Snow showers, 27th/28th

Nqp15hhu

Temps stayed around 2.5c all night and we have graupel and icy rain!

Though icon did forecast some milder air during the night. We will see what happens with this system tonight.

I would love to drive to 300 metres but I crashed my car in snow last winter and am very anxious driving in snow now.

Synoptically, the airmass is almost saturated. Meaning that the air is too saturated to cool around the snow flakes on descent.

http://theweatherprediction.com/habyhints4/1005/

“ The cooling will dramatically slow once the relative humidity reaches 100% since the rate of evaporation will be considerably less. ”

So definitely no low level snow today. Despite the low temps.

Danno wrote: »

True that, but you have to factor in heavier bursts that can bring down the freezing level, then couple in areas that can maintain a sub 1c air column because of geographical features.

It all gets messy in these marginal set-ups.

The ever eternal optimists cling on to these blind-spots. (I do sometimes too.)

Yes I’m looking around visually and the snow line is varying a lot this morning, even on some hills there are different snow lines laterally. It is very marginal.

I can see a snow line of 250 metres to as high as 350metres. So I think we can throw this one in the bin, it’s not happening.

Rougies wrote: »

A good rule of thumb is -0.5C per 100m. So ~3C at sea level would put freezing level at about 600m. This is the level where snow will stick and stay stuck. At lower levels there would be snow to wet snow to sleet to rain, with the snow zone compromising of gradually decreasing stickiness and stuckness properties

I always thought the dry bulb temperature dropped about 1c every 400 feet ascended, but in these saturated air masses it’s difficult to estimate the freezing level.

Nqp15hhu

For those of you who wonder why it sometimes rains at 1c-2c.

This article explains that snow at above freezing temperatures occurs due to the removal of heat from the air as the snowflake evaporates, this process sustains an envelope of sub zero air within the positive temps. (As evaporation will pull heat out of the air.)

So with a high humidity and temp of 2c there is little to no evaporation occurring, or not enough to sustain a constant envelope of subzero air around the snowflake.

http://www.sciencebits.com/SnowAboveFreezing

From the chart, you can see with a temp of 2.5c, the RH must be no higher than 70%. With the no melting line being at 60%.

catrat12

Light dusting of snow this morning and Baltic out in the wind
Dublin mountains

*eadaoin

My family are reporting heavy sleet showers in Ballina, Co Tipp this morning.

Gaoth Laidir

Be careful assuming certain lapse rates (rate of cooling with height) because it varies widely from day to day and setup to setup.

For a well-mixed atmosphere (a convective setup) the environmental lapse rate will be roughly the same as the dry adiabatic lapse rate (DALR, 9.8 °C/km), so about 1 degree per 100 m; but only if the air is not saturated. Once it reaches saturation it will cool much more slowly, about 4.5 °C/km or half a degree per 100 m. That's the saturated adiabatic lapse rate, SALR.

In frontal situations it can be completely different, and the ELR can even be negative if there is an inversion. That's why soundings are so important.

Unfortunately we don't have any from 06Z this morning but Valentia's 00Z one shows a warm dry layer following the DALR (red lines) up to about 950 hPa (~300 m), where it becomes saturated and roughly follows the SALR (green dashed lines). Extrapolate the cyan trajectory line down to the surface and it will give you the temperature that a snowflake will follow.

Of course that was hours ago and during the frontal passage. The forecast soundings show things much colder now. The one for Sligo for 10 am is shown second. The snowline would be at about 100 m with that.

Here is a post I did a while back.

SouthWesterly

Just had a hail shower.
2.7c
North kerry

Gaoth Laidir

Latest wet-bulb temperatures. We need them to fall a bit more for comfort. Mullingar, Casement and Dublin Airport are all just below 1.0, but we'd like them closer to 0.5 or below.

*eadaoin

Sleet thats turning into heavy snow at times now, close to Thurles, Co Tipp.

Gaoth Laidir

Based on the Met Éireann 12Z aviation chart. Mostly rain, sleet and hail showers, but isolate snow showers, more frequent on mountains.

The UKMO's 18Z chart has a more concentrated area just ahead of that approaching occlusion, encompassing the midlands northeast, with isolated snow showers.

King of Spades

Had some snowflakes blowing in the breeze a short while ago. Tara, Meath. 500 ft asl.

Graces7

Gaoth Laidir wrote: »

The UKMO's aviation chart for 06Z has an area including all but the midlands and southeast of Ireland in which it gives occasional heavy sleet and hail showers, with occasional heavy snow showers "mainly on mountains". Not allowed to post it due to copyright.

We have had substantial hail showers. It is banked against the wall and had blocked the door :eek:

prosaic

Truskmore has a fairly good covering. Ends of mountains closer to coast don't have any snow

Kermit.de.frog

Today is text book wintry showers at lower elevations, a mix of everything.

Reckless Abandonment

Showers coming from the North West never really make it to Dublin. We need something a bit more organised

pad199207

Status Yellow - Snow/Ice warning for Cavan, Monaghan, Donegal, Longford, Louth, Leitrim, Roscommon and Sligo

Met Éireann Weather Warning

Wintry showers today (Sunday) and tonight with some accumulations possible. Risk of icy stretches on untreated surfaces.

Valid: 06:00 Sunday 27/12/2020 to 07:00 Monday 28/12/2020

Issued: 10:04 Sunday 27/12/2020

Graces7

Kermit.de.frog wrote: »

Today is text book wintry showers at lower elevations, a mix of everything.

Yep! And the cold is astonishing . It has gone very very dark out here and something is coming down....

west mayo offshore

Nqp15hhu

Gaoth Laidir wrote: »

Based on the Met Éireann 12Z aviation chart. Mostly rain, sleet and hail showers, but isolate snow showers, more frequent on mountains.

The UKMO's 18Z chart has a more concentrated area just ahead of that approaching occlusion, encompassing the midlands northeast, with isolated snow showers.

What about tonight’s system?

Gaoth Laidir

catrat12 wrote: »

Light dusting of snow this morning and Baltic out in the wind
Dublin mountains

Nqp15hhu wrote: »

What about tonight’s system?

That chart hasn't been issued yet.

Nqp15hhu

Think I might take a scoot up to 300 metres and see what’s there. Probably nothing!

loughside

Nqp15hhu wrote: »

Think I might take a scoot up to 300 metres and see what’s there. Probably nothing!

Strange, over to your east (Antrim Glens) there seems to be plenty -> https://www.bbc.co.uk/news/uk-northern-ireland-55458879

Nqp15hhu

Drove up to 400 feet and decided to turn round because it was hailing intensely and road was getting covered. I am not crashing again.

Also snowline is so random. Some hills have nothing, others are plastered. There was even a hill at 1,000 feet that was green.

Not sure what that’s all about.

screamer

Have faith in the frog, I’m sure the hills around here will have snow, they had a couple of weeks back. North KK/ Laois border.

Nqp15hhu

Oh dear a lot of negativity on Netweather. I was hoping to see something tonight.

I hate these marginal events because it’s random who gets snow.

Such a waste of cold air, it’s not even that warm.

Snowbiee21

Nqp15hhu wrote: »

Oh dear a lot of negativity on Netweather. I was hoping to see something tonight.

I hate these marginal events because it’s so random who gets snow.

That place is always full of negative posts!

Nqp15hhu

Snowbiee21 wrote: »

That place is always full of negative posts!

No it’s on the Irish forum. They are saying snow on the highest hills only.

Such a nightmare.

munsterlegend

Nqp15hhu wrote: »

No it’s on the Irish forum. They are saying snow on the highest hills only.

Such a nightmare.

I know snow is nice to see but this Atlantic muck is more a pain than anything else. Hopefully with a SSW we will see some stuff that’s lasts a day or two.

Nqp15hhu

I usually do really well out of Northwesterlies but not this year.

screamer

And the snow is falling here north Kk/ Laois border. Wet snow won’t stick but it’s belting down and the kids are delighted to see it

OldRio

Snowing like crazy here in Leitrim.

Graces7

I went out to check the mountains and get coal and great swathes of yellow-grey clouds over all the horizons. Half filled the bucket before getting drenched.

The hail is still lying
;
We shall see later. I am so glad folk are getting their snow!.

West Mayo