're looking for.

Anyway, look ahead. Any nice storms on the way?

The cold wasn't for clare. Last time I checked clare wasn't on the east coast

Gonzo

JCX BXC wrote: »

I'm rarely this negative, but god this has been the worst failure of a weather event in a long time. Minimum temperature here in West Clare was -0.7c over the whole cold spell! There was barely ice on the car. Even the UK had bitter disappointment, with the forecasts being even more certain than here just for most areas to get sleet or rain with maybe 5 minutes of snow. Looks like we were the wrong side of marginal. Oh well, we can't expect every easterly to be the deep freeze we're looking for.

Anyway, look ahead. Any nice storms on the way?

agree with everything, as usual the media hyped this but most of us here knew this spell was never really going to amount of much. Easterly's are usually great, this wasn't a proper easterly, just a breakaway blob of cold that went awol. Next 2 weeks is looking very mild, possibly almost feeling warm next weekend where a few places could sneak a 15 or 16C, then possibly cooler after that. Nothing really stormy on the horizon, just unsettled and mild.

average_runner

Gonzo wrote: »

agree with everything, as usual the media hyped this but most of us here knew this spell was never really going to amount of much. Easterly's are usually great, this wasn't a proper easterly, just a breakaway blob of cold that went awol. Next 2 weeks is looking very mild, possibly almost feeling warm next weekend where a few places could sneak a 15 or 16C, then possibly cooler after that. Nothing really stormy on the horizon, just unsettled and mild.

Bring on the warm weather. Time to look forward to a nice summer and worry about winter next Nov.

Predicting weather is not an exact science, but ye lot do a great job and keep people alert that something could happen so we can plan around it.

Graces7

Gonzo wrote: »

agree with everything, as usual the media hyped this but most of us here knew this spell was never really going to amount of much. Easterly's are usually great, this wasn't a proper easterly, just a breakaway blob of cold that went awol. Next 2 weeks is looking very mild, possibly almost feeling warm next weekend where a few places could sneak a 15 or 16C, then possibly cooler after that. Nothing really stormy on the horizon, just unsettled and mild.

Sounds.. bliss.

Gaoth Laidir

lucernarian wrote: »

There is nothing in the soundings to show clear skies or the lack thereof had any impact on the upper level air mass itself. Air temperatures are what determine if snow will stick for the most part in any source I've read and in various cases I've lived through. You said earlier that wet bulb temps would be negative when dewpoints hit 0, and then you've clarified/backtracked on that.

What follows about snow sticking is what I'm skeptical about. Ground temperatures play a part, accumulation rate plays a tiny part, but air temperatures and the temperature of the snow itself is the overwhelming factor.

Back in Nov 30th 2010, from about 12pm to 3pm, snow wasn't sticking in Dublin city centre and roads were extremely slushy. Why? It wasn't because it had snowed that morning - which would cool the underlying ground far more than a surface frost because water and ice have such high heat capacity - but because air temperatures were hitting 1.5/2 degrees Celsius (in hindsight probably the temperature where wet bulb temp turned positive).

The melted ice and surface water that afternoon on the roads in inner city Dublin had little bearing on subsequent hours, as history shows us.

OK I think you're misunderstanding what I'm saying. I never said wet bulb is negative when dewpoint is 0. Read it again. Wet bulb is always higher than dewpoint, except when it's 100% relative humidity, when all three are the same value. If wet bulb is below about 0.5 degrees then snow will not melt easily.

So air temperature and dewpoint/wbt play a part in whether snow will stick because these directly affect the snow itself as it's falling. Wet snow will not accumulate as easily and will form more slush than dry snow. Which type of snow we get is related to the air and humidity. Dry snow falling at the same rate (liquid equivalent) as wet snow will form a deeper layer, and the air trapped inside it will act as an insulator against any warmth in the ground. Wet snow will melt easier than dry snow for the same ground temperature.

The type of ground also has a bearing. Snow will accumulate on grass much easier than concrete (due to the insulating effect of the air between the blades of grass), which is why a city street may be slushy while a grassy park is white.

The sounding above is a simple dry adiabatic profile in the lowest few hundred. That means that the air is cooling quickly with height, so anything that will cool the surface layer will help.prolonge melting as the snow falls.

Villain

From Camara hill a few mins ago, snowline is rather high!

https://twitter.com/carlowweather/status/830749279497121792

horsefarm

Its bitter out. Temp has dropped to 2.5c again with icey hail and a windchill of -5.4c S.Dub 260m
A truely poxy day