Scotland/Alba weather discussion - Autumn 2020 onwards

[Sceptical]

6 minutes ago, CatchMyDrift said:

The Met-Office outlooks seem ok

That reads fine. No doubt about that.

The problem is the Mets 10 day trend is somewhat different. Strong easterly winds next week but the source of the air is the Med.

 

[Quinach]

A day of two halves.

Morning lovely and sunny with a nice crispy white frost covering everything.

Then I learnt I should put more faith in the Met Office as, right enough, there was some snow mid-afternoon which was enough to whiten everything. 

No Narnia photos like previous posts but it's the closest we seem to get here these days.

Temperature is already rising outside (+0.5c and the shed roof snow is melting) so that scuppers any hope of some snow tomorrow.  Mmm, cold rain, can't wait. 

[101_North]

A surprise light snow shower here. Radar suggests it should be heavier than it is though! 

Edited December 30, 2020 by 101_North

[edo]

8 minutes ago, 101_North said:

A surprise light snow shower here. Radar suggests it should be heavier than it is though! 

your snow reports are getting boring 

[101_North]

3 minutes ago, edo said:

your snow reports are getting boring 

It's OK! This arrived today so there won't be too many more snow reports

[LomondSnowstorm]

Good to see some areas getting a bit of a top up today - while this was sort of on the radar (to pardon the pun, especially given the amount of false echoes I saw nearby to start with) it wasn't really widely flagged up, especially given the wind direction, south of the Grampians, to the point I'd not really tuned in properly to it being a real possibility until I saw a few flakes when I was out walking today! It was in fact a wrap around occlusion, not an especially strong one away from the northwest Highlands but definitely fits with the 'get the snow in and cold will follow' (even if the cold pool is a little on the shallow side today):

And I see the radar is still pretty active even now!

Tomorrow's feature is another of these relatively rare beasts - the warm/occluded front from the north!

The triple point of the fronts and the occlusions are the key to the snowfall tomorrow - if you're under this, or to the west of it, you're likely to see the heaviest precipitation and you're most likely to see it as snow. As per the FAX chart we can see this has moved a bit to the west over the last few runs, with it now sitting around Glasgow by midday. The warm sector also shows up quite nicely on the theta-e charts - a pretty marked warm sector by midday:

 

Prior to the arrival of the front, though, we're looking at some low temperatures, with skies clearing overnight:

There's a bit of a difference between the NMM and UKV on this though, I think partly to do with the timing of the front - the latter has the front coming through a bit earlier, meaning the lows are higher as cloud moves in earlier to Fife and Stirling:

and ICON has something in between:

This does make quite a big difference even aside from the placement of the front, as it means precipitation starts off as either snow or freezing rain as it runs into the cold air. While this, sadly, probably won't be enough for coastal parts of the northeast, or even many places below 100m more generally with a wind off the Moray Firth in addition to the warm sector, it does mean that the front is quite likely to bring wintry precipitation to start with as it reaches central Scotland:

 

It's also notable how much difference there is on the placement of the main front, and how this impacts on the main snow risk - the UKV is the furthest west of the three, to the point where I think it's really limiting snow potential to higher ground and doesn't really have much frontal precipitation for Fife or the Lothians. The ICON keeps the triple point much further east but sliding southwest as it moves through, meaning the snow risk is much more widespread, and continues through to tea time:

 

Unsurprisingly this is quite a snowy run, with a covering for almost all of mainland Scotland at some point during the day:

The UKV, on the other hand, really doesn't bring very much snow, with it mostly confined to high ground and areas where there's currently a notable amount of snow cover (this is the maximum extent):

And the NMM is, again, somewhere in the middle (slightly higher accumulations north of the central belt during the morning on this that melt later on):

 

We are really dealing with very fine margins again, and while it's likely we'll see some snow melt with temperatures getting up to 4-5C in places behind the front some places could still end up gaining on the day if something closer to the ICON setup pans out.

The margins are emphasised, again, with this sounding for when the front is passing over on the NMM for central Fife:

Both the dewpoint and temperature hug the 0C isotherm up to 900hPa. Further west it's pretty similar, but with the dewpoint at the surface lower:

 

This does create a risk for freezing rain, particularly further east as the warmer upper air moves over the cold surface, so I would certainly watch out for that as well.

Which setup is more likely? I think the most recent satellite image does suggest it's a bit further north than the UKV suggests, so I'd tend to think they're a bit fast with the arrival of the front, although we're already seeing temperatures of around 5-6C on Orkney and 4C on the north coast. I think you'd do well to get a couple of inches out of this if you're below, say 150m, but the further west and higher up you are the better shot you've got, and there's certainly a lot to look forward to beyond Hogmanay (but more on that either tomorrow or when I'm suitably hungover on the 1st!)

 

[edo]

fab stuff LS........ i look fwd to the jam tomorrow

and by that i mean decent falls next week......maybe

[howham]

Cold and frosty at the moment at -1.0C.

[LomondSnowstorm]

1 hour ago, Sceptical said:

That reads fine. No doubt about that.

The problem is the Mets 10 day trend is somewhat different. Strong easterly winds next week but the source of the air is the Med.

 

Interesting outlook - while I can't really argue with the vast majority of the forecast, especially the bit about it not being the sort of 'beast from the east' with direct sourced Arctic air for England at least, I don't think it's necessarily true that the airmass will be universally warmer either - more locally the air is coming from Scandinavia, and we do see significantly sub -5C upper air temperatures (albeit with significantly higher surface pressure) for the first time since Christmas Eve:

And I'm not sure it's likely, on the current runs at least, for that yellow tongue curving into the Baltic to really have much of an influence up here anyway (the high will end up pretty much over us for a bit and then, hopefully, the cold reload will come from the Arctic as the vortex is torn up).

The sort of modest, slack eastnortheasterly shown on that chart though, with enough of a cold pool for a bit of convection but not enough that it really shows up on the models, is just the sort of setup that can produce unexpected snowfalls here...

[mardatha]

Woke up at 4 with a sore back, very light dusting of snaw ootside I think - unless it's heavy frost, canny see properly. Drinking tea and eating liquorice toffee with Beeglie.

[howham]

1.6C, heavy rain showers. 

[Norrance]

It has just started here as snow though fairly light. Settling on the ground right away.

Edit. Soon got heavier and turned into graupel. Still -1.4C so not helping the iced up side roads and pavements. How long before it turns to rain?

Edited December 31, 2020 by Norrance

[Sceptical]

The heavy rain woke me up around 0530 and its been constant rain since. Further inland, and with elevation, could be  getting hammered with snow.

[Ravelin]

39 minutes ago, Sceptical said:

The heavy rain woke me up around 0530 and its been constant rain since. Further inland, and with elevation, could be  getting hammered with snow.

Need to be higher than me as its currently 1.9/1.5C here and has been raining. Local weather station shows that it got back above freezing not long after midnight and the rain dtarted around 3am.

[chemikal]

Netweather radar says sleet just now but lamp post says snow. Temperature is creepy up slowly though...

[Benvironment]

1.6C here with the biggest snowflakes I have ever seen

[101_North]

Main band just about to hit but what will it be? Temp is -1.5c dp -3.7c so fingers crossed for snow, at least for a while!

That front looks well west too. On current trajectory Edinburgh and the Lothians could be out of ppn pretty quickly! Something @LomondSnowstorm highlighted in that great summary last night!

 

Edited December 31, 2020 by 101_North

[Eastern Scotland WX]

It started snowing here 20-25 minutes ago with a temperature of -1C . The snow became more and more sleety as it approached 0C. It’s currently light sleet at 0.3C. I am thinking this is due to the fact that on the skew t chart it wasn’t showing any temperature drop ( slight warming even ) until around 500m elevation. This must be allowing the snow flakes to partly melt. 

[Norrance]

Now a wintry mix of graupel, rain and snow flakes. Air temp  up to -0.3C A warmer layer somewhere aloft perhaps causing this mix?

edit. Pretty much as Max just posted above. 

Edited December 31, 2020 by Norrance

[Richard Taylor]

Rain showers. Apart from that brief wintry spell Xmas Eve I've seen nothing sustained or worthwhile. A big fat bust for us. We just can't get the winds far enough into the north for long enough in wintertime these days.

[Hawesy]

18 minutes ago, Norrance said:

Now a wintry mix of graupel, rain and snow flakes. Air temp  up to -0.3C A warmer layer somewhere aloft perhaps causing this mix?

edit. Pretty much as Max just posted above. 

Morning all, plain old rain here in Pittenweem at 0.8c. My hopes of seeing snow for an hour or so are dashed - oh well maybe next time!  Judging by the reports freezing rain must be a concern this morning, as @LomondSnowstorm flagged last night. Not something we see much of in this country.

[Sceptical]

44 minutes ago, Ravelin said:

Need to be higher than me as its currently 1.9/1.5C here and has been raining. Local weather station shows that it got back above freezing not long after midnight and the rain dtarted around 3am.

Agreed with your elevation point.

The house looks onto Cairn William which sits at 450 meters ASL and the snows disappeared up there. Slightly warmer up this end of the valley at 3C.

Win some, lose some.

[Cheggers]

At last Snaw, nice big flakes. Be nice if it stayed this way for a wee while. 

[Harsh Climate]

Looks like Edinburgh is about to get a good spell of snow. I notice this area always seems to get snow streamers when showers packing in from the north with any kind of easterly influence! Great place to live i this kind of set-up.

[A Winter's Tale]

Quite large snowflakes falling down - settling for now.