Cold Spell - Feb 7th to 13th 2021 - Technical Discussion

Gonzo

The jump in temperature is certainly here earlier than expected. I think tonights frontal event will be rain or sleet for many with snow much more confined this time around. Another snow/rain shadow expected here in south Meath so i've already ruled out any snow covering here by the morning.

The last trace bits of snow is now gone and it is fairly sunny here, if it wasn't for that horrible wind it would actually feel on the mild side. The milder temperatures isn't just a result of the Atlantic, it is combining with the beginning of this warm air winter plume moving up from Portugal/Spain. This is partly why the UK mainland will also lose it's depth of cold very quickly from tomorrow. It is blowtorch warmth moving northwards and then eastwards (for the time of year).

Nqp15hhu

Yes the wind is doing the cold air no favours... though the Met Office show a rapid drop to -1c tonight we will see.

I am not convinced.

Tyrone212

Its a touch warmer than forecast at present but temperatures will fall back before the front hits so its immaterial to the forecast for tomorrow IMO.

I think an orange warning will be issued for Donegal, Cavan and Monaghan and Amber for parts of here.

Nqp15hhu

I’m just asking why the rapid rise in temps despite no change in synoptic situation from yesterday.

Nqp15hhu

Nqp15hhu wrote: »

We have had a massive jump in temperature here. What happened? I thought we were under the cold air until late Saturday?

Well us Easterners would tell you never to rely on the models
I was supposed to have 4cms of snow this morning
What happened?

Gaoth Laidir

There's a dewpoint spread of up to 11.1 degrees in the east today (Casement temp 3.9, dewpoint -7.2 C). Perfect February weather. Only in the far south is it more close to saturated. WBT at zero or below over much of the midlands, north and east.

nacho libre

Gonzo wrote: »

T

The milder temperatures isn't just a result of the Atlantic, it is combining with the beginning of this warm air winter plume moving up from Portugal/Spain. This is partly why the UK mainland will also lose it's depth of cold very quickly from tomorrow. It is blowtorch warmth moving northwards and then eastwards (for the time of year).

The culprit is the low just sitting out there in the Atlantic, although longer term it might just work out in our favour to have all that Warm Air going northwards.

Reversal

Gaoth Laidir wrote: »

I haven't noticed such a pattern before and I've never seen it mentioned anywhere. Maybe it has something to do with statute miles, which is what is used for all visibilities in the USA METARs. 4000 and 1200 m would be 2.5 and 0.75 statute miles, respectively, which seem round numbers that would be reported in US METARs. Of course, aviation uses nautical miles for everything else, so here you have the confusing mix of units again.

Or else it's just coincidence. I see Aldergrove's TAF reports 5000 and 2000 metres (3.1 and 1.25 S.M.).

TAF EGAA 121104Z 1212/1312 12016KT 9999 FEW030
TEMPO 1212/1312 13020G32KT
BECMG 1308/1311 SCT007 BKN012
TEMPO 1308/1312 5000 -SN
PROB30 TEMPO 1309/1312 2000 SN BKN006=

I've seen Cb bases forecast at different heights than just 1800 ft, but given our climate, 1800 ft is probably the most common. That would be a 4.5-degree dewpoint depression (multiply dewpoint depression x 400 to estimate cumulus base height agl).

Maybe my imagination so. Thanks.

Tyrone212

5 to 10cm widely, maybe more

https://www.metoffice.gov.uk/weather/videos

Gaoth Laidir

Nqp15hhu wrote: »

I’m just asking why the rapid rise in temps despite no change in synoptic situation from yesterday.

Just less cloud, I reckon. You got a bit more solar radiation in the hour up to midday than you did yesterday. Plus there's less snow coverage over NI today in general.

Nqp15hhu

Naw. I managed around 1.5c high the other day with sunshine.

The airmass has been moderated.

Calibos

WRT to tonights likely Non Event for the East, I've made peace with it (at the risk of sounding melodramatic ). My Ninja 5cm in January that lasted 3 days (including the day it fell) meant Winter 2021 wasn't a total write off for me. I'll be happy enough if Spring bloomed and this was the last of the deep cold we got. Equally though, I'll be happy if we got another bite of the Cold/Snow Cherry late February or early March. Unlike others I've never been chasing long lasting deep cold and snow. A few days with a few inches on the ground is more than enough to make me very happy so the limitations to longevity of Late Feb or March Snow are of no concern to me really.

The fact that the models show nothing of interest out to day 10 doesn't have me throwing in the towel either. Day 10 takes us to the 22nd of February. The 2018 Snow didn't get going till the 26th or thereabouts. In other words, back in 2018 the Big Event wasn't showing up on the models on the 12th either. I'll only call it quits if theres nothing showing on the models first week of March for Paddy's Day. :D

Rebelbrowser

GL, you have a chart for everything! I'm on here a lot in winter but there are two charts you have posted on this page that I have never seen before....

Rh at my station in Arklow is down to 48%
Incredible for a wind off the Irish Sea

yourdeadwright

So are we still expecting some snow fall tomorrow morning in Dublin , T

Gonzo

yourdeadwright wrote: »

So are we still expecting some snow fall tomorrow morning in Dublin , T

I wouldn't be banking on it. If it does snow it may not be enough to stick and if it does stick temporarily it will be washed away very quickly tomorrow with a big increase in temperatures by the evening.

Gaoth Laidir

The 18Z aviation chart shows the occlusion still stationary, lying NW-SE from Mace head - Shannon - Cork. The warm front behind is now slowing down to 15 knots, from 25 knots at 12Z.

Meteorite58

Models all fairly well grouped , all showing a decent amount of snow, AROME I thought did well the nearer to yesterdays snow, this time showing quite heavy snowfall as highlighted for those areas in the chart below ( this is cumulative amount, actual amount would be less ). Have noticed that the next front that was earlier shown to follow quickly is now much more delayed to early Sun so might enable snow in NE areas to last that bit longer.

Quite windy also.

Big rainfall totals along Southern areas.

Big temperature contrast between the SW and NE tomorrow.

Maybe wind warnings yet in the SW and along S counties, will be gusting up around 80- 90 k/h, either way very windy along coasts especially the S with onshore wind there

pad199207

Going by those charts even Dublin will be lucky to see anything tonight

Gaoth Laidir

Current airport warnings.

Dublin EIDW AD WRNG 01 VALID 130500/131000 SNOW FBL LESS THAN 1 CM FCST=
Casement EIME AD WRNG 02 VALID 130400/131000 SNOW FBL LESS THAN 1 CM FCST=
Knock EIKN AD WRNG 01 VALID 122300/130800 SNOW FBL 3 to 5 CM FCST=

The UKMO aviation chart for 00Z has that occlusion broken up and lying across western Connacht, moving NE at 10 kts, while the warm front is just into western Kerry, moving NE at 15 knots.

The weather described for west of a line Sligo-Waterford is widespread moderate, isolated heavy rain. For eastern Connacht it is light/moderate rain, but heavy snow on mountains and locally isolated heavy snow or freezing rain at lower levels.
Elsewhere (NE of a line Sligo-Waterford), isolated light rain/sleet/snow.

Gaoth Laidir

What a Wicklow shadow!

Snowbiee21

Gaoth Laidir wrote: »

What a Wicklow shadow!

This cold spell summed up in a nutshell

Nqp15hhu

Not sure what to expect here. Some chart seem to show 10cm others show 2cm.

https://twitter.com/Arklowweather/status/1360261243299368964?s=19

pad199207

Flakes of snow in Kildare now surprisingly

3.7°c

Dp -4.5°c

Donegal Ken

The Met Eireann warning reads
Snow accumulations of 5 cm possible (more on higher ground), accompanied by fresh to strong southeast winds.

There Criteria

STATUS YELLOW Snow/Ice
3cm or more in 24 hours

STATUS ORANGE Snow/Ice
3cm or greater in 6 hrs
5cm or greater in 12 hrs
10cm or greater in 24 hrs

Parts of the northwest and north based on there Criteria and model outputs including the Met.ie Harmonie model should be under a Orange warning.

ZeroSum76

AuntySnow wrote: »

https://twitter.com/Arklowweather/status/1360261243299368964?s=19

Well Aunty how are we looking? Reckon we will get anything?

Nqp15hhu

I am concerned that temps will not drop to freezing with the wind.

ZeroSum76

ZeroSum76 wrote: »

Well Aunty how are we looking? Reckon we will get anything?

I do
But are you a night owl ?

ninebeanrows

AuntySnow wrote: »

I do
But are you a night owl ?

The timing could not be worse! This has been a very painful cold spell:o

Let's hope it ends in a flurry!